Evolution of the electrocardiogram in young dogs with congenital heart disease leading to right ventricular hypertrophy

Abstract

In 18 pups obtained from a breeding colony established for investigation of hereditary heart disease, ECG's were recorded shortly after birth. The ECG's, as well as clinical examinations, were repeated weekly in pups surviving the first week of life. The QRS modal axis was constructed in the frontal, transverse and sagittal planes. Cardiac catheterization was performed on all pups reaching the age of 8 to 12 weeks. VCG's were taken on selected pups. All dogs were necropsied terminally. In pups with severe pulmonic stenosis a pathological right ventricular hypertrophy was recognized immediately after birth. No evolution to a left ventricular dominance occurred in the serial tracings. Pups with milder grades of right ventricular outflow obstruction showed a normal evolution pattern or some minor deviations from the normal QRS complex evolution. In pups with patent ductus arteriosus (PDA) and left-to-right shunt, there was no difference from the normal ECG evolution within the first 12 weeks of life, except for some increase in amplitude. Two cases of PDA and right-to-left shunt were not different from the "physiologic right ventricular hypertrophy" at birth, but developed a severe right ventricular hypertrophy pattern within the first 12 weeks of life without any clinical signs of a left-to-right shunting within the period.