Sildenafil Improves Exercise Hemodynamics in Fontan Patients
Background—Patients with Fontan circulation have reduced exercise capacity. The absence of a pre-systemic pump may limit flow through the pulmonary circulation restricting ventricular filling and cardiac output. We evaluated exercise hemodynamics and the effect of sildenafil on exercise hemodynamics in Fontan patients.
Methods and Results—Ten Fontan patients (6 male, 20±4 years) underwent cardiac magnetic resonance (CMR) imaging at rest and during supine bicycle exercise before and after sildenafil. Systemic ventricular volumes were obtained at rest and during low (34±15 Watt), moderate (69±29 Watt), and high (97±36 Watt) intensity exercise using an ungated, free-breathing CMR sequence and analyzed correcting for cardiac phase and respiratory translation. Radial and pulmonary artery pressures and cGMP were measured. Before sildenafil, cardiac index (CI) increased throughout exercise (4.0±0.9, 5.9±1.1, 7.0±1.6, 7.4±1.7 L/min.m²; P<0.0001) with 106±49% increase in heart rate. Stroke volume (SVi)(P=0.015) and end-diastolic volume (EDVi)(P=0.001) decreased during exercise. End-systolic volume (ESVi) remained unchanged (P=0.8). Total pulmonary resistance (TPRi)(P=0.005) increased whereas systemic vascular resistance (SVRi) decreased during exercise (P<0.0001). Sildenafil increased CI (P<0.0001) and SVi (P=0.003) especially at high-intensity exercise (interaction P=0.004 and P=0.003 respectively). SVRi was reduced (P<0.0001-interaction P=0.1) whereas TPRi was reduced at rest and reduced further during exercise (P=0.008-interaction P=0.029). Whereas cGMP remained unchanged before sildenafil (P=0.9), it increased significantly after sildenafil (P=0.019).
Conclusions—In Fontan patients, sildenafil improved CI during exercise with a decrease in TPRi and an increase in SVi. This implies that pulmonary vasculature represents a physiological limitation, which can be attenuated by sildenafil, the clinical significance of which warrants further study.
- Fontan procedure
- pulmonary circulation
- cardiac magnetic resonance imaging
- Received July 9, 2013.
- Accepted January 16, 2014.