QTc interval in survivors of out of hospital cardiac arrest☆
Introduction
In the UK, there are approximately 60,000 out of hospital cardiac arrests (OHCA) each year, Resuscitation is attempted by Emergency Medical Services in 28,000 of these cases with only 8.6% patients surviving to hospital discharge [1,2]. Around two thirds of cases of OHCA are attributed to a coronary cause, whether mediated by an acute coronary syndrome (ACS) or ischaemic scar [1,3,4]. However, 2% of patients show no structural cardiac abnormality on autopsy [5], rising to 40% in patients aged ≤35 years [6] indicating the potential of a primary arrhythmic cause for OHCA in this patient cohort. A previous study from our unit has demonstrated that in a cohort of 217 cases admitted with an OHCA, 10.1% were felt to have sustained a cardiac arrest due to a non-coronary cause [7].
Given the high prevalence of myocardial ischaemia as a cause for OHCA, many centres have adopted the practice of immediate transfer for angiography. The Bristol Heart Institute (BHI) is a tertiary centre which serves a population of 5.29 million in the South West of England. In this region, all survivors of OHCA without a clear non-cardiac cause are transferred to the BHI for urgent angiography [8] and potential angioplasty as per our care pathway. If intubated, patients are then transferred to intensive care, where iatrogenic lowering of body temperature (targeted temperature management (TTM)) is generally employed for its favourable effects on neurological recovery [[9], [10], [11]].
Post cardiac arrest, the appearance of a prolonged QTc interval on the surface electrocardiogram (ECG) has been described [12,13]. It is unclear whether this is a transient phenomenon, or a manifestation of an underlying arrhythmic substrate such as Long QT syndrome (LQTS). Furthermore, QTc interval prolongation has been described in association with TTM, although previous studies have not linked this with increased incidence of malignant arrhythmias [[12], [13], [14], [15], [16]].
In this observational study, we sought to clarify the incidence of QTc interval prolongation post-OHCA, the behaviour of QTc interval during admission and persistence at discharge. Specifically, we aimed to identify any pattern between QTc behaviour and aetiology of arrest with the hypothesis that the incidence of QTc prolongation on admission post OHCA and subsequent behaviour may relate to aetiology of cardiac arrest. Specifically, we were interested in the QTc on and after admission in those with a primary arrhythmic cause of arrest and we hypothesised that there may be a more prolonged QTc which persisted in these patients.
We also sought to evaluate QTc alongside the use of TTM and investigate whether the use of TTM appears to be associated with the development of further malignant arrhythmia.
Section snippets
Methods
A retrospective review of electronic and paper case notes was performed of survivors of OHCA who were admitted to the BHI between March 2014 and November 2015.
Inclusion criteria included patients who sustained OHCA requiring intubation pre-hospital or on arrival to hospital. All patients included underwent immediate coronary angiography on arrival, and had a minimum of an ECG at the point of admission (“time-zero”) and at least one further ECG over the course of admission (in order to assess
Demographics
In total, from 217 patients with OHCA during the study period, the final study cohort consisted of 60 patients (males 51/60 (85%), mean age 63.1 years (range 21–86 years)). 44/60 patients (73.3%) had at least one documented co-morbidity, of which the most common were hypertension (50%), dyslipidaemia (35%) and pre-existing ischaemic heart disease (30%). The mean number of ECGs available per patient for analysis was 3.0 (range 2–5).
The majority (57/60 patients, 95.0%) of patients underwent TTM
Discussion
In this observational study we provide a descriptive account of the admission and behaviour of QTc interval in a non-selected group of patients presenting with OHCA.
Our data demonstrates that a prolonged QTc interval was present in more than half of our study population at time of admission. However, our data shows that the QTc interval resolves to within the normal range in the majority.
More detailed analysis by one-way ANOVA shows no significant difference between QTc on admission or
Conclusions
Despite more than half of patients having a prolonged QTc interval post-OHCA, this resolves in the vast majority. There is no distinct pattern in QTc according to aetiology of arrest and most patients who suffer a cardiac arrest and have a prolonged QTc interval on admission do not have a primary arrhythmic aetiology to their arrest. Importantly, a normal QTc interval on the admission ECG does not preclude a diagnosis of Long QT syndrome. Larger, prospective studies are warranted to draw firm
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All authors take responsibility for all aspects of the reliability and freedom from bias of the data presented and their discussed interpretation
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Joint first authors.