Noninvasive Assessment of Right Ventricular-Pulmonary Arterial Coupling in Repaired Tetralogy of Fallot by Magnetic Resonance Imaging

Abstract

Background: Right ventricular (RV) to pulmonary arterial coupling (RVPAc) quantifies RV contractility in relation to its afterload but traditionally requires high-fidelity catheter derived pressure-volume loops. We sought to evaluate a noninvasive volume-based RVPAc parameter in children and adults with repaired tetralogy of Fallot in relation to pulmonary regurgitation (PR), RV outflow tract obstruction (RVOTO), and exercise capacity.

Methods: We retrospectively studied 92 pediatric and 105 adult patients with repaired tetralogy of Fallot who had cardiovascular magnetic resonance imaging and cardiopulmonary exercise testing within a 1-year interval. RVPAc was calculated as the ratio of RV end-systolic volume over stroke volume. RVOTO gradient was obtained by echocardiography; RV ejection fraction, and PR fraction by cardiovascular magnetic resonance imaging. Exercise capacity was measured as the percentage of predicted peak oxygen consumption during cardiopulmonary exercise testing. Subgroups were established depending on the combination of PR-RVOTO (cutoff defined as PR >30% and RVOTO >25 mm Hg).

Results: RVPAc was significantly higher in adult versus pediatric patients (1.23 [1.03-1.48] versus 1.00 [0.88-1.15]; P<0.001). RVPAc was comparable in the 4 pediatric hemodynamic subgroups (P=0.38) but tended to be higher in adults with either RVOTO, PR, or RVOTO+PR (P=0.05). RVPAc highly correlated with RVEF (r=-0.991, P<0.001) but was not associated with percentage of predicted peak oxygen consumption.

Conclusions: Worse RVPAc in adult versus pediatric patients with repaired tetralogy of Fallot may signify progressive RV-PA uncoupling with age- or era-related effects. However, the clinical use of volumetric RVPAc in repaired tetralogy of Fallot appears limited, as it does not provide additional information over RVEF and is not associated with exercise capacity.

Keywords: outflow tract obstruction; pulmonary regurgitation; right ventricular function; tetralogy of Fallot; ventricular‐arterial coupling.

Figure 1. CMR‐derived RVPAc.

Boxplot comparing RVPAc between pediatric and adult cohorts with rTOF and control group. CMR indicates cardiac magnetic resonance; rTOF, repaired tetralogy of Fallot; and RVPAc, right ventricle to pulmonary artery coupling. P values indicated in graph are result of Mann–Whitney U testing.

Figure 2. RVPAc in subgroups with different loading conditions.

Boxplots illustrating RVPAc for RVOTO/PR subgroups for both patient cohorts. Kruskal–Wallis between groups for both pediatric and adult cohorts: P=0.379 and P=0.053 respectively P values for Mann–Whitney U test between pediatric and adult subgroup indicated in both graphs. No RVOTO—no PR indicates RVOTO <25 mm Hg and PR <30%; no RVOTO—PR, RVOTO <25 mm Hg and PR >30%; PR, pulmonary regurgitation; RVOTO, right ventricular outflow tract obstruction; RVOTO—PR, RVOTO <25 mm Hg and PR <30%; RVOTO—PR, RVOTO >25 mm Hg and PR >30%; and RVPAc, right ventricle to pulmonary artery coupling.

Figure 3. Effective RVPAc in subgroups with different loading conditions.

Boxplots illustrating effective RVPAc for RVOTO/PR subgroups for both patient cohorts. Kruskal–Wallis between groups for both pediatric and adult cohorts P<0.001. P values for Mann–Whitney U test between pediatric and adult subgroup indicated in graph. No RVOTO—no PR indicates RVOTO <25 mm Hg and PR <30%; no RVOTO—PR, RVOTO <25 mm Hg and PR >30%; PR, pulmonary regurgitation; RVOTO, right ventricular outflow tract obstruction; RVOTO—PR, RVOTO <25 mm Hg and PR <30%; RVOTO—PR, RVOTO >25 mm Hg and PR >30%; and RVPAc, right ventricle to pulmonary artery coupling.

Figure 4. Association between RVPAc and RVEF.

Scatterplot showing a nearly perfect association between RVEF and RVPAc both determined by CMR volumetry. CMR indicates cardiac magnetic resonance; RVEF, right ventricular ejection fraction; and RVPAc, right ventricle to pulmonary artery coupling.

Figure 5. Association between RVPAc and calculated RVPAc.

Scatterplot showing a very strong linear association between calculated RVPAc determined by [1/RVEF − 1] and RVPAc determined by [RV ESV/SV]. ESV indicates end‐systolic volume; RV, right ventricular; RVEF, right ventricular ejection fraction; RVPAc, right ventricle to pulmonary artery coupling; and SV, stroke volume.

Figure 6. Association between exercise capacity and RVPAc.

Scatterplot showing absent correlation between RVPAc and exercise capacity measured as %VO₂. %VO₂ indicates percentage of predicted of peak oxygen consumption; and RVPAc, right ventricle to pulmonary artery coupling.

Figure 7. Association between exercise capacity and effective RVPAc.

Scatterplot showing absent correlation between effective RVPAc and exercise capacity measured as %VO₂. %VO₂ indicates percentage of predicted of peak oxygen consumption; and effective RVPAc, effective right ventricle to pulmonary artery coupling.