Echocardiographic determination of pulmonary arterial capacitance

Abstract

A growing body of evidence has demonstrated that pulmonary arterial capacitance (PAC) is the strongest hemodynamic predictor of clinical outcomes across a wide spectrum of cardiovascular disease, including pulmonary hypertension and heart failure. We hypothesized that a ratio of right ventricular stroke volume (RVOT VTI) to the associated peak arterial systolic pressure (PASP) could function as a reliable non-invasive surrogate for PAC. We performed a prospective study of patients undergoing simultaneous transthoracic echocardiography and right heart catheterization (RHC) for various clinical indications. Measurements of the RVOT VTI/PASP ratio from echocardiographic measurements were compared against PAC calculated from RHC measurements. Correlation coefficients and Bland-Altman analysis compared the RVOT VTI/PASP ratio with PAC. Forty-five subjects were enrolled, 38% were female and mean age was 54 years (SD 13 years). The reason for referral to RHC was most commonly post-heart transplant surveillance (40%), followed by heart failure (22%), and pulmonary hypertension (18%). Pre-capillary pulmonary hypertension was present in 18%, isolated post-capillary pulmonary hypertension was present in 13%, and combined pre-and post-capillary pulmonary hypertension was present in 29%. The RVOT VTI/PASP ratio was obtainable in the majority of patients (78%), and Pearson's correlation demonstrated moderately-strong association between PAC and the RVOT VTI/PASP ratio, r = 0.75 (P < 0.001). Bland-Altman analysis demonstrated good agreement between measurements without suggestion of systematic bias and a mean difference in standardized units of - 0.133. In a diverse population of patients and hemodynamic profiles, we validated that the ratio of RVOT VTI/PASP to be a reliably-obtained non-invasive marker associated with PAC.

Keywords: Echocardiography; Heart failure; Imaging and diagnostics; Pulmonary hypertension.

Figure 1.

Scatter Plot of Right Ventricular Displacement to PASP ratio versus Pulmonary Arterial Capacitance. PAC: Pulmonary artery capacitance (ml/mmHg). PASP: Peak arterial systolic pressure (mmHg). RVOT VTI: Right ventricular outflow track velocity time integral (cm). TAPSE: Tricuspid annular plane systolic excursion (cm). RV FAC: Right ventricular fractional area of change (% change). RV S’: Right ventricular Doppler tissue velocity (cm/s). No PH: no pulmonary hypertension Pre-capillary pulmonary hypertension (mPAP <25 mmHg, PVR <3 Wood units, PCWP <15 mmHg). Pre-capillary PH: Pre-capillary pulmonary hypertension (mPAP >25 mmHg, PVR >3 Wood units, PCWP <15 mmHg). Post capillary PH: Post-capillary pulmonary hypertension (mPAP >25 mmHg, PVR <3 Wood units, PCWP >15 mmHg). Combined PH: Combined pre and post-capillary pulmonary hypertension (mPAP >25 mmHg, PVR >3 Wood units, PCWP >15 mmHg).

Figure 2.

Bland and Altman plot of RVOT VTI/PASP and PAC. PAC: Pulmonary artery capacitance (ml/mmHg). PASP: Peak arterial systolic pressure (mmHg). RVOT VTI: Right ventricular outflow track velocity time integral (cm).