Polymorphism, coupling interval and prematurity index in dogs with degenerative mitral valve disease and ventricular arrhythmias
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Ventricular arrhythmias (VA) are a recognized concern in dogs with degenerative mitral valve disease (DMVD). The coupling interval (CI) and the prematurity index (PI) have been shown to accurately differentiate between benign and malignant VA in people, where ventricular arrhythmias are known to be associated with an increased risk of development of signs of heart failure or sudden death. In this study, we characterized ventricular arrhythmias in dogs with symptomatic and asymptomatic DMVD. Seventy dogs with naturally-occurring DMVD and ventricular arrhythmias were retrospectively studied. A cross-sectional investigation including dogs with either symptomatic (stages C/D; n = 41) or asymptomatic (stages B1/B2; n = 29) DMVD was performed. Electrocardiographic tracings were reviewed to calculate both the CI and PI. In eight dogs these indices were compared with those obtained from both a Holter recording and a standard ECG tracing and no statistical differences were found (CI, p = 0.97; PI, p = 0.17). Even though CI and PI were determined in all animals enrolled in the study, VPC characteristics were only compared between symptomatic and asymptomatic dogs when a 24-h Holter recording was available (n = 49). The PI was different (p = 0.01) between symptomatic (0.65 ± 0.17) and asymptomatic (0.56 ± 0.18) dogs, but CI was considered similar (p = 0.91). Also, the symptomatic dogs had more polymorphic VPC (p = 0.002) and supraventricular arrhythmias (p = 0.0002) than the asymptomatic animals. Polymorphism, and repeating patterns of ventricular premature complexes, were characteristics frequently present in overtly symptomatic animals affected by mitral endocardiosis.