Reminder of important clinical lesson
CASE REPORT
Subaortic membrane mimicking hypertrophic cardiomyopathy Mark Joseph Anderson,1 Adelaide Arruda-Olson,2 Bernard Gersh,2 Jeffrey Geske2 1
Department of Internal Medicine, Mayo Clinic, Rochester, Minnesota, USA 2 Department of Medicine/ Cardiology, Mayo Clinic, Rochester, Minnesota, USA Correspondence to Dr Jeffrey Geske, [email protected] Accepted 19 October 2015
SUMMARY A 34-year-old man was referred for progressive angina and exertional dyspnoea refractory to medical therapy, with a presumptive diagnosis of hypertrophic cardiomyopathy (HCM). Transthoracic echocardiography (TTE) revealed asymmetric septal hypertrophy without systolic anterior motion of the mitral valve leaflet and with no dynamic left ventricular outflow tract (LVOT) obstruction. However, the LVOT velocity was elevated at rest as well as with provocation, without the characteristic late peaking obstruction seen in HCM. Focused TTE to evaluate for suspected fixed obstruction demonstrated a subaortic membrane 2.2 cm below the aortic valve. Coronary CT angiography confirmed the presence of the subaortic membrane and was negative for concomitant coronary artery disease. Surgical resection of the subaortic membrane and septal myectomy resulted in significant symptomatic relief and lower LVOT velocities on postoperative TTE. This case reminds the clinician to carefully evaluate for alternative causes of LVOT obstruction, especially subaortic membrane, as a cause of symptoms mimicking HCM.
BACKGROUND Hypertrophic cardiomyopathy (HCM) is the most common heritable cardiomyopathy and often presents with symptoms of heart failure.1 Conversely, a subaortic membrane is a rare cause of symptoms that may mimic HCM. Identifying mimics of HCM is essential because treatment strategies differ based on the underlying aetiology.
CASE PRESENTATION A 34-year-old man initially presented to local providers, with 1 year of angina and New York Heart Association class III exertional dyspnoea. His medical history was significant for paroxysmal atrial fibrillation controlled with sotalol. There was no family history of cardiomyopathy. Transthoracic echocardiography (TTE) revealed asymmetric septal hypertrophy and an elevated peak transaortic valve velocity on continuous wave Doppler (2.8 m/s). Owing to progressive symptoms refractory to medical therapy, the patient was referred to our centre, with a presumptive diagnosis of HCM.
INVESTIGATIONS To cite: Anderson MJ, Arruda-Olson A, Gersh B, et al. BMJ Case Rep Published online: [please include Day Month Year] doi:10.1136/bcr-2015212321
Examination revealed a grade II/VI systolic ejection murmur over the left sternal border, which remained unchanged with Valsalva manoeuver and following squat-to-stand. The ECG demonstrated atrial paced rhythm and left ventricular (LV) hypertrophy (figure 1). Initial TTE revealed asymmetric
LV hypertrophy with maximal thickness of 19 mm at the basal septum. Evidence of obstruction was present at rest with an elevated LV outflow tract (LVOT) velocity (2.3 m/s). However, there was minimal change in velocity with provocation (2.8 m/s with Valsalva, 2.8 m/s with amyl nitrite). Although the aortic valve appeared structurally normal, the Doppler pattern appeared similar to that typically seen in aortic stenosis, and the characteristic late peaking obstruction associated with dynamic obstruction in HCM was absent (figure 2). Minimal subvalvular mitral chordal systolic anterior motion (SAM) was demonstrated at rest, without involvement of the mitral valve leaflets (videos 1 and 2). Given evidence of a fixed obstruction, repeat TTE revealed a subaortic membrane 2.2 cm below the aortic valve, with resultant narrowing of the outflow tract to 1.1 cm (figure 3). CT angiography was negative for concomitant coronary artery disease, and confirmed the presence of the subaortic membrane and asymmetric septal hypertrophy (figure 4). Cardiac catheterisation revealed a fixed LVOT obstruction at rest (figure 5). Isoproterenol infusion at 5 mg/min revealed a mild dynamic component to the obstruction with an increase in gradient from 22 mm Hg at rest to 50 mm Hg after pharmacological provocation (figure 6). The characteristic ‘spike and dome’ contour of the aortic pressure tracing due to late systolic obstruction seen in HCM was attenuated in the setting of a primarily fixed obstruction, and the absence of a decrease in pulse pressure in the post-premature ventricular complex (PVC) beat was also consistent with a fixed subaortic obstruction rather than HCM (figure 6).2
DIFFERENTIAL DIAGNOSIS Several other potential mimics are considered in the evaluation of a patient with suspected HCM, since they demand unique management strategies (table 1). Asymmetric septal hypertrophy can be seen in patients with systemic hypertension. In addition, LV thickness >15 mm may be present in cases of hypertensive heart disease, making the distinction from HCM based on imaging alone even more difficult.3 However, the hypertrophy in hypertensive heart disease is often symmetric, suggesting against HCM.4 Our patient’s lack of a significant history of hypertension made this diagnosis unlikely. In contrast to hypertensive heart disease, LV hypertrophy secondary to valvular aortic stenosis (AS) should be distinguishable based on echocardiographic findings. In these patients, demonstration of symmetric hypertrophy, valvular
Anderson MJ, et al. BMJ Case Rep 2015. doi:10.1136/bcr-2015-212321
1
Reminder of important clinical lesson
Figure 1 ECG demonstrating atrial paced rhythm and left ventricular hypertrophy.
calcification and impaired cusp mobility will assist in distinguishing AS from HCM.5 Both valvular and subvalvular stenosis will demonstrate a fixed LVOT obstruction by continuous wave Doppler. Our patient’s lack of significant strength or endurance training by history excluded athlete’s heart as a diagnostic consideration. Moreover, he achieved a low workload during treadmill testing with VO2 of 16.8 mL/kg/min (39% of peak predicted) and completion of only 5.3 min of exercise (4.8 METs). However, physiological remodelling secondary to intense physical conditioning may produce a hypertrophic LV that may be confused with HCM in the right clinical setting. This entity can be distinguished by demonstrating either reduction in LV mass after a short period of deconditioning or LV end-diastolic dimension >55 mm.6 Also, the presence of either delayed gadolinium enhancement on cardiac MRI or impaired diastolic filling on tissue Doppler-derived indices supports HCM rather than athlete’s heart as the more likely diagnosis.6 7
Similar to our case, cardiac amyloid may present with heart failure, a non-dilated LV, increased ventricular wall thickness, preserved systolic function and dynamic LVOT obstruction. However, the absence of biventricular increased wall thickness, pericardial effusion, thickened valve leaflets, or a ‘speckled’ myocardial appearance on echocardiography favours a diagnosis of HCM.4 Classically, low voltage of the QRS complexes is associated with cardiac amyloid as well; however, its absence does not exclude the diagnosis in the right clinical setting. Peak longitudinal strain and peak longitudinal strain rate have been shown to be decreased in amyloidosis, with a pattern of apical sparing, which may allow for differentiation from HCM.8 9 This distinction is critical, since the treatment and prognosis both differ significantly between HCM and amyloidosis. The presence of cardiomyopathy has prognostic implications in primary light chain amyloidosis as well as in familial amyloidosis.10 In our patient, serum protein electrophoresis and
Figure 2 Transthoracic echocardiography. Continuous wave Doppler. Left ventricular outflow tract. 2
Anderson MJ, et al. BMJ Case Rep 2015. doi:10.1136/bcr-2015-212321
Reminder of important clinical lesson
Video 1 Transthoracic echocardiography demonstrating minimal subvalvular mitral chordal systolic anterior motion at rest without involvement of the mitral valve leaflets.
immunofixation did not demonstrate a monoclonal protein, and there was no family history of amyloidosis. Patients with Fabry disease, an X linked deficiency of α-galactosidase that has been confused with HCM, may present with heart failure in the third to fourth decade of life, with significant ventricular hypertrophy and even SAM of the mitral valve.4 However, a multisystem constellation of findings including angiokeratomas and renal failure in combination with symmetric, biventricular enlargement should raise suspicion for Fabry disease, as we have previously reported.11 The lack of other systemic findings in our patient made this diagnosis less likely, however, a normal α-galactosidase level was confirmed as part of our standard evaluation. Although the frequency of Fabry being misdiagnosed as HCM has been reported with varying frequency across different institutions,12 13 this entity should be considered as a possible HCM mimic, because failure to recognise it prevents the patient from access to enzyme replacement therapy.
Figure 3 Transthoracic echocardiography. Parasternal long axis. Left ventricular outflow tract in early systole. Yellow arrows—subaortic membrane. Red arrow—aortic valve leaflets.
Friedrich ataxia can also present with heart failure symptoms in association with increased septal thickness or increased thickness of the posterior LV wall, despite normal LV size and function.4 However, asymmetric septal hypertrophy and outflow tract obstruction are uncommon, and the neurological manifestations of the disease almost always precede the emergence of cardiac manifestations.4 Malformation syndromes such as Noonan syndrome and additional inborn errors of metabolism including glycogen storage diseases, lysosomal storage diseases, mitochondrial disorders and disorders of amino acid or fatty acid metabolism can produce cardiac manifestations that are similar to the traditional HCM phenotype caused by mutations in sarcomeric genes.14 These disorders are more commonly encountered in the
Video 2 Transthoracic echocardiography with Doppler demonstrating minimal subvalvular mitral chordal systolic anterior motion at rest without involvement of the mitral valve leaflets.
Anderson MJ, et al. BMJ Case Rep 2015. doi:10.1136/bcr-2015-212321
3
Reminder of important clinical lesson patient. The postoperative course was complicated by episodes of atrial fibrillation with rapid ventricular response, with reversion to sinus rhythm after sotalol up-titration.
OUTCOME AND FOLLOW-UP The patient tolerated the procedure well with significant symptomatic improvement. TTE performed 1 week postoperatively showed resolution of the elevated LVOT velocity (1.6 m/s at rest), and ECG demonstrated resolution of postoperative atrial fibrillation.
DISCUSSION Figure 4 Coronary CT angiography. Coronal view (AV, Aortic valve; AO, Aorta; LV, left ventricle).
paediatric and adolescent populations, but require discussion and awareness as certain cases may be detected later in life.14
TREATMENT Surgical resection of the circumferential subaortic membrane (figures 7 and 8) and septal myectomy were performed on the
Elucidation of the underlying cause of heart failure is critical in patients with structural heart disease, as treatment strategies and prognoses differ based on the aetiology. For example, further medical therapy or alcohol septal ablation for suspected HCM would have been ineffective in our patient. A recent report describes a 67-year-old patient with progressive dyspnoea who was initially suspected to have HCM after TTE demonstrated asymmetric septal hypertrophy and dynamic LVOT obstruction.15 Importantly, the LVOT continuous wave Doppler velocity waveform was not late peaking, and continued evaluation with transesophageal echocardiography (TEE) revealed a previously unseen subaortic membrane prompting therapeutic surgical resection.15
Figure 5 Continuous cardiac catheterisation pressure tracing underresting conditions demonstrating absence of a ‘spike and dome’ pattern of the aortic pressure contour and tardus of the aortic upstroke, consistent with predominantly fixed obstruction. Black—left ventricular pressure. Blue—aortic pressure.
Figure 6 Continuous cardiac catheterisation pressure tracing demonstrating fixed obstruction with a mild dynamic component provoked by isoproterenol infusion and characterised by an attenuated ‘spike and dome’ pattern. Red arrowhead— attenuated ‘spike and dome’ pattern. Red arrow—premature ventricular complex (PVC). Blue arrow—post-PVC beat demonstrating absence of a decrease in pulse pressure (P-P), consistent with fixed subaortic obstruction. Black—left ventricular pressure. Blue—aortic pressure.
4
Anderson MJ, et al. BMJ Case Rep 2015. doi:10.1136/bcr-2015-212321
Reminder of important clinical lesson Table 1
Mimics of hypertrophic cardiomyopathy
Mimic
Distinguishing characteristics
Hypertensive heart disease
Maximal left ventricular (LV) thickness typically 55 mm Normal diastolic filling Low-voltage QRS complexes Biventricular increased wall thickness Pericardial effusion Thickened valve leaflets ‘Speckled’ myocardial appearance on echocardiogram Decreased longitudinal strain and strain rate in an apical sparing pattern Deficient α-galactosidase level Angiokeratomas Renal involvement Symmetric biventricular enlargement GAA trinucleotide repeat Preceding neurological abnormalities Symmetric hypertrophy GAA mutation Hypotonia Failure to thrive AGL mutation Hypoglycaemia Failure to thrive PHKA1 mutation Hepatomegaly Growth retardation GNPTAB mutation Short stature GUSB mutation Macrocephaly Hepatosplenomegaly Pulmonary stenosis Atrial septal defect Short stature Pectus excavatum Webbed neck
Aortic stenosis
Athlete’s heart
Cardiac amyloid
Fabry disease
Friedrich ataxia
Type II glycogen storage disease
Type III glycogen storage disease
Type IX glycogen storage disease
Mucolipidosis II α/β Mucopolysaccharidosis type VII
Noonan syndrome
Figure 7 Intraoperative transesophageal echocardiography. Mid-esophageal short axis. Dotted lines—narrowed left ventricular outflow tract in the setting of subaortic membrane. Anderson MJ, et al. BMJ Case Rep 2015. doi:10.1136/bcr-2015-212321
Figure 8
Operative specimen from resection of subaortic membrane. 5
Reminder of important clinical lesson Guidelines from the American College of Cardiology Foundation and American Heart Association Task Force suggest that additional imaging such as TEE can be useful in patients in whom subaortic membrane should be excluded and when TTE is inconclusive.16 In another case of mistaken identity, Carr et al17 described a case of subaortic membrane mimicking valvular AS in a 47-year-old woman with heart failure referred for consideration of aortic valve replacement. Careful echocardiography revealed a subaortic membrane with an elevated gradient, which resolved after surgical resection.17 Guidelines from the European Society of Cardiology recommend that subaortic membrane should be considered in patients with LVOT obstruction, particularly if there are clues to suggest an alternative diagnosis, such as absence of leaflet SAM.14 The diagnosis of subaortic membrane is typically made with echocardiography, but the use of cardiac MRI (CMR) has been described in select cases. Teis et al18 report the case of a 31-year-old woman with dyspnoea presumed to be due to severe valvular AS in which an initial TTE revealed turbulent flow in the LVOT, without a clear aetiology. CMR identified a discrete subaortic membrane, and intraoperative TEE confirmed the presence of a circumferential membrane, which was ultimately resected. Considered together, these cases highlight the importance of careful evaluation for alternative causes of LVOT obstruction, especially when considering therapeutic interventions. The indications for resection of subaortic membrane rely on the severity of LVOT obstruction to guide management decisions. Intervention is recommended in patients with a mean Doppler gradient ≥30 mm Hg or peak instantaneous gradient ≥50 mm Hg (class I, level of evidence C), and surgery may be considered at lower gradients for patients with LV hypertrophy, those planning pregnancy, or in athletes planning to engage in competitive sports (class IIb, level of evidence C).19 Concomitant aortic regurgitation (AR) may have diagnostic as well as therapeutic implications. Since AR can occur in greater than half of patients with a subaortic membrane, its presence in a clinical scenario similar to our case may further suggest the possibility that a subaortic membrane is present. In addition, surgical intervention is recommended at lower gradients in patients with progressive AR and LV end-systolic diameter >50 mm, or LV ejection fraction
CASE REPORT
Subaortic membrane mimicking hypertrophic cardiomyopathy Mark Joseph Anderson,1 Adelaide Arruda-Olson,2 Bernard Gersh,2 Jeffrey Geske2 1
Department of Internal Medicine, Mayo Clinic, Rochester, Minnesota, USA 2 Department of Medicine/ Cardiology, Mayo Clinic, Rochester, Minnesota, USA Correspondence to Dr Jeffrey Geske, [email protected] Accepted 19 October 2015
SUMMARY A 34-year-old man was referred for progressive angina and exertional dyspnoea refractory to medical therapy, with a presumptive diagnosis of hypertrophic cardiomyopathy (HCM). Transthoracic echocardiography (TTE) revealed asymmetric septal hypertrophy without systolic anterior motion of the mitral valve leaflet and with no dynamic left ventricular outflow tract (LVOT) obstruction. However, the LVOT velocity was elevated at rest as well as with provocation, without the characteristic late peaking obstruction seen in HCM. Focused TTE to evaluate for suspected fixed obstruction demonstrated a subaortic membrane 2.2 cm below the aortic valve. Coronary CT angiography confirmed the presence of the subaortic membrane and was negative for concomitant coronary artery disease. Surgical resection of the subaortic membrane and septal myectomy resulted in significant symptomatic relief and lower LVOT velocities on postoperative TTE. This case reminds the clinician to carefully evaluate for alternative causes of LVOT obstruction, especially subaortic membrane, as a cause of symptoms mimicking HCM.
BACKGROUND Hypertrophic cardiomyopathy (HCM) is the most common heritable cardiomyopathy and often presents with symptoms of heart failure.1 Conversely, a subaortic membrane is a rare cause of symptoms that may mimic HCM. Identifying mimics of HCM is essential because treatment strategies differ based on the underlying aetiology.
CASE PRESENTATION A 34-year-old man initially presented to local providers, with 1 year of angina and New York Heart Association class III exertional dyspnoea. His medical history was significant for paroxysmal atrial fibrillation controlled with sotalol. There was no family history of cardiomyopathy. Transthoracic echocardiography (TTE) revealed asymmetric septal hypertrophy and an elevated peak transaortic valve velocity on continuous wave Doppler (2.8 m/s). Owing to progressive symptoms refractory to medical therapy, the patient was referred to our centre, with a presumptive diagnosis of HCM.
INVESTIGATIONS To cite: Anderson MJ, Arruda-Olson A, Gersh B, et al. BMJ Case Rep Published online: [please include Day Month Year] doi:10.1136/bcr-2015212321
Examination revealed a grade II/VI systolic ejection murmur over the left sternal border, which remained unchanged with Valsalva manoeuver and following squat-to-stand. The ECG demonstrated atrial paced rhythm and left ventricular (LV) hypertrophy (figure 1). Initial TTE revealed asymmetric
LV hypertrophy with maximal thickness of 19 mm at the basal septum. Evidence of obstruction was present at rest with an elevated LV outflow tract (LVOT) velocity (2.3 m/s). However, there was minimal change in velocity with provocation (2.8 m/s with Valsalva, 2.8 m/s with amyl nitrite). Although the aortic valve appeared structurally normal, the Doppler pattern appeared similar to that typically seen in aortic stenosis, and the characteristic late peaking obstruction associated with dynamic obstruction in HCM was absent (figure 2). Minimal subvalvular mitral chordal systolic anterior motion (SAM) was demonstrated at rest, without involvement of the mitral valve leaflets (videos 1 and 2). Given evidence of a fixed obstruction, repeat TTE revealed a subaortic membrane 2.2 cm below the aortic valve, with resultant narrowing of the outflow tract to 1.1 cm (figure 3). CT angiography was negative for concomitant coronary artery disease, and confirmed the presence of the subaortic membrane and asymmetric septal hypertrophy (figure 4). Cardiac catheterisation revealed a fixed LVOT obstruction at rest (figure 5). Isoproterenol infusion at 5 mg/min revealed a mild dynamic component to the obstruction with an increase in gradient from 22 mm Hg at rest to 50 mm Hg after pharmacological provocation (figure 6). The characteristic ‘spike and dome’ contour of the aortic pressure tracing due to late systolic obstruction seen in HCM was attenuated in the setting of a primarily fixed obstruction, and the absence of a decrease in pulse pressure in the post-premature ventricular complex (PVC) beat was also consistent with a fixed subaortic obstruction rather than HCM (figure 6).2
DIFFERENTIAL DIAGNOSIS Several other potential mimics are considered in the evaluation of a patient with suspected HCM, since they demand unique management strategies (table 1). Asymmetric septal hypertrophy can be seen in patients with systemic hypertension. In addition, LV thickness >15 mm may be present in cases of hypertensive heart disease, making the distinction from HCM based on imaging alone even more difficult.3 However, the hypertrophy in hypertensive heart disease is often symmetric, suggesting against HCM.4 Our patient’s lack of a significant history of hypertension made this diagnosis unlikely. In contrast to hypertensive heart disease, LV hypertrophy secondary to valvular aortic stenosis (AS) should be distinguishable based on echocardiographic findings. In these patients, demonstration of symmetric hypertrophy, valvular
Anderson MJ, et al. BMJ Case Rep 2015. doi:10.1136/bcr-2015-212321
1
Reminder of important clinical lesson
Figure 1 ECG demonstrating atrial paced rhythm and left ventricular hypertrophy.
calcification and impaired cusp mobility will assist in distinguishing AS from HCM.5 Both valvular and subvalvular stenosis will demonstrate a fixed LVOT obstruction by continuous wave Doppler. Our patient’s lack of significant strength or endurance training by history excluded athlete’s heart as a diagnostic consideration. Moreover, he achieved a low workload during treadmill testing with VO2 of 16.8 mL/kg/min (39% of peak predicted) and completion of only 5.3 min of exercise (4.8 METs). However, physiological remodelling secondary to intense physical conditioning may produce a hypertrophic LV that may be confused with HCM in the right clinical setting. This entity can be distinguished by demonstrating either reduction in LV mass after a short period of deconditioning or LV end-diastolic dimension >55 mm.6 Also, the presence of either delayed gadolinium enhancement on cardiac MRI or impaired diastolic filling on tissue Doppler-derived indices supports HCM rather than athlete’s heart as the more likely diagnosis.6 7
Similar to our case, cardiac amyloid may present with heart failure, a non-dilated LV, increased ventricular wall thickness, preserved systolic function and dynamic LVOT obstruction. However, the absence of biventricular increased wall thickness, pericardial effusion, thickened valve leaflets, or a ‘speckled’ myocardial appearance on echocardiography favours a diagnosis of HCM.4 Classically, low voltage of the QRS complexes is associated with cardiac amyloid as well; however, its absence does not exclude the diagnosis in the right clinical setting. Peak longitudinal strain and peak longitudinal strain rate have been shown to be decreased in amyloidosis, with a pattern of apical sparing, which may allow for differentiation from HCM.8 9 This distinction is critical, since the treatment and prognosis both differ significantly between HCM and amyloidosis. The presence of cardiomyopathy has prognostic implications in primary light chain amyloidosis as well as in familial amyloidosis.10 In our patient, serum protein electrophoresis and
Figure 2 Transthoracic echocardiography. Continuous wave Doppler. Left ventricular outflow tract. 2
Anderson MJ, et al. BMJ Case Rep 2015. doi:10.1136/bcr-2015-212321
Reminder of important clinical lesson
Video 1 Transthoracic echocardiography demonstrating minimal subvalvular mitral chordal systolic anterior motion at rest without involvement of the mitral valve leaflets.
immunofixation did not demonstrate a monoclonal protein, and there was no family history of amyloidosis. Patients with Fabry disease, an X linked deficiency of α-galactosidase that has been confused with HCM, may present with heart failure in the third to fourth decade of life, with significant ventricular hypertrophy and even SAM of the mitral valve.4 However, a multisystem constellation of findings including angiokeratomas and renal failure in combination with symmetric, biventricular enlargement should raise suspicion for Fabry disease, as we have previously reported.11 The lack of other systemic findings in our patient made this diagnosis less likely, however, a normal α-galactosidase level was confirmed as part of our standard evaluation. Although the frequency of Fabry being misdiagnosed as HCM has been reported with varying frequency across different institutions,12 13 this entity should be considered as a possible HCM mimic, because failure to recognise it prevents the patient from access to enzyme replacement therapy.
Figure 3 Transthoracic echocardiography. Parasternal long axis. Left ventricular outflow tract in early systole. Yellow arrows—subaortic membrane. Red arrow—aortic valve leaflets.
Friedrich ataxia can also present with heart failure symptoms in association with increased septal thickness or increased thickness of the posterior LV wall, despite normal LV size and function.4 However, asymmetric septal hypertrophy and outflow tract obstruction are uncommon, and the neurological manifestations of the disease almost always precede the emergence of cardiac manifestations.4 Malformation syndromes such as Noonan syndrome and additional inborn errors of metabolism including glycogen storage diseases, lysosomal storage diseases, mitochondrial disorders and disorders of amino acid or fatty acid metabolism can produce cardiac manifestations that are similar to the traditional HCM phenotype caused by mutations in sarcomeric genes.14 These disorders are more commonly encountered in the
Video 2 Transthoracic echocardiography with Doppler demonstrating minimal subvalvular mitral chordal systolic anterior motion at rest without involvement of the mitral valve leaflets.
Anderson MJ, et al. BMJ Case Rep 2015. doi:10.1136/bcr-2015-212321
3
Reminder of important clinical lesson patient. The postoperative course was complicated by episodes of atrial fibrillation with rapid ventricular response, with reversion to sinus rhythm after sotalol up-titration.
OUTCOME AND FOLLOW-UP The patient tolerated the procedure well with significant symptomatic improvement. TTE performed 1 week postoperatively showed resolution of the elevated LVOT velocity (1.6 m/s at rest), and ECG demonstrated resolution of postoperative atrial fibrillation.
DISCUSSION Figure 4 Coronary CT angiography. Coronal view (AV, Aortic valve; AO, Aorta; LV, left ventricle).
paediatric and adolescent populations, but require discussion and awareness as certain cases may be detected later in life.14
TREATMENT Surgical resection of the circumferential subaortic membrane (figures 7 and 8) and septal myectomy were performed on the
Elucidation of the underlying cause of heart failure is critical in patients with structural heart disease, as treatment strategies and prognoses differ based on the aetiology. For example, further medical therapy or alcohol septal ablation for suspected HCM would have been ineffective in our patient. A recent report describes a 67-year-old patient with progressive dyspnoea who was initially suspected to have HCM after TTE demonstrated asymmetric septal hypertrophy and dynamic LVOT obstruction.15 Importantly, the LVOT continuous wave Doppler velocity waveform was not late peaking, and continued evaluation with transesophageal echocardiography (TEE) revealed a previously unseen subaortic membrane prompting therapeutic surgical resection.15
Figure 5 Continuous cardiac catheterisation pressure tracing underresting conditions demonstrating absence of a ‘spike and dome’ pattern of the aortic pressure contour and tardus of the aortic upstroke, consistent with predominantly fixed obstruction. Black—left ventricular pressure. Blue—aortic pressure.
Figure 6 Continuous cardiac catheterisation pressure tracing demonstrating fixed obstruction with a mild dynamic component provoked by isoproterenol infusion and characterised by an attenuated ‘spike and dome’ pattern. Red arrowhead— attenuated ‘spike and dome’ pattern. Red arrow—premature ventricular complex (PVC). Blue arrow—post-PVC beat demonstrating absence of a decrease in pulse pressure (P-P), consistent with fixed subaortic obstruction. Black—left ventricular pressure. Blue—aortic pressure.
4
Anderson MJ, et al. BMJ Case Rep 2015. doi:10.1136/bcr-2015-212321
Reminder of important clinical lesson Table 1
Mimics of hypertrophic cardiomyopathy
Mimic
Distinguishing characteristics
Hypertensive heart disease
Maximal left ventricular (LV) thickness typically 55 mm Normal diastolic filling Low-voltage QRS complexes Biventricular increased wall thickness Pericardial effusion Thickened valve leaflets ‘Speckled’ myocardial appearance on echocardiogram Decreased longitudinal strain and strain rate in an apical sparing pattern Deficient α-galactosidase level Angiokeratomas Renal involvement Symmetric biventricular enlargement GAA trinucleotide repeat Preceding neurological abnormalities Symmetric hypertrophy GAA mutation Hypotonia Failure to thrive AGL mutation Hypoglycaemia Failure to thrive PHKA1 mutation Hepatomegaly Growth retardation GNPTAB mutation Short stature GUSB mutation Macrocephaly Hepatosplenomegaly Pulmonary stenosis Atrial septal defect Short stature Pectus excavatum Webbed neck
Aortic stenosis
Athlete’s heart
Cardiac amyloid
Fabry disease
Friedrich ataxia
Type II glycogen storage disease
Type III glycogen storage disease
Type IX glycogen storage disease
Mucolipidosis II α/β Mucopolysaccharidosis type VII
Noonan syndrome
Figure 7 Intraoperative transesophageal echocardiography. Mid-esophageal short axis. Dotted lines—narrowed left ventricular outflow tract in the setting of subaortic membrane. Anderson MJ, et al. BMJ Case Rep 2015. doi:10.1136/bcr-2015-212321
Figure 8
Operative specimen from resection of subaortic membrane. 5
Reminder of important clinical lesson Guidelines from the American College of Cardiology Foundation and American Heart Association Task Force suggest that additional imaging such as TEE can be useful in patients in whom subaortic membrane should be excluded and when TTE is inconclusive.16 In another case of mistaken identity, Carr et al17 described a case of subaortic membrane mimicking valvular AS in a 47-year-old woman with heart failure referred for consideration of aortic valve replacement. Careful echocardiography revealed a subaortic membrane with an elevated gradient, which resolved after surgical resection.17 Guidelines from the European Society of Cardiology recommend that subaortic membrane should be considered in patients with LVOT obstruction, particularly if there are clues to suggest an alternative diagnosis, such as absence of leaflet SAM.14 The diagnosis of subaortic membrane is typically made with echocardiography, but the use of cardiac MRI (CMR) has been described in select cases. Teis et al18 report the case of a 31-year-old woman with dyspnoea presumed to be due to severe valvular AS in which an initial TTE revealed turbulent flow in the LVOT, without a clear aetiology. CMR identified a discrete subaortic membrane, and intraoperative TEE confirmed the presence of a circumferential membrane, which was ultimately resected. Considered together, these cases highlight the importance of careful evaluation for alternative causes of LVOT obstruction, especially when considering therapeutic interventions. The indications for resection of subaortic membrane rely on the severity of LVOT obstruction to guide management decisions. Intervention is recommended in patients with a mean Doppler gradient ≥30 mm Hg or peak instantaneous gradient ≥50 mm Hg (class I, level of evidence C), and surgery may be considered at lower gradients for patients with LV hypertrophy, those planning pregnancy, or in athletes planning to engage in competitive sports (class IIb, level of evidence C).19 Concomitant aortic regurgitation (AR) may have diagnostic as well as therapeutic implications. Since AR can occur in greater than half of patients with a subaortic membrane, its presence in a clinical scenario similar to our case may further suggest the possibility that a subaortic membrane is present. In addition, surgical intervention is recommended at lower gradients in patients with progressive AR and LV end-systolic diameter >50 mm, or LV ejection fraction
