Hypertrophic cardiomyopathy: Clinical sciences

Hypertrophic cardiomyopathy, or HCM, is a genetic condition associated with left ventricular hypertrophy that cannot be attributed to another cardiac, systemic, or metabolic disease. In HCM, ventricular hypertrophy causes decreased compliance, which results in poor left ventricular filling.

In some of these patients, ventricular septal hypertrophy combined with abnormal motion of the mitral valve causes left ventricular outflow obstruction, which can manifest as syncope or sudden cardiac death during intense physical activity.

If a pediatric patient presents with a chief concern suggesting hypertrophic cardiomyopathy, you should first perform an ABCDE assessment to determine if your patient is stable or unstable.

If the patient is unstable, stabilize the airway, breathing, and circulation. Unstable patients can present with life-threatening arrhythmias such as ventricular tachycardia, so attach a cardiac monitor, and be ready to perform defibrillation if needed! Next, obtain IV access, consider IV fluids, and begin continuous vital sign monitoring, including blood pressure, heart rate, and oxygen saturation. Finally, if needed, provide supplemental oxygen.

Here’s a high-yield fact! Hypertrophic cardiomyopathy is the most common cardiac condition associated with sudden cardiac death in young athletes. In these cases, sudden death can be the first presentation of HCM, since most affected individuals are asymptomatic. So, be sure to perform a careful cardiac examination in patients presenting for a sports pre-participation physical.

Okay, now let’s go back to the ABCDE assessment and look at stable patients.

Your next step here is to perform a focused history and physical examination. Patients might report symptoms like exertional dyspnea, atypical chest pain, palpitations, or syncope; but keep in mind that many patients with HCM are asymptomatic. Family history could reveal other family members with HCM or sudden cardiac death. Physical exam findings typically include a systolic ejection murmur at the lower left sternal border that decreases in intensity with maneuvers that increase preload, like squatting; and increases in intensity with maneuvers that decrease preload, like the Valsalva or standing. You might also detect an S4 gallop. Palpation of the chest typically reveals a prominent apical point of maximum impulse; as well as a bifid carotid pulse, called “pulsus bisferiens.”

Based on these findings, you should suspect hypertrophic cardiomyopathy and order an echocardiogram, or echo, as well as a baseline 12-lead electrocardiogram, or ECG.

Findings on echo will include left ventricular hypertrophy that’s especially prominent in the ventricular septum, as well as reduced left ventricular chamber size, abnormal motion of the mitral valve, and mitral regurgitation. Approximately three-quarters of patients will also have left ventricular outflow tract obstruction. When it comes to the ECG, it typically demonstrates left ventricular hypertrophy, or LVH. You might also see inverted T waves and deep Q waves in the inferior or lateral leads.

Next, assess the diagnostic criteria for HCM which includes left ventricular wall thickness that is more than 2 standard deviations above the mean for the patient's age, sex, and body surface area. If these criteria are not met, consider an alternative diagnosis, such as uncontrolled hypertension, aortic stenosis, or septal hypertrophy in an infant born to a mother with diabetes.
On the flip side, if these criteria are met, you should proceed with genetic testing, since HCM is inherited in an autosomal dominant fashion. A mutation in a gene coding for sarcomeric proteins, such as MYBPC3 or MYH7, confirms the diagnosis of HCM.

Okay, here’s a clinical pearl to keep in mind! Hypertrophic cardiomyopathy can also occur in association with systemic disorders, like mitochondrial myopathies, glycogen and lysosomal storage diseases, Fabry disease, and amyloidosis. Even though the magnitude of LVH in these conditions can be similar to that seen in HCM caused by sarcomeric gene mutations, keep in mind that the pathophysiology, natural history, and treatment of these conditions are not the same. For this reason, HCM caused by sarcomeric gene mutations is considered a separate entity from these systemic disorders.

Now, once you’ve diagnosed HCM, advise your patient to avoid conditions that decrease preload, such as dehydration or the use of vasodilator medications and high-dose diuretics, since these can aggravate their symptoms in the presence of left ventricular outflow tract obstruction. Additionally, while individuals with HCM should be encouraged to maintain healthy activity levels, high-intensity physical activity and competitive sports may increase the risk of syncope or sudden cardiac death. Because of this, they should seek guidance from a specialist before engaging in high-intensity activities. Finally, provide screening for first-degree relatives, including an ECG and echo, as well as genetic testing if your patient’s genetic testing was positive.

Next, perform a risk assessment for sudden cardiac death, or SCD. Your patient is at high risk of SCD if they’ve had a prior episode of sustained ventricular tachycardia, ventricular fibrillation, or cardiac arrest. Other risk factors include a family history of SCD from HCM, 2 or more unexplained episodes of syncope, or previously documented non-sustained ventricular tachycardia. Finally, echocardiographic risk factors include massive LVH, a left ventricular apical aneurysm, or a reduced ejection fraction.