Coronary collateral development during chronic ischemia: serial assessment using harmonic myocardial contrast
J D Mills1, D Fischer, F S Villanueva
1Department of Medicine, University of Pittsburgh School of Medicine, Pennsylvania, USA.
Insights
Coronary collateral development in chronic myocardial ischemia occurs rapidly. Myocardial contrast echocardiography (MCE) effectively tracks this collateral growth in vivo.
Area of Science:
- Cardiovascular Research
- Echocardiography
- Ischemic Heart Disease
Background:
- Coronary collaterals are vital for maintaining heart muscle viability during ischemia.
- Studying the natural progression and drivers of collateral development in living organisms is challenging.
Purpose of the Study:
- To investigate and characterize the development of coronary collaterals in a canine model of chronic myocardial ischemia.
- To evaluate the utility of myocardial contrast echocardiography (MCE) for serial assessment of collateral growth.
Main Methods:
- A chronic canine model of myocardial ischemia was created using a hydraulic occluder and ameroid constrictor on the left anterior descending coronary artery (LAD).
- Myocardial contrast echocardiography (MCE) with intravenous microbubbles was performed serially over six weeks during LAD occlusion.
- Radiolabeled microsphere measurements were used to quantify myocardial blood flow.
Main Results:
- The size of the MCE-defined risk area significantly decreased from 32% on day 0 to 1% by day 42 (p<0.001).
- Normalized LAD flow, relative to left circumflex flow, increased substantially from 0.14 to 0.90 between day 0 and day 42 (p<0.02).
Conclusions:
- Collateral development in this chronic ischemic heart model is a rapid and early process.
- MCE provides a noninvasive method to track the spatial and temporal dynamics of collateral growth.
- MCE may serve as a valuable tool for assessing the effectiveness of in vivo angiogenic therapies.
Objectives:
We sought to characterize collateral development in an experimental model of chronic myocardial ischemia by using myocardial contrast echocardiography (MCE).
Background:
Coronary collaterals maintain myocyte viability during myocardial 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 enable reversible and gradual total LAD occlusion, respectively. Myocardial contrast echocardiography was performed using intravenous injection of perfluorocarbon gas-containing microbubbles during two-dimensional harmonic echocardiographic imaging. Myocardial contrast echocardiography images and radiolabeled microsphere flow measurements were obtained during transient LAD occlusion on day 0. Over the ensuing six weeks, MCE imaging was performed during 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 course 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< or =0.001 vs. day 0). Radiolabeled microsphere-derived LAD flow, normalized to left circumflex flow, correspondingly increased between day 0 and day 42 (0.14+/-0.02 to 0.90+/-0.07, p<0.02).
Conclusions:
Collateral development occurs relatively early and rapidly in this chronic canine model. Myocardial contrast echocardiography using harmonic imaging and intravenous injection of microbubbles can uniquely track the spatial and temporal course of collateral growth, and may be a powerful tool for noninvasively mapping the efficacy of therapeutic angiogenic strategies in vivo.
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