VENTRICULAR AND MYOCARDIAL EFFICIENCIES DURING ACUTE AORTIC REGURGITATION IN CONSCIOUS DOGS

Background Alterations in cardiac efficiency may signal pathologic str esses and energetic adaptation during aortic regurgitation (AR). Metho ds and Results LV systolic function, left coronary blood flow, and AVO , difference were measured in conscious dogs to assess LV and contract ile efficiencies at baseline, 1 day (n=10), 1 week (n=10), and 3 weeks (n=8) of AR. LV systolic function was assessed by the preload recruit able stroke work relationship. Total LV Efficiency (TEFF=SWxHeart Rate / MVO2) and contractile efficiency (CEFF=1/the slope of the MVO2 -pres sure-volume area relationship) and steady-state potential energy (PVA- SWxHR), mechanical coupling efficiency (MCE=SWxHR/PVA) were calculated . LV systolic function decreased by 17% at 1 day (P<.05) and by 24% at 3 weeks (P<.05). CEFF decreased from 58+/-8% to 38+/-10% (P<.05) at 1 day, normalized at 1 week, and decreased to 28+/-14% at 3 weeks (P<.0 5). TEFF was not altered at 1 day and 1 week but decreased by 3 weeks (P<.05). MCE trended downward from baseline of 47+/-5%, reaching signi ficance at 3 weeks (34+/-6%, P<.05). Conclusions CEFF decreases acutel y, indicating diminished economy of myocardial contraction. CEFF norma lizes at 1 week, suggesting adequate compensation. TEFF is not altered in early AR. By 3 weeks, LV systolic dysfunction is accompanied by de pressed TEFF, mechanical coupling, and CEFF signaling the onset of dec ompensated AR. Thus, volume overload of acute AR resulted in early com pensation at the expense of myocardial efficiency with subsequent glob al dysfunction characterized by depressed LV systolic mechanics, mecha nical, coupling, and contractile efficiencies.