What’s New in the Patient Safety World
April 2015
Anesthesia and QTc Prolongation
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”
June 10, 2014 “Another
Clinical Decision Support Tool to Avoid Torsade de Pointes”
References:
CredibleMeds™ website.
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
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3406265/
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
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1413604/
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
http://www.mayoclinicproceedings.org/article/S0025-6196%2813%2900071-2/abstract
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
http://circoutcomes.ahajournals.org/content/early/2014/05/06/CIRCOUTCOMES.113.000651.abstract
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