Relationship Between Selected Echocardiographic Variables Before and After Radioiodine Treatment in 91 Hyperthyroid Cats

Abstract

Ninety-one spontaneously hyperthyroid cats were studied by two-dimensional and M-mode echocardiography with in a week before and 2-3 months following oral radioiodine administration. A statistical search was made for a correlation between any of the linear echocardiographic variables (pre- or posttreatment) and the serum total thyroxine concentrations (pre- or posttreatment). No clinically useful relationships were found. Echocardiographic values were compared with a 95% confidence interval constructed from a previous multiinstitutional report on unsedated normal cats. Observed pretreatment abnormalities were primarily increases in interventricular septal and left ventricular wall thickness with reversion toward normal following treatment. The presence or absence of previous treatment with methimazole or concurrent treatment with cardiac-related drugs (beta-adrenergic blocker, calcium channel blocker, or angiotensin-converting enzyme inhibitor) had no statistically identifiable effect on the echocardiographic variables. About 37% of the cats had one or more echocardiographic variable(s) outside the calculated normal range before radioiodine treatment, but about 32% of the cats had one or more echocardiographic variable(s) outside that range after treatment (45% of these were normal before treatment). The conclusions are that pretreatment T-4 assessment was not useful in determining which cats may have potentially relevant echocardiographic abnormalities, that some echocardiographic abnormalities may emerge after treatment, and that less than 10% of the pre- or posttreatment abnormalities would be considered clinically relevant.

Avaliação ecocardiográfica de gatos com tirotoxicose induzida

“…Esses achados sugerem que a tirotoxicose instituída promoveu uma hipertrofia concêntrica do miocárdio ventricular secundário a um estado hipercinético do coração, fato também observado no hipertiroidismo endógeno em felinos (BOND et al, 1988;WEICHSELBAUM et al, 2005) e em humanos (GOKCE et al, 2003;SMIT et al, 2005;ARINC et al, 2006). SYME (2007) cita que, quando há uma marcante hipertrofia concêntrica, deve-se considerar a ocorrência conjunta de hipertiroidismo e cardiomiopatia hipertrófica idiopática.…”

“…O exato mecanismo para as anormalidades cardíacas não é claro, mas parece envolver a combinação da ação direta dos hormônios tiroidianos sobre o coração, as interações entre os hormônios tiroidianos e o sistema nervoso simpático e as mudanças cardíacas compensatórias à alteração da função de tecidos periféricos (MOONEY, 2005). Estudos realizados sobre os mecanismos fisiopatológicos dos hormônios tireoidianos no sistema cardiovascular de seres humanos e modelos animais indicam o desenvolvimento de efeitos cronotrópicos positivos, a diminuição da resistência vascular, o aumento da pressão arterial sistólica e o aumento do débito cardíaco (SYME, 2007) Estudos retrospectivos avaliando gatos com hipertiroidismo endógeno demonstram que as alterações ecocardiográficas mais frequentemente observadas são: hipertrofia da parede livre do ventrículo esquerdo, hipertrofia do septo interventricular, dilatação atrial e ventricular esquerdas e aumento da fração de encurtamento MOISE & DIETZE, 1986;BOND et al, 1988;FOX et al, 1999;WEICHSELBAUM et al, 2005). Entretanto, segundo SYME (2007), a maioria das mensurações ecocardiográficas pode apresentar-se dentro dos padrões de normalidade ao momento do diagnóstico, sendo incomum a ocorrência de insuficiência cardíaca congestiva em gatos hipertiroideos na ausência de alterações cardíacas pré-existentes.…”

Cardiac Manifestations of Systemic Diseases

“…In a study, only the left ventricular free wall thickness prior to treatment could be correlated to serum T4 concentration [38]. In 37% of cases, one or more parameters were abnormal before treatment [38]. In another study, pretreatment echocardiographic changes were minimal and most parameters remained within normal values (Figure 16-17).…”

“…Several studies have compared the echocardiographic parameters in hyperthyroid cats prior to and following radioiodine ( 131 I) treatment. In a study, only the left ventricular free wall thickness prior to treatment could be correlated to serum T4 concentration [38]. In 37% of cases, one or more parameters were abnormal before treatment [38].…”

“…The most frequent abnormalities-septal or free wall hypertrophy-tended to be reversible following treatment [38].…”