Hypertrophic Cardiomyopathy Workup

Updated: Apr 29, 2022
  • Author: Sandy N Shah, DO, MBA, FACC, FACP, FACOI; Chief Editor: Gyanendra K Sharma, MD, FACC, FASE  more...
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Workup

Approach Considerations

Approach to hypertrophic cardiomyopathy (HCM) starts with a comprehensive history and physical examination. Multiple tests are used not only in the evaluation of patients with possible HCM but also to determine the diagnosis of HCM, severity of left ventricular (LV) outflow tract gradient, degree of mitral regurgitation, types of arrhythmias, LV function, and prognosis.

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Laboratory Studies

First-line laboratory tests are similar in adults and children. [9]  Routine laboratory studies may aid in the evaluation of the etiology and/or exacerbating factors underlying the left ventricular (LV) dysfunction.

  • Hemoglobin level: Anemia exacerbates chest pain and dyspnea
  • Fasting glucose levels
  • Renal function tests: Impaired renal function may be seen with severe LV dysfunction
  • Liver function tests (LFT)
  • Brain natriuretic peptide (BNP), N-terminal proBNP (NT-proBNP), and troponin T levels: Elevated BNP, NT-proBNP, and troponin T levels are associated with a higher risk of cardiovascular events, heart failure, and death. However, BNP and NT-proBNP do not correlate well with heart failure symptoms in HCM patients.
  • Thyroid function tests: In patients on amiodarone, thyroid studies should be obtained at the time of diagnosis and monitored every 6 months 

Additional laboratory tests can be performed after a specialist evaluation, as needed.

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Two-Dimensional Echocardiography and Doppler Studies

When considering a diagnosis of hypertrohic cardiomyopathy (HCM), all patients should undergo complete transthoracic echocardiography (TTE) with two dimensional (2D), color Doppler, spectral Dopler, and tissue Doppler. TTE aids in evaluation of the cardiac morphology, systolic and diastolic function, presence and severity of left venticular outflow tract (LVOT) gradient, and the degree of mitral  regurgitation. 

LV hypertrophy (LVH)

LVH is evaluated primarily in the parasternal short-axis plane during diastole at the level of mitral valve and papillary muscles. Parasternal long-axis and apical 2- and 4- chamber views are also utilized with short-axis images of LVH.

Unexplained LV wall thickness of ≥15 mm anywhere within the LV confirms the diagnosis of HCM.  LV wall thickness ≥13 mm in the presence of a family history of HCM may also be considered diagnostic of HCM. The most common location of LVH is the basal anterior septum. About 10% of patients have LV wall thickening involving one or two LV segments.

Systolic anterior motion (SAM) of the mitral valve

SAM of the mitral valve is positioned in the LVOT. When there is contact between the mitral valve and septum, LVOT obstruction will develop. The greater the duration of the mitral-septum contact, the higher the LVOT obstruction. 

LVOT obstruction

LVOT obstruction gradient can be measured noninvasively using echocardiography continuous-wave Doppler. The best views to determine the LVOT gradient is the apical long-axis window. SAM and mitral regurgitation are often present together, and it can be difficult to distinguish LVOT signal from mitral regurgitation. 

Outflow gradient varies from day to day. It is influenced by myocardial contractility and loading conditions such as dehydration, alcohol, etc. If patients do not have an LVOT gradient at rest, then provoking the gradient is important for patient management. Exercise (stress) echocardiography using the standard Bruce protocol is the preferred method because it represents daily activities. A pharmacologic approach using amyl nitrite, dobutamine, or isoproterenol and the Valsalva maneuver are alternative approaches to provoke the LVOT gradient. However, note that the pharmacologic and nonpharmacologic approaches do not represent true LVOT gradient during daily activities.

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Ambulatory ECG Monitoring

Ambulatory electrocardiographic (ECG) monitoring should be performed all patients with hypertrophic cardiomyopathy (HCM) for risk assessment of not only ventricular arrhythmias but also for sudden cardiac death. It should be also be performed in patients with palpitations to assess for atrial fibrillation / atrial flutter. Ambulatory ECG monitoring is performed for 24-48 hours.  

Routine use of extended ambulatory monitoring for longer than 48 hours to detect ventricular arrhythmia for risk stratification is not determined.

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Cardiac Magnetic Resonance Imaging

Cardiac magnetic resonance imaging (CMRI) provides far more information compared to echocardiography. CMRI should be performed when a diagnosis of hypertrophic cardiomyopathy (HCM) is not certain after echocardiography. 

CMRI can be performed to risk stratify, detect left ventricular hypertrophy that is unrecognized or not well seen on echocardiography, consider septal reduction therapy in those whose mitral valve and papillary muscle anatomy is not well defined by echocardiography, or to determine septal ablation versus surgical myectomy. CMRI also aids in determining the ischemia burden in HCM, which has been associated with morphologic markers of disease severity, fibrosis, arrhythmia, and functional capacity. [10]

Contrast-enhanced CMRI uses intravenous injection of gadolinium for hyperenhancement (late gadolinium enhancement). This hyperenhancement represents myocardial fibrosis. CMRI also provides the following information:

  • Assessment of diastolic function
  • Assessment of regional myocardial function
  • Identification and quantification of right ventricular hypertrophy
  • Evidence of microvascular dysfunction
  • Subtle structural abnormalities 
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Electrocardiography

Electrocardiography (ECG) should be performed on all patients with possible hypertrophic cardiomyopathy (HCM), although ECG is not specific for HCM.

The ECG is normal in 10% of cases of HCM; thus, it typically abnormal with the most common ECG abnormality being repolarization changes.  Other commmon ECG abnormalities are as follows:

  • Left-axis deviation
  • P-wave abnormalities, suggesting left and/or right atrial enlargement. Right atrial enlargment with left ventricular hypertrophy strongly suggest HCM.
  • Abnormal Q waves in the inferior and lateral leads suggest septal depolarization of the hypertrophied myocardium.
  • Deeply inverted T waves in the mid-precordial leads (V2-V4) are seen in the apical variant of HCM.
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Cardiac Catheterization

Although not required for the diagnosis of hypertrophic cardiomyopathy (HCM), a diagnostic cardiac catheterization is useful to determine the degree of outflow obstruction, cardiac hemodynamics, the diastolic characteristics of the left ventricle and LV anatomy, and, of particular importance, the coronary anatomy. Cardiac catheterization is also reserved for situations when invasive modalities of therapy, such as a pacemaker or surgery, are being considered.

Therapeutic cardiac catheterization interventions, utilized in well selected cases of hypertrophic cardiomyopathy, include transcatheter septal alcohol ablation to relieve the LV outflow obstruction by intentional infarction of a portion of the interventricular septum.

Cardiac catheterization frequently reveals diminished diastolic LV compliance and, in cases of obstructive hypertrophic cardiomyopathy, a systolic intracavitary pressure gradient within the body of the left ventricle, related to subaortic systolic anterior motion of the mitral valve abutting the markedly hypertrophied septum. The subaortic pressure gradient may be quite labile and may vary between 0 and 175 mm Hg in the same patient under different conditions.

The arterial pressure tracing found on cardiac catheterization may demonstrate a "spike and dome" configuration similar to the carotid pulse recording. As a consequence of diminished left ventricular compliance, the mean left atrial pressure and, particularly, the a wave, in the left atrial pressure pulse and left ventricular end-diastolic pressures are usually elevated.

Artifactual outflow gradients may occur if the left ventricular catheter becomes entrapped in the trabeculae of a markedly hypertrophied left ventricle.

Cardiac output may be depressed in patients with long-standing severe gradients, but in the majority of patients, it is normal. Occasionally, cardiac output is elevated in patients with markedly hyperdynamic LV systolic function.

Hemodynamic abnormality in hypertrophic cardiomyopathy (HCM) is not limited to the left side of the heart. Approximately one fourth of patients demonstrate pulmonary hypertension. It is usually mild, but in some cases, it can be moderate to severe, due (at least in part) to elevated mean left atrial pressures resulting from diminished LV compliance. A pressure gradient in the right ventricular outflow tract occurs in approximately 15% of patients who have obstruction to LV outflow and appears to result from markedly hypertrophied right ventricular tissue. Right atrial and right ventricular end-diastolic pressures may be slightly elevated.

Outflow gradient variability

A feature characteristic of HCM is the variability and lability of the LV outflow gradient. A patient may demonstrate a large gradient on one occasion and have none at another time. In some patients without a resting gradient, it may be temporarily provoked.

Three basic mechanisms involved in the production of dynamic gradients include increased contractility, decreased preload, and decreased afterload. In many patients with HCM, the gradient is midventricular and may be intensified by increased contractility, which exerts a direct muscular sphincter action.

The stimuli that provoke or intensify LV outflow tract gradients in HCM generally improve myocardial performance in normal subjects and in patients with most other forms of heart disease. Conversely, reductions in contractility or increases in preload or afterload, which increased LV dimensions, reduce or abolish the LV outflow gradient.

One of the most potent stimuli for enhancing the LV outflow gradient is postextrasystolic potentiation, which may occur after a spontaneous premature contraction or be induced by mechanical stimulation with a catheter. The resultant increase in contractility in the beat after the extrasystole is so marked that it produces an increase in the outflow gradient. A characteristic change often occurs in the directly recorded arterial pressure tracing, which, in addition to displacing a more marked spike and dome configuration, exhibits a pulse pressure that fails to increase as expected or actually decreases (the so-called Brockenbrough-Braunwald phenomenon).

This is one of the more reliable signs of dynamic obstruction of the LV outflow tract. In some patients, the postextrasystolic murmur is attenuated despite an increase in the outflow gradient, apparently because, in this setting, the murmur mirrors to a greater degree changes in the severity of mitral regurgitation than changes in the outflow tract gradient.

Left ventriculography

Left ventriculography typically shows a hypertrophied ventricle and the presence of an outflow gradient. The anterior leaflet of the mitral valve moves anteriorly during systole and encroaches on the outflow tract. Associated with this motion is mitral regurgitation, which is a constant finding in patients with gradients. The LV cavity is often small, and systolic ejection is typically vigorous, resulting in virtual obliteration of the ventricular cavity at end systole. In patients with apical involvement, the extensive hypertrophy may convey a spade-like configuration to the left ventricular angiogram.

Other findings

In patients older than age 45 years, obstructive coronary artery disease may be present, although the symptoms of ischemic pain are indistinguishable from those of patients with normal coronary angiograms and HCM. The left anterior descending and septal perforator coronary arteries may demonstrate phasic narrowing and associated abnormalities of flow during systole

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Electrophysiologic Studies

A diagnostic electrophysiology study (EPS) uses programmed electrical stimulation to identify conduction abnormalities, sinus node dysfunction (SND), and the potential for inducible arrhythmias. In hypertrophic cardiomyopathy (HCM), syncope and presyncope are due to arrhythmia, left ventricular outflow tract (LVOT) obstruction, or inappropriate vasodilatation with adequate cardiac output. EPSs rarely discover the mechanism of sudden death, and they are not indicated for decision making on implantable cardioverter-defibrillator (ICD) therapy for primary prevention of sudden death.

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Exercise testing

Exercise stress testing should be performed on patients with known or suspected hypertrophic cardiomyopathy (HCM) for risk stratification and evaluation of the left ventricular outflow tract (LVOT) gradient. It is preferred over pharmacologic stress testing. Exercise stress testing provides information on functional capacity, exercise-induced ischemia, arrhythmia, and obstruction.

Echocardiographic images should be utilized with stress testing.

Exercise stress testing should be performed prior to the institution of therapy. Follow-up exercise testing may be helpful to assess treatment. Important findings during exercise testing include the following:

  • Symptoms of angina, dyspnea, palpitations, or presyncope
  • Hypotension or lack of blood pressure response with exercise
  • Arrhythmia (atrial fibrillation or ventricular tachycardia)
  • ST-segment depression 
  • Increase of or developing LVOT gradient
  • Increase of or developing mitral regurgitation
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