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Hypertrophic Cardiomyopathy: Assessment of Therapy
Acknowledgment
The authors acknowledge Dr. Paul Szmitko, who was the first author of this chapter in the second edition of the textbook.
Dynamic left ventricular outflow tract obstruction (LVOTO) is an important clinical feature of hypertrophic cardiomyopathy (HCM). Resting or provocable LVOTO occurs in 70% of patients with HCM. The presence of resting LVOTO (traditionally defined as an left ventricular outflow tract (LVOT) gradient of ≥30 mm Hg at rest) is associated with a significant increased risk of HCM-related death. The initial treatment for symptomatic patients with obstructive HCM is pharmacotherapy with negative inotropic agents (β-blockers, verapamil, disopyramide). However, in patients who remain symptomatic and who generally have a resting or provocable LVOT gradient of at least 50 mm Hg, invasive septal reduction therapy should be considered. The different invasive interventions available for the management of obstructive HCM are outlined in Chapter 59 .
Medical treatment is optimized by monitoring symptom response to medications and by performing serial echocardiographic and Doppler studies to assess the LVOT gradient. The LVOT gradient can be documented by the continuous-wave (CW) Doppler technique. , If the LVOT gradient at rest is 30 to 50 mm Hg and the patient’s symptoms are suggestive of underlying obstruction, then a provocative maneuver can be performed to detect for an inducible LVOT gradient. , There are numerous techniques for eliciting provocable LVOTO. , Provocation with exercise is the most physiologic method for detecting a provocable LVOT gradient. , , Although the Valsalva maneuver is the most commonly used method of provocation, one large study has demonstrated that the Valsalva-induced LVOT gradient is underestimated compared with the exercise-induced LVOT gradient.
Pharmacotherapy
β-Blockers are the first-line agents in the management of symptomatic obstructive HCM. By decreasing myocardial contractility, β-blockers lead to a reduction in the left ventricular (LV) ejection velocity, which causes the delayed onset of mitral leaflet systolic anterior motion (SAM), and consequently results in a decrease in the magnitude of LVOTO. Other effects of the β-blocker class of drugs include sympathetic modulation of the heart rate, relief of myocardial ischemia, and prolongation of diastole, which allows for increased passive ventricular filling. Nondihydropyridine calcium channel blockers (e.g., verapamil, diltiazem) can be used in patients with HCM who have contraindications, side effects, or unresponsiveness to β-blockers. Nevertheless, both verapamil and diltiazem should be used very cautiously in patients with high LVOT gradients, advanced heart failure, or sinus bradycardia. In particular, in the setting of severe LVOTO, an elevated pulmonary artery wedge pressure, and low systemic blood pressure, the vasodilatation from calcium channel blockers may trigger an increase in SAM and in the severity of the LVOTO, and may precipitate pulmonary edema.
Disopyramide is highly effective in the management of patients with obstructive HCM. , , Although classified as a type IA antiarrhythmic agent, disopyramide has significant negative inotropic properties that decrease SAM and the magnitude of LVOTO. If symptoms and an increased LVOT gradient persist despite monotherapy with β-blockers or verapamil, disopyramide can be introduced. The addition of disopyramide results in an improvement in cardiac symptoms and a significant reduction in the resting LVOT gradient. , Data from experienced HCM centers have shown that disopyramide can be safely administered on a long-term basis. ,
Surgical Myectomy
For patients with obstructive HCM and symptoms unresponsive to medical therapy, septal myectomy is considered the definitive treatment for patients who are acceptable candidates for open heart surgery. Myectomy is performed using a transaortic approach and involves the resection of the hypertrophied basal (to mid) ventricular septum. Subaortic muscle resection results in the enlargement of the outflow tract, decreased SAM of the mitral valve, and abolition of the LVOTO. Operative mortality rates in the contemporary era are very low for myectomy when it is performed at HCM centers with recognized expertise in the surgical management of obstructive HCM. , , Surgical myectomy produces substantial symptomatic improvement and leads to excellent postoperative long-term survival. , , ,
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