Hypertrophic Cardiomyopathy
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Direct answer
Hypertrophic cardiomyopathy is an inherited sarcomere disorder causing unexplained left ventricular hypertrophy, usually asymmetric and septal, and it is a leading cause of sudden cardiac death in young athletes. In many patients the septum obstructs the left ventricular outflow tract through systolic anterior motion of the mitral valve, producing a crescendo-decrescendo murmur that increases with Valsalva. Beta-blockers or verapamil are the first drugs for symptoms, and septal reduction treats refractory obstruction.
What you must remember
- Genetics: autosomal dominant, most often from MYH7 or MYBPC3 sarcomere variants, with variable expression.
- Diagnosis: a wall thickness of 15 mm or more in an adult without another cause of hypertrophy such as hypertension or aortic stenosis; lower thresholds apply in relatives.
- Murmur: a crescendo-decrescendo ejection systolic murmur at the lower left sternal edge that rises with Valsalva, standing and post-extrasystolic beats, and falls with squatting and handgrip.
- Obstruction: a gradient of 30 mmHg or more at rest or on provocation, caused by systolic anterior motion of the mitral valve; 50 mmHg or more is the usual threshold for septal reduction.
- Sudden death risk: prior arrest, unexplained syncope, family history of sudden death, non-sustained VT, massive hypertrophy of 30 mm or more, and an abnormal blood pressure response to exercise.
- Drugs: beta-blockers and verapamil relieve symptoms and obstruction; disopyramide helps refractory cases; nitrates, hydralazine and dehydration worsen obstruction.
- Septal reduction: alcohol septal ablation or surgical myectomy for refractory obstruction; cardiac myosin inhibitors such as mavacamten are used for obstructive disease per current guidance.
- Athletes: competitive sport is restricted in many patients, and ICD decisions follow formal risk stratification.
Walking a murmur through the manoeuvres
A 19-year-old footballer collapses on the field, and after resuscitation his echo shows septal thickness of 22 mm. Before the family is counselled, the clinician must establish how the disease behaves in him.
- Test standing and Valsalva: Both reduce venous return, shrink the cavity and worsen the obstruction, so the murmur grows louder and longer.
- Test squatting and handgrip: Squatting raises venous return and afterload, and handgrip raises afterload, so the gradient lessens and the murmur softens.
- Separate from aortic stenosis: Valsalva reduces the aortic stenosis murmur but increases the hypertrophic one, which is the key bedside discriminator.
- Check the pulse and echo: The carotid pulse is brisk with a bisferiens contour rather than slow-rising. The echo confirms systolic anterior motion of the mitral valve and quantifies the gradient at rest and with provocation.
- Estimate sudden death risk: Risk is estimated from family history, the degree of thickening, Holter findings and the exercise blood pressure response, and the ICD decision follows that estimate.
- Treat symptoms and obstruction: Beta-blockade is started for symptoms. Persistent obstruction despite drugs leads to consideration of alcohol septal ablation or surgical myectomy, depending on anatomy and local expertise.
Where the examiner builds the trap
Four traps recur in hypertrophic cardiomyopathy questions.
- Trap: choosing aortic stenosis for any ejection murmur at the left sternal edge. Correct: the manoeuvres separate the two, because Valsalva and standing amplify the hypertrophic murmur while reducing the aortic one.
- Trap: choosing nitrates or vasodilators for chest pain or hypertension. Correct: nitrates, hydralazine and other vasodilators worsen the gradient, so examiners use them as tempting wrong answers.
- Trap: automatic exclusion or automatic ICD for the young athlete. Correct: the right response is formal risk assessment, which then guides the decision on sport and device therapy.
- Trap: missing the bedside clue of the disease. Correct: expect the double apical impulse, a presystolic and systolic bulge at the apex, as a clinical sign of this disease.
Frequently asked questions
What is the murmur of hypertrophic cardiomyopathy?
The murmur of hypertrophic cardiomyopathy is a crescendo-decrescendo ejection systolic murmur at the lower left sternal edge. It increases with Valsalva and standing and decreases with squatting.
How does Valsalva change the murmur of hypertrophic cardiomyopathy compared with aortic stenosis?
Valsalva increases the murmur of hypertrophic cardiomyopathy by reducing ventricular volume and worsening outflow obstruction, but it decreases the murmur of aortic stenosis. This contrast is a frequently tested bedside discriminator.
Which drugs should be avoided in hypertrophic cardiomyopathy?
In hypertrophic cardiomyopathy, nitrates, hydralazine and dehydration worsen dynamic outflow obstruction and should generally be avoided, along with inotropic agents. Vasodilators are a common error in stems about chest pain or hypertension.
What is the first-line drug in obstructive hypertrophic cardiomyopathy?
Beta-blockers are first-line in obstructive hypertrophic cardiomyopathy, reducing contractility and heart rate to lessen the outflow gradient and relieve exertional symptoms. Verapamil is an alternative when beta-blockers are not tolerated.
What are the main risk factors for sudden death in hypertrophic cardiomyopathy?
Sudden death risk in hypertrophic cardiomyopathy rises with prior cardiac arrest, unexplained syncope, family history of sudden death, non-sustained ventricular tachycardia, massive hypertrophy of 30 mm or more, and an abnormal blood pressure response to exercise.