CARDIOPULMONARY VALUES IN NORMAL AND HEARTWORM-INFECTED DOGS

To characterize several physiologic aspects of the cardiopulmonary system of heartworm-infected dogs not in congestive heart failure, data from 34 infected dogs were compared with data from 14 normal dogs. In infected dogs, results of the electrocardiogram (ECG) indicated a tendency for clockwise rotation of the mean electrical axis (frontal plane) and counterclockwise rotation when lead aVF was plotted against lead V10 (sagittal plane). P-wave notching occurred more frequently in normal dogs, whereas conduction disturbances appeared more frequently in infected dogs. The incidence of T-wave variation and sinus arrhythmia was similar in dogs of both groups. Results of the phonocardiograms (PCG) of infected dogs indicated significant increase (at the 5% level) in the interval from onset of the QRS complex of the ecg to onset of the 2nd heart sound when recorded at the apex and on the right side. The incidence of systolic murmurs was also higher. Blood pressures in the main pulmonary artery and right ventricle were significantly higher (at the 2% and 5% levels, respectively) in the infected dogs. No significant difference was observed in oxygen consumption; however, significant increase in tidal volume (at the 2% level) and decrease in respiration rate (at the 5% level) were observed in infected dogs. Significant differences were not observed in cardiac output or cardiac index between the 2 groups of dogs. Stroke volume was greater (at the 10% level) in infected dogs. The circulation time from the right ventricle to the left ventricle was increased significantly (at the 1% level) in the infected dogs.