Finding the cause of out-of-hospital cardiac arrest (OHCA) is generally considered to be useful in order to prevent recurrence and subsequent clinical deterioration. As acute coronary syndrome (ACS) is a frequent cause of OHCA, several experts claim that resuscitated patients of presumed cardiac cause should undergo immediate coronary angiography with subsequent percutaneous coronary intervention (PCI) if indicated, regardless of clinical symptoms and/or electrocardiogram (ECG) criteria [1]. This strategy is supported by several strong arguments. First, there is a very high prevalence of coronary lesions in these arrest patients. In a recent meta-analysis, the prevalence of significant coronary artery disease ranged from 59 to 71 % in patients without an obvious non-cardiac aetiology (Table 1) [2]. This high prevalence of recent coronary occlusion provides a strong rationale for performing coronary angiography in OHCA patients with no obvious extra-cardiac cause, in order to detect the culprit lesion. Second, early coronary angiography also enables immediate PCI, when indicated. Since the publication of the pioneering study by Spaulding and co-workers in 1997 [3], many observational studies have reported the feasibility and possible survival benefit from an early invasive approach. In a cohort of 435 OHCA patients without obvious extra-cardiac cause, successful PCI was an independent factor for survival, regardless of the post-resuscitation ECG findings (odds ratio (OR) 2.1 [95 % confidence interval (CI) 1.2–3.7]) [4]. In this issue, Bougouin and colleagues [5] report on the characteristics of 3,816 cases of treated OHCA in Paris; after adjustment for other prognostic factors, coronary angiography was associated with survival (OR 2.4, 95 % CI 1.4–4.0, P = 0.001). As the data are derived from a ‘real-life’, large, population-based registry, this result underlines that the benefit of early reperfusion is not restricted to specialised ‘cardiac arrest centres’. Finally early PCI is also associated with a better long-term outcome: among 1,001 OHCA survivors discharged from hospital in the USA, Dumas and associates reported a 5-year survival of 78.7 % in those treated with PCI compared with 54.4 % in those not treated with PCI (p < 0.01). Moreover, PCI was associated with a lower risk of death after adjustment for confounders (hazard ratio 0.56 [95 % CI 0.34, 0.61], p < 0.01) [6]. The benefit of early revascularization may not be restricted to crude survival but could also be associated with an improved quality of life. Specifically focusing on quality of life, daily functioning and participation in social activities, in a long-term follow-up of 63 OHCA survivors (after a mean follow-up of 36 ± 18.8 months) PCI was associated with better cognitive function, participation in social activities and instrumental daily activities compared with patients not treated with PCI [7]. Even in the absence of large randomised studies, it is highly probable that early coronary revascularisation, when required, is associated with a clinically relevant benefit in OHCA survivors. To decrease the risk of undertaking an invasive procedure unnecessarily, early coronary angiography should be restricted to OHCA patients with a high probability of recent coronary occlusion, i.e. those with a definite ACS. However, eliminating the diagnosis of ACS after OHCA is very difficult. In contrast to the usual presentation of ACS in non-cardiac arrest patients, the usual tools to assess coronary ischaemia are less accurate in this setting. Clinical data, ECG and biomarkers lack sensitivity and specificity to predict an acute coronary artery occlusion as the cause of OHCA. Taken together, these findings support the performance of coronary angiography in all OHCA patients without an obvious non-cardiac cause. Even a negative coronary angiogram provides useful diagnostic information because the absence of a culprit lesion will prompt a search for alternative causes of cardiac arrest.

Table 1 Coronary artery disease among out-of-hospital cardiac arrest patients with no obvious extra-cardiac cause [2]
Full size table

Hypoxic–ischaemic brain injury is the cause of death in approximately two-thirds of the patients who die after admission to an intensive care unit (ICU) following OHCA [8]. Although much of this brain injury occurs during the period of cardiac arrest (no flow) and during cardiopulmonary resuscitation (low flow), the damage may continue to evolve for hours to days after circulation and oxygenation have been restored [9]. There is evidence that a period of mild hypothermia started after return of spontaneous circulation (ROSC) can reduce the severity of neurological injury after cardiac arrest. One randomised trial [10] and a pseudorandomised trial [11] demonstrated improved neurological outcome among comatose survivors of ventricular fibrillation out-of-hospital cardiac arrest (VF OHCA) who were cooled to 32–34 °C for 12–24 h compared with those who were not cooled. On the basis of these results and data from animal studies [12], in 2003 the International Liaison Committee on Resuscitation (ILCOR) recommended the use of therapeutic hypothermia (TH) for patients remaining comatose after VF OHCA [13]. At that time, there were few data on the use of TH in comatose patients following cardiac arrest from other rhythms or after in-hospital cardiac arrest (IHCA), but the ILCOR advisory statement indicated that TH might also be beneficial under such circumstances. Since then, several observational studies with historical or concurrent control groups have shown benefit after cooling in comatose survivors after OHCA from non-shockable rhythms [14], although such studies carry risk of bias, and some observational studies have shown no benefit for TH after cardiac arrest from non-shockable rhythms [15]. Contrary to the prevailing opinion several years ago, mild hypothermia may also be beneficial in the presence of cardiogenic shock: in a case series of 14 such patients, cooling improved cardiac index, stroke volume and mean arterial blood pressure [16].

In the recent targeted temperature management (TTM) trial unconscious survivors of all-rhythm OHCA were assigned randomly to TTM at either 33 or 36 °C; there was no difference in all-cause mortality or neurological function at 180 days [17]. The message from this study is not that we should abandon temperature control; patients in both arms of the trial had their temperature controlled and, most importantly, fever, which is associated with poor neurological outcome after cardiac arrest [18], was prevented. Even after return to normothermia after a period of TH, continued temperature control is important. In a recent study of 270 patients resuscitated and treated with TH following all-rhythm OHCA, post-hypothermia fever of 38.5 °C or higher was associated with increased 30-day mortality even after controlling for potential confounders [19]. The results of the TTM trial have left us with some uncertainty about the optimal target temperature but some form of temperature control after cardiac arrest remains important.

In the study of treated OHCAs in this issue, application of TTM was associated with improved survival, although after risk adjustment this association was lost [5]. Given the prospective randomised data showing benefit for TTM after OHCA from shockable rhythms and the observational data showing benefit for TTM after OHCA from non-shockable rhythms, in our opinion TTM should be included as part of the post-resuscitation care of all comatose OHCA patients admitted to an ICU. Observational studies indicate that, after risk adjustment, optimal long-term outcomes after OHCA are achieved with a combination of TTM and PCI [6]. Thus, in our opinion, all comatose survivors of OHCA without an obvious non-cardiac cause should undergo both PCI and TTM.