Right ventricular-vascular coupling ratio in pediatric pulmonary arterial hypertension: A comparison between cardiac magnetic resonance and right heart catheterization measurements

Abstract

Background: In pulmonary arterial hypertension (PAH), right ventricular (RV) failure is the main cause of mortality. Non-invasive estimation of ventricular-vascular coupling ratio (VVCR), describing contractile response to afterload, could be a valuable tool for monitoring clinical course in children with PAH. This study aimed to test two hypotheses: VVCR by cardiac magnetic resonance (VVCR_CMR) correlates with conventional VVCR by right heart catheterization (VVCR_RHC) and both correlate with disease severity.

Methods and results: Twenty-seven patients diagnosed with idiopathic and associated PAH without post-tricuspid shunt, who underwent RHC and CMR within 17 days at two specialized centers for pediatric PAH were retrospectively studied. Clinical functional status and hemodynamic data were collected. Median age at time of MRI was 14.3 years (IQR: 11.1-16.8), median PVRi 7.6 WU × m² (IQR: 4.1-12.2), median mPAP 40 mm Hg (IQR: 28-55) and median WHO-FC 2 (IQR: 2-3). VVCR_CMR, defined as stroke volume/end-systolic volume ratio was compared to VVCR_RHC by single-beat pressure method using correlation and Bland-Altman plots. VVCR_CMR and VVCR_RHC showed a strong correlation (r = 0.83, p < 0.001). VVCR_CMR and VVCR_RHC both correlated with clinical measures of disease severity (pulmonary vascular resistance index [PVRi], mean pulmonary artery pressure [mPAP], mean right atrial pressure [mRAP], and World Health Organization functional class [WHO-FC]; all p ≤ 0.02).

Conclusions: Non-invasively measured VVCR_CMR is feasible in pediatric PAH and comparable to invasively assessed VVCR_RHC. Both correlate with functional and hemodynamic measures of disease severity. The role of VVCR assessed by CMR and RHC in clinical decision-making and follow-up in pediatric PAH warrants further clinical investigation.

Keywords: Cardiac magnetic resonance; Pediatric pulmonary hypertension; Right heart catheterization; Right ventricular function; Ventricular-vascular coupling ratio.

Figure 1:

Schematic overview of a) the single-beat method of determining VVCR_RHC and b) the volume method of estimating VVCR_CMR. a) At 1., theoretical maximum pressure of the right ventricle (P_max) is estimated by fitting a sinusoid from early systolic (end-diastolic pressure (P_ed) to maximum dP/dt) and early diastolic (minimum dP/dt to pressure equal to P_ed) portion of the RV pressure tracing. This P_max would occur in isovolumic contraction and is therefore located at end-diastolic volume in the pressure-volume loop. End-systolic pressure (P_es) is estimated as the pressure 30 ms before minimum dP/dt (P_30ms). At 2., end-systolic elastance (E_es) is estimated by the ratio of P_max minus P_es, to stroke volume (SV). Arterial elastance (E_a) is estimated as the ratio of P_es to SV. b) In the volume method, E_es is estimated as the ratio of P_es to end-systolic volume (ESV), in which volume at zero pressure (V₀) is neglected. E_a is, similar to the single-beat method, estimated as the ratio of P_es to SV.

Figure 2:

a) correlation and 95% confidence interval between catheterization-derived (VVCR_RHC) and CMR-derived ventricular-vascular coupling ratio (VVCR_CMR). b) Bland-Altman plot demonstrating the differences between VVCR_RHC and VVCR_CMR. Mean ventricular-vascular coupling ratio (VVCR) is calculated as (VVCR_CMR + VVCR_RHC)/2. Mean difference between VVCR_CMR and VVCR_RHC (middle black line) is 0.19 with a 95% interval of −0.23 to 0.61 (dashed lines).

Figure 3:

CMR- and RHC-derived ventricular-vascular coupling ratio (VVCR_CMR, blue; VVCR_RHC, orange) to a) Pulmonary vascular resistance, indexed (Wood units × m²), b) Mean pulmonary artery pressure (mmHg), c) Mean right atrial pressure (mmHg) and d) WHO functional class; all in quartiles. The boxes represent the middle 50% of the studied population, with the black line being the median, and the whiskers represent 25% each. The cutoff points for quartiles were 4.1, 7.6, 12.2 Wood Units×m² for PVRi; 4, 6 and 8 mmHg for mRAP and 28, 40 and 55 mmHg for mPAP.