Impaired Exercise Tolerance after Repair of Tetralogy of Fallot—Insights from Real-Time Cardiovascular Magnetic Resonance Imaging

Objectives: Surgical correction of tetralogy of Fallot (cTOF) frequently results in residual pulmonary valve stenosis/regurgitation and impaired right ventricular (RV) function. Reduced capacity in cardiopulmonary exercise testing (CPET) in cTOF patients, however, cannot entirely be explained by these findings. The present study sought to assess biventricular cardiac function during exercise using a comprehensive CPET and real-time cardiovascular magnetic resonance exercise testing (CMR-ET) protocol.

Methods: A total of 33 cTOF patients (age 35.6 + 11.3 years) and 33 matched healthy controls (age 34.4 +11.9 years) underwent CPET and CMR-ET. Real-time SSFP and phase contrast sequences were obtained during supine bicycle in scanner CMR-ET at 50, 70, and 90 W. RV and LV volumetry and flow quantification of the pulmonary trunk (Qp) were performed. Correlation between CPET and CMR-ET parameters was investigated using Spearman’s rank test.

Results: Exercise capacity on CPET was significantly lower in cTOF than in healthy controls. With incremental exercise levels on CMR-ET, cTOF patients failed to recruit both RV and LV functions and Qp (Table 1). Correlation analysis revealed higher CPET values in those cTOF patients with higher Qp (Qp 90 W vs. VE/VCO₂%: r = −0.519, p < 0.05), higher LV EDVi (LV EDVi at 50 W vs. VO₂% r = 0.452, p < 0.05) and less change in LV EF (LV-EF at 90 W vs. W % r = −0.463, p < 0.05). No correlation was found with RV EF. Significant RV–LV interaction was observed at 70 W CMR-ET (correlation of RV and LF EF r = 0.52, p < 0.05).

Conclusion: Compared with healthy controls, cTOF patients displayed impaired exercise capacity due to a lack in recruitment of both RV function and pulmonary blood flow but also of LV function. RV and LV functions during exercise showed significant interdependence. CMR-ET may be a helpful tool in the assessment of cardiac function in cTOF patients.

Acknowledgment: The study was supported by Fördergemeinschaft Deutsche Kinderherzzentren e.V.

Table 1 CPET and CMR-ET data of cTOF versus controls

CPET (max. exercise)		cTOF	Controls	p-Value
		Mean ± SD	Mean ± SD
Abbreviations: EF, ejection fraction; Qp, pulmonary blood flow; VO2 max., maximal oxygen uptake.
VO2 max.	(% predicted)	73.9 ± 11.4	101.4 ± 11.4	<0.05
CMR-ET
RV EF 0 W	(%)	47 ± 7	50 ± 3	0.06
RV EF 90 W	(%)	47 ± 6	57 ± 6	<0.05
LV EF 0 W	(%)	56 ± 3	56 ± 3	0.67
LV EF 90 W	(%)	59 ± 5	63 ± 5	<0.02
Qp 0 W	(L/min × m2)	2.28 ± 0.53	2.46 ± 0.64	0.08
Qp 90 W	(L/min × m2)	3.96 ± 1.37	4.86 ± 0.57	<0.05

No conflict of interest has been declared by the author(s).