Cardiac Reserve as Assessed by Augmentation in Cardiac Power Efficiency Predicts Response to Intravascular Ventricular Assist System Support

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The intravascular ventricular assist system (iVAS) is a durable, ambulatory counterpulsation device that is currently under investigation for advanced heart failure patients. Baseline cardiac power efficiency (CPE) has previously been reported to predict hemodynamic success after iVAS. We investigated the role of change in CPE after inotropic challenge, a marker of cardiac reserve, as a prognostic tool prior to iVAS support. Hemodynamic data at the time of right heart catheterization was collected on patients just prior to iVAS implantation. A subset of patients underwent milrinone loading followed by repeat hemodynamic assessment 10 min after a 50 mcg/kg milrinone infusion. Cardiac power index (CPI) was calculated as [CPI = cardiac index (CI) x mean arterial pressure (MAP)/451)] and CPE was calculated as [CPE = CPI/Pulmonary capillary wedge pressure (PCWP)]. CPE at baseline and after inotropic challenge was calculated and a percent augmentation of 25% or greater in CPE was used as a cutoff indicative of cardiac reserve. The combined endpoint of independently adjudicated heart failure events, dependency on inotropes 7 days after implant, need for escalation to ECMO or death was evaluated. 40 patients from a single institution underwent iVAS implantation. 39 patients underwent RHC prior to iVAS (11.7 +/- 14.0 days before surgery). 11 patients underwent milrinone loading followed by repeat hemodynamic assessment. Baseline hemodynamics revealed an average CPE of 0.0227 +/- 0.0148 watts*mmHg/m2 for the entire cohort. In the subset of patients who underwent milrinone loading, CPE increased on average 41% from 0.0141 +/- 0.0055 watts*mmHg/m2 to 0.0236 +/- 0.0114 watts*mmHg/m2 (p = 0.003). There was a trend towards freedom from death, ECMO, HF events, or inotrope dependency in those who were able to augment CPE by more than 25% (N = 8), compared to those with less (N = 3) cardiac reserve OR = 0.071 (95% CI 0.003 - 1.73, p = 0.105). Cardiac reserve as defined as a greater than 25% augmentation in CPE after milrinone challenge may predict future success with counterpulsation with iVAS. This hypothesis generating question warrants further investigation.