Source of electrocardiographic ST changes in subendocardial ischemia

Area of Science:

• Cardiovascular Physiology
• Computational Biology
• Medical Imaging

Background:

• Electrocardiographic ST depression is a key indicator of myocardial ischemia.
• The precise origin of ST depression relative to the ischemic region remains debated.
• Understanding this relationship is crucial for accurate diagnosis and localization of cardiac events.

Purpose of the Study:

• To elucidate the source of ST depression observed on electrocardiograms during myocardial ischemia.
• To differentiate between epicardial and endocardial contributions to ST potential changes.
• To validate findings using a computational bidomain model.

Main Methods:

• Developed a sheep model of sequential subendocardial ischemia by partially constricting coronary arteries.
• Simultaneously mapped epicardial and endocardial ST potentials.
• Employed a computer simulation utilizing the bidomain technique to model electrical activity.

Main Results:

• Epicardial ST depression distributions were similar between ischemic territories but did not directly correlate with the ischemic region.
• Endocardial potentials revealed ST elevation directly associated with reduced blood flow.
• Computer simulations indicated ST depression is generated at the lateral boundary between ischemic and normal tissue, not within the ischemic zone.

Conclusions:

• Epicardial ST depression reflects the boundary of ischemic regions, particularly on the free wall of the left ventricle.
• The bidomain model supports the boundary hypothesis for ST depression generation.
• These findings explain the limitations of body surface ST depression in localizing cardiac ischemia in humans.