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 tw o populations of cats diagnosed at The Animal Medical Center from 1992 to 1 993 (n=202) and 1979 to 1982 (n=131). The prevalence of sinus tachycardia a nd increased R-wave voltage in lead II were both lower in the 1993 populati on compared with the 1982 population (p less than 0.001), A low frequency o f atrial and ventricular arrhythmias and intraventricular conduction abnorm alities were recorded in both populations, No significant differences betwe en populations were recorded in the number of cats with mild, moderate, and severe cardiomegaly seen on thoracic radiographs, The percentage of cats i n 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 conge stive 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 redu ced in cats diagnosed between 1992 and 1993 compared with those diagnosed b etween 1979 and 1982.