HEART-RATE-VARIABILITY IN RELATION TO SEVERITY OF MITRAL REGURGITATION IN CAVALIER-KING-CHARLES SPANIELS

Heart rate variability was measured in 81 Cavalier King Charles spanie ls to investigate if it could be used to evaluate the severity of mitr al regurgitation and to predict decompensation. Heart rate variability was assessed by the natural logarithm of the variance of the R-R inte rvals for 20 consecutive beats obtained from electrocardiographic reco rdings. Twenty-two of the dogs were clinically normal and 59 had mitra l regurgitation caused by chronic valvular disease. The severity df mi tral regurgitation was evaluated by echocardiography and thoracic radi ography. Heart rate variability was found to be reduced (P < 0.001) am ong dogs with severe left atrial and ventricular dilatation and clinic al signs of congestion. No significant differences in heart rate varia bility were found among normal dogs, dogs with only cardiac murmur, an d dogs with echocardiographic evidence of slight to moderate left atri al and ventricular dilatation. Overall, an association was found betwe en heart rate variability and left atrial to aortic root ratio and lef t ventricular end diastolic diameters (r = 0.72 and 0.64, respectively , P < 0.001), as well as heart and respiratory rate (r = 0.80 and 0.69 , respectively, P < 0.001). Multiregression analysis showed that, in o rder of importance, heart rate, left atrial diameter and respiratory r ate had significant effects on heart rate variability. Among these par ameters, heart rate variability and left atrial diameter were found to be most efficient in separating decompensated dogs from compensated. It is concluded that heart rate variability may provide the clinician with valuable information when assessing the severity of mitral regurg itation caused by chronic valvular disease.