Prolonged QT Interval

Report:

Sinus rhythm 51/min

VEB

Left anterior hemiblock (QRS axis -45o)

Old anteroseptal infarct

Diffuse ST/T changes [!xe "T wave:inversion:post-LBBB-like VT" \b!]

Markedly prolonged QT interval[!xe "QT interval:sotalol" \b!]

QT 0.68" (QTc 0.62")

Comment:

The QT interval is measured from the onset of the QRS complex to the end of the T wave; it is usually corrected (QTc) for heart rate using the Bazett's formula:[!xe "QTc formula" \b!][!xe "Bazett's formula" \b!]

QTc = (in seconds)

The upper limit of normal for both sexes is 0.44".

The marked increase in the QTc in this patient can be attributed to sotalol, a β-blocker with Class III anti-arrhythmic activity193.

There is always a question of U wave being there as well; it is often unanswerable and seldom important. Leads V2-3 suggest that there is one, while aVL, where U wave is usually isoelectric, suggests otherwise. It may be that, as suggested by D. H. Spodick, JT interval is what should be measured instead of QT interval194.

The repolarisation changes - including the prolonged QT interval - may also be due to previous VT, which had LBBB morphology ( Fig 261a below). This would be analogous to post-LBBB or post-pacemaker (also with LBBB morphology) changes195. In fact, any paroxysmal tachycardia, like SVT, can produce transient T wave changes in subsequent sinus rhythm; this is sometimes dignified by the name of post-tachycardia syndrome.

261a. The preceding VT, showing slow S descent in LBBB-like complex of V1. The negative concordance is less important, diagnostically; LAD is worthless.

262. 25 year old body builder with advanced Peyronie's disease