The ECG was recorded from a patient admitted to the coronary care unit following myocardial infarction.
ECG. Rhythm: The underlying rhythm is sinus – QRS complexes are seen preceded by P waves in all 12 leads of the standard ECG. In the rhythm strip the narrow QRS complexes are all preceded by P waves although careful inspection of the T waves of the preceding beats is sometimes necessary to appreciate this. Broad QRS complex beats are also seen, and at times these occur in pairs (known as couplets). The broad complex beats occur early and are therefore premature beats. In many places P waves can be seen in the premature beat or accompanying ST segment or T wave. The position of these P waves varies suggesting that atrial and ventricular depolarization are not linked. The broad complex beats are therefore ventricular in origin.
Morphology: There are pathological Q waves in leads II, III and aVF. The raised ST segments of acute myocardial infarction are also present in these leads. The appearances are of recent inferior myocardial infarction.
Comment. Ventricular premature beats are common following myocardial infarction and certain patterns (frequent premature beats and occurrence in pairs) are said to indicate an increased risk of ventricular fibrillation. It is a worthwhile exercise to plot the positions of the P waves in this ECG and note the way that these distort the premature beats.