Not So Fast on That Post-Resuscitation ECG

Sooner was not better when using ECG to determine candidates for urgent coronary angiography after out-of-hospital cardiac arrest (OHCA), according to the PEACE study from Europe.

The earlier the ECG acquisition after return of spontaneous circulation (ROSC), the higher the false positive rate, as determined by the proportion of patients with ECG findings suggestive of ST-segment elevation MI (STEMI) who were subsequently found to have no significant obstructive coronary artery disease on angiography:

• ECG time under 8 minutes: false positive rate 18.5%
• ECG time 8-33 minutes: 7.2% false positives (OR 0.34, 95% CI 0.13-0.87)
• ECG time over 33 minutes: 5.8% false positives (OR 0.27, 95% CI 0.15-0.47)

“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,” wrote the group led by Enrico Baldi, MD, of Fondazione IRCCS Policlinico San Matteo in Pavia, Italy. Their manuscript was published online in JAMA Network Open.

“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,” according to Baldi’s group.

U.S. and European guidelines alike stress ECG acquisition after ROSC to identify STEMI patients who might benefit from urgent coronary angiography, since these patients may have significant obstructive coronary artery disease that is the cause of their cardiac arrest.

There are no rules on the exact timing of ECG acquisition, however. 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, Baldi and colleagues 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,” noted Rajat Kalra, MD, and Demetris Yannopoulos, MD, both of University of Minnesota Medical School in Minneapolis.

Later ECG acquisition would be a “practical” way to limit the uncertainty surrounding ECG interpretation soon after ROSC, Kalra and Yannopoulos agreed in an accompanying editorial.

“However, in our minds, the PEACE study points to even 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,” the editorialists 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.

PEACE investigators conducted the study in 2015-2018 at three participating centers in Italy, Switzerland, and Austria.

The study included a final cohort of 370 consecutive adults who had been resuscitated from OHCA, received a post-ROSC ECG, and underwent coronary angiography (77.6% men, median age 62 years).

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.

PEACE results remained consistent after adjustment for sex, age, number of segments with ST-elevation, QRS duration, heart rate, epinephrine administered, shockable initial rhythm, and three or more shocks delivered, the authors reported.

Major limitations of the study were its retrospective design and limited sample, Baldi and colleagues acknowledged.

Hints of selection bias included the finding that approximately 25% of patients who underwent coronary angiography during the study period did so without a post-ROSC ECG and had to be excluded, according to Kalra and Yannopoulos.

“Additionally, more than half of patients without ST elevation on their initial electrocardiograms progressed to coronary angiography and revascularization, implying a high false-negative rate,” the duo wrote.

Even so, the study results “challenge important dogmas in resuscitation science and provide important food for thought,” the editorialists maintained.