CHANGES IN LEFT-VENTRICULAR VOLUME, MASS, AND FUNCTION DURING THE DEVELOPMENT AND REGRESSION OF SUPRAVENTRICULAR TACHYCARDIA-INDUCED CARDIOMYOPATHY - DISPARITY BETWEEN RECOVERY OF SYSTOLIC VERSUS DIASTOLIC FUNCTION

Chronic supraventricular tachycardia causes a dilated cardiomyopathy in man. Terminating this tachycardia appears to result in symptomatic improvement; however, its effects on left ventricular (LV) volume, mass, and function have not been fully examined. Accordingly, hemodynamic studies using simultaneous echocardiography and catheterization were performed in three groups of pigs: 1) those subjected to rapid left atrial pacing (240 beats/min) for 3 weeks (SVT, n = 8), 2) those subjected to supraventricular tachycardia for 3 weeks followed by termination of pacing and a 4-week recovery period (PSVT, n = 9), and 3) sham-operated controls (CTR, n = 10). Systolic pump function was assessed using fractional shortening (FS), peak ejection rate [peak (-)dD/dt], and maximum rate of pressure development [peak (+)dP/dt]. Diastolic function was assessed using the time constant of isovolumic pressure decline (tau), peak early diastolic filling rate [peak (+)dD/dt], the chamber stiffness constant (K(c)), and the myocardial stiffness constant (K(m)). Supraventricular tachycardia caused LV dilation (end-diastolic dimension [EDD] increased from 3.5 +/- 0.4 cm in CTR to 4.9 +/- 0.5 cm in SVT, p < 0.05) but no change in LV mass (LV weight-to-body weight ratio [LV/BW]) was 2.58 +/- 0.3 g/kg in CTR and 2.66 +/- 0.4 g/kg in SVT, all indexes of systolic function became abnormal (FS fell from 30 +/- 4% in CTR to 13 +/- 5% in SVT, p < 0.05), and the indexes of relaxation and filling were slowed ( tau increased from 36 +/- 3 msec in CTR to 51 +/- 13 msec in SVT, p < 0.05). There were no significant changes in K(c) or K(m). After terminating the supraventricular tachycardia, LV volume fell but remained greater than that in CTR (EDD was 4.2 +/- 0.4 cm in PSVT, p < 0.05 versus CTR) and substantial LV hypertrophy developed (LV/BW was 3.48 +/- 0.5 g/kg in PSVT, p < 0.05 versus CTR). Systolic function returned to normal (FS was 31 +/- 5% in PSVT) but diastolic function remained abnormal. In PSVT, tau remained prolonged (49 +/- 12 msec, p < 0.05 versus CTR), K(c) increased from 3.7 +/- 1.0 in CTR to 7.4 +/- 1.2 (p < 0.05), and K(m) increased from 4.4 +/- 1.5 in CTR to 13.9 +/- 9.7 (p < 0.05). Thus, the improvement in systolic function that occurs after the termination of supraventricular tachycardia is associated with the development of LV hypertrophy and persistent diastolic dysfunction.