We performed a prospective study involving a large, well-characterized population of patients with ST-segment elevation for whom percutaneous coronary intervention was intended. Our study provides new insights into the relation between time from symptom onset and the presence of baseline Q waves on one-year mortality in patients randomized within 24 hours of symptom onset. We found that baseline Q waves were superior to time from symptom onset as an independent prognostic factor for all-cause and vascular mortality in patients with ST-segment elevation. This provides robust evidence supporting the use of baseline Q waves as a marker of infarct evolution.
In a prior study, we found that patients with ST-segment elevation who were randomly assigned to the study treatment within a shorter period (i.e., < 6 h) had higher-risk ST-segment elevation admission criteria (i.e., ≥ 2 mm ST-segment elevation in two anterior or lateral leads or a total of ≥ 8 mm ST deviation for patients with inferior MI in whom ≥ 2 mm ST-segment elevation in two inferior leads was required) and for whom follow-up was limited to 90 days. In general, the overall incidence of Q waves in the lower-risk PLATO population of 46.1% was comparable to the 55.4% seen in the APEX-AMI trial, despite the broader window of randomization.
We found that patients presenting with Q waves were older, more often male, had higher heart rates and higher Killip class than patients without Q waves. As well, they more often had noninferior infarcts with greater baseline ST-segment elevation and ST deviation, and they had higher baseline and peak biomarkers indicative of both earlier and greater myocardial necrosis. These patients presented later after symptom onset and had a longer time lag to percutaneous coronary intervention, and the frequency of Q waves rose progressively over the 24-hour period (i.e., from 40% at less than three hours to 52.6% beyond six hours).
Among the patients for whom ECG data were available at three days after admission, those with Q waves at baseline were less likely to achieve adequate ST resolution as determined by a discharge ECG. This likely relates to their longer time to reperfusion, larger subsequent infarcts and the potential role of residual-associated motion abnormalities in the left ventricular wall.
Our current study provides evidence to support greater and more systematic attention toward the presence of baseline Q waves on initial ECGs in patients with STEMI. This simple bedside metric provides additive value in staging the evolution of STEMI. As well, this metric should be of assistance in the selection of reperfusion strategies, triage for planned percutaneous coronary intervention and assessing prognosis. Moreover, in the not-infrequent circumstance when the time from the onset of symptoms is unclear, our findings could be especially useful. The increased role and emphasis on pre-hospital ECGs are well aligned with our evidence to support the use of a readily available baseline measure (i.e., Q waves) by a variety of health care providers.
We acquired our data from a large, well-characterized population of patients with ST-segment elevation who were followed carefully for long-term mortality. Although the patients were drawn from a clinical trial, which might lead some to argue against the generalizability of our results, the liberal ECG criteria and large randomization period make our current results more clinically applicable than those from prior work. Additionally, the consistency of our findings, even after the inclusion of patients with prior MI and baseline Q waves outside the distribution of ST-segment elevation, is a further indication of the relevance of our results. The enhanced relations between baseline Q waves and the prespecified component of the primary outcome (i.e., vascular mortality) provides further support for our findings.
Conclusions and implications for further research
Baseline Q waves in patients with ST-segment elevation is a simple, readily accessible and cost-effective metric that constitutes a new tool that can provide additional insight as an indicator of the evolution of infarction. Baseline Q waves are an independent prognostic factor for one-year mortality in patients with STEMI. Our study adds prospective confirmation about the prognostic value of baseline Q waves in broadly inclusive ST-segment elevation criteria for patients who presented within 24 hours of the onset of symptoms. This metric should prove useful in assisting therapeutic decisions about reperfusion therapy and the triage of patients with ST-segment elevation, especially when the time from the onset of symptoms is unclear.