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Differential Diagnosis
- Ventricular tachycardia
- Supraventricular tachycardia (SVT) with aberrancy
- Atrioventricular reentrant tachycardia
- Atrial flutter
- Atrial tachycardia
Diagnosis
The diagnosis in this case is supraventricular tachycardia (SVT) with aberrancy. The ECG shows tachycardia with a regular rhythm and a rate of 180 beats per minute. There is leftward axis deviation and a widened QRS complex (>120ms). There are no overt signs of acute ischemia.
Discussion
The ECG in this case is a regular wide-complex tachycardia. Of the possible etiologies for this pattern, the most likely and most dangerous is ventricular tachycardia (VT). If there is any uncertainty about the definitive diagnosis, the rhythm should be treated as VT to avoid the risk of inappropriate management and potential clinical deterioration.1-3 If the patient is stable, it is safe to evaluate the ECG to determine the underlying rhythm. Note the appearance of an rSR’ pattern in the anterior precordial leads (V1, V2) and a deep S-wave in the lateral leads (I, V6) consistent with a right bundle branch block (RBBB) pattern (Figure 2). The patient also has a leftward axis deviation. Causes of left axis deviation include: left bundle branch block (or paced rhythm); prior inferior myocardial infarction (ie, due to large inferior Q waves); left ventricular hypertrophy; ventricular preexcitation; and left anterior fascicular block.
Although there is high voltage in aVL, which suggests left ventricular hypertrophy (LVH), the degree of left axis deviation is more extreme than typically seen with LVH alone. In this case, the leftward axis deviation is caused by another disruption to the conduction pathway—left anterior fascicular block.4
