Complex ECGs like this one have to be approached systematically. Firstly, we can see a normal sinus rhythm. A is the first beat of a wide complex tachycardia. This must be a ventricular tachycardia. Although there is a P-wave before the first beat of the tachycardia, it is not premature. Therefore, there is no SVT with aberrant conduction. The first beat of the tachycardia looks different from the subsequent beats because there is a fusion beat present. The VT conducts 1:1 back to the atria (a small negative P-wave can be seen at the end of the QRS complex in V1).

76-year-old man, with a history of inferior wall myocardial infarction. He experiences recurrent episodes of brief palpitations, often lasting only 5-15 seconds. In this ECG, at the beginning, the last part of a wide-complex tachycardia is visible. After 2 sinus beats, another wide-complex tachycardia begins (with the same QRS configuration).

ECG 1 is from a 57-year-old male with no prior cardiac disease. He reports acute shortness of breath for 2 days. We see a sinus rhythm with left anterior fascicular block (LAFB) and conspicuous T-wave inversions in the inferior leads and in V1-V6. These are typical ECG changes that may indicate a pulmonary embolism. ECG 2 was taken from the same patient 1 year earlier. The patient has an acute pulmonary embolism. Sinus tachycardia may be present in acute pulmonary embolism. However, as in this example, the heart rate can also be completely normal.

Why is this left atrial atypical atrial flutter (ECG 1)? Atrial fibrillation can be excluded because nice flutter waves (all look the same) can be clearly identified. With typical right atrial flutter, the reentry circle runs counterclockwise and we see typical saw tooth patterns in the inferior leads (negative flutter waves). The flutter waves are positive in V1 (ECG 2). With typical right atrial flutter with a clockwise reentry circle, the flutter waves in the inferior leads are positive.