High incidence of severely prolonged QT interval after cardiac surgery

Introduction

A prolonged QT interval may be associated with torsades de pointes and lead to sudden cardiac death. The aim of this study was to determine both the frequency of QT prolongation and administration of QT prolonging drugs perioperatively in cardiac surgery.

Methods

This prospective observational study included 82 patients (mean age 67 years) undergoing elective cardiac surgery (coronary bypass grafting 37, valve surgery 29, combination 16). The QT interval was manually measured in lead II and V2 of a 12-lead electrocardiogram (ECG) and corrected for heart rate (corrected QT interval, QTc, calculated from Bazett's formula) on the day before surgery, immediately after surgery, daily until day 5 and before hospital discharge. A QTc interval >440 ms in men and >460 ms in women in either ECG lead II or V2 was defined as moderately prolonged. A QTc interval >500 ms was considered to be moderately prolonged in patients showing complete left or right bundle block, and severely prolonged in patients without complete bundle block. All administered drugs that may prolong the QT interval were identified and classified according to the QTdrugs.org Advisory Board: drugs with a definite risk of torsades de pointes (class 1, for example amiodarone, sotalol, haloperidol) or with a possible risk (class 2, for example granisetron, risperidone).

Results

A total of 489 ECG were analyzed (mean six ECG per patient). The QTc interval was moderately prolonged in 40/82 patients before surgery (48.8%). Five out of 40 patients (12.5%) had received drugs from class 1 preoperatively and 1/40 (2.5%) from class 2. The QTc interval was severely prolonged in 3/82 patients before surgery (3.7%), of which none had received QT prolonging drugs preoperatively. In 38/82 patients (46.3%) moderate QTc prolongation was newly discovered in at least one postoperative ECG. Seventeen put of 38 patients (44.7%) received drugs from class 1, and 3/38 (7.9%) from class 2 perioperatively. In 16/82 patients (19.5%) severe QTc prolongation newly appeared in at least one postoperative ECG. Seven out of 16 patients (43.8%) received drugs from class 1 and 1/16 (6.3%) from class 2 perioperatively.

Conclusions

Severe QT interval prolongation >500 ms occurs in onequarter of cardiac surgical patients in the perioperative period while moderate prolongation occurs in most of them. In nearly one-half of these cases, QT prolonging drugs like amiodarone and haloperidol may be involved. Before and during administration of such drugs in cardiac surgical patients perioperatively, assessment of the QT interval from routine ECG is recommended.