The effects of acute afterload change on systolic ventricular function in conscious dogs with normal vs. failing hearts.

BACKGROUND: To date, no data exist on the linearity and, therefore, the usefulness of the preload recruitable stroke work (PRSW) and end-systolic pressure-volume (ESPVR) relationships during acute afterload changes in heart failure. AIMS: Our aim was, therefore, to characterize both relationships in a model of ventricular pacing induced heart failure at baseline and during acute changes in afterload. METHODS: Dynamic left ventricular volume and transmural pressure were measured in 10 conscious dogs using sonomicrometry and micromanometry under control conditions and during heart failure produced by 3 weeks of rapid right ventricular pacing. Afterload was varied from baseline with intravenous infusions of nitroprusside and phenylephrine. Left ventricular function was assessed using the PRSW and ESPVR relationships. RESULTS: Cardiac output demonstrated a linear inverse relationship with afterload in both normal and failing hearts (r2>0.5, P<0.001) with failure producing a parallel, downward shift of the afterload (x) vs. cardiac output (y) relationship (P<0.01). Yet, afterload variation did not affect PRSW or ESPVR relationships in either normal or failing hearts (r2<0.12, P>0.05). CONCLUSION: Thus, the PRSW and ESPVR relationships are insensitive to acute afterload changes in both failing and normal hearts, and the failing left ventricle is no more afterload-sensitive than the normal heart.