LEFT-VENTRICULAR INOTROPIC AND LUSITROPIC RESPONSES TO PACING-INDUCEDTACHYCARDIA IN PATIENTS WITH VARYING DEGREES OF VENTRICULAR DYSFUNCTION

Background In the failing human heart contractile reserve during tachy cardia is attenuated or absent, However, it is not known whether durin g tachycardia diminished inotropic reserve depends on the degree of ve ntricular dysfunction or lusitropic reserve is also diminished in pati ents with left ventricular (LV) dysfunction, Methods We studied 18 pat ients with dilated cardiomyopathy or mildly depressed LV function and 13 subjects in a control group (ejection fraction 0.67 +/- 0.09), The patients were classified into two groups based on whether their ejecti on Fraction was less than or more than 0.40 (group 1, ejection fractio n 0.27 +/- 0.05; group 2, ejection fraction 0.49 +/- 0.07), LV pressur es were measured with a catheter-tip manometer during incremental righ t atrial pacing up to a heart rate of 150 beats/min. Results With incr emental pacing LV peak positive dP/dt rose progressively in both the n ormal group and in group 2, but the increase was less for group 2 than for the normal group; in group 1 the increase was slight or absent, I n contrast, a significant and progressive decrease occurred in the tim e constant of LV relaxation in all three groups, Although their values remained significantly different at each heart rate, no intergroup di fferences in absolute or percent changes were present. Conclusions The se findings suggest that during tachycardia LV inotropic reserve may b e diminished depending on the degree of ventricular dysfunction, and l usitropic reserve may be preserved in patients with depressed function despite an attenuated inotropic response.