Defining the mechanical border zone: a study in the pig heart.

Area of Science:

• Cardiology
• Physiology
• Biomedical Engineering

Background:

• Myocardial ischemia can induce wall motion abnormalities.
• The extent and mechanisms of these abnormalities in non-ischemic areas are not fully understood.

Purpose of the Study:

• To map the mechanical border zone surrounding acute myocardial ischemia.
• To determine the extent of abnormal wall motion in non-ischemic myocardium.

Main Methods:

• Sonomicrometer crystals were implanted in pigs to measure regional systolic shortening fraction.
• Myocardial ischemia was induced by occluding the left anterior descending artery.
• Wall motion was assessed in ischemic, border, and remote zones.

Main Results:

• Systolic shortening fraction was depressed in border zones up to 9.3 mm from the ischemic margin.
• Abnormal wall motion was detected as far as 12 mm from the ischemic margin.
• Mechanical tethering is presumed to cause wall motion abnormalities in contiguous non-ischemic areas.

Conclusions:

• Myocardial ischemia induces significant mechanical abnormalities in adjacent non-ischemic myocardium.
• Wall motion depression extends considerably beyond the ischemic zone.
• Mechanical tethering is a likely mechanism for these remote effects.