Background The function of the coronary collateral circulation in heart transplant patients has not been investigated in a controlled fashion. Since it partly belongs to the microcirculation, which is affected by transplant vasculopathy, the hypothesis was tested that the coronary collateral circulation in heart transplant recipients is less developed than in coronary artery disease (CAD) patients.

Methods 40 heart transplant patients underwent a total of 51 quantitative, coronary pressure-derived collateral measurements and intravascular ultrasound (IVUS). The collateral flow index (CFI) was calculated as mean coronary occlusive pressure divided by mean aortic pressure, both subtracted by central venous pressure. A propensity score matching for angiographic coronary stenosis severity, heart rate, the presence of arterial hypertension and dyslipidaemia was performed using CAD patients of the institutional CFI database (n=1076) as the control group.

Results Eighty per cent (32/40) of the heart transplant patients showed transplant vasculopathy as assessed by IVUS (intima thickness ≥0.5 mm). Without propensity score matching, CFI was equal to 0.152±0.102 in the heart transplant group (age 55±14 years) and 0.189±0.134 in the entire CAD group (p=0.054). After matching, CFI was 0.152±0.102 in the heart transplant group and 0.176±0.096 (p=0.37) in the matched CAD group (age 63±10 years). IVUS data were unrelated to CFI in the heart transplant group.

Conclusions Heart transplant patients present with the same degree of functional collateral flow compared with a matched group of CAD patients.