Right ventricular outflow tract diameter change with exercise: a prospective exercise echocardiography and invasive CPET study

While cardiac output reserve with exercise predicts outcomes in cardiac and pulmonary vascular disease, precise quantification of exercise cardiac output requires invasive cardiopulmonary testing (iCPET). To improve the accuracy of cardiac output reserve estimation with transthoracic echocardiography (TTE), this prospective study aims to define changes in right ventricular outflow tract diameter (RVOTd) with exercise and its relationship with invasively measured haemodynamics. Twenty subjects underwent simultaneous TTE and iCPET, with data collected at rest, leg-raise, 25 W, 50 W (n = 16), 75 W (n = 14), and 100 W (n = 6). This was followed by a second exercise study with real-time RV pressure-volume loops at similar stages (except leg-raise). The overall cohort included heart failure with preserved ejection fraction (n = 12), pulmonary arterial hypertension (n = 5), and non-cardiac dyspnoea (n = 3). RVOTd was reverse engineered from the TTE-derived RVOT velocity time integral (VTI) and iCPET-derived stroke volume, using the formula: Fick stroke volume = RVOT VTI × RVOT area (wherein RVOT area = π × [RVOTd/2]2). RVOTd increased by nearly 3-4% at every 25 W increment. Using linear regression models, where each subject is treated as a categorical variable and adjusting for subject intercept, RVOTd was correlated with haemodynamic variables (cardiac output, heart rate, pulmonary artery and RV pressures). Of all the predictor haemodynamic variables, cardiac output had the highest r2 model fit (adjusted r² = 0.68), with a unit increase in cardiac output associated with a 0.0678 increase in RVOTd (P < 0.001). Our findings indicate that RVOTd increases by 3-4% with every 25 W increment, predominantly correlated with cardiac output augmentation. These results can improve the accuracy of cardiac output reserve estimation by adjusting for RVOTd with graded exercise during non-invasive CPET and echocardiogram. However, future studies are needed to define these relationships for left ventricular outflow tract diameter.