Moving Beyond the Sarcomere to Explain Heterogeneity in Hypertrophic Cardiomyopathy: JACC Review Topic of the Week

Hypertrophic cardiomyopathy (HCM) has been considered a heterogeneous cardiac disease ascribed solely to single sarcomere gene mutations. However, limitations of this hypothesis suggest that sarcomere mutations alone do not adequately explain all HCM clinical and pathobiological features. Disease-causing sarcomere mutations are absent in ∼70% of patients with established disease, and sarcomere gene carriers can live to advanced ages without developing HCM. Some features of HCM are also inconsistent with the single sarcomere gene hypothesis, such as regional left ventricular hypertrophy and myocardial fibrosis, as well as structurally abnormal elongated mitral valve leaflets and remodeled intramural coronary arterioles, which involve tissue types that do not express cardiomyocyte sarcomere proteins. It is timely to expand the HCM research focus beyond a single molecular event toward more inclusive models to explain this disease in its entirety. The authors chart paths forward addressing this knowledge gap using novel analytical approaches, particularly network medicine, to unravel the pathobiological complexity of HCM.

Clinical Spectrum and Management Implications of Left Ventricular Outflow Obstruction With Mild Ventricular Septal Thickness in Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HC) has historically been characterized as a disease of substantial left ventricular hypertrophy, often associated with dynamic left ventricular outflow tract obstruction. However, we have recently encountered patients with subaortic obstruction and only minimal basal septal thickness, raising important management implications. Thereby, we sought to characterize the natural history and treatment strategies for this under-recognized subgroup of HC patients with dynamic obstruction. Of 1,591 consecutive patients with a HC diagnosis, 113 (7%) were identified with outflow obstruction due to elongated mitral valve leaflets producing systolic anterior motion and septal contact typical of HC (gradient, 84 ± 29 mm Hg at rest or with exercise), with maximal ventricular septal thickness ≤15 mm, including 14 patients with only 10 to 12 mm. In addition to the mechanism of outflow obstruction, other evidence supporting a HC diagnosis prominently included: positive HC family history and/or pathogenic sarcomere mutation, arrhythmic sudden death event, typical histopathology of septal muscle, and characteristic mitral valve and papillary muscle anomalies. Over 3.8 ± 3.5 years, 41 patients (36%) developed severe heart failure including 36 who have undergone myectomy associated with reconstruction of the outflow tract and mitral valve apparatus, resulting in relief of gradient without iatrogenic ventricular septal defect or mitral valve replacement. Postoperatively, all 36 patients have survived with symptom relief to New York Heart Association classes I/II. In conclusion, these observations expand the HC clinical profile and phenotype to include an under-appreciated subgroup in which disease expression includes outflow obstruction due primarily to an elongated mitral valve, associated with only minimal (or normal) ventricular septal thickness. Such HC patients can develop marked functional limitation amenable to an operative strategy that effectively relieved symptoms due to outflow obstruction, but without mitral valve replacement.

Left ventricular apical aneurysm in hypertrophic cardiomyopathy as a risk factor for sudden death at any age

In hypertrophic cardiomyopathy (HCM) aging has proved protective against sudden death (SD) risk and aggressive recommendations for prophylactic ICDs are uncommon in patients ≥60 years. Nevertheless, we present a patient with an unexpected but aborted sudden death event at the advanced age of 71 years due to a left ventricular apical aneurysm (LVAA) which has emerged as a novel SD marker. Subsequent reappraisal of the Tufts HCM database, specifically the 118 LVAA patients, showed that 36% of SD events occurred at ≥60 years. Of HCM patients ≥ 60 years, SD was 8-fold more common with aneurysm than without aneurysms (16% vs 2%; P < 0.001). Risk in HCM with LVAA persists throughout life and senior LVAA patients should also be considered for primary prevention of SD with the ICD.

Clinical Profile of Nonresponders to Surgical Myectomy with Obstructive Hypertrophic Cardiomyopathy

BACKGROUND

Surgical myectomy reverses heart failure symptoms in the vast majority of obstructive hypertrophic cardiomyopathy patients. However, a small subgroup fails to experience sustained postoperative improvement despite relief of obstruction. Clinical profile of such patients has not been well defined.

METHODS

Consecutive obstructive hypertrophic cardiomyopathy patients undergoing myectomy at Tufts Medical Center for drug-refractory New York Heart Association III/IV heart failure symptoms, 2004 to 2017, were followed postoperatively for 2.5 ± 2.8 years and assessed for outcome.

RESULTS

Of the 503 patients, there were 4 postoperative deaths (0.8%); 480 patients (96%) had sustained improvement to New York Heart Association classes I or II (responders), but 19 (3.8%) developed advanced symptoms (classes III or IV) in the absence of obstruction (nonresponders). Compared with responders, nonresponders were younger (40 ± 13 vs 53 ± 14 years; P < .001) and had greater septal thickness (25 ± 9 vs 20 ± 4 mm; P < .001). Massive hypertrophy (≥30 mm) was 5-fold more common in nonresponders (P < .01). Seven nonresponders developed systolic dysfunction (ejection fraction 20%-47%), 2 days to 6.1 years postoperatively. Four nonresponders underwent heart transplant 3.4 to 9.2 years after myectomy, and 2 others have been listed.

CONCLUSIONS

Surgical myectomy is highly effective at reversing heart failure symptoms in the vast majority of patients with obstructive hypertrophic cardiomyopathy. However, a small minority experience persistent functional limitation despite surgical relief of outflow obstruction. Predictors of adverse postoperative course were substantial/massive septal thickness and youthful age. Patients who failed to respond symptomatically to myectomy were considered for advanced heart failure treatment, including heart transplantation.

Impact of Advanced Therapies for Improving Survival to Heart Transplant in Patients with Hypertrophic Cardiomyopathy

Heart transplant has become an increasingly important option for patients with end-stage nonobstructive hypertrophic cardiomyopathy (HC). However, clinical details related specifically to the overall HC transplant experience remain sparse. We assessed outcomes of HC heart transplants, from 2002 to 2016, at Tufts Medical Center. Fifty-two nonobstructive severely symptomatic patients underwent evaluation at 47 ± 13 years; 11 (21%) declined or failed to qualify, most commonly because of co-morbidities (n = 7). Of the remaining 41 patients ultimately listed, 6 (15%) died of heart failure awaiting transplant (11%/year), 26 underwent transplant, and 9 remained active on the list. Survival rates on the waiting list depended on ≥1 treatment intervention: inotropic medications (n = 20), ventricular assist devices (n = 7), or implantable defibrillators terminating ventricular tachyarrhythmias (n = 7). Of the 26 transplanted patients, 24 survived for 4.8 ± 3.4 years (up to 12), including 23 who are currently alive. The survival rate 5 years post transplant is 92%. Compared with heart transplants for other cardiomyopathies, patients with HC had similar mortality while wait-listed and post transplant (p = 0.77 and 0.13, respectively). In conclusion, a large proportion of patients with HC considered for transplant ultimately received hearts and experienced excellent short- and long-term survival rates. The survival rate on the waiting list was directly attributable to major interventions: implantable cardioverter-defibrillators, inotropic drugs, and ventricular assist devices, and the perception that patients with HC have low wait-list mortality risk does not appear justified. Neither normal ejection fraction nor peak oxygen consumption > 14 ml/kg/min should exclude drug refractory severely symptomatic patients with HC from heart transplant consideration.

Size as an Important Determinant of Chest Blow-induced Commotio Cordis

PURPOSE

Commotio cordis is sudden cardiac death caused by a relatively innocent blow to the left chest wall. Adolescents account for the majority of the cases; whether this is due to the higher frequency of adolescents playing ball sports or whether there is some maturational reduction of risk is not known.

METHODS

In a swine model of commotio cordis, the effect of body weight/size (directly related to age) to the susceptibility of chest impact-induced ventricular fibrillation (VF) is examined.

METHODS

Ball impacts were delivered at escalating velocities from 48.3 to 96.9 km·h (30-60 mph) to 128 swine ranging in weight from 5 to 54 kg.

RESULTS

VF occurred in 29% of impacts to the smallest animals compared with 34% in the 14- to 239-kg group, 27% in the 24- to 33.9-kg group, 30% in 34- to 43-kg group, and 15% in the 44- to 54-kg animals. The highest-weight group was associated with a significantly lower incidence of VF compared with other weights (P = 0.002). In a multivariate logistic regression analysis, controlling for repeated measures, four variables predicted VF: body weight (P = 0.0008), velocity (P < 0.0001), distance from the center of the heart, (P < 0.0001), and peak left ventricular pressure induced by the blow (P = 0.0007).

CONCLUSIONS

In this experimental model, animals weighing <44 kg seem to have a similar susceptibility to commotio cordis, whereas animals weighing ≥44 kg have a lower susceptibility. An increase in size of the individual, rather than reduced play of ball sports, is the likely reason for the decreased commotio cordis incidence in older individuals.

Surgical Approaches to Hypertrophic Obstructive Cardiomyopathy

Left ventricular outflow tract obstruction secondary to hypertrophic obstructive cardiomyopathy remains a challenging entity facing clinicians. Despite the success of invasive therapies, some clinicians remain hesitant because of early results with unacceptable morbidity and mortality rates. However, current literature strongly suggests improved short- and long-term outcomes with extended septal myectomy and alcohol septal ablation compared with patients not undergoing such interventions. This review evaluates hypertrophic obstructive cardiomyopathy treatment with a focus on short- and long-term outcomes, perioperative complications, and major tenets of surgical intervention. The data reveal mortality rates approaching zero, and perioperative complications occur infrequently. Alcohol septal ablation and extended septal myectomy both consistently decrease left ventricular outlet tract pressure gradients and result in improved functional capacity with lower New York Heart Association class and should be recommended as treatment for patients with symptoms refractory to standard medical treatment.