R-peak time in clinically healthy dogs with different thoracic conformations

R-peak time (RPT) is an electrocardiographic parameter that represents the time taken for electrical activation to spread from the endocardium to the epicardium. In human medicine, right ventricular RPT is measured from lead V₁ to lead V₂, and left ventricular RPT from lead V₅ to lead V₆. The aim of the present study was to define RPT duration in a group of clinically healthy dogs with different thoracic conformations. Sixty clinically healthy dogs underwent a 12-lead electrocardiogram recorded using a previously described precordial system. The dogs were allocated into three morphologic groups. In the brachymorphic group, the median and 25th-75th percentiles for RPT in V₁ were 10.5 ms (10-12 ms); V₂, 18 ms (16.5-20 ms); V₃, 19 ms (18-22 ms); V₄, 20 ms (17-23.5 ms); V₅, 21 ms (18.5-24 ms); and V₆: 22 ms (18.5-25.5 ms). In the mesomorphic group, RPT in V₁ was 16 ms (14-18 ms); V₂, 22 ms (20-24 ms); V₃, 23 ms (21-25 ms); V₄, 23 ms (22-25 ms); V₅, 25 ms (23-27 ms); and V₆, 28 ms (25-30 ms). In the dolichomorphic group, RPT in V₁ was 15 ms (13-17 ms); V₂, 29 ms (26-32.5 ms); V₃, 30 ms (27-33.5 ms); V₄, 29.5 ms (26-35 ms); V₅, 30 ms (28-34 ms); and V₆, 31.5 ms (28-35 ms). RPT in V₁ was significantly shorter than RPT in V₂ to V₆ in all morphotypes (P < 0.05). In all precordial leads, RPT was significantly different between morphotypes (P < 0.05). These results are in agreement with previous findings in humans and with the observation that V₁ reads the right ventricle and V₂ to V₆ read the left ventricle. These preliminary data provide RPT ranges in clinically healthy dogs of different morphotypes.