Size, shape, and stamina: the impact of left ventricular geometry on exercise capacity

Abstract

Although several studies have examined the cardiac functional determinants of exercise capacity, few have investigated the effects of structural remodeling. The current study evaluated the association between cardiac geometry and exercise capacity. Subjects with ejection fraction > or = 50% and no valvular disease, myocardial ischemia, or arrhythmias were identified from a large prospective exercise echocardiography database. Left ventricular mass index and relative wall thickness were used to classify geometry into normal, concentric remodeling, eccentric hypertrophy, and concentric hypertrophy. All of the subjects underwent symptom-limited treadmill exercise according to standard Bruce protocol. Maximal exercise tolerance was measured in metabolic equivalents. Of 366 (60+/-14 years; 57% male) subjects, 166 (45%) had normal geometry, 106 (29%) had concentric remodeling, 40 (11%) had eccentric hypertrophy, and 54 (15%) had concentric hypertrophy. Geometry was related to exercise capacity: in descending order, the maximum achieved metabolic equivalents were 9.9+/-2.8 in normal, 8.9+/-2.6 in concentric remodeling, 8.6+/-3.1 in eccentric hypertrophy, and 8.0+/-2.7 in concentric hypertrophy (all P<0.02 versus normal). Left ventricular mass index and relative wall thickness were negatively correlated with exercise tolerance in metabolic equivalents (r=-0.14; P=0.009 and r=-0.21; P<0.001, respectively). Augmentation of heart rate and ejection fraction with exercise were blunted in concentric hypertrophy compared with normal, even after adjusting for medications. In conclusion, the pattern of ventricular remodeling is related to exercise capacity among low-risk adults. Subjects with concentric hypertrophy display the greatest limitation, and this is related to reduced systolic and chronotropic reserve. Reverse remodeling strategies may prevent or treat functional decline in patients with structural heart disease.

Figure 1. Relationship between left ventricular structure and exercise capacity

[A] Geometry was related to exercise capacity measured in maximal achieved METs: in descending order, METs were 9.9±2.8 in normal (NL) geometry, 8.9±2.6 in concentric remodeling (CR) (p=0.008 vs NL), 8.6±3.1 in eccentric hypertrophy (EH) (p=0.016 vs NL), and 8.0±2.7 in concentric hypertrophy (CH) (p<0.001 vs NL). Squares represent means and bars represent standard deviations. [B & C] Left ventricular (LV) mass index and relative wall thickness were negatively correlated with achieved METs (r= -0.14; p=0.009 and r= -0.21; p<0.001, respectively). Solid lines represent mean regression lines and dotted lines represent the 95% confidence intervals.

Figure 2. Change in exercise echocardiographic parameters from rest to stress

The change in parameters from rest to peak stress (Δ) differed among geometry groups (where NL, Normal geometry; CR, concentric remodeling; EH, eccentric hypertrophy; CH, concentric hypertrophy). The increase in systolic blood pressure (SBP) with exercise tended to be smaller in CH compared to NL. The augmentation of heart rate (HR) and ejection fraction (EF) with exercise were notably blunted in CH compared to NL, even after adjusting for medications, while the increase in echo-estimated filling pressures (E/e’ ratio) with exercise was similar among groups. *p<0.02 vs NL by Dunnett's test