Right Ventricular Mechanical Changes after Septal Myectomy for Obstructive Hypertrophic Cardiomyopathy: Vector Velocity Imaging Study

Objectives: The impairment of right ventricular (RV) myocardial mechanics is evident in hypertrophic cardiomyopathy (HCM). It is independently influenced by LV mechanics and correlated to the severity of LV phenotype. We investigated the changes in RV global and regional deformation following surgical septal myectomy using vector velocity imaging (VVI). Methods: 25 HCM patients, 68% males with mean age (34.5 ± 12 years) were examined before and within two months after surgical myectomy using VVI. In addition to conventional echocardiographic parameters, peak systolic strain (esys), strain rate (SR) and time to peak esys (TTP) of regional RV free wall (RVFW) & septal walls were analyzed in longitudinal (long) directions from apical four-chamber view and their (Δ) changes were calculated. Similar parameters were quantified in LV from apical 2 & 4 CH views. Intra-V-delay was defined as SD of TTP and inter-V dyssynchrony was estimated from TTP difference between the most delayed LV segment & RVFW. Results: All study patients showed improvement of their functional class from NYHA class III to class I and reduction of LVOT gradient to below 20 mmHg except one patient who had 30 mmHg gradients at rest. There was significant reduction of septal thickness, left atrial diameter & volume, LVOT gradient, LVMI, severity of mitral regurgitation, tricuspid annular velocities (P < 0.0001), RV diameter (P < 0.02) and increase in LV internal dimensions(P < 0.001) post myectomy. However, there was significant reduction of RV and LV systolic mechanics; RV global esys % (from -16.1% ± 4.4% to -12.9% ± 2.9%, P < 0.0001) and LV global esys %: from -11.6% ± 2.8% to -9.4% ± 2.2%, P < 0.0001) respectively. The magnitude of reduction of RV strain (ΔRV esys %, ΔSRsys) was directly correlated LV maximal wall thickness (r = 0.46, P < 0.01) and ΔRV dyssynchrony (TTP-SD) (r = 0.4, P < 0.05) and negatively correlated to age (r = -0.46, P < 0.02), pre-op RV SRsys (r = -0.52, P < 0.01) and pre-op LV EF % (r = -0.43, P < 0.03). Meanwhile, the reduction in RV diastolic mechanics: ΔRV SRe & SRa were directly correlated to PAP and LVOT gradient before surgery (r = 0.62, P < 0.002). Conclusion: Despite the improvement of patient functional status and reduction LVOT gradient, RV mechanics shows further deterioration after surgical myectomy. The magnitude of reduction is modestly related to cardiac phenotype and pre-op mechanical function.