False-Positives Found To Be Higher If ECG Is Done Too Soon After Cardiac Arrest
Out-of-hospital cardiac arrests (OHCA) are one of the leading causes of death worldwide. Emergency medical services treat an estimated 30 to 97.1 per 100,000 individuals every year. A critical component of survival is the ECG.
Recently, a multinational PEACE European study found that the earlier the electrocardiography (ECG) acquisition after return of spontaneous circulation (ROSC) in patients who experienced OHCA, the higher the false-positive rate of ECG findings suggestive of ST-segment elevation myocardial infarction (STEMI).
Both the U.S. and European guidelines stress having ECG acquisition after ROSC in order to identify STEMI patients who could benefit from urgent coronary angiography. This is significant because these patients may have significant obstructive coronary artery disease which is the cause of their cardiac arrest.
However, multiple studies have shown that ECGs obtained promptly after ROSC might reflect ST elevation in the absence of significant epicardial stenoses. Collectively, the literature evidence points to variable associations of early post-ROSC ECGs with critical coronary artery stenoses. The consequence is significant heterogeneity in the performance of coronary angiography based on these ECGs.
Currently, neither of the countries’ guidelines offer specific recommendations about the best time for ECG acquisition after ROSC.
Enrico Baldi, MD, of Fondazione IRCCS Policlinico San Matteo in Pavia, Italy, spoke about the percentage of false-positive ECG findings. Among those performed 7 minutes or less after ROSC (18.5%) the false positive was significantly higher than those performed between 8 and 33 minutes (7.2%) and those over 33 minutes (5.8%) after ROSC.
“It may be reasonable to delay post-ROSC ECG by at least 8 minutes after ROSC or repeat the acquisition if the first ECG is diagnostic of STEMI and is acquired early after ROSC,” they wrote.
370 adults who had been resuscitated from OHCA were studied from 2015 to 2018 consecutively. They received a post-ROSC ECG, and underwent coronary angiography at one of three participating high-volume hospitals in Italy, Switzerland, and Austria. Patients had a median age of 62, and most were men (77.6%).
Patients were divided according to their post-ROSC ECGs, namely the 172 that were not diagnostic of STEMI and 198 that did suggest STEMI.
The two groups shared similar characteristics in terms of sex, age, paramedics’ arrival time, bystander CPR rate, and survival outcome.
However, the group with diagnostic ECGs suggestive of STEMI were more likely to have had OHCAs at home and witnessed by emergency medical services. Their initial rhythms were also more frequently shockable. Additionally, they received more shocks delivered and higher doses of epinephrine administered.
Bivariable analysis showed that results remained consistent after adjustment for sex, age, number of segments with ST-elevation 9 (anterior, lateral, posterior, inferior, and right), QRS duration, heart rate, epinephrine administered, shockable initial rhythm, and three or more shocks delivered.
Major limitations of the study were its retrospective design and limited sample, Baldi and colleagues acknowledged.
False-positive ECG findings were higher when ECG was conducted soon after ROSC, such that there was a false-positive rate of 18.5% when ECG time was under 8 minutes.
“This finding supports our hypothesis that, in the early post-ROSC phase, ECG findings could reflect not only the ischemia due to a coronary obstruction but also ischemia due to no blood flow and/or low blood flow during cardiac arrest,” Baldi and team wrote.
There are no rules on the exact timing of ECG acquisition. An immediate invasive approach has not been proven beneficial in patients whose ECG shows no sign of STEMI, except in the case of electrical or hemodynamic instability, the researchers noted.
“[T]he vast metabolic, electrolyte, and electromechanical abnormalities that emerge during OHCA and likely persist after ROSC may cause a greater number of false-positives and false-negatives on early ECG,” wrote Rajat Kalra, MD, and Demetris Yannopoulos, MD, both of University of Minnesota Medical School in Minneapolis, in an accompanying editorial.
The authors of the study felt like assuming a later ECG would be the most practical way after ROSC, but the study also led to greater findings and larger questions. “How do we understand, measure, and limit the metabolic derangement associated with OHCA?” they wrote.
“The most obvious of these steps is to ensure early, high-quality CPR and early defibrillation to maintain adequate coronary and visceral perfusion. While this notion is hardly novel in the field of resuscitation science, the addition of routine mechanical CPR and impedance-threshold devices may further improve the quality of CPR on a population level,” they added.
Other helpful possibilities, they suggested, include the addition of novel agents early after ROSC and the reorganizing of public health infrastructure to promote the transfer of patients to expert cardiac arrest hubs with advanced hemodynamic tools such as extracorporeal membrane oxygenation.
Overall, the study challenges many dogmas associated with resuscitation and can lead to innovations in cardiac arrest in the world to come.