Tachycardia exacerbates abnormal left ventricular-arterial coupling in heart failure.

The purpose of this study was to assess the effect of heart rate on left ventricular (LV)-arterial coupling and LV mechanical efficiency before and after heart failure (CHF). The production of LV stroke work (SW) and mechanical efficiency depends on the coupling of the LV and arterial system. The response of LV-arterial coupling to tachycardia may be altered in heart failure. We compared the response of LV-arterial coupling to increased heart rate (HR) in six conscious, instrumented dogs before and after pacing-induced CHF. Coupling was quantified as E(ES)/ E(A), where E(ES) is the slope of end-systolic pressure ( P)-volume ( V) relation, and E(A) is arterial elastance. Mechanical efficiency was determined as the ratio of SW to a total P-V area (PVA). Before CHF, E(ES) and E(A) increased similarly with increased heart rate to 180 min(-1). Thus, E(ES)/ E(A) remained unaltered (0.96 +/- 0.08 vs 0.94 +/- 0.35), and SW/PVA was unchanged (0.62 +/- 0.03 vs 0.59 +/- 0.06). Compared with the results prior to CHF and after CHF the resting E(ES) was decreased, thus both E(ES)/ E(A) (0.58 +/- 0.09) and SW/PVA (0.48 +/- 0.06) were less ( P << 0.05) than baseline. After CHF, an increase in HR to 180 min(-1) increased E(A) but not E(ES), thus E(ES)/ E(A) fell to 0.44 +/- 0.06 ( P << 0.05) and SW/PVA fell to 0.41 +/- 0.05 ( P << 0.05). Under normal conditions, LV-arterial coupling remains optimal during increases in HR. After CHF, tachycardia exacerbates the suboptimal baseline LV-arterial coupling, reducing the efficiency of producing SW.