HYPERTROPHIC CARDIOMYOPATHY Flashcards
What is hypertrophic cardiomyopathy (HCM)?
A primary cardiac disorder characterized by myocardial hypertrophy and a nondilated left ventricle in the absence of accountable increases in cardiac afterload or underlying systemic/metabolic disease.
The hypertrophy is caused by pathogenic variants of cardiac sarcomere proteins.
What is the prevalence of HCM?
About 1:500 in the general population (0.2%). HCM affects men and women equally across various countries and ethnic groups.
Which genetic mutations are commonly associated with HCM?
Mutations in cardiac troponin T, cardiac troponin I, myosin regulatory light chain, myosin essential light chain, cardiac myosin binding protein C, alpha and beta-cardiac myosin heavy chain, cardiac alpha actin, alpha tropomyosin, titin, and muscle LIM protein (MLP).
Mutations in MYBPC3, MYH7, and the troponin genes (TNNI3, TNNT2, TPM1) account for about two-thirds of all mutations.
How is HCM inherited?
As an autosomal dominant trait, with a 50% chance of transmission to offspring.
Penetrance is incomplete, meaning not all gene carriers develop the full HCM phenotype.
Who should be screened for HCM?
Patients with known HCM mutations without evidence of disease and first-degree relatives of patients with HCM.
Screening includes history, physical examination, ECG, and echocardiography, traditionally every 12-18 months until age 21.
What is the purpose of genetic testing in HCM?
To identify disease-causing abnormalities and facilitate predictive testing for at-risk family members.
It is recommended in families with sudden cardiac deaths or clinical presentations suggesting HCM phenocopies.
What are the histologic characteristics of HCM?
Hypertrophy of cardiac myocytes, myocardial fiber disarray, increased interstitial collagen matrix volume, and disorganized arrangement of matrix components.
Almost all HCM patients have some degree of disarray.
What are the common types of HCM?
- Asymmetrical septal hypertrophy (ASH)
- Concentric left ventricular hypertrophy (LVH)
- Apical HCM
- Obstructive HCM (OHCM)
- Nonobstructive HCM (NHCM)
ASH is the most common, detected in over 80% of HCM patients.
What are the most common symptoms of HCM?
- Dyspnea
- Angina pectoris
- Syncope and presyncope
Dyspnea is caused mainly by LV diastolic dysfunction and dynamic LV outflow tract obstruction.
How is HCM differentiated from athlete’s heart?
Key parameters include LV wall thickness, pattern of hypertrophy, LV end-diastolic dimension, and family history of HCM.
HCM typically shows asymmetric hypertrophy greater than 16 mm, while athlete’s heart shows symmetric hypertrophy.
What is the classic murmur of obstructive HCM?
A harsh crescendo-decrescendo systolic murmur, best heard between the left sternal border and apex.
It may radiate to the axilla but not into the neck vessels.
How does the carotid pulse in obstructive HCM differ from that in valvular aortic stenosis?
In obstructive HCM, the pulse has an initial brisk rise followed by a midsystolic decline (pulsus bisferiens). In aortic stenosis, the pulse is diminished in amplitude and delayed (pulsus parvus and tardus).
What noninvasive studies are helpful in diagnosing HCM?
ECG and echocardiography are primary diagnostic tools.
Common ECG abnormalities include ST-segment changes, voltage criteria for LVH, and left atrial enlargement.
What is systolic anterior motion (SAM)?
The abnormal anterior displacement of the anterior mitral leaflet toward the septum during midsystole.
Several mechanisms have been proposed for SAM in the context of HCM.
What is systolic anterior motion (SAM)?
SAM is the abnormal anterior displacement of the anterior mitral leaflet toward the septum during midsystole.
SAM can be caused by multiple mechanisms including Venturi effect and abnormal blood flow due to hypertrophied septum or maloriented papillary muscles.
What are the two-dimensional echo findings in hypertrophic cardiomyopathy (HCM)?
In nonobstructive HCM, predominant thickening of the apical segments with a wide open left ventricular outflow tract (LVOT) is observed. In obstructive HCM, a protruding subaortic septum makes systolic contact with the mitral valve.
Late-peaking continuous-wave-Doppler LV outflow profile indicates dynamic obstruction.
What is the mechanism of left ventricular outflow tract (LVOT) obstruction in HCM?
LVOT obstruction in HCM is produced by SAM of the anterior mitral leaflet and midsystolic contact with the hypertrophic ventricular septum.
The subaortic gradient is often dynamic and responds to provocative maneuvers.
What are the characteristic hemodynamic findings during cardiac catheterization in obstructive HCM?
Typical hemodynamic findings include:
* Subaortic or midventricular outflow gradients
* Spike-and-dome pattern of aortic pressure tracing
* Elevated left atrial and LV end-diastolic pressures
* Increased pulmonary capillary wedge pressure
* Elevated pulmonary arterial pressures
Cardiac catheterization is usually not required for diagnosing HCM.
What is the Brockenbrough-Braunwald sign?
The Brockenbrough-Braunwald sign describes the decrease in stroke volume and systolic pressure after a PVC, leading to a decrease in pulse pressure in patients with HCM.
Normally, increased contractility after a PVC leads to increased systolic blood pressure.
What are the risk factors for sudden cardiac death (SCD) in patients with HCM?
Major risk factors for SCD include:
* Prior cardiac arrest or sustained ventricular tachycardia
* Family history of SCD
* Unexplained syncope
* Massive left ventricular hypertrophy (LVH) with wall thickness ≥30 mm
* LV apical aneurysm
* Impaired LV ejection fraction
Extensive late gadolinium enhancement (LGE) on cardiac MRI also increases SCD risk.
