Postoperative QT prolongation common

By Eleanor McDermid, Senior MedWire Reporter

Most patients have QT interval prolongation immediately after undergoing noncardiac surgery, say researchers.

They report that 80% of 429 patients had a prolonged corrected QT (QTc) interval in the postanesthesia care unit relative to that at baseline - by an average of 23 ms.

"The exact cause of postoperative QTc prolongation and its clinical relevance, however, are unclear," say Peter Nagele (Washington University, St Louis, Missouri, USA) and colleagues in Anesthesiology.

They add: "Nevertheless, an association between postoperative QTc prolongation and risk for torsades de pointes is likely. It therefore seems prudent to increase the vigilance for perioperative QTc prolongation."

Perioperative torsades de pointes is extremely rare, making the association with QTc interval difficult to establish. One patient in the researchers' study developed torsades de pointes, which they say, "may be a mere coincidence or an indicator that perioperative torsades de pointes is more common than previously assumed and substantially underreported."

Although it can be fatal, torsades de pointes is usually self-limiting, which could contribute to underreporting, they suggest.

The patient who developed torsades de pointes had a QTc interval prolongation of 29 ms to 468 ms, but 39% of patients had prolongation of more than 30 ms, 8% of more than 60 ms, and 0.5% of more than 100 ms.

QTc interval prolongation was not associated with changes in heart rate and did not persist beyond the day of surgery.

A large number of medications were associated with the likelihood for QTc interval prolongation of more than 30 ms. These included angiotensin II receptor blockers; isoflurane, methadone, and ketorolac; several antibiotics; and epinephrine and ephedrine.

Neither ondansetron nor droperidol was associated with QTc interval prolongation, despite previous reports of an association and droperidol having received a black-box warning to that effect.

But Nagele et al note that the overall strength of evidence linking droperidol to QTc interval prolongation is unclear, and also warn that their analysis of the possible drug associations "should be interpreted with caution and as exploratory."

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