Left ventricular outflow obstruction occurs immediately after exercise in patients with non-obstructive hypertrophic cardiomyopathy.

We evaluated the hemodynamic and geometric determinants of latent obstruction (LO, trans-left ventricular outflow tract (LVOT) gradient ≥30 mmHg with provocation) in patients with non-obstructive hypertrophic cardiomyopathy (HCMP). A total of 35 patients with non-obstructive HCMP underwent stepwise supine bicycle exercise echocardiography. Trans-LVOT pressure gradients, mitral geometric parameters, left ventricular ejection fractions (LVEF) and left ventricular end-systolic and diastolic dimensions (LVESD, LVEDD) were measured at each stage. The highest peak LVOT pressure gradient predominantly occurred immediately after exercise (n = 32, 91.3%) rather than during peak exercise (n = 3, 8.7%). Significant LO developed in nine patients (25%). No significant differences were found in resting echocardiographic parameters. Compared to the remaining patients, however, patients with LO had longer residual mitral leaflets (defined as residual portions of leaflets after coaptation; 4 ± 4 vs. 13 ± 4 mm, respectively; p = 0.001) and higher resting LVOT pressure gradients (7.4 ± 3.7 vs. 12.9 ± 5.8 mmHg, respectively; p = 0.001). Substantial decreases in mitral annular diameters from peak exercise to recovery after exercise were observed in the LO group, while mitral annular diameters increased after exercise in the non-LO group. In conclusion, the highest peak LVOT pressure gradient predominantly occurred immediately after exercise rather than during peak exercise, regardless of LO. Abrupt decrease of mitral annular diameter immediately after exercise, a longer residual mitral leaflet and a higher resting LVOT pressure gradient at rest might be related to LO.