Quantification of respiratory sinus arrhythmia in control dogs and in dogs with various severity classes of myxomatous mitral valve disease

Introduction: Loss of respiratory sinus arrhythmia (RSA) is a negative prognostic factor in dogs with myxomatous mitral valve disease (MMVD). The aim of this study was to calculate the percentage (%) of RSA in healthy dogs and dogs in various MMVD classes. Animals: Control and MMVD dogs were prospectively included in the study. Materials and methods: Respiratory sinus arrhythmia was calculated from a dual channel electrocardiography and breathing curve recording using the peak-to-trough method, in percent of the average heart rate. Results: One hundred and forty-nine dogs were studied, including 24 control and 125 MMVD dogs of different severity classes. An overall %RSA decrease was documented with increasing disease severity up to the Ca class along with a relative %RSA increase in the Cc class. The %RSA magnitude differed between B2 and Ca (P<0.001), and between Ca and Cc (P = 0.001) groups, respectively. The %RSA showed a medium negative correlation with the La:Ao ratio (r2 = -0.568, P<0.001) and with the E-wave velocity (r2 = -0.561, P<0.001). Discussions: A decrease in %RSA was shown with increased disease severity up to acute congestive heart failure (CHF). Dogs receiving cardiac therapy leading to stabilized CHF might restore their ability to exhibit RSA, often revealing a higher %RSA compared to those in acute CHF. Study limitations: Low number of respiratory cycles for analysis. Therapy effect not evaluated. Conclusions:<bold> </bold>The findings of this study can serve as the basis for future risk stratification and carry the potential of proving an additional clinical marker for diagnostic and therapeutic decisions making when managing MMVD dogs.