Myocardial blood flow, metabolism, and function with repeated brief coronary occlusions in conscious ponies.

The research examined the impact of intermittent brief blockages of blood supply to the heart in conscious ponies. It revealed that such disruptions lead to initial decrease in heart function and increase in the release of certain substances, but with repeated incidents, heart function improved and substance release decreased, suggesting a protection mechanism due to “ischemic preconditioning“.

Experimental Setup

• The study was conducted on conscious ponies that were surgically equipped with a Doppler flow probe and hydraulic occluder on the left anterior descending coronary artery (LAD), sonomicrometry crystals, an intraventricular micromanometer in the left ventricle, and catheters in the left atrium and anterior interventricular vein.
• The left anterior descending coronary artery was intermittently blocked for two minutes every 30 minutes, either continuously or during working hours.
• Regional myocardial blood flow was measured using the microsphere method both before and after these occlusion regimes.

Data Collection and Results

• Data on the release of catabolites (potassium, hydrogen ions, and lactate) and norepinephrine from the dysfunctional region of the heart were collected during the regimen of occlusions.
• A significant release of these substances was observed in association with early occlusions when heart segment function was significantly reduced.
• However, as occlusions continued, the release of these substances decreased while heart function improved.
• The blood flow in the initially dysfunctional region drastically dropped during an early occlusion but returned to the control level during later occlusions.

Interpretation and Implications

• The metabolic results suggest the presence of a mechanism known as “ischemic preconditioning” that provides protection to the heart by making it more resistant to subsequent ischemic events.
• The inverse relation between the release of catabolites and the heart function suggests a flow-dependent mechanism.
• The findings corroborate a previous assumption that protection against regional myocardial dysfunction under these conditions is due to increased collateral perfusion, which refers to the development of new vascular routes in the heart to compensate for the blocked blood flow.