Symptomatic myopericarditis has been described after smallpox vaccination using replication-competent vaccinia strains.

We examined the incidence of new electrocardiogram (ECG) abnormalities and evaluated the safety and immunogenicity related to vaccination. Volunteer subjects (n=90) aged 18 to 32 years were enrolled in a National Institutes of Health-sponsored phase I smallpox vaccination trial (Division of Microbiology and Infectious Diseases 02-017) and observed over a 26-week period after 2 injections of IMVAMUNE, Modified Vaccinia Ankara vaccine (Bavarian Nordic A/S, Copenhagen, DK), followed by scarification with Dryvax (Wyeth Laboratories, Marietta, Penn). Diagnostic computer-derived ECG statements were available to the clinical study team and compared with those of a board-certified cardiologist who independently read the ECG tracings.

Serial ECG tracings available for 89 of the subjects revealed new ST-segment abnormalities in 2.2% and new T-wave abnormalities in 15.7%; the majority (71.4%) resolved on subsequent tracings. Cardiologist over-read of computer statements resulted in frequent changes in readings, particularly negation of cardiac arrhythmias. A cardiology consultation was requested in 17 subjects for nonspecific cardiac symptoms or new abnormal ECG findings. Echocardiograms were performed in 12 of the 17 subjects and were normal except for 1 subject with possible myopericarditis after receiving Dryvax.

New minor ECG abnormalities are common in apparently young healthy volunteers considered for smallpox vaccination trials. Cardiologist over-read of computer-generated ECG statements in vaccine trials using ECG as a screening tool for safety can reduce false-positive computer-determined ECG diagnoses and the need for inappropriate cardiology referral and additional noninvasive testing.