Novel pulse-amplitude index is correlated with cardiac index in patients with heart failure or aortic stenosis

Background Hemodynamic assessment is an important aspect of the management of patients with cardiovascular disease. Cardiac index (CI), a key metric, is conventionally measured via invasive cardiac catheterization, limiting its utility. Consequently, effective non-invasive methods for assessing hemodynamics, such as CI, should be developed. The pulse-amplitude index (PI), derived from photoplethysmography (PPG), reflects microcirculatory perfusion. The PI value was calculated as a following formula: PI = (pulsatile light absorbance/total light absorbance) × 100 (%). Hemodynamic parameters are associated with microcirculatory perfusion. Whereas the PI value is simple and easily measured indicator, its application remains unestablished in hemodynamic assessment. Purpose This study aimed to investigate the correlation between PI and hemodynamic parameters in adult cardiovascular disease patients undergoing catheterization, aiming to evaluate PI's potential as a non-invasive hemodynamic assessment tool. Methods We analyzed consecutive 216 patients who had hemodynamic parameters assessed by cardiac catheterization and PI value measured by PPG simultaneously in Kyushu University Hospital from October, 2023 to March, 2024. Results The mean age was 63.1 years and male was 115 (53%). The underlying diseases were ischemic heart disease (IHD) in 6%, aortic stenosis (AS) in 15%, other valvular heart diseases (VHD) in 15%, heart failure (HF) in 20%, post-heart transplantation in 17%, LVAD implantation in 6%, and pulmonary hypertension in 19%. PI values ranged from 0.05% to 12.72% and its mean and median PI values were 1.97% and 1.56%, respectively (Figure 1). When analyzed including all patients, PI was not associated with cardiac index (CI), mixed venous oxygen saturation (SvO2), or pulmonary capillary wedge pressure (PCWP). On the other hand, PI was positively correlated with CI in patients with PI < 2% (r = 0.337, p < 0.001, n = 138) (Figure 2). In particular, the correlation was clearly observed in patients with AS (r = 0.541, p = 0.009, n = 22) and HF (r = 0.451, p = 0.012, n = 30) in the range of PI values < 2%. In addition, PI tended to be associated with CI in patients with PH (r = 0.466, p = 0.051, n = 18). Conclusions In the range of PI values < 2%, PI was positively correlated with CI in patients with AS or HF. PI may be useful for hemodynamic assessment as a simple, non-invasive, and repeatable indicator of cardiac output in cardiovascular disease.