Derivation and Validation of Formula relating Pulmonary Acceleration Time and Mean Pulmonary Artery Pressure in Indian Population

Abstract

Background: Pulmonary acceleration time (PAT) forms a valuable echocardiographic parameter in deriving the mean pulmonary artery pressure (MPAP). The present study aims to derive and validate a formula relating MPAP and PAT in an Indian population. Materials and methods:Preoperative echocardiography was performed in 22 adult cardiac surgery patients undergoing coronary artery bypass grafting (CABG) and/or mitral valve replacement. The PAT, PAT/right ventricular ejection time (RVET), PAT corrected for heart rate [(HR) HRcPAT], and tricuspid regurgitation (TR) peak velocity were correlated with MPAP measured from pulmonary artery (PA) catheter, and a new formula relating MPAP and PAT was derived and subsequently validated in another cohort of 21 patients. Results:The PAT, HRcPAT, and PAT/RVET correlated well (r 2 = 0.69, 0.68 and 0.47 respectively, p < 0.0001), while TR velocity correlated poorly with MPAP (r 2 = 0.20, p = 0.046). The cutoff values of PAT and HRcPAT for diagnosing pulmonary artery hypertension (PAH) (MPAP = 25 mm Hg) were 74 and 99 respectively, with 92% sensitivity and 100% specificity. The derived formula (MPAP = 62.4 − 0.3 PAT) correlated well with the standard formula (79−0.45 PAT) on applying in the validation cohort (Bland-Altman plot, bias <10%). In subgroup analysis, patients with severe PAH (MPAP = 50 mm Hg) showed better correlation than patients with less than severe PAH (r 2 =0.633, p=0.038 and r 2 = 0.46, p = 0.108 respectively). Similarly, the formula for deriving pulmonary vascular resistance index (PVRI) from PAT [(PVRI = 14.9−0.09 pulmonary artery acceleration time (PAAT)] correlated well with the existing formula (PVRI = 9 − 0.07 PAAT). The inter-and intraobserver variabilities were not significant. Conclusion:The indexed formula is better in predicting MPAP from PAT in Indian population, particularly in patients with severe PAH (MPAP = 50 mm Hg) and the cutoffs of PAT and HRcPAT in predicting PAH (MPAP = 25 mm Hg) in an Indian population are 74 and 99 msec respectively.