Hypertrophic cardiomyopathy: A complex disease
ABSTRACT
Hypertrophic cardiomyopathy (HCM) is a complex cardiovascular disease with wide phenotypic variations. Despite significant advances in imaging and genetic testing, more information is needed about the roles and implications of these resources in clinical practice. Patients with suspected or established HCM should be evaluated at an expert referral center to allow for the best multidisciplinary care. Research is needed to better predict the risk of sudden cardiac death in those judged to be at low risk by current risk-stratification methods.
KEY POINTS
- Obstruction of the left ventricular outflow tract is a key pathophysiologic mechanism in HCM.
- Because most of the genetic variants that contribute to HCM are autosomal dominant, genetic counseling and testing are suggested for patients and their first-degree relatives.
- Transthoracic echocardiography is the first-line imaging test, followed by magnetic resonance imaging.
- Beta-blockers are the first-line drugs for treating symptoms of HCM.
- An implantable cardioverter-defibrillator can be considered for patients at risk of sudden cardiac death.
- When medical therapy fails or is not tolerated in patients with severe symptoms of obstructive HCM, surgery to reduce the size of the ventricular septum can be considered. Alcohol septal ablation is an alternative.
Septal reduction therapy
If medical therapy fails or is not tolerated in patients with severe symptoms, surgery can be considered for obstructive HCM.
Ventricular septal myectomy has been the long-standing gold standard of invasive therapy. Multiple studies have demonstrated long-term survival after myectomy to be equivalent to that in the general population and better than that of HCM patients who do not undergo this surgery.47–50 Factors that may be associated with better surgical outcomes include age younger than 50, left atrial size less than 46 mm, and resolution of atrial fibrillation during follow-up.51
Septal reduction therapy may also be considered in patients at high risk of sudden cardiac death based on a history of recurrent ventricular tachycardia or risk-stratification models as described above. Retrospective analyses have shown that surgical myectomy can markedly reduce the incidence of appropriate implantable cardioverter-defibrillator discharges and the risk of sudden cardiac death.52
Alcohol septal ablation is an alternative. This percutaneous procedure, first described in the mid-1990s, consists of injecting a small amount of alcohol into the artery supplying the septum to induce myocardial necrosis, ultimately leading to scarring and widening of the left ventricular outflow tract.53
Up to 50% of patients develop right bundle branch block after alcohol septal ablation, and the risk of complete heart block is highest in those with preexisting left bundle branch block. Nevertheless, studies have shown significant symptomatic improvement after alcohol septal ablation, with long-term survival comparable to that in the general population.53–56
Several meta-analyses compared alcohol septal ablation and septal myectomy and found that the rates of functional improvement and long-term mortality were similar.57–59 However, the less-invasive approach with alcohol septal ablation comes at the cost of a higher incidence of conduction abnormalities and higher left ventricular outflow tract gradients afterward. One meta-analysis found that alcohol septal ablation patients may have 5 times the risk of needing additional septal reduction therapy compared with their myectomy counterparts.
Current US guidelines recommend septal myectomy, performed at an experienced center, as the first-line interventional treatment, leaving alcohol septal ablation to be considered in those who have contraindications to myectomy.9 The treatment strategy should ultimately be individualized based on a patient’s comorbidities and personal preferences following informed consent.
A nationwide database study recently suggested that postmyectomy mortality rates may be as high as 5.9%,60 although earlier studies at high-volume centers showed much lower mortality rates (< 1%).50–52,61 This discrepancy highlights the critical role of expert centers in optimizing surgical management of these patients. Regardless of the approach, interventional therapies for HCM should be performed by a multidisciplinary team at a medical center able to handle the complexity of these cases.
Additional surgical procedures
A handful of other procedures may benefit specific patient subgroups.
Apical myectomy has been shown to improve functional status in patients with isolated apical hypertrophy by reducing left ventricular end-diastolic pressure and thereby allowing for improved diastolic filling.63
Mitral valve surgery may need to be considered at the time of myectomy in patients with degenerative valve disease. As in the general population, mitral valve repair is preferred to replacement if possible.
