The main finding of this study was that patients with HF suffering IHCA display very poor outcomes, with only one out of ten patients surviving to five years, as compared with one out of three patients with acute MI who suffer an IHCA. Moreover, while overall survival in the 30 days following IHCA has improved during 2008 to 2019 in all groups examined, the increases in patients with HF and acute MI (41% increase) and HF alone (15% increase) were less pronounced than in individuals with acute MI alone (55% increase). We also found that patients with HFrEF, overall, had a better survival than patients with HFpEF, although there was a U-shaped relationship between LVEF and mortality, which was highest in individuals with a very low LVEF and in those with a LVEF ≥50%. We also found that roughly 93% of survivors among HF patients had a good neurological outcome at hospital discharge.
It can be argued that patients with reduced LVEF are more likely to have coronary artery disease, history of MI and myocardial scar, neurohumoral activation and electrolyte abnormalities. All these factors increase the risk of ventricular arrhythmias and, consequently, a higher prevalence of shockable initial rhythm (as we observed) and probability of survival.
Conversely, the poorer survival in patients with HFpEF could be due to location of IHCA and promptness of early management, patient factors or both. We adjusted for initial rhythm, time to CPR and witnessed status, making procedural issues less likely to explain our findings. We also adjusted for age and sex, but we did not adjust for other comorbidities. Our findings might also seem to indicate a paradox whereby patients with HFpEF, overall, have a lower mortality rate than patients with HFrEF but, when they experience an IHCA, have a lower chance of survival. However, these two observations are not incompatible as patients hospitalized with HF represent the more severe end of the clinical spectrum and, although cardiac arrest may be less common, overall in patients with HFpEF, compared with HFrEF, the causes of arrest in HFpEF may be less amenable to correction (as exemplified by the 2-fold difference in the rate of shockable rhythm), the patients overall may be less likely to recover or both. It can be argued that the higher survival rate among patients with HFrEF compared to HFpEF is due to the differences in initial rhythm, and though this is a factor, our sensitivity analysis stratified upon initial rhythm would suggest this not the entire case behind the differences in survival between different HF phenotypes, since patients with HFpEF and an initial shockable rhythm has a moderately lower survival rate at 1 year compared to patients with HFrEF and an initial shockable rhythm (Supplementary figure 3D).
Patients with a very low LVEF also displayed high mortality. This may also reflect a different type of initial electrical event or just the known poor prognosis of patients with severe left ventricular systolic dysfunction and the difficulty in such sick heart recovering contractile function after a period of arrest (3).
Levy and colleagues studied factors associated with good neurological outcome at discharge for patients with acute HF and IHCA during the period 2000 to 2007. They reported that 20.0% survived to hospital discharge, and among those, 88.5% had good neurological outcome (23). Our data from 2008–2009 shows 30-day survival around 20–25%, and this percentage has increased, in absolute numbers, by almost 1% annually (Figure 4). With regards to neurological function, we show that 92.0% and 93.3% of patients with HF alone and HF with acute MI, respectively, have a good neurological outcome at discharge. These are encouraging findings since they highlight that successful resuscitation attempts are very likely to result in good neurological outcome. Also, previous studies have shown that while patients with HF fear the potential neurological disabilities, the majority would choose to have cardiopulmonary resuscitation should they need it (24,25).
This study is limited due to being a retrospective observational study, and thus affected by the limitations of such design. The SRCR lacks data on medication, and only few comorbidities are recorded. Moreover, data on LVEF was only available for 55% of cases with HF alone. It is possible that these cases represent a selected subgroup. This is suggested by the fact that cases with no recent LVEF measurement displayed different clinical characteristics (including being older) and worse survival. HF patients in Sweden typically undergo echocardiographic examination once yearly, which implies that some LVEF measurement are randomly missing, while others will have missing measurements due to non-random reasons; the group with missing measurements was presumably enriched with patients with less active care, in more advanced stages of heart failure.