Clinical paperPeripheral perfusion index and diagnostic accuracy of the post-ROSC electrocardiogram in patients with medical out-of-hospital cardiac arrest
Introduction
Out-of-hospital cardiac arrest (OHCA) is one of the leading causes of death worldwide, because of its high incidence and low survival rate.1., 2. The chain of survival represents the sequence of actions to improve the chance of achieving the return of spontaneous circulation (ROSC):3 however, post-resuscitation care is still a challenge.
In the last 10 years, the American Heart Association and the European Resuscitation Council’s guidelines have focused on post-ROSC treatment,4., 5. recommending some diagnostic and therapeutic steps in order to discover and treat the underlying cause of the cardiac arrest with the final aim to improve survival. A 12-lead electrocardiogram (ECG) is the first recommended diagnostic tool to be acquired after ROSC to identify ST-segment elevation myocardial infarction (STEMI), one of the most frequent causes of cardiac arrest which requires an urgent invasive coronary angiography (ICA). This has been shown to improve survival in STEMI patients,6 in contrast to those patients without ST segment elevation in which the beneficial effect of a myocardial revascularization in presence of a false-negative ECG could balance the harm of a coronary angiography performed in case of other non-cardiac causes of OHCA (i.e. brain hemorrhage, aortic dissection). Thus, the diagnostic accuracy of the post-ROSC ECG is of pivotal importance to improve the post-ROSC treatment.
In a previous multicenter cohort study, the ROSC to ECG time was shown to affect the ECG accuracy as the percentage of false-positive ECG findings was three times greater when the ECG was acquired within the first 7 min after ROSC.7 Reasonably, in the early post-ROSC phase, the ECG findings could reflect not only the ischemia due to coronary artery disease, but also the ischemia secondary to both the post-ROSC hypoperfusion and the absent or low coronary flow during resuscitation. Waiting some minutes after ROSC to restore a good perfusion allows to acquire a more reliable ECG.7., 8. However, this might not be enough for all patients and that is why we have focused our attention on perfusion analysis.
The perfusion index (PI) is the ratio of the pulsatile blood flow to the non-pulsatile or static blood in peripheral tissue. It represents a non-invasive measure of peripheral perfusion which can be continuously obtained by a standard pulse-oximeter as the ratio between the absorbed light to the emitted light.9 Up to now the role of PI has been established for various clinical uses. In anesthesiology, it is used to early detect hemodynamic changes during general anesthesia.10., 11. or to assess the effectiveness of peripheral blocks.12., 13. In neonatology, PI has been proposed to early recognize congenital heart disease14., 15. and to discriminate survival.16 In emergency department it has been shown to predict hospital outcome and mortality.17 In the setting of out-of-hospital cardiac arrest, the post-ROSC peripheral PI has found application as an independent predictor of 30-day mortality or of poor neurological outcome (Cerebral Performance Category scale > 2) in resuscitated patients.18
Considering that low PI values reflect worse perfusion and that the period of no flow and/or low flow during cardiac arrest can lead to a transmural myocardial ischemia not necessarily of coronary origin, we aimed to assess the association between PI values after ROSC and the percentage of false-positive ECG findings for STEMI.
Section snippets
Study population
This is a single center, observational, retrospective analysis of prospectively collected data approved by the ethics committee of the Fondazione IRCCS Policlinico San Matteo of Pavia. We considered all the consecutive patients resuscitated from an OHCA occurred in the Province of Pavia between January 1st, 2015 and December 31st, 2020 which were prospectively enrolled in our cardiac arrest registry.19 We defined OHCA as the cessation of cardiac mechanical activity as confirmed by the absence
Data collection
The variables associated with OHCA and the outcomes were collected according to the 2014 Utstein style recommendations.20 The pre-hospital data related to OHCA were obtained from the prospective Cardiac Arrest Registry of the Lombardy Region (Lombardia CARe; ClinicalTrial.gov NCT03197142), approved by the ethics committee of the Fondazione IRCCS Policlinico San Matteo in Pavia. Study data were collected and managed after being anonymized using REDCap electronic data capture tools hosted at
Baseline characteristics
A total of 4619 OHCAs were enrolled in the registry, and in 2982 cases resuscitation was attempted. A pre-hospital ROSC was achieved in 491 patients and 351 of them were transported to the Fondazione IRCCS Policlinico San Matteo in Pavia. 260 patients were excluded because a 30-min PI monitoring values and a post-ROSC ECG were unavailable and 7 cases were excluded because they did not undergo ICA, resulting in a final population of 84 patients (Fig. 1).
Baseline characteristics of patients are
Discussion
To our knowledge, this is the first study investigating whether post-ROSC peripheral perfusion after OHCA could affect the reliability of post-ROSC ECG for the diagnosis of STEMI. We found that MPI30 values were associated with the percentage of false-positive ECG. This suggests that ECG may disclose a transmural myocardial ischemia without a significant obstructive coronary artery disease deserving PTCA, especially in the patients with a low peripheral perfusion after ROSC. As a matter of
Limitations
The first limitation is that this is an observational study. However, the evidence about the use of perfusion index in a clinical setting derived from observational studies. Second, although we started from a large population of cardiac arrest patients, the final sample size was quite limited, due to a series of reasons: (1) the pulse-oximeter was either not positioned after ROSC or not maintained for at least 30-minutes of monitoring in all the patients; (2) the post-ROSC ECG was available
Conclusion
Post-ROSC perfusion assessed with peripheral perfusion index relates with the reliability of post-ROSC ECG at least in medical OHCA. High MPI30 values were associated with a lower probability of recording an ECG falsely positive for STEMI regardless of cardiac arrest duration. An easy and inexpensive parameter as perfusion index can improve post-ROSC ECG interpretation to correctly identify patients who may benefit from an urgent coronary angiography.
CRediT authorship contribution statement
Sara Compagnoni: Conceptualization, Writing – original draft, Writing – review & editing, Formal analysis, Methodology, Data curation. Francesca Romana Gentile: Data curation, Investigation, Writing – original draft, Writing – review & editing. Enrico Baldi: Writing – original draft, Writing – review & editing, Formal analysis, Methodology, Data curation. Enrico Contri: Data curation, Investigation. Alessandra Palo: Data curation, Investigation. Roberto Primi: Data curation, Investigation.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgment
We would like to thank all the Lombardia CARe researchers and all the EMS personnel. EB, EC and SS are part of the European Resuscitation Council Research-Net. Lombardia CARe is a partner of the ESCAPE-NET consortium.
Funding
Lombardia CARe is partially supported by Fondazione Banca del Monte di Lombardia.
Dr Baldi’s salary was partially funded by grant 733381 from the European Union Horizon 2020 Research and Innovation Program of ESCAPE-NET.
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