Sun31October0735PM 5

Are the following electrocardiogram (ECG) changes associated with a suspected myocardial infarction?

True / False

Myocardial infarction causes 'convex upwards' S-T elevation Correct

Myocardial infarction cannot be diagnosed in the presence of right bundle branch block Correct

True posterior left ventricular infarction is characterised by pathological Q waves, tall R waves and inverted T waves in V1 and V2 Correct

Right ventricular infarction cannot be diagnosed using a standard 12 lead ECG Incorrect answer selected

In a subendocardial MI, S-T elevation and T wave inversion occurs in leads facing the infarcted area Correct

Explanation

The usual ECG changes following an acute myocardial infarction include S-T elevation greater than 1 mm (convex upwards, concave downwards) developing within the first few hours. Tall peaked T waves may also be seen in the acute stages.

Pathological Q waves (representing transmural infarction), a reduction in R wave height and deeply inverted T waves (in the leads facing the infarcted muscle) may develop over the next 72 hours.

The absence of Q waves implies partial-thickness infarction. A subendocardial MI is associated with flat S-T depression (not elevation) and T wave inversion in leads facing the infarction.

The S-T segment changes following a myocardial infarct usually resolve within days. The T wave changes often persist for weeks but may be permanent. The Q waves are usually, but not always, permanent.

It is possible to diagnose an acute MI in the presence of right bundle branch block and also in left bundle branch block when using non-standard ECG criteria.

True posterior left ventricular infarction is characterised by tall R waves, S-T depression and peaked upright (not inverted) T waves in leads V1 and V2. Right ventricular infarction does not produce a specific pattern in the standard 12 lead ECG, so the use of right-sided precordial leads (V4R - V6R) are required.

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Times answered: 266