Coronary collateral development during chronic ischemia: Serial assessmentusing harmonic myocardial contrast echocardiography

OBJECTIVES We sought to characterize collateral development in an experimen tal model of chronic myocardial ischemia by using myocardial contrast echoc ardiography (MCE). BACKGROUND Coronary collaterals maintain myocyte viability during myocardia l ischemia. The natural history and determinants of collateral development are difficult to study serially in vivo. METHODS The left anterior descending coronary artery (LAD) in nine dogs was encircled (day 0) with a hydraulic occluder and ameroid constrictor to ena ble reversible and gradual total LAD occlusion, respectively. Myocardial co ntrast echocardiography was performed using intravenous injection of perflu orocarbon gas-containing microbubbles during two-dimensional harmonic echoc ardiographic imaging. Myocardial contrast echocardiography images and radio labeled microsphere flow measurements were obtained during transient LAB oc clusion on day 0. Over the ensuing six weeks, MCE imaging was performed dur ing LAD occlusion at 10-day intervals. RESULTS Myocardial contrast echocardiography risk area size (expressed as a percent of the left ventricular short axis slice) decreased over the cours e of six weeks (32% +/- 3% on day 0, 21% +/- 3% at day 10, 5 +/- 3% at day 20, 1% +/- 1% at day 30 and 1% +/- 1% at day 42, p less than or equal to 0, 001 vs. day 0). Radiolabeled microsphere-derived LAD flow, normalized to le ft circumflex flow, correspondingly increased between day 0 and day 42 (0.1 4 +/- 0.02 to 0.90 +/- 0.07, p < 0.02). CONCLUSIONS Collateral development occurs relatively early and rapidly in t his chronic canine model. Myocardial contrast echocardiography using harmon ic imaging and intravenous injection of microbubbles can uniquely track the spatial and temporal course of collateral growth, and may be a powerful to ol for noninvasively mapping the efficacy of therapeutic angiogenic strateg ies in vivo. (C) 2000 by the American College of Cardiology.