The systolic paradox in hypertrophic cardiomyopathy

Abstract

Objective: We explored cardiac volumes and the effects on systolic function in hypertrophic cardiomyopathy (HCM) patients with left ventricular hypertrophy (HCM LVH+) and genotype-positive patients without left ventricular hypertrophy (HCM LVH-).

Methods: We included 180 HCM LVH+, 100 HCM LVH- patients and 80 healthy individuals. End-Diastolic Volume Index (EDVI), End-Systolic Volume Index (ESVI) and ejection fraction (EF) were assessed by echocardiography. Left ventricular (LV) global longitudinal strain (GLS) was measured by speckle tracking echocardiography.

Results: EDVI and ESVI were significantly smaller in HCM LVH+ compared with HCM LVH- patients (41±14 mL/m² vs 49±13 mL/m² and 16±7 mL/m² vs 19±6 mL/m², respectively, both p<0.001) and in healthy individuals (41±14 mL/m² vs 57±14 mL/m² and 16±7 mL/m² vs 23±9 mL/m², respectively, both p<0.001). HCM LVH- patients had significantly lower EDVI and ESVI compared with healthy individuals (49±13 mL/m² vs 57±14 mL/m² and 19±6 mL/m² vs 23±9 mL/m², both p<0.001). EF was similar (61%±7% vs 60%±8% vs 61%±6%, p=0.43) in the HCM LVH+, HCM LVH- and healthy individuals, despite significantly worse GLS in the HCM LVH+ (-16.4%±3.7% vs -21.3%±2.4% vs -22.3%±3.7%, p<0.001). GLS was worse in the HCM LVH- compared with healthy individuals in pairwise comparison (p=0.001). Decrease in ESVI was closely related to EF in HCM LVH+ and HCM LVH- (R=0.45, p<0.001 and R=0.43, p<0.001) as expected, but there was no relationship with GLS (R=0.02, p=0.77 and R=0.11, p=0.31). Increased maximal wall thickness (MWT) correlated significantly with worse GLS (R=0.58, p<0.001), but not with EF (R=0.018, p=0.30) in the HCM LVH+ patients.

Conclusion: HCM LVH+ had smaller cardiac volumes that could explain the preserved EF, despite worse GLS that was closely related to MWT. HCM LVH- had reduced cardiac volumes and subtle changes in GLS compared with healthy individuals, indicating a continuum of both volumetric and systolic changes present before increased MWT.

Keywords: Hypertrophic cardiomyopathy; echocardiography and heart failure with preserved ejection fraction.

Figure 1

Bar chart of cardiac volumes and EF in the healthy individuals, HCM LVH− patients and HCM LVH+ patients. Blue bars show the indexed diastolic volumes (EDVI (mL/m²)), light blue bars show the indexed systolic volumes (ESVI (mL/m²)) and grey bars show EF (%). The dark blue vertical lines are reference for average EDVI, ESVI and EF in healthy individuals. The horizontal arrows indicate the difference in average indexed diastolic and systolic volumes and EF between HCM LVH− and HCM LVH+ patients compared with healthy individuals. *p<0.01 versus healthy  individuals, †p<0.01 versus HCM LVH−. EDVI, End-Diastolic Volume Index; EF, ejection fraction; HCM, hypertrophic cardiomyopathy; ESVI, End-Systolic Volume Index; HCM, hypertrophic cardiomyopathy; HCM LVH−, genotype-positive patients without increased wall thickness; HCM LVH+, patients with increased wall thickness; LVH, left ventricular hypertrophy.

Figure 2

Bar chart of systolic function in healthy individuals, HCM LVH− patients and HCM LVH+ patients. GLS was significantly worse in the HCM LVH+ patients compared with HCM LVH− patients and healthy individuals (both p<0.001). In addition, GLS was worse in the HCM LVH− compared with healthy individuals (p=0.005). GLS, global longitudinal strain; HCM, hypertrophic cardiomyopathy; HCM LVH−, genotype-positive patients without increased wall thickness; HCM LVH+, patients with increased wall thickness; LVH, left ventricular hypertrophy.

Figure 3

Scatter plot of relationship between MWT, GLS and EF upper panel shows that GLS was closely related to MWT with worse LV function by GLS correlating to increased wall thickness (R=0.58, p<0.001) in the HCM LVH+ patients (red dots), but with no correlation between GLS and MWT (R=0.16, p=0.13) in the HCM LVH− (blue dots) and the healthy individuals (R=0.07, p=0.53) (green dots). Lower panel shows that there was no significant correlation between EF and MWT in the HCM LVH+ patients (R=0.018, p=0.30) or in the HCM LVH− patients and the healthy individuals (R=0.05, p=0.60 and R=0.01, p=0.91).  EF, ejection fraction; GLS, global longitudinal strain; HCM LVH+, hypertrophic cardiomyopathy patients with hypertrophy; HCM LVH−, genotype-positive patients without hypertrophy; MWT, maximal wall thickness.