Calculation Of Cardiac Power Output With Right Atrial Pressure

Background The initial derivation of cardiac power output (CPO) included the difference between mean arterial pressure (MAP) and right atrial pressure (RAP) in the numerator, before multiplying by cardiac output (CO). In common use, CPO is calculated without RAP. Whereas the omission of RAP from the CPO calculation may be inconsequential for those with normal right-sided pressures, we hypothesized that the inclusion of RAP will enhance the prognostic performance of this parameter in those with elevated RAP. Methods We retrospectively analyzed consecutive patients undergoing right heart catheterization with milrinone drug study at our institution (2/2013-11/2019). CPO was calculated as [(MAP-RAP)xCO)]/451 Watts (W), and was then analyzed with RAP above or below the median. Univariable analysis was done for the primary outcome of freedom from advanced therapies, defined as need for inotropes, temporary mechanical circulatory support, left ventricular assist device, orthotopic heart transplant, or death at 30 days. Receiver operator characteristic analyses were completed to determine the optimal cutpoints, and Kaplan-Meier (KM) analyses were implemented. Results The cohort included 224 patients, median age 57 (IQR 48-66) years, 34% women, and 31% ischemic cardiomyopathy. Median RAP was 13 mmHg. CPO with RAP < 13 were older (61 vs 56 years-old, p=0.001) and had a lower ejection fraction (19% vs 23%, p=0.02) than CPO with RAP ≥ 13. Median CPO with RAP ≤ 13 (n=120) was 0.60 W (IQR 0.49-0.73) and CPO with RAP > 13 (n=104) was 0.52 W (IQR 0.40-0.65). In univariable analysis CPO with RAP ≤ 13 (OR 0.003, 95%CI 0.00-0.05, p<0.001) and CPO with RAP > 13 (OR 0.004, 95%CI 0.00-0.08, p<0.001) were both significantly associated with the primary outcome. In KM analysis, CPO with RAP ≤ 13 had no significant difference in the primary outcome (54% CPO < 0.67 W vs 73% CPO ≥ 0.67 W, p=0.10), while CPO with RAP > 13 had a significant difference in the primary outcome (55% CPO < 0.67 W vs 87% CPO ≥ 0.67 W, p=0.01). Conclusion In the setting of elevated, compared to normal, RAP, there is a significant difference in 30-day clinical outcomes when assessing heart failure patients using the original CPO calculation. The initial derivation of cardiac power output (CPO) included the difference between mean arterial pressure (MAP) and right atrial pressure (RAP) in the numerator, before multiplying by cardiac output (CO). In common use, CPO is calculated without RAP. Whereas the omission of RAP from the CPO calculation may be inconsequential for those with normal right-sided pressures, we hypothesized that the inclusion of RAP will enhance the prognostic performance of this parameter in those with elevated RAP. We retrospectively analyzed consecutive patients undergoing right heart catheterization with milrinone drug study at our institution (2/2013-11/2019). CPO was calculated as [(MAP-RAP)xCO)]/451 Watts (W), and was then analyzed with RAP above or below the median. Univariable analysis was done for the primary outcome of freedom from advanced therapies, defined as need for inotropes, temporary mechanical circulatory support, left ventricular assist device, orthotopic heart transplant, or death at 30 days. Receiver operator characteristic analyses were completed to determine the optimal cutpoints, and Kaplan-Meier (KM) analyses were implemented. The cohort included 224 patients, median age 57 (IQR 48-66) years, 34% women, and 31% ischemic cardiomyopathy. Median RAP was 13 mmHg. CPO with RAP < 13 were older (61 vs 56 years-old, p=0.001) and had a lower ejection fraction (19% vs 23%, p=0.02) than CPO with RAP ≥ 13. Median CPO with RAP ≤ 13 (n=120) was 0.60 W (IQR 0.49-0.73) and CPO with RAP > 13 (n=104) was 0.52 W (IQR 0.40-0.65). In univariable analysis CPO with RAP ≤ 13 (OR 0.003, 95%CI 0.00-0.05, p<0.001) and CPO with RAP > 13 (OR 0.004, 95%CI 0.00-0.08, p<0.001) were both significantly associated with the primary outcome. In KM analysis, CPO with RAP ≤ 13 had no significant difference in the primary outcome (54% CPO < 0.67 W vs 73% CPO ≥ 0.67 W, p=0.10), while CPO with RAP > 13 had a significant difference in the primary outcome (55% CPO < 0.67 W vs 87% CPO ≥ 0.67 W, p=0.01). In the setting of elevated, compared to normal, RAP, there is a significant difference in 30-day clinical outcomes when assessing heart failure patients using the original CPO calculation.