Introduction In the UK there are approximately 60,000 out of hospital cardiac arrests (OHCA) annually. Post arrest, a prolonged QTc interval (QTc) on the electrocardiogram (ECG) has been described1. It is unclear whether this is transient, an effect of therapeutic hypothermia, or a substrate of underlying condition. This observational study aims to investigate the incidence and behaviour of prolonged QTc post OHCA.
Methods A retrospective review of patient casenotes was performed on survivors of OHCA admitted to the Bristol Heart Institute (BHI), from March 2014 to November 2015. ECGs recorded throughout the admission were reviewed and categorised into time frames post OHCA. The QT interval was measured manually and QTc calculated using Bazett’s formula. Statistical analyses were performed using Excel and Graphpad Prism.
Results We identified 106 consecutive OHCA survivors presenting at our centre. On admission, the median QTc across the cohort was 495ms (20.91 SEM, range 376 - 745), male 492ms (8.5 SEM), female 516ms (22.0 SEM). All patients underwent emergency angiography. Subsequently, 105 patients were taken to ITU with the majority (101 patients, 96.2%) undergoing targeted temperature management (TTM) to 32–34C° for 24 hours.
Of 106 individuals with OHCA, 58 (55%) were due to acute coronary syndrome (ACS), 20 (19%) were scar related, 15 (14%) were due to a primary arrhythmia, and 13 (12%) were non-cardiac or other. 79/106 (75%) had a prolonged QTc post cardiac arrest, defined as >460ms (males) or >470ms (females). Of these, 14 were excluded due to incomplete data, resulting in a final cohort of 65 patients. Among patients with a prolonged QTc on admission, there was no significant difference according to cause of OHCA.
From immediately post-arrest (T0) to discharge, the median QTc decreased from 495ms (20.9 SEM, range 376 - 745ms) to 421ms (11.7 SEM, range 360 - 561ms). This did not vary significantly by cause of arrest (figure 1). For the ACS group, mean QTc decreased from 505 11.8ms (range 376 – 745, male 503.5 12.9ms, female 516 34.4ms) to 447 15.0ms (range 278 – 561, male 408 15.7ms, female 462 37.8ms). The scar related group decreased from 507.5 21.3ms (range 423 – 745, all male) to 492 18.8ms (range 400 – 511). In those who sustained an OHCA due to primary arrhythmia the mean QTc was 501 9.7ms (range 456 – 536ms, male 503 10.2ms). The one female in this group saw an increase in QTc from 466ms on admission to 560ms at discharge and was subsequently diagnosed with congenital LQT2 syndrome.
Despite most patients demonstrating an improvement in QTc, a prolonged QTc was persistent in eight (12.3%) patients (figure 2).
Conclusion QTc interval is prolonged in a large proportion of patients following cardiac arrest, however this resolves in the majority pre-discharge. Despite concerns regarding the safety of TTM in a cohort who often have a prolonged QTc, we have shown resolution of the QTc in most despite nearly all patients receiving TTM.
In our cohort, only one patient was found to have congenital long QT syndrome.
Conflict of Interest None