Evolution of ventricular hypertrophy and myocardial mechanics in physiological and pathological hypertrophy

Left ventricular hypertrophy (LVH) is an adaptive response to physiological or pathological stimuli, and distinguishing between the two has obvious clinical implications. However, asymmetric septal hypertrophy and preserved cardiac function are noted in early stages in both cases. We characterized the early anatomic and functional changes in a mouse model of physiological and pathological stress using serial echocardiography-based morphometry and tissue velocity imaging. Weight-matched CF-1 male mice were separated into Controls (n 10), treadmill Exercise 1 h daily for 5 days/wk (n 7), and transverse aortic constriction (TAC, n 7). Hypertrophy was noted first in the left ventricle basal septum compared with other segments in Exercise (0.84 0.02 vs. 0.79 0.03 mm, P 0.03) and TAC (0.86 0.05 vs. 0.77 0.04 mm, P 0.02) at 4 and 3 wk, respectively. At 8 wk, eccentric LVH was noted in Exercise and concentric LVH in TAC. Septal E/E= ratio increased in TAC (32.6 3.7 vs. 37 6.2, P 0.002) compared with the Controls and Exercise (32.3 5.2 vs. 32.8 3.8 and 31.2 4.9 vs. 28.2 5.0, respectively, nonsignificant for both). Septal s= decreased in TAC (21 3.6 vs. 17 4.2 mm/s, P 0.04) but increased in Exercise (19.6 4.1 vs. 29.2 2.3 mm/s, P 0.001) and was unchanged in Controls (20.1 4.2 vs. 20.9 5.1 mm/s, nonsignificant). With similar asymmetric septal hypertrophy and normal global function during the first 4 – 8 wk of pathological and physiological stress, there is an early marginal increase with subsequent decrease in systolic tissue velocity in pathological but early and progressive increase in physiological hypertrophy. Tissue velocities may help adjudicate between these two states when there are no overt anatomic or functional differences.