Cannan, Charles R.

Hypertrophic cardiomyopathy (HCM) is the most common inherited cardiomyopathy. It follows an autosomal dominant inheritance pattern in most cases, with incomplete penetrance and heterogeneity. It is familial in 60% of cases and most of these are caused by pathogenic variants in the core sarcomeric genes (MYH7, MYBPC3, TNNT2, TNNI3, MYL2, MYL3, TPM1, ACTC1). Genetic testing using targeted disease-specific panels that utilize next-generation sequencing (NGS) and include sarcomeric genes with the strongest evidence of association and syndrome-associated genes is highly recommended for every HCM patient to confirm the diagnosis, identify the molecular etiology, and guide screening and management. The yield of genetic testing for a disease-causing variant is 30% in sporadic cases and up to 60% in familial cases and in younger patients with typical asymmetrical septal hypertrophy. Genetic testing remains challenging in the interpretation of results and classification of variants. Therefore, in 2015 the American College of Medical Genetics and Genomics (ACMG) established guidelines to classify and interpret the variants with an emphasis on the necessity of periodic reassessment of variant classification as genetic knowledge rapidly expands. The current guidelines recommend focused cascade genetic testing regardless of age in phenotype-negative first-degree relatives if a variant with decisive evidence of pathogenicity has been identified in the proband. Genetic test results in family members guide longitudinal clinical surveillance. At present, there is emerging evidence for genetic test application in risk stratification and management but its implementation into clinical practice needs further study. Promising fields such as gene therapy and implementation of artificial intelligence in the diagnosis of HCM are emerging and paving the way for more effective screening and management, but many challenges and obstacles need to be overcome before establishing the practical implications of these new methods.

Background Endothelin (ET), a coronary vasoconstrictor, mediates its activity through the specific receptors ET-A and ET-B, which may demonstrate different activity under pathophysiological conditions. Thoracic inferior vena cava constriction (TIVCC) is an experimental model of congestive heart failure that is characterized by a decrease in cardiac output and an increase in circulating ET concentrations. The present study was designed to test the hypothesis that experimental heart failure altered coronary vascular responsiveness to ET-A– and ET-B–receptor stimulation in vivo. Methods and Results ET-1 was infused at a rate of 2 ng/kg per minute into the left circumflex coronary artery in normal dogs (n=5) and in dogs subjected to TIVCC (TIVCC dogs, n=6). Similarly, sarafotoxin, an ET-B–receptor agonist, was infused at the same dosage in normal (n=5) and TIVCC (n=6) dogs. Intracoronary infusion of ET-1 significantly decreased coronary blood flow and increased coronary vascular resistance in normal dogs; this effect was significantly attenuated in TIVCC compared with normal dogs. The percent changes in coronary blood flow and coronary vascular resistance in the TIVCC compared with the normal dogs was −11±8% versus −48±7% ( P <.01) and 29±10% versus 105±23% ( P <.01), respectively. There was no significant effect on coronary blood flow, coronary vascular resistance, or coronary artery diameter in normal dogs that received an intracoronary infusion of sarafotoxin. In contrast, the administration of intracoronary sarafotoxin in TIVCC compared with normal dogs resulted in significant percent changes in coronary blood flow and coronary vascular resistance (−31±4% versus −7±3% [ P <.001] and 53±12% versus 12±8% [ P <.02], respectively). Conclusions The present study demonstrates an attenuated coronary vasoconstrictor response to ET-1 with an enhanced vasoconstrictor response to sarafotoxin and suggests an alteration in coronary ET receptor sensitivity in experimental heart failure.

Background Endothelin-1 (ET-1) is an endothelium-derived vasoconstrictor peptide. Controversy persists regarding the predominant ET receptor that mediates coronary vasoconstriction at pathophysiological concentrations. The aim of the present study was to test the hypothesis that ET mediates local coronary vasoconstriction via the ET-A receptor at low concentrations of exogenous ET-1 designed to mimic pathophysiological states compared with pharmacological concentrations. Methods and Results ET-1 (group 1, n=5) or sarafotoxin, a specific ET-B receptor agonist (group 3, n=6) (each at 2 ng/kg per minute), was infused into the left circumflex coronary artery in the anesthetized dog. In group 2 dogs (n=5), the same dose of ET-1 was infused with 4 μg/kg per minute of the specific ET-A receptor antagonist FR-139317. In group 4 (n=5), the same dose of sarafotoxin was infused with 50 μg/kg per minute of the specific inhibitor of nitric oxide formation, N G -monomethyl- l -arginine (L-NMMA). No difference in hemodynamics, coronary blood flow (CBF), coronary vascular resistance (CVR), or coronary artery diameter (CAD) was observed at baseline between the groups. In group 1, intracoronary ET-1 significantly decreased CBF and CAD in association with an increase in CVR. The percentage decrease in CBF and CAD in the group that received ET-1 and the ET-A receptor antagonist (group 2) was significantly less than that in the group that received ET-1 alone (group 1) (−12±3% versus −48±6% [ P <.001] and −4.6±0.8 versus 1.0±0.3 [ P <.05], respectively). The administration of the ET-A receptor antagonist (group 2) abolished the ET-mediated increase in CVR (7±5% versus 105±21%, P <.005). There was no significant effect on CBF, CVR, or CAD in the group receiving sarafotoxin alone (group 3). The administration of L-NMMA and sarafotoxin (group 4) resulted in a significant percentage decrease in CBF compared with the group that received sarafotoxin alone (−28±7% versus −8±2% [ P <.05]). Conclusions The present study demonstrates that low concentrations of exogenous ET-1, which may mimic pathophysiological concentrations, result in coronary vasoconstriction mediated predominantly via the ET-A receptor because such vasoconstriction is significantly attenuated by blockade with FR-139317. The ET-B receptor may have a dual vasoconstrictive and vasodilatory effect.

Background Hypertrophic cardiomyopathy is a disease entity characterized by marked heterogeneity in morphology and natural history. Most of our knowledge of the natural history of this disorder derives from the study of hospital-based populations and is influenced by referral bias. Therefore, this population-based study was undertaken to examine the natural history of hypertrophic cardiomyopathy among unselected residents of Olmsted County, Minnesota. Methods and Results Patients with hypertrophic cardiomyopathy, confirmed by echocardiography, were identified by use of the resources of the Rochester Epidemiology Project. Patients with the echocardiographic features of hypertrophic cardiomyopathy but with long-standing hypertension requiring drug therapy were categorized as having hypertensive hypertrophic cardiomyopathy. Baseline clinical details and follow-up events were obtained by retrospective chart review. Thirty-seven patients were diagnosed with hypertrophic cardiomyopathy and 24 with hypertensive hypertrophic cardiomyopathy. Eight additional patients were first diagnosed at autopsy. The mean age of the 37 patients with hypertrophic cardiomyopathy was 59±20 years (range, 1 week to 92 years); the mean ventricular septal thickness was 17.5±3 mm. Follow-up was obtained for a median of 7.7 years (range, 45 days to 17.2 years). The 1- and 5-year survival rates were 95% and 92%, respectively; these rates did not differ from those of an age- and sex-matched population ( P =NS). The annual risk of cardiac death was 0.7%. The mean age of patients with hypertensive hypertrophic cardiomyopathy was 79±8 years (range, 62 to 91 years), and the mean ventricular septal thickness was 19±2.5 mm. Follow-up was obtained for a median of 2.8 years (range, 4 days to 16.7 years). The 1- and 5-year survival rates were 75% and 43%, respectively, which differed sharply from the expected rates of 94% and 70% ( P =.0028). The annual risk of cardiac death was 5%. Atrial fibrillation and evidence for myocardial infarction on ECG, use of digoxin and diuretics, and a high New York Heart Association functional class at presentation were all associated with decreased survival by multivariate analysis for both groups combined. A history of myocardial infarction, atrial fibrillation, and mitral annular calcification at presentation were associated with cardiac death. Conclusions Hypertrophic cardiomyopathy is a more benign disease than previously reported from tertiary referral centers. Patients assessed as having hypertensive hypertrophic cardiomyopathy represent a subset at higher risk for cardiac and noncardiac death, with an overall decreased survival rate.

Abstract —Endothelin (ET) may mediate the enhanced coronary vasoconstriction associated with hypercholesterolemia. We hypothesized that short-term inhibition of ET receptors attenuates the coronary epicardial vasoconstrictor response to acetylcholine in experimental hypercholesterolemia. ET-1 (group I, n=5; 5 ng · kg −1 · min −1 ) and acetylcholine (group III, n=7; 10 −6 to 10 −4 mol/L) were given by intracoronary infusion in pigs. ET-1 and acetylcholine were also infused with the specific ETA-receptor blocker FR-139317 (5 μg · kg −1 · min −1 ; group II, n=6; group IV, n=6). Acetylcholine was also infused with the combined ET-receptor blocker, bosentan (0.5 mg/kg plus 1 mg · kg −1 · h −1 , group V, n=5). The ETB-receptor agonist sarafotoxin 6c (5 ng · kg −1 · min −1 ; n=4) was also infused. The percentage change in coronary artery diameter (%ΔCAD) to the infusions was measured at baseline and after 10 weeks of high-cholesterol diet in all animals. Sarafotoxin 6c mildly reduced %ΔCAD at baseline and 10 weeks (−10±2% and −12±3%, respectively). FR-139317 did not attenuate the epicardial vasoconstrictor response to ET-1 at baseline (%ΔCAD −18±8% for group I versus −12±6% for group II; P =NS) but did at 10 weeks (%ΔCAD −77±14% for group I versus −14±6% for group II; P <.05). FR-139317 did not affect the response to acetylcholine at baseline (%ΔCAD 5±2% for group III versus 7±3% for group IV, P =NS) or at 10 weeks (%ΔCAD −23±12% for group III versus −19±7% for group IV; P =NS). Bosentan did not affect the response to acetylcholine at baseline or 10 weeks. Short-term ET-receptor inhibition in experimental hypercholesterolemia attenuated the enhanced coronary epicardial vasoconstrictor effects of ET-1 but not acetylcholine-induced coronary epicardial vasoconstriction, suggesting that acetylcholine-induced coronary epicardial vasoconstriction may not be mediated by ET receptors.