Mellat Park, Vali Asr Avenue, Tehran, Iran


Background - The electrocardiogram (ECG) of patients with a permanent pacemaker may conceal the changes of acute myocardial infarction (AMI), which can delay both its recognition and treatment. We studied electrocardiographic criteria for the diagnosis of AMI in the presence of a functioning pacemaker.
Patients - We paced (endocardial, single chamber) patients with documented AMI (confirmed by enzyme studies and ST elevation) and compared their ECG with the electrocardiograms of the control patients, who had functioning permanent pacemakers. The electrocardiographic criteria for the diagnosis of AMI were then studied in an independent sample of patients presenting with acute chest pain and a functioning pacemaker. The ECGs of 62 patients with documented AMI during right ventricular apical pacing were compared with those of 60 patients with a permanent pacemaker.
Results - The three electrocardiographic criteria with independent value in the diagnosis of AMI in these patients were an ST-segment elevation of 1mm or more which was concordant with the QRS complex, an ST-segment depression of 1mm or more in lead V1, V2 or V3, and an ST- segment elevation of 5mm or more, which was discordant with the QRS complex. We used these three criteria to develop a scoring system (0 to 5) that allowed a highly specific diagnosis of AMI to be made.
Conclusion - In conclusion, we developed and validated a clinical prediction rule based on a set of electrocardiographic criteria for the diagnosis of AMI in patients with chest pain and functioning pacemakers. The use of these criteria, which are based on simple ST-segment changes, may help identify patients with AMI who can then receive appropriate treatment