South Asian-Specific MYBPC3 Δ25bp Deletion Carriers Display Hypercontraction and Impaired Diastolic Function Under Exercise Stress.

A 25-base pair (25bp) intronic deletion in the gene enriched in South Asians (SAs) is a risk allele for late-onset left ventricular (LV) dysfunction, hypertrophy, and heart failure (HF) with several forms of cardiomyopathy. However, the effect of this variant on exercise parameters has not been evaluated. As a pilot study, 10 asymptomatic SA carriers of the variant (52.9 ± 2.14 years) and 10 age- and gender-matched non-carriers (NCs) (50.1 ± 2.7 years) were evaluated at baseline and under exercise stress conditions using bicycle exercise echocardiography and continuous cardiac monitoring. Baseline echocardiography parameters were not different between the two groups. However, in response to exercise stress, the carriers of Δ25bp had significantly higher LV ejection fraction (%) (CI: 4.57 ± 1.93; < 0.0001), LV outflow tract peak velocity (m/s) (CI: 0.19 ± 0.07; < 0.0001), and higher aortic valve (AV) peak velocity (m/s) (CI: 0.103 ± 0.08; = 0.01) in comparison to NCs, and E/A ratio, a marker of diastolic compliance, was significantly lower in Δ25bp carriers (CI: 0.107 ± 0.102; = 0.038). Interestingly, LV end-diastolic diameter (LVID) was augmented in NCs in response to stress, while it did not increase in Δ25bp carriers (CI: 0.239 ± 0.125; = 0.0002). Further, stress-induced right ventricular systolic excursion velocity s' (m/s), as a marker of right ventricle function, increased similarly in both groups, but tricuspid annular plane systolic excursion increased more in carriers (slope: 0.008; = 0.0001), suggesting right ventricle functional differences between the two groups. These data support that is associated with LV hypercontraction under stress conditions with evidence of diastolic impairment.