Fig. 9.1
Mechanism of LVOT obstruction and mitral regurgitation (MR) in patients with HCM. In early systole (left): The left ventricular outflow tract (LVOT) is narrowed by the hypertrophic interventricular septum and the anteriorly displaced papillary muscle. This creates flow acceleration during systole, dragging the anterior mitral leaflet into the LVOT and contacting the septum (Venturi effect), causing LVOT obstruction in late systole (right). The systolic anterior motion of the anterior leaflet (SAM) results in a failure of coaptation of the mitral leaflets and the onset of mitral regurgitation (MR). In most cases of HCM, the MR jet is directed posterior into the left atrium. Reproduced from [3], with permission of Wolters Kluwer
Diastolic dysfunction: due to impaired ventricular relaxation and decreased ventricular compliance (increased chamber stiffness). This leads to impaired ventricular diastolic filling.
Myocardial ischemia: often occurs without artherosclerotic coronary artery disease. The postulated mechanisms include: ventricular hypertrophy causing obliteration of septal perforators; inadequate number of capillaries for the degree of LV mass; impaired coronary filling due to impaired relaxation.
Mitral regurgitation (MR): systolic anterior motion of mitral valve (SAM) results in varying degrees of MR due to incomplete coaptation of mitral leaflets. The severity of MR is directly proportional to the degree of LVOT obstruction.
- 3.
What is the genetic background of HCM?
HCM is inherited in an autosomal dominant Mendelian pattern with variable expression and age-related penetrance. The most common mutation in HCM is a missense mutation (a single normal amino acid is replaced for another) in the genes encoding the cardiac sarcomere. There is no clear relationship between the genotype and phenotype in HCM. It is impossible to predict the extent of expression or clinical outcome based on individual mutations [7–9].
- 4.
What are the common symptoms of HCM?
- (1)
Dyspnea on exertion: most common symptom of HCM, occurring in over 90% of symptomatic patients. Dyspnea can result from diastolic dysfunction, mitral regurgitation, or impaired LV emptying and poor cardiac output due to LVOT obstruction.
- (2)
Chest pain: occurs in 25–30% of symptomatic HCM patients, usually in the setting of a normal coronary angiogram.
- (3)
Syncope and presyncope: occurs in about 20–25% of symptomatic HCM patients. Multiple mechanisms include arrhythmia, severe LVOT obstruction with exertion or myocardial ischemia.
- (4)
Sudden cardiac death: occurs in about 15% of symptomatic HCM patients. HCM is the most common cause of sudden death in otherwise apparently healthy athletes [10].
- (5)
Arrhythmia: supraventricular arrhythmias, most commonly atrial fibrillation; ventricular arrhythmias can also occur.
- (6)
Signs of advanced congestive heart failure are uncommon in HCM patients but may include orthopnea, paroxysmal dyspnea, and edema.
Physical exam is most commonly notable for systolic murmur on auscultation. A harsh systolic murmur can be best heard at the apex, caused by LVOT obstruction and/or mitral regurgitation. This murmur is dynamic in nature, and its intensity varies with changes in cardiac loading conditions and contractility. Maneuvers that decrease LV preload (e.g., changing to upright position from supine, Valsalva maneuver), enhance LV contractility and decrease LV afterload will all lead to worsening LVOT obstruction, thus increase the murmur intensity.
Other signs on physical exam are nonspecific, such as a brisk upstroke and bifid carotid pulse, resulting from sudden deceleration of blood due to LVOT obstruction.
- 5.
How to diagnose HCM?
Besides clinical history, the following diagnostic methods are often used for diagnosis:
- (1)
Electrocardiography (ECG): over 90% of HCM patients have an abnormal ECG. Typically ECG shows localized or widespread repolarization changes. Patients may have abnormal Q waves, especially in the inferior or lateral leads. These changes reflect septal depolarization of the hypertrophied myocardium. Signs of LV hypertrophy (LVH) also exist, resulting in left axis deviation and ST-T wave abnormalities (horizontal or downsloping ST segment and T wave inversions).
- (2)
Echocardiography: transthoracic echocardiography (TTE) should be performed in all patients suspected of having HCM. A clinical diagnosis of HCM is confirmed when LV wall thickness ≥15 mm without LV dilation, in the absence of any identifiable cause such as hypertension or valve disease. The most common location of LV hypertrophy is the basal anterior septum in continuity with the anterior free wall. Other important TTE findings of HCM include: systolic anterior motion of mitral valve (SAM) and dynamic LVOT obstruction (see Fig. 1). For patients who do not have LVOT obstruction (LVOT gradient ≤30 mm Hg) at rest, provoking maneuvers should be performed to evaluate the gradient between the LVOT and aorta. Exercise stress echo is the preferred method [11].
- (3)
Exercise stress test: is recommended for all patients with known or suspected HCM as part of the risk stratification and to assess the degree of LVOT obstruction. Positive findings during exercise testing include symptoms of dyspnea or angina, an increase or development of LVOT peak instantaneous gradient ≥30 mm Hg, an increase or development of mitral regurgitation, ST segment depression, and failure of the BP to increase appropriately with exercise [1, 2, 11].
- (4)
Cardiac MRI: provides superior spatial resolution compared to TTE. It can demonstrate myocardial scarring or thickening in segments which are difficult to assess via echocardiography. Cardiac MRI can be considered for patients suspected of having HCM but the diagnosis remains uncertain after TTE.
- (5)
Genetic testing: routine genetic testing is not recommended for diagnostic purposes due to the poor correlation between genotype, clinical presentation and outcome.
- 6.
What is the pharmacological treatment of HCM?
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