Changes in left atrial mechanics following surgical myectomy: the key component of clinical improvement

Abstract

Abstract Funding Acknowledgements Type of funding sources: None. Objectives The impairment of left atrial mechanics(LA) is previously described in hypertrophic cardiomyopathy (HCM). It is independently influenced by left ventricular(LV) mechanics and correlated to the severity of LV phenotype. We examined the alterations in LA structure and mechanics following surgical septal myectomy using vector velocity imaging. Methods Twenty-five HCM patients, 60% males with mean age (34.5 ± 12 years) were investigated before and six months after surgical myectomy using VVI. In addition to LA size and volume index (LAD, LAVI), LA reservoir function using peak systolic strain(εsys) & systolic strain rate(SRsys), and LA conduit(SRe) and LA contractile(SRa) functions were analyzed. Electrophysiologic properties of the LA were investigated using the difference between longest and shortest cycle; time to peak SRa(TTP-d) and the standard deviation(SD) of TTP-mean derived from regional SRa curves. Similar longitudinal εsys parameters were quantified in LV and right ventricle (RV) from apical views. The magnitude of changes in LA function (Δ) was expressed as the difference between pre and post myectomy values. Results Post myectomy, the studied cohort demonstrated atrial reverse remodeling and 68% of patients showed normalization of LAVI (<34ml/m2). All patients demonstrated a reduction of: LVOT gradient to < 20 mmHg, septal thickness, LV mass index, severity of mitral regurgitation and improvement of functional class from NYHA class III to class I. Following myectomy, although there was significant reduction of LV and RV systolic mechanics, there was a considerable increase in LA reservoir function (εsys:26 ± 13 vs 31 ± 16%, P<.03, SRsys:0.9 ± 0.4 vs 1.2 ± 0.5% s-1, P < 0.02) and contractile function (SRa: -0.8 ± 0.4 vs -1.2 ± 0.9 s-1, P < 0.04) respectively. LA Δ εsys was inversely correlated to pre-myectomy maximal wall thickness (r=-.494, P<.003) & LAVI (r=-.489, P<.01) and directly correlated to pre-myectomy LA εsys % (r=.639, P<.001) and LA SRa (r=.536, P<.008). Δ SRe showed direct correlation to LV εsys (r=.405, P< .04) and LA SRe (r=.635, P<.001) before surgery, respectively. ΔSRa was directly correlated to LA εsys % before surgery (r=.701, P<.0001). ΔTTP-SD and ΔTTP-d, showed inverse correlation to LV systolic mechanics before surgery (r=-.418, P<.038 and r=-.395, P<.050) respectively. Stepwise linear regression analysis identified global LV εsys% and RV εsys pre-myectomy as independent determinants of normalization of LAVI following myectomy, (β: 0.6, 95% CI: -4.22 - -1.96, p< 0.001) (β: 0.4, 95% CI: -4.06 - -0.57, p < 0.04) respectively. Conclusion Surgical myectomy is associated with improvement of LA mechanical properties and reverse remolding in HCM patient with symptomatic improvement despite subclinical reduction of LV and RV systolic mechanics.