What are the classic signs of myocardial ischemia observable on an ECG?

The classic signs of myocardial ischemia observable on an ECG include ST segment depression and T wave inversion. These changes typically indicate that the heart muscle is not receiving enough blood flow, often due to partial blockage of a coronary artery.

ST segment depression occurs when the ST segment drops below the baseline, signaling a lack of oxygenation to the heart muscle, especially during exertion or stress. T wave inversion can follow as the heart's electrical recovery process is also affected by the ischemic condition. Both of these changes are crucial indicators used by clinicians to diagnose ischemia and assess its severity.

The other options refer to different conditions or are not specific indicators of ischemia. For example, prolonged QT interval is associated with a risk of arrhythmias but does not specifically indicate ischemia. ST segment elevation and Q waves are more commonly associated with myocardial infarction rather than ischemia alone. Normal sinus rhythm indicates a healthy, functioning heart rhythm without abnormal changes and does not reflect the signs of ischemia.