Chapter 31-12: Hypertrophic Cardiomyopathy (HCM)

TEXTBOOK PRESENTATION

HCM may be asymptomatic and discovered due to a family history of sudden cardiac death, during the evaluation of an asymptomatic systolic murmur, during preparticipation athletic screening, or when symptoms occur (syncope, HF, atrial fibrillation, or cardiac arrest).

DISEASE HIGHLIGHTS

1. The most common cause of cardiovascular death in young people and among young athletes

2. A variety of mutations in sarcomere constituents (eg, myosin) result in myocyte hypertrophy with disarray, increased cardiac fibrosis, and diastolic dysfunction. Over 1400 mutations (usually autosomal dominant) in 11 genes have been reported.

3. Affects 0.02–0.23% of adults in the general population

4. The hallmark of the disease is LVH in the absence of loading conditions (hypertension, aortic stenosis, etc.)

   1. LVH may develop in childhood, adolescence, or adulthood.

   2. LVH can affect any part of the LV, although often preferentially affects the ventricular septum, which can cause left ventricular outflow tract obstruction (LVOTO).

   3. LVOTO increases the risk of progression to HF, stroke, and sudden cardiac death. The outflow obstruction can be fixed or dynamic.

   4. The pathophysiology of obstruction is complex and due to (1) septal hypertrophy causing narrowing of the LV subaortic outflow tract and (2) the subsequent drag pulling the mitral valve leaflets of into contact with the outflow tract. The motion of the mitral valve may also cause mitral regurgitation.

   5. Chamber size affects the severity of obstruction. A smaller chamber size (ie, from hypovolemia) brings the anterior leaflet of mitral valve closer to the hypertrophied septum and increases obstruction. This occurs when preload decreases (such as with standing), when afterload decreases or when contractility increases.

5. Most patients are asymptomatic or mildly symptomatic.

6. Complications include HF, angina, mitral regurgitation, atrial fibrillation, stroke, syncope, and sudden cardiac death.

   1. HF

      1. Typically due to diastolic dysfunction, but systolic dysfunction may develop

      2. More common in patients with LVOTO

      3. Develops due to a combination of outflow obstruction and diastolic dysfunction

      4. Dyspnea on exertion is the most common symptom.

      5. Aggravated by concomitant mitral regurgitation when present

   2. Angina

      1. May be typical or atypical in quality

      2. Develops in 25–30% of patients

      3. May occur secondary to one or more of the following:

         1. Ischemia without CAD from mismatched supply and demand

         2. CAD

         3. LVOTO

   3. Syncope

      1. Develops in 15–25% of patients with HCM

      2. May be due to ventricular arrhythmias, outflow tract obstruction and, rarely, conduction blocks

      3. Unexplained syncope in HCM is a risk factor for sudden cardiac death.

   4. Sudden cardiac death is the most dreaded complication.

      1. Often occurs in previously asymptomatic patients

      2. Usually secondary to ventricular tachyarrhythmias (which may be triggered by myocardial fibrosis and disarray, outflow tract obstruction, or ischemia). Occasionally due to asystole, heart block, pulseless electrical activity or thromboembolism.

      3. Annual risk among all patients with HCM: 1–2%

      4. Major risk factors include the following:

         1. Prior events

            1. Prior cardiac arrest

            2. Spontaneous sustained VT

         2. High-risk clinical factors

            1. Family history of sudden cardiac death in first-degree relative younger than 40 years (with or without HCM) or in first-degree relative of any age in ...