The relationship between ECG signs of atrial infarction and the development of supraventricular arrhythmias in patients with acute myocardial infarction ECGs obtained on arrival at the hospital from 277 patients with acute myocardial infarction were analyzed retrospectively for PR displacements, which were classified as major or minor criteria for atrial infarction and related to the later occurrence of supraventricular arrhythmia in the hospital. Major criteria were (1) PR segment elevation >0.5 mm in leads Vs and Vs with reciprocal PR segment depression in leads VI and VP, (2) PR segment elevation >0.5 mm in lead I with reciprocal PR segment depression in leads II and III, and (3) PR segment depression >1.5 mm in precordial leads and >1.2 mm in leads I, II, and III. Abnormal P waves were classified as minor criteria. Major and minor criteria were found in 15 (5.4%) and 19 (6.9%) patients, respectively. Eight (53.3%) patients with major and six (31.6%) with minor criteria had supraventricular arrhythmias, giving odds ratios of 9.9 and 3.7, respectively. Enzyme-estimated infarct size, the occurrence of heart failure, and mortality rates did not differ in patients with or without major criteria for atrial infarction. We conclude that the occurrence of PR segment displacements on the admission ECG may predict the risk of developing supraventricular arrhythmias during hospitalization for myocardial infarction. (AM HEART J 1992;123:69.) Finn Erland Nielsen, Henning Hoby Andersen, Paul Gram-Hansen, Henrik Toft S$rensen, and Ib Christian Klausen. Adborg, Denmark It is well known that acute myocardial infarction (MI) may involve the atria,rT6 but thus far clinicians have not paid special attention to this fact. The fre- quency of atria1 infarction varies considerably,1-3 but an incidence of 17 % , as suggested by Cushing et al.,2 is considered the most likely.5 Supraventricular arrhythmias often complicate atria1 infarctions,l, 2y 5l7~ 8 and these arrhythmias, in- cluding atria1 fibrillation, are the most common and may have hemodynamic consequences.gp lo Early pre- diction of their occurrence is important because they may influence the choice of therapy during the early stages of the infarctions.” The ECG is the only means of diagnosing atria1 infarctions before death,5l 6 and the aim of the present study was to find out whether there was a relationship between ECG changes on arrival at the hospital and later development in the hospital of supraventricular arrhythmias in patients with MI. From the Department of Cardiology, Aalborg Hospital South. Received for publication Nov. 8, 1990; accepted June 28, 1991. Reprint requests: Finn Erland Nielsen, Department of Internal Medicine F, Herlev University Hospital, DK-2730 Herlev, Denmark. 4/l/33600 METHODS The study included all patients who were admitted with a first episode of MI to the department of cardiology, Aal- borg Hospital, betweenJanuary 1 and December 31,1987. This department, which admits approximately 550 pa- tients with acute MI annually, wasequipped for continu- ous ECG monitoring of 28 patients. The patients were monitored until the day before their planned discharge from the hospital. Two specially trained nurses observed the patients’ heart rhythms from a central monitoring of- fice. If an arrhythmia developed, an ECG strip was made out. The medical officer on call diagnosed the arrhythmia immediately. The heart rhythm of eachpatient wasnoted every hour on a special arrhythmia chart, and at the following morning or eveninground a senior medicalofficer wrote down the arrhythmia diagnosis on the ECG strip and signed it before it wasfiled separately. The diagnosis of MI was based on the presence of typ- ical pain, typical ECG changes, or both accompaniedby increases in enzymelevels. The ECG changes included (1) appearance of abnormal Q waves in at least two leads,(2) loss of R waves (more than 50% reduction in the R ampli- tude) in at least two leadscomparedto previous ECGs, (3) ST elevation >=0.2 mV in leadsVi and Vs and ST eleva- tion >=O.l mV in the other leads,and (4) ST depression >=O.l mV or abnormal T wave inversion in at least two leads.The department usedlactic dehydrogenase (normal 69