Abstract
Introduction: The ventriculoarterial coupling (VAC) ratio, defined as the ratio of arterial elastance (Ea) to ventricular end-systolic elastance (Ees), reflects the mechanoenergetic efficiency of the cardiovascular system. Extreme high or low values of VAC ratio imply inefficient energy transfer. Despite increasing rates of morbidity and mortality in patients with Fontan circulation, little is known about VAC ratio in this population. We used a previously described cardiac magnetic resonance (CMR) method to assess VAC in a large Fontan cohort and examined its relation to outcomes. Methods and Results: We retrospectively measured VAC from CMR and noninvasive blood pressure data on 195 Fontan patients (age 19.6±10.7 years) and 42 controls (age 15.2±2.2 years). VAC was calculated as Ea/Ees (Ea= mean arterial blood pressure (MBP)/ventricular stroke volume; Ees= MBP/end-systolic volume). Compared with controls, Fontan patients had lower body surface area (BSA) adjusted median Ees (1.54 vs. 2.4, p<0.001) and Ea (1.35 vs. 1.48, p=0.01) and a higher median VAC ratio (0.88 vs 0.62, p<0.001) (Figure). After a median follow-up of 4 years (range 1-10), 20 patients reached a composite endpoint of death or heart transplant listing. As seen in the Figure, extreme values of the VAC ratio were associated with higher risk of reaching the endpoint. In a multivariable Cox regression model controlling for EDV/BSA, which has been shown to be a risk factor, being in the highest tertile of the VAC was no longer a risk factor, but patients in the lowest tertile of VAC ratio showed a trend towards being more likely to reach the endpoint (Hazard Ratio 4.06 vs middle tertile, p=0.08). Conclusion: In this cohort, Fontan patients demonstrated inefficient VAC as compared with controls. A lower VAC ratio tended to be associated with death or transplantation listing even when controlling for ventricular size. Further investigation of CMR-derived VAC in the Fontan circulation is warranted.
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