In several of our prior columns (see list at the end of today’s column) we’ve discussed the risks of developing ventricular tachycardia and, specifically, Torsade de Pointes in hospitalized patients with prolonged QT intervals. There are a number of reasons why this syndrome is more likely to both occur and result in death in hospitalized patients. Hospitalized patients have a whole host of other factors that may help precipitate malignant arrhythmias in vulnerable patients. They tend to have underlying heart disease, electrolyte abnormalities (eg. hypokalemia, hypomagnesemia, hypocalcemia), renal or hepatic impairment, and bradycardia, all of which may be precipitating factors. More importantly they may have the sorts of conditions for which we prescribe the drugs that are primarily responsible for prolonging the QT interval (eg. haloperidol, antibiotics, antiarrhythmic agents, etc.). And many of those drugs are given intravenously and in high doses in the hospital as compared to the outpatient arena. Rapid intravenous infusion of such drugs may be more likely to precipitate Torsade de Pointes than slow infusion. For a full list of drugs that commonly cause prolongation of the QT interval and may lead to Torsade de Pointes, go to the CredibleMeds™ website. That site also has a list of drugs that prolong the QT interval and might possibly cause Torsade de Pointes and another list of drugs that have conditional risk (eg. only when combined with other drugs).
But one factor we have never mentioned is surgery and anesthesia. Many of those hospitalized patients noted above were in the hospital for surgery or had some sort of surgery performed during their hospital stay. Now a new study demonstrates that QTc interval prolongation is actually not uncommon after surgery and anesthesia (Duma). Researchers from that same group (Nagele 2012) had previously shown that postoperative QT-interval prolongation is common and that several perioperatively administered drugs are associated with a substantial QT-interval prolongation. In the new study Duma et al. prospectively looked at 300 patients undergoing a variety of surgical procedures. QTc duration was continuously recorded by 12-lead Holter ECG from 30 minutes preoperatively to up to 60 minutes postoperatively. They found that QTc prolongation is not an isolated postoperative phenomenon and is common during surgery under general and spinal anesthesia but not under local anesthesia. Long QTc episodes (QTc > 500 ms for at least 15 minutes) were over 5 times more frequent with general anesthesia than with spinal anesthesia.
In their previous study (Nagele 2012) the researchers had found 80% (345 of 429) of the patients experienced a significant QTc interval prolongation at the end of surgery. In 8% the increase in QTc interval was >60 msec. One patient developed torsades de pointes. Several drugs had a large effect on the change in QTc: isoflurane, methadone, ketorolac, cefoxitin, zosyn, unasyn, epinephrine, ephedrine, and calcium. Postoperative body temperature had a weak negative correlation with the change in QTc and they found no correlation with serum magnesium, potassium, and calcium concentrations.
The above studies did not assess the impact of QT-interval prolongation on patient outcomes. At least one previous study, done in heart failure patients undergoing cardiac surgery, found that pre-operative QTc interval prolongation have increased mortality rates (Vrtovec 2006). But we don’t know of any studies looking at the impact of post-operative QTc interval prolongation on patient outcomes.
Clearly, a study looking at the impact of post-operative QTc interval prolongation on patient outcomes is in order. However, in the meantime, hospitals should consider use of a clinical decision support tool like that developed at the Mayo Clinic (Haugaa 2013) as described in our April 9, 2013 Patient Safety Tip of the Week “Mayo Clinic System Alerts for QT Interval Prolongation” or that developed by Tisdale et al. (Tisdale 2014) as described in our June 10, 2014 Patient Safety Tip of the Week “Another Clinical Decision Support Tool to Avoid Torsade de Pointes”. While we would not recommend a full post-operative EKG in all patients, most do have some sort of cardiac monitoring post-op that could serve as a source for a QTc interval measurement that could be fed into a clinical decision support system.
The Duma and Nagel studies, at a minimum, add yet another potential precipitating factor into the equation and may help identify patients at risk for Torsade de Pointes or other serious arrhythmias.
Some of our prior columns on QT interval prolongation and Torsade de Pointes:
June 29, 2010 “Torsade de Pointes: Are Your Patients At Risk?”
February 5, 2013 “Antidepressants and QT Interval Prolongation”
April 9, 2013 “Mayo Clinic System Alerts for QT Interval Prolongation”
Duma A, Pal S, Helsten DL, Stein PK, Nagele P. A High-Fidelity Analysis of Perioperative QTc-Prolongation in General, Spinal, and Local Anesthesia. Abstract 1020. American Society of Anesthesiologists Annual Meeting 2014
Nagele P, Pal S, Brown F, et al. Postoperative QT interval prolongation in patients undergoing noncardiac surgery under general anesthesia. Anesthesiology 2012; 117(2): 321-328
Vrtovec B, Yazdanbakhsh AP, Pintar T, et al. QTc Interval Prolongation Predicts Postoperative Mortality in Heart Failure Patients Undergoing Surgical Revascularization. Tex Heart Inst J 2006; 33: 3-8
Haugaa KH, Bos JM, Tarrell RF, et al. Institution-Wide QT Alert System Identifies Patients With a High Risk of Mortality. Mayo Clin Proc 2013; 88(4): 315-325
Tisdale JE, Jaynes HA, Kingery J, et al. Effectiveness of a Clinical Decision Support System for Reducing the Risk of QT Interval Prolongation in Hospitalized Patients. Circulation: Cardiovascular Quality and Outcomes 2014; published online before print May 6, 2014
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