ECG Puzzler A regular feature of the American Journal of Critical Care, the ECG Puzzler addresses electrocardiogram (ECG) interpretation for clinical practice. To send an eLetter or to contribute to an online discussion about this article, visit www.ajcconline.org and click “Respond to This Article” on either the full-text or PDF view of the article. We welcome letters regarding this feature.
Drug Induced ECG Abnormalities By Teri M. Kozik, RN, PhD, CNS, CCRN, Mary G. Carey, RN, PhD, Salah S. Al-Zaiti, RN, PhD, CRNP, and Michele M. Pelter, RN, PhD Scenario: This electrocardiogram (ECG) rhythm strip in lead II is from a 50-year-old woman who came to the emergency department after having fallen at home during an episode of syncope. She complained of “dizziness” prior to falling. She is currently prescribed
escitalopram for depression, which she has taken for 5 years, and recently (2 days earlier) levofloxacin for bronchitis. She is a nonsmoker and has no other health conditions. Upon arrival, her vital signs were within normal limits.
II
Interpretation Questions: 1. Is the ECG properly calibrated (10 mm) and are leads properly placed? If no, interpret cautiously. 2. Is this a sinus rhythm (one P wave preceding every QRS complex)? If no, check for number of P waves in relation to QRS complexes. 3. Is the heart rate (R-R interval) normal (60-100 beats/min)? If no, check for supra-ventricular or ventricular arrhythmias. 4. Is the QRS complex narrow (duration 2 mm in V2-V3, or > 1 mm in other leads)? If yes, check for similar deviations in contiguous cardiac territories. 6. Is the T wave inverted in relation to the QRS (> 0.5 mV)? If yes, check for ST deviation or conduction abnormalities. 7. Is the QT interval lengthened (> 450 ms [women] or > 470 ms [men])? If yes, check for ventricular arrhythmias or left ventricular hypertrophy. 8. Is R- or S-wave amplitude enlarged (S wave V1 + R wave V5 > 35 mm)? If yes, check for axis deviation or other chamber hypertrophy criteria.
❏ Yes
❏ No
❏ NA
❏ Yes
❏ No
❏ NA
❏ Yes
❏ No
❏ NA
❏ Yes
❏ No
❏ NA
❏ Yes
❏ No
❏ NA
❏ Yes
❏ No
❏ NA
❏ Yes
❏ No
❏ NA
❏ Yes
❏ No
❏ NA
Teri M. Kozik is a nurse researcher at St. Joseph’s Medical Center, Stockton, California. Mary G. Carey is associate director for clinical nursing research, Strong Memorial Hospital, Rochester, New York. Salah S. Al-Zaiti is an assistant professor at the Department of Acute and Tertiary Care Nursing, University of Pittsburgh, Pennsylvania. Michele M. Pelter is an assistant professor at the the Department of Physiological Nursing at University of California, San Francisco, California. ©2015 American Association of Critical-Care Nurses doi: http://dx.doi.org/10.4037/ajcc2015712
www.ajcconline.org
AJCC AMERICAN JOURNAL OF CRITICAL CARE, July 2015, Volume 24, No. 4
Downloaded from ajcc.aacnjournals.org at Zone Universite Laval on July 5, 2015
365
II
Answers: 1. Yes, the ECG is properly calibrated (see calibration mark right side). 2. Yes, a P wave precedes every QRS complex. 3. Yes, the heart rate is normal at 75 beats/min. 4. Yes, the QRS complex is narrow at approximately 80 milliseconds (ms) duration 5. No, the ST segment is not deviated. 6. No, the T wave is upright. 7. Yes, the QT interval is lengthened; best measured using the 8th and 9th beats (see arrows above). In both beats, the start of the QRS complex lands very close to the dark line of the ECG grid, which marks the start of the QT interval. The T wave ends 12 small boxes (ie, ~480 ms) from this point. Once corrected for heart rate using Bazett’s formula: QTc = QT /√ RR = 480 / √ 0.8 = 537 ms, the QT interval exceeds the normal limit of 450 for women. 8. Chamber hypertrophy cannot be assessed because Leads V1 and V5 are not shown.
Interpretation and Rationale Normal sinus rhythm at 75 beats/min and QT interval prolongation. Given the recently prescribed levofloxacin and symptoms on arrival, it is fair to suspect acquired long QT syndrome (aLQTS).
Mechanism and Management Channelopathies are caused by a malfunction in ion channels that regulate the movement of ions in and out of the myocardial cells during depolarization and repolarization. One channelopathy caused by medications affects cardiac repolarization by blocking the hERG channel during phase 3 of the action potential. This results in prolongation of the QT interval, termed long-QT syndrome (LQTS), and increases the risk for life-threatening arrhythmias. LQTS can be either genetic or acquired, with the latter occurring from clinical therapies such as induced hypothermia, electrolyte disturbances (hypokalemia, or hypomagnesemia), or therapy with medications known to prolong the QT-interval. Importantly, both types of LQTS predispose patients to ventricular arrhythmias, in particular torsades de pointes (TdP), which can lead to ventricular fibrillation and sudden cardiac death. The incidence of aLQTS is unknown, but it is estimated that more than 15 000 patients die of sudden cardiac death caused by aLQTS each year. This highlights
366
the importance of immediate identification and actions to reverse aLQTS. Thus, the Food and Drug Administration has published recommended guidelines for the pharmaceutical industry on proper testing of new agents and their effect on the QT/QTc interval. Identification of aLQTS following pharmacological therapy is challenging because more than 100 medications from varied classifications are associated with this syndrome. This patient was prescribed 2 medications known to lengthen the QT interval; escitalopram for depression, and levofloxacin to treat a respiratory infection. Levofloxacin appears to be the offending agent because the patient had taken escitalopram for years without symptoms suggestive of TdP (eg, syncope). Fortunately, aLQTS is reversible following cessation and metabolization of the offending medication(s). This patient did not have a prior ECG for comparison, but changing her antibiotic immediately is warranted. She should be admitted to the hospital and her ECG continuously monitored until the QT interval returns to normal. If her QT interval remains prolonged, the escitalopram may also need to be carefully tapered and stopped. Referral to an electrophysiologist to rule out the genetic form of LQTS may be indicated if the QT interval remains lengthened. This patient should be advised to notify all health care providers about this incident and have this noted in her medical record.
AJCC AMERICAN JOURNAL OF CRITICAL CARE, July 2015, Volume 24, No. 4
Downloaded from ajcc.aacnjournals.org at Zone Universite Laval on July 5, 2015
www.ajcconline.org
Drug Induced ECG Abnormalities Teri M. Kozik, Mary G. Carey, Salah S. Al-Zaiti and Michele M. Pelter Am J Crit Care 2015;24:365-366 doi: 10.4037/ajcc2015712 © 2015 American Association of Critical-Care Nurses Published online http://www.ajcconline.org Personal use only. For copyright permission information: http://ajcc.aacnjournals.org/cgi/external_ref?link_type=PERMISSIONDIRECT
Subscription Information http://ajcc.aacnjournals.org/subscriptions/ Information for authors http://ajcc.aacnjournals.org/misc/ifora.xhtml Submit a manuscript http://www.editorialmanager.com/ajcc Email alerts http://ajcc.aacnjournals.org/subscriptions/etoc.xhtml
AJCC, the American Journal of Critical Care, is the official peer-reviewed research journal of the American Association of Critical-Care Nurses (AACN), published bimonthly by The InnoVision Group, 101 Columbia, Aliso Viejo, CA 92656. Telephone: (800) 899-1712, (949) 362-2050, ext. 532. Fax: (949) 362-2049. Copyright © 2015 by AACN. All rights reserved.
Downloaded from ajcc.aacnjournals.org at Zone Universite Laval on July 5, 2015
Drug Induced ECG Abnormalities By Teri M. Kozik, RN, PhD, CNS, CCRN, Mary G. Carey, RN, PhD, Salah S. Al-Zaiti, RN, PhD, CRNP, and Michele M. Pelter, RN, PhD Scenario: This electrocardiogram (ECG) rhythm strip in lead II is from a 50-year-old woman who came to the emergency department after having fallen at home during an episode of syncope. She complained of “dizziness” prior to falling. She is currently prescribed
escitalopram for depression, which she has taken for 5 years, and recently (2 days earlier) levofloxacin for bronchitis. She is a nonsmoker and has no other health conditions. Upon arrival, her vital signs were within normal limits.
II
Interpretation Questions: 1. Is the ECG properly calibrated (10 mm) and are leads properly placed? If no, interpret cautiously. 2. Is this a sinus rhythm (one P wave preceding every QRS complex)? If no, check for number of P waves in relation to QRS complexes. 3. Is the heart rate (R-R interval) normal (60-100 beats/min)? If no, check for supra-ventricular or ventricular arrhythmias. 4. Is the QRS complex narrow (duration 2 mm in V2-V3, or > 1 mm in other leads)? If yes, check for similar deviations in contiguous cardiac territories. 6. Is the T wave inverted in relation to the QRS (> 0.5 mV)? If yes, check for ST deviation or conduction abnormalities. 7. Is the QT interval lengthened (> 450 ms [women] or > 470 ms [men])? If yes, check for ventricular arrhythmias or left ventricular hypertrophy. 8. Is R- or S-wave amplitude enlarged (S wave V1 + R wave V5 > 35 mm)? If yes, check for axis deviation or other chamber hypertrophy criteria.
❏ Yes
❏ No
❏ NA
❏ Yes
❏ No
❏ NA
❏ Yes
❏ No
❏ NA
❏ Yes
❏ No
❏ NA
❏ Yes
❏ No
❏ NA
❏ Yes
❏ No
❏ NA
❏ Yes
❏ No
❏ NA
❏ Yes
❏ No
❏ NA
Teri M. Kozik is a nurse researcher at St. Joseph’s Medical Center, Stockton, California. Mary G. Carey is associate director for clinical nursing research, Strong Memorial Hospital, Rochester, New York. Salah S. Al-Zaiti is an assistant professor at the Department of Acute and Tertiary Care Nursing, University of Pittsburgh, Pennsylvania. Michele M. Pelter is an assistant professor at the the Department of Physiological Nursing at University of California, San Francisco, California. ©2015 American Association of Critical-Care Nurses doi: http://dx.doi.org/10.4037/ajcc2015712
www.ajcconline.org
AJCC AMERICAN JOURNAL OF CRITICAL CARE, July 2015, Volume 24, No. 4
Downloaded from ajcc.aacnjournals.org at Zone Universite Laval on July 5, 2015
365
II
Answers: 1. Yes, the ECG is properly calibrated (see calibration mark right side). 2. Yes, a P wave precedes every QRS complex. 3. Yes, the heart rate is normal at 75 beats/min. 4. Yes, the QRS complex is narrow at approximately 80 milliseconds (ms) duration 5. No, the ST segment is not deviated. 6. No, the T wave is upright. 7. Yes, the QT interval is lengthened; best measured using the 8th and 9th beats (see arrows above). In both beats, the start of the QRS complex lands very close to the dark line of the ECG grid, which marks the start of the QT interval. The T wave ends 12 small boxes (ie, ~480 ms) from this point. Once corrected for heart rate using Bazett’s formula: QTc = QT /√ RR = 480 / √ 0.8 = 537 ms, the QT interval exceeds the normal limit of 450 for women. 8. Chamber hypertrophy cannot be assessed because Leads V1 and V5 are not shown.
Interpretation and Rationale Normal sinus rhythm at 75 beats/min and QT interval prolongation. Given the recently prescribed levofloxacin and symptoms on arrival, it is fair to suspect acquired long QT syndrome (aLQTS).
Mechanism and Management Channelopathies are caused by a malfunction in ion channels that regulate the movement of ions in and out of the myocardial cells during depolarization and repolarization. One channelopathy caused by medications affects cardiac repolarization by blocking the hERG channel during phase 3 of the action potential. This results in prolongation of the QT interval, termed long-QT syndrome (LQTS), and increases the risk for life-threatening arrhythmias. LQTS can be either genetic or acquired, with the latter occurring from clinical therapies such as induced hypothermia, electrolyte disturbances (hypokalemia, or hypomagnesemia), or therapy with medications known to prolong the QT-interval. Importantly, both types of LQTS predispose patients to ventricular arrhythmias, in particular torsades de pointes (TdP), which can lead to ventricular fibrillation and sudden cardiac death. The incidence of aLQTS is unknown, but it is estimated that more than 15 000 patients die of sudden cardiac death caused by aLQTS each year. This highlights
366
the importance of immediate identification and actions to reverse aLQTS. Thus, the Food and Drug Administration has published recommended guidelines for the pharmaceutical industry on proper testing of new agents and their effect on the QT/QTc interval. Identification of aLQTS following pharmacological therapy is challenging because more than 100 medications from varied classifications are associated with this syndrome. This patient was prescribed 2 medications known to lengthen the QT interval; escitalopram for depression, and levofloxacin to treat a respiratory infection. Levofloxacin appears to be the offending agent because the patient had taken escitalopram for years without symptoms suggestive of TdP (eg, syncope). Fortunately, aLQTS is reversible following cessation and metabolization of the offending medication(s). This patient did not have a prior ECG for comparison, but changing her antibiotic immediately is warranted. She should be admitted to the hospital and her ECG continuously monitored until the QT interval returns to normal. If her QT interval remains prolonged, the escitalopram may also need to be carefully tapered and stopped. Referral to an electrophysiologist to rule out the genetic form of LQTS may be indicated if the QT interval remains lengthened. This patient should be advised to notify all health care providers about this incident and have this noted in her medical record.
AJCC AMERICAN JOURNAL OF CRITICAL CARE, July 2015, Volume 24, No. 4
Downloaded from ajcc.aacnjournals.org at Zone Universite Laval on July 5, 2015
www.ajcconline.org
Drug Induced ECG Abnormalities Teri M. Kozik, Mary G. Carey, Salah S. Al-Zaiti and Michele M. Pelter Am J Crit Care 2015;24:365-366 doi: 10.4037/ajcc2015712 © 2015 American Association of Critical-Care Nurses Published online http://www.ajcconline.org Personal use only. For copyright permission information: http://ajcc.aacnjournals.org/cgi/external_ref?link_type=PERMISSIONDIRECT
Subscription Information http://ajcc.aacnjournals.org/subscriptions/ Information for authors http://ajcc.aacnjournals.org/misc/ifora.xhtml Submit a manuscript http://www.editorialmanager.com/ajcc Email alerts http://ajcc.aacnjournals.org/subscriptions/etoc.xhtml
AJCC, the American Journal of Critical Care, is the official peer-reviewed research journal of the American Association of Critical-Care Nurses (AACN), published bimonthly by The InnoVision Group, 101 Columbia, Aliso Viejo, CA 92656. Telephone: (800) 899-1712, (949) 362-2050, ext. 532. Fax: (949) 362-2049. Copyright © 2015 by AACN. All rights reserved.
Downloaded from ajcc.aacnjournals.org at Zone Universite Laval on July 5, 2015
