Data acquired in over 4,500 STEMI patients treated with primary PCI, provide novel and compelling evidence about the importance of a Q-wave on the baseline ECG as an independent prognostic marker of clinical outcome, according to a study in the April 28 issue of the Journal of the American College of Cardiology.

Researchers suggest the baseline Q-waves be used in evaluating patients for triage and potential transfer for planned primary PCI.

Paul W. Armstrong, MD, from the University of Alberta, Edmonton in Canada, and colleagues from various institutions assessed the incremental value of baseline Q-waves over time from symptom onset as a marker of clinical outcome in STEMI.

They evaluated baseline Q-waves and ST-segment resolution 30 minutes after primary PCI ECGs in 4,530 STEMI patients without prior infarction. Additionally, they assessed peak biomarkers, 90-day mortality, and the composite of death, congestive heart failure (CHF), or cardiogenic shock.

They found that 56 percent of patients had baseline Q-waves: they were older, more frequently male and diabetic, and had a more advanced Killip class. Patients with baseline Q-waves had greater mortality and a higher composite rate of death, CHF, and shock versus patients without baseline Q-waves at 90 days. The difference was significant.

Complete ST-segment resolution was highest, whereas 90-day mortality and the composite outcome were lowest among those randomized less than three hours without baseline Q-waves. After multivariable adjustment, baseline Q-wave but not time from symptom onset was significantly associated with a 78 percent relative increase in the hazard of 90-day mortality and a 90 percent relative increase in the hazard of death, shock, and CHF.

“Patients presenting within six hours of symptom onset who exhibit Q-waves on their baseline ECG seem to have a distinct clinical profile that portends more advanced disease—older men with diabetes, a more advanced Killip class, more frequent noninferior MI, greater baseline ST-segment deviation, and delayed presentation,” the authors wrote.

“Whereas it has been argued that baseline Q-waves are ‘a poor predictor of symptom duration,’ our data support prior observations from fibrinolytic-treated patients contending that they are independent from time from symptom onset and likely represent a more accurate reflection of the wave front of myocardial necrosis,” the authors concluded.