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.