Electrocardiographic evaluation of broilers during the onset of pulmonary hypertension initiated by unilateral pulmonary artery occlusion

Electrocardiography previously has been used as a noninvasive method for detecting cardiac hypertrophy associated with pulmonary hypertension syndrome (PHS, ascites). In the present study, 36 of 100 male broiler chicks were selected for inclusion in the experiment based on their hatch weight (greater than or equal to 40 g), Day 1 to 14 BW gain (upper 50% of population distribution), and the normalcy of their Day 14 electrocardiogram (ECG). On Day 16, 10 chicks were assigned to the unoperated control group (CONTROL), sham operations were performed on 10 chicks (SHAM), and pulmonary hypertension was initiated by clamping the left pulmonary artery in 16 chicks (PA-CLAMP). Electrocardiogram leads I, II, III, and aV(F) were recorded daily until Day 27, when 6 of the 12 birds surviving in the PA-CLAMP group had developed clinical ascites. The right:total ventricular weight ratio (RV:TV) was higher and BW was lower in the PA-CLAMP group than in the CONTROL and SHAM groups on Day 27. The RS, R, and S wave amplitudes in lead II for the CONTROL and SHAM groups did not change, whereas in lead II for the PA-CLAMP group the S wave attained a more negative amplitude by Day 21, the RS wave attained a more negative amplitude by Day 22, and the R wave declined to a less positive amplitude by Day 23 when compared with presurgery values. Similar differences were observed for the RS and S waves for leads III and aV(F). The mean electrical axis (MEA) and mean resultant vector (MRV) of the CONTROL and SHAM groups did not change; however the PA-CLAMP group the MEA rotated significantly from +3 degrees to -72 degrees and then to -88 degrees on Days 14, 22, and 27, respectively, and the MRV amplitude increased from 0.052 to 0.108 mV and then to 0.179 mV on Days 14, 22, and 27, respectively. When data from all treatment groups were combined, higher absolute and BW-normalized RV:TV ratios were inversely correlated (r = -0.859 to -0.880) with increasingly negative S wave amplitudes in leads II and aV(F). Higher absolute and BW-normalized RV:TV ratios were directly correlated (r = 0.786 to 0.789) with increasing MRV amplitudes. These ECG characteristics constitute accurate, noninvasive predictive criteria suitable for detecting cardiac changes occurring early during the onset of primary pulmonary hypertension.