Angiographic significance of a discordant ST-segment elevation of ≥5 millimeters in patients with ventricular-paced rhythm and acute myocardial infarction

Abstract

I 1989, a survey of cardiac pacing revealed that 1 million people in the United States had an implanted pacemaker.1 As the general population ages, the number of patients with both an implanted pacemaker and symptoms suggestive of acute ischemia is certain to increase. Unfortunately, the diagnosis of acute ischemia in the presence of a paced rhythm is at best difficult. A discordant ST-segment elevation of 5 mm has previously been considered to be the most specific electrocardiographic criterion for acute myocardial infarction (AMI) in patients with ventricularpaced rhythm (VPR).2 The angiographic significance of such a finding has not been previously evaluated. We analyzed coronary angiograms of patients with VPR who were admitted for evaluation of acute chest pain and had an enzymatically confirmed AMI. This study assesses the angiographic significance of a discordant ST-segment elevation of 5 mm found on the admission electrocardiogram of such patients. • • • The medical records of patients with implanted pacemakers who were admitted to Albert Einstein Medical Center for evaluation of acute chest pain between 1994 and 2002 were reviewed. All patients with enzymatically confirmed AMI were eligible. Inclusion criteria required 100% VPR at the time of admission along with coronary angiography as part of the evaluation of the current clinical event. Exclusion criteria were the use of thrombolytic therapy during the current clinical event and/or delay in the coronary angiography of 1 week after presentation. Patients in whom the pacemaker was placed as a consequence of the current coronary event were also excluded. Electrocardiographic parameters were collected from the admission electrocardiogram. At least 1 standard 12-lead electrocardiogram was required in all patients. The presence or absence of a discordant ST-segment elevation of 5 mm was determined. Two cardiologists performed analysis of the tracings independently. In the event of disagreement, a third independent reading was obtained. A cardiologist who was not aware of the result of the electrocardiographic readings interpreted coronary angiographic findings. To quantify the severity of the underlying coronary artery disease, the Friesinger index (a validated score ranging from 0 to 15 points) was used.3,4 The culprit artery was defined as the coronary vessel believed to be responsible for the acute episode based on its morphologic appearance on angiography. The rate of identification of the culprit artery and the Thrombolysis In Myocardial Infarction (TIMI) flow through it were used as surrogate variables for the severity of the acute ischemic event. They were also scrutinized and recorded in every patient. To perform the statistical analysis, TIMI 0 and 1 flows were considered as occlusive disease, whereas TIMI flow 2 and 3 flows represented patency of the culprit artery. Historical data regarding age, gender, race, risk factors for coronary artery disease, indication for the pacemaker, and type of pacemaker placed were also recorded. We hypothesized that the study outcomes (Friesinger index, rate of identification of the culprit artery, and TIMI flow through it) worsen with the presence of a discordant ST-segment elevation of 5 mm on the admission electrocardiogram. We compared the mean values of the Friesinger index in patients with and without a discordant ST-segment elevation of 5 mm using a 2-sample t test. We computed the difference between the means and the corresponding 95% confidence interval (CI). To assess the differences in both the rate of identification of and TIMI flow through the culprit artery, we used Fisher’s exact test. All p values were 2 sided and a p value 0.05 was considered statistically significant. Statistical analysis was performed using Stata version 6.0 (College Station, Texas). In all, 20 patients with an implanted pacemaker were admitted for evaluation of acute chest pain and had enzymatically confirmed AMI during the study period. Seven patients were excluded because of inhibition of the pacemaker by the patient’s own rhythm (n 3), the administration of thrombolytic therapy (n 1), or the lack of performance of coronary angiography (n 3). The mean SD time from admission to coronary angiography was 35 29 hours. Of the 13 patients meeting the inclusion criteria, 11 were men and 2 were women (mean age SD 75.3 8.45 years [range 54 to 88]) (Table 1). Analysis of the admission electrocardiograms in the 13 patients revealed that only 5 patients (38%) had a discordant ST-segment elevation of 5 mm (Figure 1). This pattern was found predominantly in the anterolateral leads, with only 1 patient exhibiting such From the Department of Medicine, Division of Cardiology, and Office of Research and Technology Development, Albert Einstein Medical Center, Philadelphia, Pennsylvania. Dr. Caldera’s address is: Department of Medicine, Albert Einstein Medical Center, 5401 Old York Road, Philadelphia, Pennsylvania 19141. E-mail: calderaa@ aehn2.einstein.edu. Manuscript received May 6, 2002; revised manuscript received and accepted July 26, 2002.