Transmural pH gradient in canine myocardial ischemia

Area of Science:

• Cardiology
• Physiology
• Biomedical Engineering

Background:

• The subendocardium is more vulnerable to ischemic events than the subepicardium.
• Previous research indicated subendocardial hypoperfusion and metabolite gradients during coronary stenosis.
• A transmural pH gradient in ischemic heart tissue had not been previously demonstrated or quantified.

Purpose of the Study:

• To demonstrate and quantify the transmural pH gradient in myocardial tissue during acute ischemia.
• To investigate the relationship between tissue pH and depth within the ischemic myocardium.

Main Methods:

• Reduced coronary blood flow in anesthetized dogs to induce ischemia.
• Implanted miniature fiber-optic pH probes in subepicardial and subendocardial layers.
• Validated the accuracy of fiber-optic pH probes for measuring tissue pH.

Main Results:

• A significant transmural pH gradient was observed within the ischemic zone.
• Subepicardial tissue maintained near-normal pH (7.36).
• Subendocardial tissue exhibited severe acidosis (pH 6.94) just 2 mm deeper.

Conclusions:

• Acute myocardial ischemia induces a substantial transmural pH gradient.
• This pH gradient between adjacent myocardial layers may play a critical role in arrhythmogenesis.
• Findings highlight the differential vulnerability of myocardial layers to ischemic acidosis.