Progressive Care Nursing Certification (PCCN) Practice Exam

What is the first clinical ECG sign of myocardial ischemia?

1. elevation of the ST segment

2. inverted T wave

3. development of Q waves

4. abnormal Q wave

The correct answer is: inverted T wave

The first clinical ECG sign of myocardial ischemia is typically the development of an inverted T wave. Ischemia occurs when there is a decrease in blood flow to the heart muscle, leading to a lack of oxygen. This reduced oxygen supply initially impacts the repolarization phase of the cardiac cycle, which is represented on the electrocardiogram by T wave changes. As myocardial ischemia progresses, the T waves can become inverted, reflecting altered ventricular repolarization due to the underlying cardiac stress and metabolic changes. The inverted T wave is a sensitive indicator of ischemia and can often be observed even before more significant alterations in the ST segment or the formation of pathological Q waves occur. While elevation of the ST segment, development of Q waves, and abnormal Q waves are critical signs of ischemia, they tend to appear later in the process. The elevation of the ST segment usually indicates more severe ischemia or even the onset of an infarction, while Q waves typically develop in the setting of myocardial necrosis, which is a later consequence of extended ischemia. In summary, the inverted T wave represents the earliest change on the ECG that indicates myocardial ischemia, making it the correct answer in identifying the first clinical sign on an ECG reading.