ECG is poor in detecting ischemia in areas supplied by which of the following vessels:
**Core Concept**
ECG is a valuable tool for detecting ischemia, but its sensitivity varies depending on the vascular territory involved. The detection of ischemia by ECG is largely dependent on the presence of ST-segment changes, which are more likely to occur in areas with a rich sympathetic innervation.
**Why the Correct Answer is Right**
The ECG is particularly poor in detecting ischemia in areas supplied by the right coronary artery (RCA). This is because the RCA supplies the right ventricle, which has a limited number of myocardial fibers and a sparse sympathetic innervation. As a result, ST-segment changes are less likely to occur in the right ventricle, making it difficult to detect ischemia in this area using ECG.
**Why Each Wrong Option is Incorrect**
**Option A:** The left circumflex artery (LCx) supplies the lateral and posterior walls of the left ventricle, which are well-represented on the ECG. Therefore, ischemia in this area is more likely to be detected by ECG.
**Option B:** The left anterior descending artery (LAD) supplies the anterior wall of the left ventricle, which is also well-represented on the ECG. Ischemia in this area is more likely to be detected by ECG.
**Option C:** The posterior descending artery (PDA) typically arises from the RCA and supplies the posterior wall of the left ventricle. While the PDA is a branch of the RCA, the ischemia it supplies is still detectable on ECG.
**Clinical Pearl / High-Yield Fact**
The "watershed" areas of the heart, including the territories supplied by the RCA, are more susceptible to ischemia due to their limited collateral blood supply.
**Correct Answer:** C.