Prolonged QT Interval

Report:

Sinus rhythm 54/min

Prolonged QT interval 0.56”

QTc 0.53”

Comment:

This trace suggests anteroseptal infarction, with QS complexes in V1-2 and anteroseptal T wave inversion. However, the ‘septal’ q wave in V6 is preserved, which is unusual in anteroseptal infarcts; the QT interval is markedly long, which is also unusual. Some QT prolongation is common in myocardial infarction and may confer additional risk of sudden death170. This one is far beyond what is found in uncomplicated infarction.

There was no episode of chest pain to indicate recent infarction; the patient was in fact admitted after one week of palpitations due to AF resistant to digoxin and amiodarone and cardioverted by 200 Joule DC shock. The ST/T changes, then, can be seen as expression of the ‘post-tachycardia syndrome’ ± amiodarone effect. Potassium level was 3.3 mEq/L on Moduretic (hydrochlorothiazide) treatment, hardly low enough to affect the repolarisation in this manner. Amiodarone was stopped and coronary angiography performed: it was normal.