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Managing chest pain in patients with concomitant left bundle-branch block Andrew Wyant, MD; Somu Chatterjee, MD, MPH; Tamara Bennett, MSPAS, PA-C
ABSTRACT Diagnosis and timely management of acute myocardial infarction (MI) relies heavily on the ST-segment elevation sum. Presence of concomitant left bundle-branch block (LBBB) in patients presenting with possible acute MI presents a diagnostic dilemma. The LBBB pattern distorts STsegment changes, delaying or preventing accurate diagnosis. This article reviews the Sgarbossa criteria and ST/S ratio and presents a treatment algorithm that may help improve patient care and reduce morbidity and mortality. Keywords: left bundle-branch block, acute myocardial infarction, Sgarbossa criteria, ST/S ratio, ECG findings, chest pain
Learning objectives Describe the major differences between the 2004 and 2013 ACC/AHA guidelines for managing patients with concomitant STEMI and LBBB. List the ECG characteristics of LBBB, ST-segment elevation or depression, and the ST/S ratio. Use the Sgarbossa criteria to determine if a patient with symptoms of acute coronary syndrome and LBBB warrants emergent reperfusion, PCI, or further diagnostic evaluation.
P
rompt reperfusion f i off patients i with i h acute myocardial di l infarction (MI) and ST-segment and T-wave changes on 12-lead ECG markedly improves outcomes, including reducing mortality.1-3 A patient with acute coronary syndrome (ACS) and concomitant left bundle-branch block (LBBB) presents diagnostic and management challenges, as the classic ECG findings of ST-segment elevation MI (STEMI) are obscured by the repolarization changes of LBBB. In addition to dubious ST-segment changes in ischemia, LBBB places patients at greater risk for acute MI, heart failure, and death.4 Andrew Wyant, Somu Chatterjee, and Tamara Bennett are assistant professors in the PA program at the University of Kentucky in Lexington, Ky. The authors have disclosed no potential conflicts of interest, financial or otherwise. DOI: 10.1097/01.JAA.0000525904.44484.5c Copyright © 2017 American Academy of Physician Assistants
FIGURE 1. Baseline changes in leads V1 and V6 in LBBB
For more than 60 years, clinicians have recognized the diagnostic and management challenges of patients with chest pain presenting with concomitant LBBB.5 Altered ventricular depolarization in patients with LBBB masks characteristic ECG changes of MI, and patients with new or persistent LBBB and acute MI have worse prognoses.4,6 Patients with suspected STEMI and LBBB (regardless of chronicity) represent a small but substantial proportion of the ACS cohort, and this patient subset has increased adverse clinical outcomes and higher complications following acute MI.4 These patients are more likely to be older, female, and have a history of preexisting cardiovascular disease, are more likely to suffer acute MI, stroke, heart failure, and death compared with patients who do not have LBBB.4 Determining which patients in this subset should receive emergent reperfusion is challenging. Uncertainty about the optimal approach to identifying acute MI in patients with LBBB has contributed to delays in diagnosis and prolonged time to revascularization.2 Historically, the American College of Cardiology/American Heart Association (ACC/AHA) guideline was to treat all patients with new (or presumed new) LBBB and symptoms of acute MI as a STEMI equivalent, mandating emergent reperfusion with fibrinolytics or percutaneous coronary intervention (PCI).7,8 This treatment approach resulted in heterogeneous and altered management approaches with
Managing chest pain in patients with concomitant left bundle-branch block
Key points Diagnosis and timely management of acute MI in patients with concomitant LBBB in patients is a diagnostic dilemma. The LBBB pattern distorts ST-segment changes, potentially delaying or preventing accurate diagnosis. The modified Sgarbossa criteria (in which the ST/S ratio is added) can be used to determine appropriate patient interventions and may reduce morbidity and mortality.
diverse outcomes. Newer guidelines eliminate the concept of treating patients with presumed new LBBB and chest pain as a STEMI equivalent based on more recent angiographic data that question the validity of this principle.4,9,10 The 2004 AHA guideline recommended reperfusion therapy for all patients with LBBB and symptoms of acute MI, resulting in overtreatment of many patients with an aggressive and expensive therapy. The 2013 AHA guideline suggested the opposite extreme—not to treat patients with LBBB and symptoms of acute MI as STEMI-equivalent, and thus not to treat with reperfusion therapy. The drastic change from using reperfusion therapy for all patients with LBBB to using it for none significantly reduces false-positive treatments but fails to recognize that some patients with chronic LBBB do have STEMI and could die if treatment is delayed.11 Hence, the need for a reliable diagnostic tool to diagnose STEMI in patients with new or chronic LBBB. Clinicians should become comfortable using the Sgarbossa criteria when faced with a patient with LBBB and chest symptoms. These criteria are particularly helpful in this setting due to their high specificity and positive predictive value. Using this tool will allow an objective triage, recognizing those patients who actually need aggressive therapy.
Despite the repolarization changes from LBBB and distorted ST segments, noninvasive diagnostic ECG criteria have been validated to further triage patients with LBBB and chest pain. The Sgarbossa ECG criteria for diagnosing acute MI in patients with LBBB have been posited to meet this diagnostic challenge.9 The addition of the ST/S ratio (creating the modified Sgarbossa criteria) lends further diagnostic validity.12 These criteria form part of a diagnostic algorithm for rapid diagnosis while minimizing treatment decision extremes.11 However, these criteria are not without controversy. The strength of this tool is on the side of diagnostic specificity with fewer false-positive acute MI diagnoses; however, the low sensitivity of 20% could result in undertreatment. Other studies suggest there may be no improvement over clinical judgment alone. Some have advocated additional criteria to improve sensitivity.4 This article reviews the management dilemma of chest pain and LBBB, the expanded Sgarbossa criteria, and recently proposed treatment algorithms. PATHOPHYSIOLOGY OF LBBB Below the level of the atrioventricular (AV) node and bundle of His, the conduction system trifurcates into a single right bundle and a bifascicular left bundle. The main left bundle branch further divides into the anterior and posterior fascicles. Compared with the right bundle branch, the left bundle is larger and anatomically deeper within the myocardium. These structural characteristics provide a degree of protection for the left bundle branches, requiring a significant ischemic injury to result in damage and conduction delay. LBBB can occur in otherwise healthy hearts but far more commonly is a marker of underlying structural or ischemic heart disease. Conditions associated with LBBB formation include aortic stenosis, hypertension, acute MI, chronic ischemic heart disease, heart failure, and cardiomyopathy. Blocks in the interventricular conduction system involving both fascicles of the left bundle result in characteristic and FIGURE 3. ST/S ratio in patients with LBBB
S
FIGURE 2. ST-segment elevation and the J point
The ST/S ratio is calculated by taking the ST-segment elevation (in millimeters, measured at the J-point) and dividing it by the R or S wave height (whichever is most prominent) in millimeters. In this waveform, the ST segment and T wave are discordant (in the opposite direction of the S wave). An ST/S ratio of -0.25 or less indicates an excessive discordance and significant ischemia. In patients with LBBB, this is most commonly seen in leads V1 and V2.
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diagnostic ECG changes (Table 1). TABLE 1. Cardiac conduction system and ECG findings in LBBB Understanding ST-segment conNormal cardiac conduction system LBBB cordance is a critical aspect in recognizing LBBB on a patient’s ECG and in using the diagnostic criteria in patients with acute MI. Concordance refers to the relationship between the major QRS (or RS) waveform and the vector of the ST segment. A concordant ST segment is oriented in the same direction as the terminal QRS waveform. In patients with LBBB, the ST segment is discordant with the QRS. This ST-segment discordance interLead V1: feres with clinical interpretation QRS and of acute ischemic changes. In the T waves baseline LBBB pattern, the characteristic notched R (an abnormal widening of QRS complex with a notched, rabbit-ears appearance, Figure 1) is followed by repolarization, yielding marked ST-segment depression in leads V5 and V6. Also in the baseline LBBB pattern, in leads V1 and V2, the rS complex normally is negative with repoLead V6: larization, resulting in ST-segment QRS and elevation (Figure 1). These findings T waves have traditionally made it difficult to interpret acute ischemia in a patient with a STEMI. Thus, in a patient with underlying, asymptomatic LBBB, an ECG will show ST-segment depression in leads V5 and V6, and ST-segment elevation in leads V1 and V2. Additional leads may also reveal distorted ST QRS 0.08-0.12 s >0.12 s duration segments. Interpreting ST-segment and T-wave Concordant with QRS Discordant with QRS T-wave inversions is key to chest deflection pain evaluation, especially in the acute setting. In fact, the initial ST-segment sum is the Patients with acute MI who present with LBBB have greater main variable influencing “door to fibrinolytics” time; the in-hospital mortality (22.6%) than patients without LBBB largest ST deviations result in the shortest times to treat(13.1%) yet are less likely to receive interventions known ment.13 Patients with chest symptoms and either a presumed to improve survival.14 Research shows that much of the new LBBB or a chronic LBBB present the clinician with a time these interventricular conduction delays are transient diagnostic dilemma because the most powerful diagnostic in nature, a myocardial reaction to an ischemic insult. tool (ST-segment change on ECG) has historically been Diagnostically, in a patient with new LBBB and clinical presumed unreadable in these patients. Uncertainty about findings that suggest ACS, the transient LBBB pattern may the age or time of onset of the LBBB further complicates infer myocardial ischemia, but this is not always the case. clinical decision making. LBBB chronicity is difficult to determine without review- EPIDEMIOLOGY ing the patient’s previous ECGs—a notable contributing The prevalence of LBBB has been estimated at 0.1% to factor is that the onset of LBBB often is asymptomatic.4 0.4% in middle-aged men in unselected populations.15 The
Managing chest pain in patients with concomitant left bundle-branch block
prevalence increases with age with a reported prevalence of less than 1% at age 50 years, rising to more than 17% among octogenarians.15 Studies demonstrate an increase in mortality, sudden death, ischemic heart disease, and heart failure in patients with LBBB compared with those without LBBB.15 Between 1% and 9% of patients seeking evaluation for suspected acute MI have LBBB (chronicity uncertain).11,16
TABLE 2.
Sgarbossa criteria and modified Sgarbossa criteria for independent predictors of acute MI in patients with LBBB
A score of 3 or more on the original Sgarbossa criteria is a diagnostic predictor of acute MI. The modified criteria do not use scores; a patient with one positive criterion should be treated for acute MI.
Sgarbossa criteria
Score
ST-segment elevation of 1 mm or greater concordant with QRS complex in any lead
5
ST-segment depression of 1 mm or greater in leads V1, V2, or V3
3
ST-segment elevation of 5 mm or greater discordant with QRS complex in any lead
2
Modified Sgarbossa criteria ST-segment elevation of 1 mm or greater concordant with QRS complex in any lead ST-segment depression of 1 mm or greater in leads V1, V2, or V3 ST/S ratio of -0.25 or less, indicating excessive discordance of the ST segment
EVOLUTION AND HISTORY OF MANAGEMENT Optimal management of patients with acute MI and evolving myocardial ischemia depends on rapidly identifying coronary occlusion and promptly providing reperfusion therapy.11,17 Triaging patients with chest pain relies heavily on identifying ST-segment elevation on a standard 12-lead ECG.13 Controlled studies have analyzed the diagnostic power of the initial ECG in patients presenting with and without chest pain. Optimum ECG variables for detection of acute MI included new ST-segment elevation at the J point in at least two contiguous leads (Figure 2); specifically, elevation of 2 mm or more in men, or 1.5 mm or more in women in leads V2 and V3 and/or elevation of 1 mm or more in one other contiguous chest or limb lead.18 With this model, 83% of patients were correctly classified with 56% sensitivity and 94% specificity.13 ECG manifestations of STEMI in patients with LBBB may be obscured or mimicked, causing treatment problems on both sides of the spectrum.11 This has resulted in undertreatment and overtreatment of ischemia and AMI in patients with chest pain and LBBB. The potential for overtreatment based on older (2004) AHA guidelines, or under treatment based on newer (2013) AHA guidelines explains the pressing need for noninvasive diagnostic tools for this patient group.11 In 1996 and 2004, the American College of Cardiology and American Heart Association (ACC/AHA) published guidelines for managing patients with concomitant STEMI and LBBB, and recommended emergent reperfusion therapy with fibrinolytics or PCI if the patient presented for treatment within 12 hours of symptom onset.7,8 These guidelines were based on older data from fibrinolytic trials in which the diagnosis of acute MI was confirmed biochemically rather than angiographically.11 Relying on biomarkers in patients with LBBB may overestimate the prevalence of acute MI. More recent studies have evaluated the actual incidence of acute MI in patients with LBBB based on angiographic evidence.9,11 Studies indicate that 6% to 51%
of all patients with suspected ACS and LBBB will ultimately be diagnosed with acute MI.4 Even in patients with known new LBBB and chest pain, MI is actually diagnosed in a minority.19 The 1996 and 2004 guidelines likely resulted in unnecessary reperfusion therapy for many patients. More recent guidelines challenge the practice of treating new LBBB as a STEMI equivalent.9 The 2013 guidelines recognize that new LBBB at presentation actually occurs infrequently, may interfere with ST-elevation analysis, and should not be considered diagnostic of acute MI.9,11 The change in approach from treating all patients with LBBB as if they have STEMI to using the diagnostic tool to target treatment will reduce complications from overuse of PCI and fibrinolytics. The excellent specificity of the original Sgarbossa criteria (Table 2) helps clinicians identify patients who may be truly negative if the score is below 3. These patients do not need to be treated as if they had acute MI. Patients scoring 3 or greater on the original Sgarbossa criteria should be treated. The modified criteria (Table 2) do not use scores but patients who meet even one criterion should receive PCI or fibrinolytics.11 The significant downside of the new guideline is the failure to recognize patients with chronic LBBB who actually do have STEMI. Delaying reperfusion in this population could be fatal or increase morbidity due to undertreatment. Hence, the critical need for a noninvasive diagnostic tool that will accurately determine appropriate interventions for these patients. DIAGNOSTIC STRATEGIES The acuity and severity of ACS demands diagnostic tests with sensitivity and specificity. Recent algorithms using the Sgarbossa criteria and the ST/S ratio together add a validated approach. Sgarbossa criteria In 1996, Sgarbossa and colleagues published three independent ECG predictors of acute MI in patients with LBBB.20 These criteria resulted from analysis
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of more than 26,000 patients in the GUSTO-1 Chest pain / suspected acute MI in patients trial. The analysis comwith LBBB and typical ischemic chest pain pared ECGs from two groups: patients with LBBB and confirmed Hemodynamically unstable acute MI (the study popNo Yes OR ulation) and patients Decompensated heart failure? with chronic ischemic heart disease and LBBB (the control group).20 Three independent ECG signs were identified that discriminate for acute Sgarbossa criteria score ≥3 ischemia with LBBB. OR Yes Each ECG predictor Discordant ST-segment Reperfusion via PCI was assigned a point sensitivity ≥20% elevation in V1-V3 with ST / S or thrombolytics value dependent upon its ratio of ≤-0.25 predictive power and validity.13,20 The Sgarbossa criteria are the most valiNo; specificity 95% dated ECG criteria for diagnosing STEMI in patients with LBBB.20 A score of 2 or less is 95% Further evaluation: specific in determining Beside echocardiogram Serial ECG absence of acute MI Serial troponin in patients with LBBB, and a score 3 or greater has a sensitivity ranging from 20% to 79% Perform noninvasive in determining presence cardiac testing of acute MI in patients with LBBB.17,20 A score of 2 based on fulfillment Yes Abnormalities on of only the last criterion further testing? is not diagnostic of acute MI and mandates furNo ther testing and clinical 17,20 judgment. ST/S ratio In 2012, FIGURE 4. Triage algorithm for chest pain in patients with LBBB on ECG11 Smith and colleagues evaluated a fourth ECG criterion designed to increase DISCUSSION the sensitivity of the third Sgarbossa criterion and increase LBBB occurs in 1% of the general population; however, the the overall sensitivity of Sgarbossa’s diagnostic tool.12 prevalence of LBBB in patients with acute MI is 6% to 9%.2 Sgarbossa’s rule uses an absolute 5 mm cutoff for disLBBB often is a marker of chronic cardiac disease and cordant ST-segment elevation. Smith and colleagues may define a subset of patients at high risk for morbidity hypothesized that an ST-segment elevation in leads V1 and and mortality, especially if they have concomitant acute V3 proportional to the preceding QRS or S wave may be MI. Patients with LBBB are older, often male, and often have a high burden of comorbidities.15 Although biomarker more useful for diagnosing STEMI in patients with LBBB 12 (Figure 3). Their hypothesis was correct, and replacing levels are essential to the diagnosis of acute MI, biomarker the third Sgarbossa criteria with the ST/S ratio improved elevation does not discriminate between STEMI and nondiagnostic sensitivity from 52% to 91%, with specificity STEMI (NSTEMI), and ST-segment elevation on ECG is remaining near 90%.12 the primary indication for emergency reperfusion therapy.
Managing chest pain in patients with concomitant left bundle-branch block
Identifying STEMI in patients with LBBB is challenging because ST-segment changes may be masked.12,15 Overzealous reperfusion leads to complications from fibrinolysis and unnecessary use of cardiac catheterization. Undertreatment can lead to death or increased morbidity. The modified Sgarbossa criteria is a diagnostic tool designed to increase both sensitivity, specificity, and diagnostic accuracy for STEMI in patients with underlying LBBB, regardless of the age or chronicity of the bundle-branch block. This validated tool has a specificity greater than 90% and a sensitivity of 91% with replacement of the ST/S ratio as the third criterion. The interobserver agreement has been validated as strong in previous studies (k = 0.81).21 Following the 2013 guidelines, a triage algorithm for patients with suspected acute MI and LBBB was developed using Sgarbossa criteria, ST/S ratio, and discerning use of additional diagnostic tools including serial ECGs, serial troponin levels, and bedside echocardiography (Figure 4). Patients with suspected acute MI and LBBB who present with hemodynamic instability or acute heart failure are triaged to PCI or fibrinolytic reperfusion, regardless of ECG criteria. Otherwise, patients with a Sgarbossa score of 3 or greater or an ST/S ratio of -0.25 or less are triaged to reperfusion based on this validated tool. Patients not meeting either of these criteria and who are hemodynamically stable receive further evaluation with bedside echocardiography, serial ECGs, and serial troponin levels to determine whether they should receive angiography or noninvasive cardiac testing.11 CONCLUSION Using the modified Sgarbossa criteria for management should facilitate more accurate diagnosis, fewer complications, better resource allocation, and improved risk stratification for patients with chest pain and LBBB. JAAPA Earn Category I CME Credit by reading both CME articles in this issue, reviewing the post-test, then taking the online test at http:// cme.aapa.org. Successful completion is defined as a cumulative score of at least 70% correct. This material has been reviewed and is approved for 1 hour of clinical Category I (Preapproved) CME credit by the AAPA. The term of approval is for 1 year from the publication date of November 2017.
REFERENCES 1. Barron HV, Bowlby LJ, Breen T, et al. Use of reperfusion therapy for acute myocardial infarction in the United States: data from the National Registry of Myocardial Infarction 2. Circulation. 1998;97(12):1150-1156. 2. Tabas JA, Rodriguez RM, Seligman HK, Goldschlager NF. Electrocardiographic criteria for detecting acute myocardial infarction in patients with left bundle branch block: a meta-analysis. Ann Emerg Med. 2008;52(4):329-336.e1. 3. Boersma E, Maas AC, Deckers JW, Simoons ML. Early thrombolytic treatment in acute myocardial infarction: reappraisal of the golden hour. Lancet. 1996;348(9030):771-775. 4. Neeland IJ, Kontos MC, de Lemos JA. Evolving considerations in the management of patients with left bundle branch block and suspected myocardial infarction. J Am Coll Cardiol. 2012;60(2):96-105.
5. Wellens HJ. Acute myocardial infarction and left bundlebranch block—can we lift the veil? N Engl J Med. 1996;334 (8):528-529. 6. Bansilal S, Aneja A, Mathew V, et al. Long-term cardiovascular outcomes in patients with angina pectoris presenting with bundle branch block. Am J Cardiol. 2011;107(11):1565-1570. 7. Antman EM, Anbe DT, Armstrong PW, et al. ACC/AHA guidelines for the management of patients with ST-elevation myocardial infarction. A report of the American College of Cardiology/ American Heart Association Task Force on Practice Guidelines (Committee to Revise the 1999 Guidelines for the Management of patients with acute myocardial infarction). J Am Coll Cardiol. 2004;44(3):E1-E211. 8. Ryan TJ, Anderson JL, Antman EM, et al. ACC/AHA guidelines for the management of patients with acute myocardial infarction. A report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Committee on Management of Acute Myocardial Infarction). J Am Coll Cardiol. 1996;28(5):1328-1428. 9. O’Gara PT, Kushner FG, Ascheim DD, et al. 2013 ACCF/AHA guideline for the management of ST-elevation myocardial infarction: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. Circulation. 2013;127(4):e362-e425. 10. Jain S, Ting HT, Bell M, et al. Utility of left bundle branch block as a diagnostic criterion for acute myocardial infarction. Am J Cardiol. 2011;107(8):1111-1116. 11. Cai Q, Mehta N, Sgarbossa EB, et al. The left bundle-branch block puzzle in the 2013 ST-elevation myocardial infarction guideline: from falsely declaring emergency to denying reperfusion in a high-risk population. Are the Sgarbossa Criteria ready for prime time? Am Heart J. 2013;166(3):409-413. 12. Smith SW, Dodd KW, Henry TD, et al. Diagnosis of ST-elevation myocardial infarction in the presence of left bundle branch block with the ST-elevation to S-wave ratio in a modified Sgarbossa rule. Ann Emerg Med. 2012;60(6):766-776. 13. Sgarbossa EB, Birnbaum Y, Parrillo JE. Electrocardiographic diagnosis of acute myocardial infarction: current concepts for the clinician. Am Heart J. 2001;141(4):507-517. 14. Shlipak MG, Go AS, Frederick PD, et al. Treatment and outcomes of left bundle-branch block patients with myocardial infarction who present without chest pain. National Registry of Myocardial Infarction 2 Investigators. J Am Coll Cardiol. 2000;36(3):706-712. 15. Koskinas KC, Ziakas A. Left bundle branch block in cardiovascular disease: clinical significance and remaining controversies. Angiology. 2015;66(9):797-800. 16. Chang AM, Shofer FS, Tabas JA, et al. Lack of association between left bundle-branch block and acute myocardial infarction in symptomatic ED patients. Am J Emerg Med. 2009; 27(8):916-921. 17. Madias JE, Sinha A, Ashtiani R, et al. A critique of the new ST-segment criteria for the diagnosis of acute myocardial infarction in patients with left bundle-branch block. Clin Cardiol. 2001;24(10):652-655. 18. Thygesen K, Alpert JS, Jaffe AS, et al. Third universal definition of myocardial infarction. Circulation. 2012;126(16):2020-2035. 19. Kontos MC, Aziz HA, Chau VQ, et al. Outcomes in patients with chronicity of left bundle-branch block with possible acute myocardial infarction. Am Heart J. 2011;161(4):698-704. 20. Sgarbossa EB, Pinski SL, Barbagelata A, et al. Electrocardiographic diagnosis of evolving acute myocardial infarction in the presence of left bundle-branch block. GUSTO-1 (Global Utilization of Streptokinase and Tissue Plasminogen Activator for Occluded Coronary Arteries) Investigators. N Engl J Med. 1996;334(8):481-487. 21. Sokolove PE, Sgarbossa EB, Amsterdam EA, et al. Interobserver agreement in the electrocardiographic diagnosis of acute myocardial infarction in patients with left bundle branch block. Ann Emerg Med. 2000;36(6):566-571.
Managing chest pain in patients with concomitant left bundle-branch block Andrew Wyant, MD; Somu Chatterjee, MD, MPH; Tamara Bennett, MSPAS, PA-C
ABSTRACT Diagnosis and timely management of acute myocardial infarction (MI) relies heavily on the ST-segment elevation sum. Presence of concomitant left bundle-branch block (LBBB) in patients presenting with possible acute MI presents a diagnostic dilemma. The LBBB pattern distorts STsegment changes, delaying or preventing accurate diagnosis. This article reviews the Sgarbossa criteria and ST/S ratio and presents a treatment algorithm that may help improve patient care and reduce morbidity and mortality. Keywords: left bundle-branch block, acute myocardial infarction, Sgarbossa criteria, ST/S ratio, ECG findings, chest pain
Learning objectives Describe the major differences between the 2004 and 2013 ACC/AHA guidelines for managing patients with concomitant STEMI and LBBB. List the ECG characteristics of LBBB, ST-segment elevation or depression, and the ST/S ratio. Use the Sgarbossa criteria to determine if a patient with symptoms of acute coronary syndrome and LBBB warrants emergent reperfusion, PCI, or further diagnostic evaluation.
P
rompt reperfusion f i off patients i with i h acute myocardial di l infarction (MI) and ST-segment and T-wave changes on 12-lead ECG markedly improves outcomes, including reducing mortality.1-3 A patient with acute coronary syndrome (ACS) and concomitant left bundle-branch block (LBBB) presents diagnostic and management challenges, as the classic ECG findings of ST-segment elevation MI (STEMI) are obscured by the repolarization changes of LBBB. In addition to dubious ST-segment changes in ischemia, LBBB places patients at greater risk for acute MI, heart failure, and death.4 Andrew Wyant, Somu Chatterjee, and Tamara Bennett are assistant professors in the PA program at the University of Kentucky in Lexington, Ky. The authors have disclosed no potential conflicts of interest, financial or otherwise. DOI: 10.1097/01.JAA.0000525904.44484.5c Copyright © 2017 American Academy of Physician Assistants
FIGURE 1. Baseline changes in leads V1 and V6 in LBBB
For more than 60 years, clinicians have recognized the diagnostic and management challenges of patients with chest pain presenting with concomitant LBBB.5 Altered ventricular depolarization in patients with LBBB masks characteristic ECG changes of MI, and patients with new or persistent LBBB and acute MI have worse prognoses.4,6 Patients with suspected STEMI and LBBB (regardless of chronicity) represent a small but substantial proportion of the ACS cohort, and this patient subset has increased adverse clinical outcomes and higher complications following acute MI.4 These patients are more likely to be older, female, and have a history of preexisting cardiovascular disease, are more likely to suffer acute MI, stroke, heart failure, and death compared with patients who do not have LBBB.4 Determining which patients in this subset should receive emergent reperfusion is challenging. Uncertainty about the optimal approach to identifying acute MI in patients with LBBB has contributed to delays in diagnosis and prolonged time to revascularization.2 Historically, the American College of Cardiology/American Heart Association (ACC/AHA) guideline was to treat all patients with new (or presumed new) LBBB and symptoms of acute MI as a STEMI equivalent, mandating emergent reperfusion with fibrinolytics or percutaneous coronary intervention (PCI).7,8 This treatment approach resulted in heterogeneous and altered management approaches with
Managing chest pain in patients with concomitant left bundle-branch block
Key points Diagnosis and timely management of acute MI in patients with concomitant LBBB in patients is a diagnostic dilemma. The LBBB pattern distorts ST-segment changes, potentially delaying or preventing accurate diagnosis. The modified Sgarbossa criteria (in which the ST/S ratio is added) can be used to determine appropriate patient interventions and may reduce morbidity and mortality.
diverse outcomes. Newer guidelines eliminate the concept of treating patients with presumed new LBBB and chest pain as a STEMI equivalent based on more recent angiographic data that question the validity of this principle.4,9,10 The 2004 AHA guideline recommended reperfusion therapy for all patients with LBBB and symptoms of acute MI, resulting in overtreatment of many patients with an aggressive and expensive therapy. The 2013 AHA guideline suggested the opposite extreme—not to treat patients with LBBB and symptoms of acute MI as STEMI-equivalent, and thus not to treat with reperfusion therapy. The drastic change from using reperfusion therapy for all patients with LBBB to using it for none significantly reduces false-positive treatments but fails to recognize that some patients with chronic LBBB do have STEMI and could die if treatment is delayed.11 Hence, the need for a reliable diagnostic tool to diagnose STEMI in patients with new or chronic LBBB. Clinicians should become comfortable using the Sgarbossa criteria when faced with a patient with LBBB and chest symptoms. These criteria are particularly helpful in this setting due to their high specificity and positive predictive value. Using this tool will allow an objective triage, recognizing those patients who actually need aggressive therapy.
Despite the repolarization changes from LBBB and distorted ST segments, noninvasive diagnostic ECG criteria have been validated to further triage patients with LBBB and chest pain. The Sgarbossa ECG criteria for diagnosing acute MI in patients with LBBB have been posited to meet this diagnostic challenge.9 The addition of the ST/S ratio (creating the modified Sgarbossa criteria) lends further diagnostic validity.12 These criteria form part of a diagnostic algorithm for rapid diagnosis while minimizing treatment decision extremes.11 However, these criteria are not without controversy. The strength of this tool is on the side of diagnostic specificity with fewer false-positive acute MI diagnoses; however, the low sensitivity of 20% could result in undertreatment. Other studies suggest there may be no improvement over clinical judgment alone. Some have advocated additional criteria to improve sensitivity.4 This article reviews the management dilemma of chest pain and LBBB, the expanded Sgarbossa criteria, and recently proposed treatment algorithms. PATHOPHYSIOLOGY OF LBBB Below the level of the atrioventricular (AV) node and bundle of His, the conduction system trifurcates into a single right bundle and a bifascicular left bundle. The main left bundle branch further divides into the anterior and posterior fascicles. Compared with the right bundle branch, the left bundle is larger and anatomically deeper within the myocardium. These structural characteristics provide a degree of protection for the left bundle branches, requiring a significant ischemic injury to result in damage and conduction delay. LBBB can occur in otherwise healthy hearts but far more commonly is a marker of underlying structural or ischemic heart disease. Conditions associated with LBBB formation include aortic stenosis, hypertension, acute MI, chronic ischemic heart disease, heart failure, and cardiomyopathy. Blocks in the interventricular conduction system involving both fascicles of the left bundle result in characteristic and FIGURE 3. ST/S ratio in patients with LBBB
S
FIGURE 2. ST-segment elevation and the J point
The ST/S ratio is calculated by taking the ST-segment elevation (in millimeters, measured at the J-point) and dividing it by the R or S wave height (whichever is most prominent) in millimeters. In this waveform, the ST segment and T wave are discordant (in the opposite direction of the S wave). An ST/S ratio of -0.25 or less indicates an excessive discordance and significant ischemia. In patients with LBBB, this is most commonly seen in leads V1 and V2.
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diagnostic ECG changes (Table 1). TABLE 1. Cardiac conduction system and ECG findings in LBBB Understanding ST-segment conNormal cardiac conduction system LBBB cordance is a critical aspect in recognizing LBBB on a patient’s ECG and in using the diagnostic criteria in patients with acute MI. Concordance refers to the relationship between the major QRS (or RS) waveform and the vector of the ST segment. A concordant ST segment is oriented in the same direction as the terminal QRS waveform. In patients with LBBB, the ST segment is discordant with the QRS. This ST-segment discordance interLead V1: feres with clinical interpretation QRS and of acute ischemic changes. In the T waves baseline LBBB pattern, the characteristic notched R (an abnormal widening of QRS complex with a notched, rabbit-ears appearance, Figure 1) is followed by repolarization, yielding marked ST-segment depression in leads V5 and V6. Also in the baseline LBBB pattern, in leads V1 and V2, the rS complex normally is negative with repoLead V6: larization, resulting in ST-segment QRS and elevation (Figure 1). These findings T waves have traditionally made it difficult to interpret acute ischemia in a patient with a STEMI. Thus, in a patient with underlying, asymptomatic LBBB, an ECG will show ST-segment depression in leads V5 and V6, and ST-segment elevation in leads V1 and V2. Additional leads may also reveal distorted ST QRS 0.08-0.12 s >0.12 s duration segments. Interpreting ST-segment and T-wave Concordant with QRS Discordant with QRS T-wave inversions is key to chest deflection pain evaluation, especially in the acute setting. In fact, the initial ST-segment sum is the Patients with acute MI who present with LBBB have greater main variable influencing “door to fibrinolytics” time; the in-hospital mortality (22.6%) than patients without LBBB largest ST deviations result in the shortest times to treat(13.1%) yet are less likely to receive interventions known ment.13 Patients with chest symptoms and either a presumed to improve survival.14 Research shows that much of the new LBBB or a chronic LBBB present the clinician with a time these interventricular conduction delays are transient diagnostic dilemma because the most powerful diagnostic in nature, a myocardial reaction to an ischemic insult. tool (ST-segment change on ECG) has historically been Diagnostically, in a patient with new LBBB and clinical presumed unreadable in these patients. Uncertainty about findings that suggest ACS, the transient LBBB pattern may the age or time of onset of the LBBB further complicates infer myocardial ischemia, but this is not always the case. clinical decision making. LBBB chronicity is difficult to determine without review- EPIDEMIOLOGY ing the patient’s previous ECGs—a notable contributing The prevalence of LBBB has been estimated at 0.1% to factor is that the onset of LBBB often is asymptomatic.4 0.4% in middle-aged men in unselected populations.15 The
Managing chest pain in patients with concomitant left bundle-branch block
prevalence increases with age with a reported prevalence of less than 1% at age 50 years, rising to more than 17% among octogenarians.15 Studies demonstrate an increase in mortality, sudden death, ischemic heart disease, and heart failure in patients with LBBB compared with those without LBBB.15 Between 1% and 9% of patients seeking evaluation for suspected acute MI have LBBB (chronicity uncertain).11,16
TABLE 2.
Sgarbossa criteria and modified Sgarbossa criteria for independent predictors of acute MI in patients with LBBB
A score of 3 or more on the original Sgarbossa criteria is a diagnostic predictor of acute MI. The modified criteria do not use scores; a patient with one positive criterion should be treated for acute MI.
Sgarbossa criteria
Score
ST-segment elevation of 1 mm or greater concordant with QRS complex in any lead
5
ST-segment depression of 1 mm or greater in leads V1, V2, or V3
3
ST-segment elevation of 5 mm or greater discordant with QRS complex in any lead
2
Modified Sgarbossa criteria ST-segment elevation of 1 mm or greater concordant with QRS complex in any lead ST-segment depression of 1 mm or greater in leads V1, V2, or V3 ST/S ratio of -0.25 or less, indicating excessive discordance of the ST segment
EVOLUTION AND HISTORY OF MANAGEMENT Optimal management of patients with acute MI and evolving myocardial ischemia depends on rapidly identifying coronary occlusion and promptly providing reperfusion therapy.11,17 Triaging patients with chest pain relies heavily on identifying ST-segment elevation on a standard 12-lead ECG.13 Controlled studies have analyzed the diagnostic power of the initial ECG in patients presenting with and without chest pain. Optimum ECG variables for detection of acute MI included new ST-segment elevation at the J point in at least two contiguous leads (Figure 2); specifically, elevation of 2 mm or more in men, or 1.5 mm or more in women in leads V2 and V3 and/or elevation of 1 mm or more in one other contiguous chest or limb lead.18 With this model, 83% of patients were correctly classified with 56% sensitivity and 94% specificity.13 ECG manifestations of STEMI in patients with LBBB may be obscured or mimicked, causing treatment problems on both sides of the spectrum.11 This has resulted in undertreatment and overtreatment of ischemia and AMI in patients with chest pain and LBBB. The potential for overtreatment based on older (2004) AHA guidelines, or under treatment based on newer (2013) AHA guidelines explains the pressing need for noninvasive diagnostic tools for this patient group.11 In 1996 and 2004, the American College of Cardiology and American Heart Association (ACC/AHA) published guidelines for managing patients with concomitant STEMI and LBBB, and recommended emergent reperfusion therapy with fibrinolytics or PCI if the patient presented for treatment within 12 hours of symptom onset.7,8 These guidelines were based on older data from fibrinolytic trials in which the diagnosis of acute MI was confirmed biochemically rather than angiographically.11 Relying on biomarkers in patients with LBBB may overestimate the prevalence of acute MI. More recent studies have evaluated the actual incidence of acute MI in patients with LBBB based on angiographic evidence.9,11 Studies indicate that 6% to 51%
of all patients with suspected ACS and LBBB will ultimately be diagnosed with acute MI.4 Even in patients with known new LBBB and chest pain, MI is actually diagnosed in a minority.19 The 1996 and 2004 guidelines likely resulted in unnecessary reperfusion therapy for many patients. More recent guidelines challenge the practice of treating new LBBB as a STEMI equivalent.9 The 2013 guidelines recognize that new LBBB at presentation actually occurs infrequently, may interfere with ST-elevation analysis, and should not be considered diagnostic of acute MI.9,11 The change in approach from treating all patients with LBBB as if they have STEMI to using the diagnostic tool to target treatment will reduce complications from overuse of PCI and fibrinolytics. The excellent specificity of the original Sgarbossa criteria (Table 2) helps clinicians identify patients who may be truly negative if the score is below 3. These patients do not need to be treated as if they had acute MI. Patients scoring 3 or greater on the original Sgarbossa criteria should be treated. The modified criteria (Table 2) do not use scores but patients who meet even one criterion should receive PCI or fibrinolytics.11 The significant downside of the new guideline is the failure to recognize patients with chronic LBBB who actually do have STEMI. Delaying reperfusion in this population could be fatal or increase morbidity due to undertreatment. Hence, the critical need for a noninvasive diagnostic tool that will accurately determine appropriate interventions for these patients. DIAGNOSTIC STRATEGIES The acuity and severity of ACS demands diagnostic tests with sensitivity and specificity. Recent algorithms using the Sgarbossa criteria and the ST/S ratio together add a validated approach. Sgarbossa criteria In 1996, Sgarbossa and colleagues published three independent ECG predictors of acute MI in patients with LBBB.20 These criteria resulted from analysis
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of more than 26,000 patients in the GUSTO-1 Chest pain / suspected acute MI in patients trial. The analysis comwith LBBB and typical ischemic chest pain pared ECGs from two groups: patients with LBBB and confirmed Hemodynamically unstable acute MI (the study popNo Yes OR ulation) and patients Decompensated heart failure? with chronic ischemic heart disease and LBBB (the control group).20 Three independent ECG signs were identified that discriminate for acute Sgarbossa criteria score ≥3 ischemia with LBBB. OR Yes Each ECG predictor Discordant ST-segment Reperfusion via PCI was assigned a point sensitivity ≥20% elevation in V1-V3 with ST / S or thrombolytics value dependent upon its ratio of ≤-0.25 predictive power and validity.13,20 The Sgarbossa criteria are the most valiNo; specificity 95% dated ECG criteria for diagnosing STEMI in patients with LBBB.20 A score of 2 or less is 95% Further evaluation: specific in determining Beside echocardiogram Serial ECG absence of acute MI Serial troponin in patients with LBBB, and a score 3 or greater has a sensitivity ranging from 20% to 79% Perform noninvasive in determining presence cardiac testing of acute MI in patients with LBBB.17,20 A score of 2 based on fulfillment Yes Abnormalities on of only the last criterion further testing? is not diagnostic of acute MI and mandates furNo ther testing and clinical 17,20 judgment. ST/S ratio In 2012, FIGURE 4. Triage algorithm for chest pain in patients with LBBB on ECG11 Smith and colleagues evaluated a fourth ECG criterion designed to increase DISCUSSION the sensitivity of the third Sgarbossa criterion and increase LBBB occurs in 1% of the general population; however, the the overall sensitivity of Sgarbossa’s diagnostic tool.12 prevalence of LBBB in patients with acute MI is 6% to 9%.2 Sgarbossa’s rule uses an absolute 5 mm cutoff for disLBBB often is a marker of chronic cardiac disease and cordant ST-segment elevation. Smith and colleagues may define a subset of patients at high risk for morbidity hypothesized that an ST-segment elevation in leads V1 and and mortality, especially if they have concomitant acute V3 proportional to the preceding QRS or S wave may be MI. Patients with LBBB are older, often male, and often have a high burden of comorbidities.15 Although biomarker more useful for diagnosing STEMI in patients with LBBB 12 (Figure 3). Their hypothesis was correct, and replacing levels are essential to the diagnosis of acute MI, biomarker the third Sgarbossa criteria with the ST/S ratio improved elevation does not discriminate between STEMI and nondiagnostic sensitivity from 52% to 91%, with specificity STEMI (NSTEMI), and ST-segment elevation on ECG is remaining near 90%.12 the primary indication for emergency reperfusion therapy.
Managing chest pain in patients with concomitant left bundle-branch block
Identifying STEMI in patients with LBBB is challenging because ST-segment changes may be masked.12,15 Overzealous reperfusion leads to complications from fibrinolysis and unnecessary use of cardiac catheterization. Undertreatment can lead to death or increased morbidity. The modified Sgarbossa criteria is a diagnostic tool designed to increase both sensitivity, specificity, and diagnostic accuracy for STEMI in patients with underlying LBBB, regardless of the age or chronicity of the bundle-branch block. This validated tool has a specificity greater than 90% and a sensitivity of 91% with replacement of the ST/S ratio as the third criterion. The interobserver agreement has been validated as strong in previous studies (k = 0.81).21 Following the 2013 guidelines, a triage algorithm for patients with suspected acute MI and LBBB was developed using Sgarbossa criteria, ST/S ratio, and discerning use of additional diagnostic tools including serial ECGs, serial troponin levels, and bedside echocardiography (Figure 4). Patients with suspected acute MI and LBBB who present with hemodynamic instability or acute heart failure are triaged to PCI or fibrinolytic reperfusion, regardless of ECG criteria. Otherwise, patients with a Sgarbossa score of 3 or greater or an ST/S ratio of -0.25 or less are triaged to reperfusion based on this validated tool. Patients not meeting either of these criteria and who are hemodynamically stable receive further evaluation with bedside echocardiography, serial ECGs, and serial troponin levels to determine whether they should receive angiography or noninvasive cardiac testing.11 CONCLUSION Using the modified Sgarbossa criteria for management should facilitate more accurate diagnosis, fewer complications, better resource allocation, and improved risk stratification for patients with chest pain and LBBB. JAAPA Earn Category I CME Credit by reading both CME articles in this issue, reviewing the post-test, then taking the online test at http:// cme.aapa.org. Successful completion is defined as a cumulative score of at least 70% correct. This material has been reviewed and is approved for 1 hour of clinical Category I (Preapproved) CME credit by the AAPA. The term of approval is for 1 year from the publication date of November 2017.
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