Electrocardiographic and radiographic changes in cats with hyperthyroidism: comparison of populations evaluated during 1992-1993 vs. 1979-1982.

Cardiovascular manifestations of feline hyperthyroidism were compared in two populations of cats diagnosed at The Animal Medical Center from 1992 to 1993 (n=202) and 1979 to 1982 (n = 131). The prevalence of sinus tachycardia and increased R-wave voltage in lead II were both lower in the 1993 population compared with the 1982 population (p less than 0.001). A low frequency of atrial and ventricular arrhythmias and intraventricular conduction abnormalities were recorded in both populations. No significant differences between populations were recorded in the number of cats with mild, moderate, and severe cardiomegaly seen on thoracic radiographs. The percentage of cats in which radiographs were deemed clinically necessary based upon history and clinical examination was 25% of the 1993 population, compared with 63% of the 1982 population. The number of cats with radiographic evidence of congestive heart failure was 8% in 1993 compared with 20% in 1982, although this difference was not statistically significant. In conclusion, the incidence and severity of certain thyrotoxic cardiovascular manifestations were reduced in cats diagnosed between 1992 and 1993 compared with those diagnosed between 1979 and 1982.