Thermal heterogeneity in stable human coronary atherosclerotic plaques is underestimated in vivo: the “cooling effect” of blood flow

Objectives This study investigated whether temperature measurements are influenced by blood flow. Background Previous ex vivo studies showed marked thermal heterogeneity in atheromatic plaques. In stable lesions, however, trivial in vivo temperature variations are recorded, perhaps due to the “cooling effect” of blood flow. Methods Eighteen patients with effort angina were studied. Coronary flow velocity was continuously recorded; over another guidewire, temperature measurements were performed at the proximal vessel wall and at the lesion before, during, and after complete interruption of blood flow by inflation of a balloon. The ΔTp was assigned as the difference between the proximal vessel wall temperature and the maximal temperature during and after balloon inflation. The ΔTl was assigned as the difference between the atherosclerotic plaque and the proximal vessel wall. Results The procedure was not complicated. During and after complete interruption of flow, ΔTp was 0.012 ± 0.01°C and −0.006 ± −0.01°C (p < 0.001), respectively. The ΔTl was 0.08 ± 0.04°C at baseline and went to 0.18 ± 0.05°C (60.5 ± 14.1% increase) during and 0.08 ± 0.04°C after flow interruption (p < 0.001). The ΔTl was greater than ΔTp during and after impairment of flow (p < 0.001). A correlation between the baseline average peak velocity and ΔTl during flow interruption was found (R = 0.57, P = 0.01). In seven patients thermal heterogeneity was not detected at baseline, and during balloon inflation ΔTl increased by 76.0 ± 8.4%. Conclusions Thermal heterogeneity is underestimated in atherosclerotic plaques in patients with effort angina. Potential in vivo underestimation of heat production locally in human atherosclerotic is due to the “cooling effect” of coronary blood flow.