Objective: A consequence in patients with d-transposition of the great arteries (d-TGA) and tetralogy of Fallot (TOF) is right ventricular hypertrophy (RVH) and right ventricular failure. Myocardial contrast echocardiography (MCE) permits the determination of the myocardial microvascular density reflected by the relative myocardial blood volume (rBV; ml/ml). This study was conducted to elucidate the relationship between RVH and myocardial microvascular changes by quantitative MCE in patients with d-TGA and TOF.
Methods: Three groups of individuals were included in the study: 22 patients with d-TGA, 18 patients with TOF and 22 healthy individuals (controls). MCE was performed at rest and during adenosine-induced hyperaemia. rBV and myocardial blood flow (MBF; ml/min per gram) were derived from steady state and refill sequences of ultrasound contrast agent.
Results: Hyperaemic septal rBV differed significantly between the groups and was highest in controls: d-TGA 0.141+/-0.060 ml/ml, TOF 0.134+/-0.080 ml/ml, controls 0.189+/-0.074 ml/ml, p=0.005. Myocardial blood flow reserve (MBFR), that is the ratio of hyperaemic to baseline MBF, differed significantly between the groups and was lowest in d-TGA (2.68+/-1.13) versus TOF (3.37+/-1.57) and controls (4.22+/-1.17, p=0.001). Hyperaemic septal rBV, MBF and MBFR showed a significant correlation with right ventricular systolic function as determined by tricuspid annular plane systolic excursion.
Conclusions: Right ventricular myocardial microvascular density of the septal wall in d-TGA and TOF patients with RVH due to pressure and/or volume overload is reduced. This appears to be related to a reduced myocardial perfusion reserve and impaired right ventricular systolic function.