T-wave alternans: a harbinger of polymorphic ventricular tachycardia.

A 54-year-old man with chronic alcoholism and malnutrition was admitted to our hospital due to disorientation. Admission laboratory data showed a mild elevation of serum liver enzyme levels and normal serum electrolyte levels. An electrocardiogram (ECG) showed normal sinus rhythm with normal QTc interval of 410 ms and normal T wave morphology. He was administered a high dose of thiamine (1500 mg/day) for a temporary diagnosis of Wernicke’s encephalopathy and served normal diet. On Day 3, he developed polymorphic ventricular tachycardia (torsades de pointes, Fig. 1A). The next ECG demonstrated a long QT interval of 680 ms and a QTc interval of 708 ms with alternate biphasic T waves (T-wave alternans) (Fig. 1B). The transthoracic echocardiography was essentially normal. Laboratory findings were as follows: serum potassium, 3.2 mmol/L; serum magnesium, 0.8 mg/dL; and serum phosphate, 1.7 mg/dL, which was consistent with refeeding syndrome. Urgent corrective measures for electrolyte imbalance were applied. An intravenous magnesium sulphate 2-g bolus dose was initially administered. Next, intravenous drip infusion of magnesium sulphate was administered slowly to maintain plasma magnesium concentration within the normal range. Additionally, intravenous dibasic potassium phosphate was administered to correct serum levels of potassium and phosphate. After correction of electrolyte imbalance, there was no arrhythmia and the ECG returned to normal.

Figure 1

(A) One-lead continuous electrocardiogram monitoring showing self-terminated polymorphic ventricular tachycardia, i.e. torsades de pointes following R-on-T phenomenon (white arrow). (B) Twelve-lead electrocardiogram showing marked QT prolongation and macroscopic T-wave alternans (black and white arrows).

T-wave alternans is a variation in timing or shape of T waves from beat to beat, which is indicative of abnormal ventricular repolarisation of the myocytes [1]. T-wave alternans is known to be a prodrome of ventricular arrhythmias, such as torsades de pointes [2]. Medications and electrolyte imbalances, including hypokalaemia and hypomagnesaemia, are major causes of T-wave alternans [3, 4]. It should be kept in mind that T-wave alternans is a potential risk for lethal ventricular arrhythmia; recognition of this ECG pattern should prompt urgent assessment for potentially reversible causes.