Frequency, Temporal Onset of Occurrence and Risk Factor Identification for Acquired Long QT Syndrome in a Critical Care Population

Abstract

Background. Acquired long QT syndrome (aLQTS) is a reversible condition characterized by a pathological prolongation of the QT interval that can lead to a polymorphic ventricular tachycardia known as Torsades de Pointe and sudden cardiac death. Identifying the incidence, onset, and risk factors for aLQTS in intensive care init (ICU) populations has not been studied and may help clinicians develop safe monitoring guidelines to identify patients early preventing devastating outcomes. Objective. The objective of this study was to determine the frequency, temporal onset of occurrence, frequency of medications and host risk factors for aLQTS in an ICU. Method. In a retrospective chart review of 88 subjects, hourly electrocardiographic data collected in an ICU were analyzed for baseline, first long, longest, and final corrected QT intervals (QTc) using Bazett's formula. aLQTS was defined as a QTc interval ≥ 500 milliseconds (ms) or a change in QTc of ≥ 60 ms from baseline. Host risk factors were collected from the physician's dictated history and physicals and nursing admission databases. Names and timing of each medication administered were collected from the medication record. Results. aLQTS occurred in 52.3% of the ICU sample. All subjects positive for aLQTS (n=46) had a mean onset of 7.4 ± 9.4 hours from ICU admission. Subjects who developed aLQTS after ICU admission (n=32) had a mean onset of 10.6 ± 9.5 hours; 14 were positive on ICU admission. A statistically significant difference was noted in subjects receiving QT prolonging medications positive for aLQTS (63.5%, n=33) compared with subjects negative for aLQTS (36.5%, n=19), (X²[1] = 6.38, p = .012). Thirteen subjects (28.3%) developed aLQTS in the absence of a known QT interval prolonging medication. No host risk factors were found to have a significant difference between groups positive and negative for aLQTS. Conclusions. aLQTS was present in approximately one-half of the sample. Approximately a quarter of the subjects developed aLQTS in the absence of a known QT prolonging medication, indicating the importance of frequent QTc monitoring in all patients in ICUs. Larger studies to determine common host risk factors associated with aLQTS in ICU populations are warranted.