Myocardial changes after chronic immunization of guinea pigs with diphtheria--tetanus--pertussis (DTP) vaccine.

Fifteen guinea pigs were immunized with diphtheria-tetanus-pertussis [DTP] vaccine once a week throughout the period of 10 months. The control group included 5 guinea pigs. ECG tracings were recorded every second week in both groups of animals. ST-T changes were the most important findings. Sometimes the ECG resembled the picture found in endocardial fibroelastosis in children. ECG abnormalities appeared 3 months after the beginning of the experiment, and were frequently variable. Less pronounced ST-T changes were found also in control animals, but they disappeared after the administration of Inderal. The histological pictures revealed a thickening of the endocardium and degenerative changes of the ganglion cells of the atria; these changes did not always correlate with electrocardiographic tracing.