Pulmonary pulse transit time (pPTT) is a novel non-invasive echocardiographic measure to assess pulmonary arterial hemodynamic. It is the time needed for the pulse wave to propagate from the right ventricular outflow tract (RVOT) to the left atrium. Pulse wave velocity (PWV) defined as the velocity of pressure waves traveling through the arterial system, correlates inversely with arterial compliance in the circulation.  With decreasing compliance, pulse wave velocity increases, and the time taken by the pressure wave to travel between 2 vascular points shortens. pPTT has been identified as clinically important surrogates for assessing arterial compliance in the pulmonary circulation but there is technical difficulties in measuring pulse wave velocity in the pulmonary circulation. Recently, Wibmer et al. defined pPTT, as the delay between onset of ventricular electrical activity (on electrocardiogram) and the arrival of the pulse wave in the pulmonary vein (as determined by Doppler echocardiography of the pulmonary vein), and found to be reduced in patients with pulmonary hypertension.  Wibmer et al. postulated that pPTT was shortened because of decreased pulmonary artery(PA) compliance and increased pulse wave velocity, and they proposed pPTT as a potential index of PA compliance.  pPTT has been studied in chronic obstructive pulmonary disease and connective tissue disorder induce pulmonary hypertension i.e precapillary hypertension. However, Gurbuz et al, demonstrated prolonged pPTT in patients with significant mitral stenosis i.e postcapillary hypertension. They found a positive correlation between pPTT with pulmonary artery systolic pressure(PASP) and inverse correlation with tricuspid annular plane systolic excursion(TAPSE) which were the predictors of increased right ventricle(RV) afterload. Also, pPTT directly related to left atrial volume index(LAVi) which is a predictor of postoperative atrial fibrillation(POAF). Both RV-PV coupling and POAF were not discussed in this study. In addition, no other study has explored the usefulness of pPTT in predicting the RV-PA uncoupling and POAF which are commonly seen in patients with left heart disease.

Therefore, the primary aim of the study is to further characterisation of pPTT in patients with left heart disease and to evaluate whether it predicts RV-PA uncoupling and POAF in this cohort of patients.