Hypertropic cardiomyopathy and hyperthyroidism in the cat

In a 21/2-year period, hypertrophic cardiomyopathy was found at necropsy of 23 cats that died (13 cats) or were euthanatized (10) because of problems associated with hyperthyroidism. Of these, 4 (17%) also had evidence of cardiac failure (pulmonary edema or pleural effusion). The mean body weight of the cats with hyperthyroidism and hypertrophic cardiomyopathy was significantly less (P less than 0.001) than that of clinically normal cats and cats with primary cardiomyopathy (congestive or restrictive) or excessive moderator band cardiomyopathy. In addition, the ratio of heart weight to body weight was significantly greater (P less than 0.001) in the 23 hyperthyroid cats than in the normal cats and cats with primary cardiomyopathy. Twenty (87%) of the cats had symmetric hypertrophy of the ventricular septum and left ventricular free wall, whereas the remaining 3 cats had disproportionate thickening of the ventricular septum, compared with the free wall, similar to what is found in cats with asymmetric hypertrophic cardiomyopathy. Histologic cardiac abnormalities included large, hyperchromatic nuclei, interstitial fibrosis, endocardial fibroplasia, fibrosis of the atrioventricular node, and marked disorganization of cardiac muscle cells. The study showed that hypertrophic cardiomyopathy develops in most hyperthyroid cats, some of which also develop congestive heart failure. Although the signs of heart disease in primary myocardial disease and thyrotoxic disease are similar, the characteristic signalment and clinical signs of hyperthyroidism should lead one to suspect the association of hypertrophic cardiomyopathy with the hyperthyroidism.     

Benazepril and subclinical feline hypertrophic cardiomyopathy: a prospective, blinded, controlled study

Twenty-one cats with hypertrophic cardiomyopathy were enrolled in this study to determine if the administration of benazepril (0.5 mg/kg body weight [BW], PO, q24h) to cats with subclinical hypertrophic cardiomyopathy improves cardiac diastolic function and reverses left ventricular hypertrophy when compared with diltiazem controlled delivery (CD) (10 mg/kg BW, PO, q24h). Cats were evaluated at day 0 and after 3 and 6 months of therapy. In the benazepril group (n = 11), the diastolic transmitral flow of the E and A waves ratio (E/A ratio) increased significantly between 0 and 6 months (P = 0.009) and the thickness of the left ventricular free wall in systole (LVFWs) decreased significantly between 0 and 3 months (P = 0.04). In the diltiazem CD group (n = 5), none of the parameters varied significantly throughout the study. There was no difference between the benazepril and the diltiazem CD group throughout the study. Therefore, the variations observed for the E/A ratio and the LVFWs may have been incidental. Further studies will be needed to establish the role of benazepril in subclinical hypertrophic cardiomyopathy in cat.     

M-MODE ECHOCARDIOGRAPHY AS A DIAGNOSTIC AID FOR FELINE CARDIOMYOPATHY

Normal cats and cats with congestive cardiomyopathy (CCM) and hypertrophic cardiomyopathy (HCM) were examined using M-mode echocardiography to determine its diagnostic capabilities. Sixteen normal cats were examined to verify previously reported data and to add further echocardiographic inforamtion (left atrial/aortic root ratio, left posterior wall thickness at end systole and end diastole, amplitude of mitral valve excursions, and velocity of valve opening and closure) to aid in differential diagnosis. Significant (p<0.05) changes were detected between the normal cats and those with cardiomyopathy. In each type of cardiomyopathy, alterations in left atrial dimension, left atrial/aortic root ratio, left ventricular dimension, left ventricular wall thickness and percentage of ventricular dimensional change were identified. Altered mitral valve motion was found with HCM. Echocardiography was found to be an accurate technique for definitive diagnosis of feline cardiomyopathy.     

Evidence for or against the efficacy of calcium channel blockers for management of hypertrophic cardiomyopathy in cats.

The positive lusitropic and direct coronary vasodilating properties of the calcium channel blocking agents are beneficial therapeutic effects not provided by the beta-adrenergic blocking agents for the management of feline HCM. Data from cats studied at the University of Tennessee suggest that diltiazem more consistently alleviates clinical signs and more effectively prolongs survival in cats with HCM than either propranolol or verapamil. Orally administered diltiazem appears to have sustained beneficial effects on left ventricular filling and cardiac performance based on its ability to reduce resting heart rate, decrease blood lactate concentration, increase venous oxygen tension, improve echocardiographic parameters, and resolve radiographic abnormalities. Long-term diltiazem administration may also reverse myocardial hypertrophy in some patients. There appear to be few if any side effects of this drug. Diltiazem, therefore, provides a safe and effective approach for the management of feline HCM.     

Echocardiography, electrocardiography, and radiography of cats with dilatation cardiomyopathy, hypertrophic cardiomyopathy, and hyperthyroidism

The echocardiographic, ECG, and radiographic findings of sequentially examined cats with dilatation cardiomyopathy (DCM, n = 7), hypertrophic cardiomyopathy (HCM, n = 8), and hyperthyroidism (HT, n = 20) were compared with those of healthy control cats (n = 11). Cats with DCM were easily differentiated from healthy cats by echocardiography and from cats with HCM and HT by a dilated left ventricle at end-diastole with a mean +/- SD of 2.20 +/- 0.36 cm, reduced fractional shortening (2.9% +/- 3.7%), reduced aortic amplitude (0.07 +/- 0.05 cm), reduced left ventricular wall amplitude (0.09 +/- 0.09 cm), and increased E-point septal separation (0.83 +/- 0.29 cm). The cats with HCM were most consistently recognized echocardiographically by increased left ventricular wall thickness at end-diastole (0.75 +/- 0.12 cm). Some cats with HT had abnormal echocardiograms with left ventricular wall hypertrophy. These cats could usually be differentiated from the cats with HCM because of normal or increased ventricular wall amplitude, aortic amplitude, or percentage of thickening of the left ventricular wall and interventricular septum. Left atrial enlargement (left atrial diameter greater than 1.57 cm or left atrium/aorta greater than 1.75) was commonly detected by the echocardiogram in cats with DCM, HCM, or HT. The echocardiogram was helpful in differentiating the type of cardiomyopathy (DCM, HCM, or HT) when plain thoracic radiographs indicated that cardiomegaly existed. The ECG may have indicated incorrectly that there was left ventricular enlargement in some cats with HT, and it did not indicate consistently that left ventricular enlargement existed when present in cats with DCM or HCM. The ECG was a poor indicator of left atrial enlargement in all cats.     

Echocardiographic findings in 103 cats with hyperthyroidism

Using M-mode echocardiography, cardiac abnormalities were studied in 103 cats with untreated hyperthyroidism. In addition, follow-up echocardiography was performed on 24 of these cats to assess the long-term (4 to 21 months) effect of treatment (thyroidectomy or radioiodine) on thyrotoxic cardiac disease. The most common echocardiographic abnormality in the 103 untreated hyperthyroid cats was hypertrophy of the left ventricular caudal wall (71.9%). Hypertrophy of the interventricular septum also was documented in 39.8% of the 103 cats. Other abnormalities included high values for left atrial diameter (70.0%), aortic root diameter (18.5%), and left ventricular diameter at end diastole (45.6%). In some of these cats, indices of contractility were enhanced; in 21.4% and 14.6% of the cats, values for shortening fraction and velocity of circumferential fiber shortening, respectively, were greater than those values measured in clinically normal cats. After treatment of the hyperthyroidism, left ventricular hypertrophy resolved or improved in many of the cats, as indicated by decreases in left ventricular caudal wall and interventricular septum thicknesses. Hyperdynamic wall motion resolved in all cats after treatment, as evidenced by consistent decreases in shortening fraction and velocity of circumferential fiber shortening. Despite these improvements, some cats had one or more persistently abnormal echocardiographic values after treatment. These results suggested that in cats, hyperthyroidism commonly is associated with largely reversible cardiomyopathy. In those cats in which cardiomyopathy persists or worsens after treatment, underlying primary cardiomyopathy or thyroid hormone-induced cardiac structural damage may exist.     

Colour M-mode tissue Doppler imaging in healthy cats and cats with hypertrophic cardiomyopathy

OBJECTIVES: To determine whether decreased diastolic and systolic myocardial velocity gradient between the endocardium and the epicardium exist in the left ventricle of cats with hypertrophic cardiomyopathy. METHODS: Myocardial velocity gradient and mean myocardial velocities were measured by colour M-mode tissue Doppler imaging in the left ventricular free wall of 20 normal cats and 17 cats with hypertrophic cardiomyopathy. RESULTS: The peak myocardial velocity gradient (sec(-1)) during the first (E1) (5.71+/-1.75 versus 11.38+/-3.1, P<0.001) and second phase (E2) (3.09+/-1.53 versus 7.02+/-3.1, P=0.005) of early diastole and also the maximum early diastolic myocardial velocity gradient (Emax) (6.12+/-2.1 versus 10.76+/-3.2, P<0.001) were reduced in cats with hypertrophic cardiomyopathy compared with normal cats. Peak myocardial velocity gradient during early systole (Se) was lower in affected cats than in normal cats (6.26+/-2.08 versus 8.67+/-2.83, P=0.006). Affected cats had a lower peak mean myocardial velocities (mm/s) during the two isovolumic periods (IVRb and IVCb) compared with normal cats (2.97+/-6.76 versus 12.74+/-5.5 and 22.28+/-9.96 versus 38.65+/-10.1, P<0.001, respectively). CLINICAL SIGNIFICANCE: This study shows that hypertrophic cardiomyopathy cats have decreased myocardial velocity gradient during both diastole and systole and also altered myocardial motion during the two isovolumic periods. Myocardial velocity gradients recorded by colour M-mode tissue Doppler imaging can discriminate between the healthy and diseased myocardium.     

Myocardial taurine concentrations in cats with cardiac disease and in healthy cats fed taurine-modified diets.

Myocardial taurine concentrations were measured in cats with cardiac disease and in healthy cats fed diets with various concentrations of taurine. Group 1 was composed of 26 cats with 3 categories of naturally developing cardiac disease: dilatative cardiomyopathy (group 1A), 10 cats; hypertrophic cardiomyopathy (group 1B), 9 cats; and volume overload (group 1C), 7 cats. These cats had been fed various commercial diets. Group 2 was composed of 40 healthy cats that had been fed diets varying in taurine concentration (0 to 1% taurine) for at least 2 years. Mean myocardial taurine concentrations did not differ significantly between group-1 cats with dilatative cardiomyopathy and those with hypertrophic cardiomyopathy or volume overload. Cats in group 1A had a mean myocardial taurine concentration 3 times higher than healthy cats fed a taurine-free diet (P less than 0.002). Mean myocardial taurine concentrations did not differ significantly between group-1A cats and healthy cats fed a diet containing 0.02% taurine; group-1A cats had significantly lower mean myocardial taurine concentrations than did healthy cats fed a synthetic diet containing 0.05 or 1.0% taurine (P less than 0.001). Acute oral administration of taurine in 5 group-1A cats appeared to increase mean myocardial taurine concentrations, compared with similar cats not given taurine during treatment for cardiac failure. In group-2 cats, mean myocardial taurine concentrations increased directly with percentage of dietary taurine.     

M-mode echocardiographic measurements in nonanesthetized healthy cats: effects of body weight, heart rate, and other variables

Body weight, heart rate, and 19 M-mode echocardiographic variables were measured in 41 nonanesthetized healthy cats. Estimated limits were determined for the echocardiographic variables, and each variable was then correlated to body weight, heart rate, and the 18 other variables. A significant (P less than 0.05) positive correlation to body weight was found with aortic diameter, left atrial dimension, septal and left ventricular systolic and left ventricular diastolic wall thicknesses, and left and right ventricular diastolic and right ventricular systolic internal dimensions. Significant inverse correlation (P less than 0.05) to heart rate was found with body weight, left ventricular systolic and diastolic and right ventricular systolic internal dimensions, left atrial dimension, left atrial dimension to aortic ratio, mitral valve E point to ventricular septal separation, and left ventricular ejection time. Left ventricular shortening fraction in the short axis and velocity of circumferential fiber shortening were significantly correlated (P less than 0.05) to heart rate. Significant correlation (P less than 0.05) was also found between many echocardiographic variables.     

Use of relaxation half-time as an index of ventricular relaxation in clinically normal cats and cats with hypertrophic cardiomyopathy

Relaxation half-time (t1/2) was evaluated as a measure of isovolumic ventricular relaxation in clinically normal cats and cats with hypertrophic cardiomyopathy. Relaxation half-time was determined directly from the left ventricular pressure tracing as the time required for the left ventricular pressure at the beginning of isovolumic relaxation to decrease by half. The value of t1/2 was unaffected by moderate changes in heart rate, inotropic state, and afterload in clinically normal cats. However, t1/2 increased significantly (P = 0.003) with increased preload. The value of t1/2 was significantly higher (P = 0.0003) in a group of cats with hypertrophic cardiomyopathy, compared with that of a group of clinically normal cats. Although t1/2 must be interpreted in the context of changes in loading conditions, the index is useful as a measure of relaxation in clinically normal cats and cats with hypertrophic cardiomyopathy.     

Assessment of left atrial appendage flow velocity and its relation to spontaneous echocardiographic contrast in 89 cats with myocardial disease

The hypotheses of this prospective study were that (1) left atrial appendage (LAA) blood flow velocities can be recorded in cats with myocardial disease by transthoracic Doppler echocardiography, (2) LA enlargement, LA mechanical dysfunction, and left ventricular (LV) diastolic abnormalities are associated with decreased LAA flow velocities, and (3) low LAA flow velocities predict the appearance of spontaneous echocardiographic contrast in cats with cardiomyopathy. Transthoracic 2-dimensional, M-mode, and Doppler echocardiographic studies were performed in 89 cats with hypertrophic, restrictive, dilated, or unclassified cardiomyopathy or with hyperthyroid heart disease. Maximal LAA flow velocity (LAAmax) was decreased (P < .001) in cats with cardiomyopathy (median, 0.28 m/s; range, 0.08-1.35) compared to normal cats. Associated with decreased LAA flow velocities were increased LA size, decreased LA function, increased severity of LV diastolic dysfunction, and the presence of congestive heart failure. Multivariate logistic regression analysis detected an LAAmax <0.20 m/s as the only independent variable to predict LA spontaneous echocardiographic contrast (odds ratio, 30.1; 95% confidence interval [CI], 4.1 222.3; P < .001). Receiver operating characteristic analysis performed to predict spontaneous echocardiographic contrast indicated an area under the curve of 0.88 (95% CI, 0.80-0.95; P < .001) with sensitivities of 100 and 74% and specificities of 69 and 83% for LAAmax <0.25 and <0.20 m/s, respectively. Thus, low LAA flow velocities identified a subgroup of patients at increased risk of spontaneous echocardiographic contrast and possible thromboembolism. These findings may have important clinical implications for anticoagulation therapy and prognostication in cats with cardiomyopathy.     

Excessive moderator bands in the left ventricle of 21 cats

Excessive numbers of moderator bands bridging the left ventricular septum and free wall and entangling papillary muscles were associated with heart failure and death in 21 cats. Clinical findings included dyspnea, anorexia, hypothermia, cardiomegaly, pleural effusion, plumonary edema, heart murmurs, gallop rhythm, electrocardiographic abnormalities (especially conduction disturbances), increased left ventricular end-diastolic pressure, angiocardiographic evidence of left ventricular restriction, and aortic thromboembolism. Pathologic changes included a morphologically distinct network of abnormal numbers of moderator bands in the left ventricle, left ventricular hypertrophy (younger cats--mean age, 4 years) or dilatation (older cats--mean age, 8.7 years), left atrial enlargement and hypertrophy, and pulmonary edema with heart failure cells in the alveoli. Heart weights of affected cats were significantly less than those of cats with congestive, hypertrophic, and restrictive cardiomyopathy (endocardial fibrosis), but were not significantly less than heart weights of clinically normal cats. Pathologic changes were characteristic of the syndrome grossly and histologically, but clinical findings were not clearly definable.     

Prevalence of myocardial hypertrophy in a population of asymptomatic Swedish Maine coon cats

Background

Maine coon cats have a familial disposition for developing hypertrophic cardiomyopathy (HCM) with evidence of an autosomal dominant mode of inheritance [1]. The current mode to diagnose HCM is by use of echocardiography. However, definite reference criteria have not been established. The objective of the study was to determine the prevalence of echocardigraphic changes consistent with hypertrophic cardiomyopathy in Swedish Maine coon cats, and to compare echocardiographic measurements with previously published reference values.

Methods

All cats over the age of 8 months owned by breeders living in Stockholm, listed on the website of the Maine Coon breeders in Sweden by February 2001, were invited to participate in the study. Physical examination and M-mode and 2D echocardiographic examinations were performed in all cats.

Results

Examinations of 42 asymptomatic Maine coon cats (10 males and 32 females) were performed. The age of the cats ranged from 0,7 to 9,3 years with a mean of 4,8 ± 2,3 years. Four cats (9,5%) had a diastolic interventricular septal (IVSd) or left ventricular free wall (LVPWd) thickness exceeding 6,0 mm. In 3 of these cats the hypertrophy was segmental. Two cats (4,8%) had systolic anterior motion (SAM) of the mitral valve without concomitant hypertrophy. Five cats (11,9%) had IVSd or LVPWd exceeding 5,0 mm but less than 6,0 mm.

Conclusion

Depending on the reference values used, the prevalence of HCM in this study varied from 9,5% to 26,2%. Our study suggests that the left ventricular wall thickness of a normal cat is 5,0 mm or less, rather than 6,0 mm, previously used by most cardiologists. Appropriate echocardiographic reference values for Maine coon cats, and diagnostic criteria for HCM need to be further investigated.     

Quantification of left ventricular diastolic wall motion by Doppler tissue imaging in healthy cats and cats with cardiomyopathy

OBJECTIVE: To assess Doppler tissue imaging (DTI) for evaluating left ventricular diastolic wall motion in healthy cats and cats with cardiomyopathy. ANIMALS: 20 healthy cats, 9 cats with hypertrophic cardiomyopathy (HCM), and 9 cats with unclassified cardiomyopathy (UCM). PROCEDURE: A pulsed wave DTI sample gate was positioned at a subendocardial region of the left ventricular free wall in the short axis view and at the lateral mitral annulus in the apical 4-chamber view. Indices of diastolic wall motion were measured, including peak diastolic velocity (PDV), mean rate of acceleration and deceleration of the maximal diastolic waveform (MDWaccel and MDWdecel, respectively), and isovolumetric relaxation time (IVRT). RESULTS: The PDV of cats with HCM and 6 of 9 cats with UCM was significantly decreased, compared with that of healthy cats. In the 3 cats with UCM that had a PDV that was not different from healthy cats, MDWaccel and MDWdecel were greater, and IVRT was shorter than those of healthy cats. The IVRT in cats with HCM was longer than that of other cats. CONCLUSIONS AND CLINICAL RELEVANCE: Indices of diastolic function in cats with HCM, and in many cats with UCM, differed from those of healthy cats and were similar to those reported in humans with HCM and restrictive cardiomyopathy, respectively. However, the hemodynamic abnormality was not the same for all cats with UCM; some cats with an enlarged left atrium and a normal left ventricle (ie, UCM) had abnormal left ventricular wall motion consistent with restrictive cardiomyopathy while others did not.     

Papillary muscle measurements in cats with normal echocardiograms and cats with concentric left ventricular hypertrophy

BACKGROUND: Papillary muscle hypertrophy can occur in conjunction with, or as the only indication of, hypertrophic cardiomyopathy or other diseases that result in left ventricular concentric hypertrophy (LVCH). Assessment of papillary muscle size is usually subjective because objective measures have not been reported. HYPOTHESIS: The study hypothesis was that papillary muscle dimensions are different between normal cats and cats with LVCH. ANIMALS: Echocardiograms from 44 normal cats and 40 cats with LVCH were included in the study. METHODS: All measurements were taken from the right parasternal short-axis view at the level of the papillary muscles at end-diastole. Three methods were used to assess papillary muscle size: the area subtraction method, the direct area trace method, and the diameter method. Measurements were compared between cat groups and method comparisons were made among methods for area determination. RESULTS: Cats with LVCH were older and had significantly greater left ventricular septal and free wall thicknesses and larger left atrial measurements than normal cats (P < .0006). Papillary muscle measurements were significantly greater by all measurement methods in cats with LVCH than in cats with normal echocardiograms (P < .0001). The area subtraction method and direct area trace method showed moderate agreement. CONCLUSIONS AND CLINICAL IMPORTANCE: Papillary muscle measurements were larger for LVCH cats than normal cats; however, some overlap was present. The establishment of these objective measures adds to the echocardiographic examination of cats.     

The effect of hydration status on the echocardiographic measurements of normal cats

BACKGROUND: Diagnosis of cardiomyopathy of cats is based on 2-dimensional (2D) echocardiography. However, circulating fluid volume largely determines diastolic cardiac chamber dimensions, and reduced diastolic volume in other species results in what has been called "pseudohypertrophy of the ventricular myocardium." HYPOTHESIS: Altered hydration produces changes on 2D echocardiography that may confound the diagnosis or severity assessment of cardiomyopathy of cats. ANIMALS: Ten normal colony-sourced mixed breed cats were included. METHODS: Cats were examined by echocardiography at baseline and at completion of 3 protocols (volume depletion and maintenance-rate and anesthetic-rate IV fluid administration) applied in randomized crossover design with a 6-7 day washout period. RESULTS: Volume depletion increased diastolic left ventricular interventricular septal (IVSd) and free wall diameter (4.5 +/- 0.4 to 5.8 +/- 0.6 mm; P < .001) with wall thickness exceeding 6 mm in 4 cats. Diastolic left ventricular internal diameter (LVIDd) decreased, and reduction in systolic left ventricular internal diameter (LVIDs) produced end-systolic cavity obliteration in 7 cats. Left-atrial-to-aortic-root ratio (LA: Ao, 1.4 +/- 0.2 to 1.2 +/- 0.1, P < .05) and left atrial area in diastole (LAAd) decreased with volume depletion. Maintenance-rate IV fluid administration increased LAAd and fractional shortening (FS%). Anesthetic-rate IV fluid administration increased LVIDd, FS%, LAAd, and LA:Ao ratios (to 1.7 +/- 0.1, P < .01), producing an LA: Ao ratio above normal limits in 6 cats. A systolic heart murmur developed with administration of fluid at maintenance (n = 1) and anesthetic rates (n = 6). CONCLUSIONS: Altered hydration status produces changes in the echocardiographic examination of normal cats that may lead to an erroneous diagnosis of cardiomyopathy or mask its presence. Hydration status should be considered during echocardiographic examination in cats.     

Change in M-mode echocardiographic values in cats given ketamine

Determination was made of changes in heart rate and certain M-mode echocardiographic values in healthy cats given ketamine (3 to 5 mg/kg, IM). Heart rate and septal and left ventricular posterior wall thickness in diastole increased, and left ventricular internal diameter in diastole and shortening fraction decreased (P less than 0.02) after ketamine was given. With the adjustment for heart rate by analysis of covariance, left ventricular internal diameter in diastole, shortening fraction, and velocity of circumferential fiber shortening were significantly decreased (P less than 0.05) from base-line values.     

猫肥厚型心肌病与心肌纤维化

肥厚型心肌病是猫最常见的原发性心脏疾病,典型特征为心脏左心室肥厚。心肌纤维化是猫肥厚型心肌病的标志性病理变化,其可导致心脏功能障碍和节律异常,是心肌病患猫预后不良的重要因素。对于猫肥厚型心肌病与心肌纤维化,目前缺乏针对性治疗,新型治疗方法亟需开发。本综述总结了猫肥厚型心肌病的病理特征以及目前关于猫心肌纤维化发病机制的研究进展,拟通过探索心肌纤维化的发病机制,从而为猫肥厚型心肌病新型治疗药物的开发寻找突破点。     

Preferences of veterinarians for drugs to treat heart disease in dogs and cats

SUMMARY Responses (473) were collated from a questionnaire sent to 5054 veterinarians in Australia enquiring about drug preferences for treating cardiac disease in dogs and cats. When treating a small breed dog with endocardiosis and mild left congestive heart failure, 74% of 472 respondents used a diuretic, 67% a theophylline derivative, 27% a vasodilator and 20% a positive inotrope. Frusemide was the preferred diuretic and digoxin the preferred inotrope, but vasodilator use varied. Low sodium diets were “often recommended” by 71% of respondents. Propranolol was preferred to diltiazem for treating feline hypertrophic cardiomyopathy. Digoxin was clearly preferred for treating supraventricular dysrhythmias, while lignocaine and digoxin were preferred equally for ventricular dysrhythmias. Respondents appeared more willing than US veterinarians to use theophylline derivatives and prasozin, and less inclined to employ nitrates, hydralazine, inotropes other than digoxin, and low sodium diets.     

Efficacy of digoxin for treatment of cats with dilated cardiomyopathy

The role of digoxin in treatment of cats with dilated cardiomyopathy and other forms of myocardial failure is unclear. We evaluated the chronotropic and inotropic effects of digoxin by comparing baseline, noninvasive indices of cardiac performance with those obtained after 9 +/- 1.3 (mean +/- SEM) days of digoxin treatment in 6 cats with heart failure attributable to dilated cardiomyopathy. Two-dimensionally directed, M-mode echocardiography and electrocardiography were used to determine left ventricular shortening fraction, preejection period (PEP), ejection time (LVET), PEP to LVET ratio, velocity of circumferential fiber shortening, electromechanical systole, heart rate, and PR interval. Treatment consisted of administration of furosemide (mean dosage, 2.4 mg/kg of body weight/day), digoxin in tablet form (approximately 0.01 mg/kg, q 48 h), aspirin (80 mg, q 48 h), and a commercial low-salt diet. In addition, 2 cats were administered short-term, low-dose fluids IV, and 2 were given taurine supplementation at rates of 500 and 1,000 mg/day. Other off-loading or inotropic agents were not administered. Therapeutic or toxic serum digoxin concentration was achieved in all cats. Significant (P less than 0.05) improvement was detected in mean values for shortening fraction, PEP, PEP to LVET ratio, and velocity of circumferential fiber shortening. Mean electromechanical systole and LVET did not change significantly. Improvement, as assessed by indices of cardiac function, was documented in 4 of the 6 cats treated with digoxin, including the 2 cats given taurine supplementation. In the cats given taurine, positive inotropic effect was observed prior to the time when taurine-induced improvement in ventricular function is detectable.(ABSTRACT TRUNCATED AT 250 WORDS)