Objective:
To investigate the potential for exercise to reveal occult left and right ventricular dysfunction in children with tetralogy of Fallot (TOF).

Methods:
We conducted a prospective study of controls (n=25) and children with repaired TOF (n=29). All children underwent echocardiography at rest and during bicycle ergometry, performed at increasing workloads until exhaustion. Those with TOF were also studied by MRI and cardiopulmonary stress testing.

Functional M-mode and tissue Doppler data was obtained for each ventricle and for the right ventricular outflow tract (RVOT) with images recorded at rest and peak exercise. Myocardial acceleration during isovolumic contraction (IVA) was measured at each 10bpm heart rate increase during exercise and force-frequency curves were constructed. In those with TOF, ventricular volumes and flow data were calculated by offline analysis of the MRI.

Data were compared between groups using standard statistical techniques and software.

Results:
By MRI, the children with TOF had RV dilatation (mean RVEDVi=153mls/m2 SD=37.3) with normal ventricular function (LVEF mean=59.3% SD=6.2, RVEF mean=50.2% SD=8.5).

Resting echocardiography detected abnormalities of right but not left ventricular function (table). Exercise revealed abnormalities of LV contractility (table) and a highly abnormal force-frequency relationship (figure) p<0.0001.

There was a weak relationship between peak exercise LV IVA and VO2 at cardiopulmonary stress testing R=0.51 p<0.02.

Conclusions:
The RV of patients with TOF has abnormal contractile properties at rest. Exercise reveals evidence of LV dysfunction and disruption of LV force-frequency relations, which may be related to impaired exercise performance. This occult dysfunction is not demonstrated by MRI.