Hypothyroidism- A cause for dilated cardiomyopathy in dogs; four year study (2008-2011)

Aim: The study was carried out to understand the thyroid dysfunction and its association with dilated cardiomyopathy in dogs. 
 
Materials and Methods: The study was done at Teaching Veterinary Hospital, Bhoiguda, College of Veterinary Science, Hyderabad for four years, i.e., from 2008 to 2011. A total of 256 dogs of various breed, age and sex were presented with typical skin and coat abnormalities. Few were also exhibiting signs of low metabolic rate. Skin sample analysis was done to rule out the causes of dermatitis. Thyroid profile was estimated to diagnose hypothyroidism. Selected cases were also subjected for echocardiography to study the association of cardiomyopathy. Based on thyroid profile, hypothyroid dogs were treated with levothyroxine @20mcg/kg wt, once daily, orally on empty stomach and dilated cardiomyopathy (DCM) associated patients were additionally supplemented with enalapril @0.5 mg/kg, twice daily, orally for 6 months. The hemato biochemical and echocardiographic aspects are discussed. 
 
Results: The classical signs that were recorded in almost all the thyroid dysfunction dogs (231) were bilateral alopecia, rat tail and pigmentation and whereas, dyspnoea at rest, exercise intolerance, obesity, pale mucosae and corneal lipidosis were the significant low metabolic rate signs noticed in 42 dogs. However, syncope and seizures were also recorded in 31 of these hypothyroid dogs. Echocardiographic evaluation revealed significantly (P


Introduction
tissue, stimulate erythropoiesis and regulate both Hypothyroidism results in decreased production cholesterol synthesis and degradation.Thyroid of thyroid hormones, thyroxine (T ) and 3, 5, 3 triiododysfunction is characterised by slow, lazy behaviour, 4 bilateral alopecia, dry skin, obesity, lethargy and thyronine (T ) from the thyroid gland.Naturally 3 respiratory distress.Uncommonly, cardiovascular occurring hypothyroidism is a common disease in abnormalities are also associated with hypothyroidogs but rare in cats [1].Thyroid hormones have dism.Further, cardiac changes that develop in dogs positive inotropic and chronotropic effects on the heart with hypothyroidism are important because of the and have catabolic effects on muscle and adipose

To cite this article:
Karlapudi SK, Srikala D, Rao DST (2012) Hypothyroidism -A Cause for dilated cardiomyopathy in dogs; four year study (2008)(2009)(2010)(2011), Vet World, 5 (12): 742 -747, doi: 10.5455/vetworld.2012.742-747high incidence of hypothyroidism and heart disease in R13 cardiac probe placed on right precardium, with some breeds [2].Any alteration in cardiac function dogs positioned in right lateral recumbancy.Access to induced by hypothyroidism could result in worsening the right side of the thorax was facilitated by use of a of pre-existing disease [3].Interest in the role of table with a special cut-out to allow the transducer to thyroid hormones on cardiac failure has increased in be directed upward towards the site of maximal recent years.The driving considerations can be cardiac pulsation.Transducer is located parasternally summarized as follows: (a) the known effects of between right third and sixth intercostal spaces between thyroxine on contractile and relaxation properties of sternum and costochondral junction.M-mode recordings the heart; (b) experimental findings offering strong were taken at the high papillary level.However, support for the hypothesis that thyroid hormone echocardiogram measurements were also recorded in signaling is critical in preserving cardiac structure and apparently healthy dogs to establish normal values.performance under normal conditions and after cardiac Based on these findings 33 hypothyroid patients injury; and (c) evidence that thyroid dysfunction is diagnosed for associated dilated cardiomyopathy were strongly associated with a worsening prognosis in selected and were treated with levothyroxine @ 20 cardiac patients in general and in cardiac failure mcg/kg, once daily on empty stomach and enalapril @ patients in particular [4,5].Diastolic function and 0.5 mg/kg once daily for 6 months.However, levothyroxine systolic function are clearly influenced by various was also supplemented for the remaining hypothyroid thyroid hormones [6].Ventricular contractile function cases for 6 months.The blood and sera samples were is also influenced by changes in hemodynamic conditions collected as per the animal ethics and the therapy was secondary to thyroxine effects on peripheral vascular also carried out as per the ethical treatment protocol.tone [7].The homeostasis of these hormones preserves

Results
positive ventricular-arterial coupling, leading to a favorable balance for cardiac work.Other studies Almost all the hypothyroid dogs revealed similar suggest reduced cardiac tissue triiodothyronine levels clinical manifestations viz., bilateral symmetrical after myocardial infarction (MI) or with development alopecia, rat tail appearance, pigmentation, bald thigh, of hypertension by upregulating type 3 deiodinase weakness, cold intolerance and lethargy.Whereas, (D3), which leads to deactivation of triiodothyronine dyspnoea at rest, exercise intolerance, corneal lipidosis and thyroxine [8].
and cyanotic tongue were recorded in 41 cases and Keeping this hypothesis in view the present seizures and syncope among 31.The mean weight and study was carried out to evaluate the association of age was 45 kg and 8 yrs, respectively.Hematologically, cardiomyopathy with thyroid dysfunction in dogs.

Materials and Methods
alkaline phosphatase (ALP) with a significantly decreased A total of 256 dogs of various breed, age and sex (P<0.05)levels of tri-iodothyronine (T3), total thyroxine that were presented from 2008 to 2011 to the (tT4), free thyroxine (fT4) and increased thyroid Veterinary Hospital, Bhoiguda, College of Veterinary stimulating hormone (TSH) were recorded in 231/256 Science, Hyderabad, with the classical signs of skin dogs, along with a significantly increased (P<0.05) and coat and metabolic abnormalities were considered creatine kinase MB (CKMB) and lactate dehydrofor the study.Almost all of these dogs were treated for genase (LDH) in 33 hypothyroid dogs in comparison dermatitis by local Veterinarian, but the condition was with apparently healthy dogs (Table -1).These dogs reported to be recurring when therapy discontinued.with abnormal cardiac markers were suspected for The owners further reported that, there was no cardiomyopathy and subjected for further detailed improvement with respect to the signs associated with investigations.Low voltage QRS complexes and low metabolic rate in few of the cases.Thorough ventricular premature complexes were the significant clinical examination was followed by blood and serum electro cardiographic (ECG) findings and whereas, analysis.Further, the hypothyroid patients presenting cardiomegaly was the radiographic abnormality.Bsigns associated with reduced metabolic rate (cyanotic mode echocardiography revealed round greatly tongue, dyspnoea at rest, lethargy and exercise enlarged globose shaped heart (fig.1).A significantly intolerance) were suspected for cardiac involvement (P<0.01)increased left ventricle end diameter (LVED) and were subjected for electrocardiography, thoracic along with significantly (P<0.05)decreased intervenradiography and 2-d echocardiography.Echocardio-tricular septum (IVS) and left ventricle free wall gram was carried out using a microconvex array c5-2 (LVWP) dimensions both at diastole (d) and systole (s) and Ejection fraction (EF) and Fractional Shortening therapy (day 180).However, a non-significant increase (FS) were the significant m-mode echocardiographic in IVSd, IVSs, LVPWd and LVPWs were also measurements.Thus, confirming associated dilated recorded (fig.3&4; table.2).cardiomyopathy among 33 hypothyroid dogs of which

Discussion
German shepherd ( 14) followed by Labrador retriever (09) were commonly affected breeds (fig. 2 Hypothyroidism is the common endocrino-Improvement in skin and coat associated signs logical disease suspected mostly in canine suffering were noticed from day 7 followed by signs associated from non-pruritic alopecia, bald thigh syndrome, rat with low metabolic rate and complete clinical recovery tail appearance with brittle, dry and change in coat with alleviation of all the signs by the end of therapy.A colour and scaling of skin [2].In the present study non-significant improvement in haematological, common manifestations include abnormalities radiological and electrogardiographic findings were associated with skin and coat followed by those related noticed by day 180.Whereas, significant improvement to decreased metabolic rate.Dermatological changes in biochemical and thyroid profile was noticed from occur in 60 to 80 per cent of hypothyroid dogs [3].The day 90 and reached to near normal by the end of the degree of obesity is usually moderate, although therapy (Table -1).With respect to left ventricle obesity is the presenting complaint in dogs of dimensions on m-mode echocardiography, a non-decreased thyroid function [9].These abnormalities significant alteration was noticed on day 90, but a could be attributed to general metabolic derangements significant (P<0.05)improvement was recorded with that occur in impaired thyroid function or may be an respect to LVEdD, LVEsD and EF and FS by the end of indication of a neuropathy or myopathy [10]   signs associated with low metabolic rate viz., general prolonged.Many of these abnormalities reverse with weakness, exercise intolerance, lethargy and listless-thyroid hormone supplementation and there appears to ness observed in hypothyroidism might be attributed be a direct correlation between the electrocardioto poor conduction of electrical impulses in hypo-graphical changes and the severity of thyroid deficiency thyroid patients [11].Ocular changes are not common [17]. in hypothyroidism but the high levels of blood Significantly decreased left ventricle dimensions cholesterol and circulating fat can sometimes leads to and indices with poor left ventricle function was corneal dystrophy.This finding is usually represented noticed among the DCM affected hypothyroid dogs.A as a small white spot on the eye surface [12,13].Non-significant increase in LVEDd and LVEDs and regenerative anaemia, hypercholesterolemia and decrease in IVSd, IVSs, LVPWd, LVPWs and hypertriglyceridemia, with mild increase in alkaline fractional shortening and ejection fraction were phosphatase, alanine amino transferase and creatine recorded in clinically affected hypothyroid human kinase activities were the common hemato-biochemical beings and dogs [3,18].Whereas, decreased left alterations noticed in the present study were in ventricle end diameter during diastole, left ventricle agreement with the previous authors [14,15].
posterior wall during diastole and systole and The significant ECG findings among hypo-fractional shortening as compared with baseline thyroid patients include bradycardia, low voltage QRS values were noticed in experimentally induced complexes and ventricular premature complexes [16].hypothyroid dogs [19].

Experimental studies of hypothyroid dogs have
The difference in these dimensions between confirmed that atrioventricular conduction time, experimentally induced and clinically affected hypofunctional refractory period of the atrioventricular thyroid dogs could be due to a difference in the severity node and duration of ventricular action potential are or duration of hypothyroidism in the experimental and   clinically affected dogs.In the present investigation arterial hypertension in a hypothyroid individual the DCM dogs were reported to be showing clinical could compound the effects of hypothyroidism and signs suggestive of hypothyroidism for a long period result in heart failure.Indeed, some hypothyroid before diagnosis.people manifest signs of congestive heart failure even Infiltration of the myocardium with mucopolyin the absence of other underlying cardiac disease sacharides or impaired coronary arterial vasodilatory [23].ability, possibly secondary to increased alpha-Conclusions adrenergic activity or atherosclerosis, might account for prolonged impairment of cardiac function [11].In From the present findings, it may be concluded addition alterations in peripheral circulation may that thyroid dysfunction not only presents the signs of return to normal slowly.Some markers of hypothyroidism skin and coat abnormalities, but also exhibits the signs at tissue level change slowly following levothyroxine associated with low metabolic rate.A thorough supplementation and normalisation of many clinical clinical evaluation and clinical chemistry is required to abnormalities often requires months of thyroid suspect the involvement of cardiovascular system.hormone supplementation [20].Because a complete However, 2-d chocardiography is highly specific and sensitive diagnostic aid to ascertain the involvement of turnover of protein occurs in the heart approximately cardiovascular system and to assess the therapeutic every three weeks [21], the 6 months period of response.Once diagnosed, supplementation of ACE levothyroxine administration in the present study inhibitors along with the specific thyroid supplements seems adequate to allow resolution of most of the helps to resolve the disorder.cardiac changes.
Following therapy with angiotensin converting Author's contribution enzyme inhibitors (ACEi) and levothyroxine, SKK and DS carried out the study under the guidance improvement in clinical signs were recorded.
of DSTR.All authors read and approved the final Although non-significant, but improvement in P and R manuscript.wave amplitudes with normal heart rate was also noticed.With respect to echocardiographic

Table . 1
Serum profile hypothyroid associated Cardiomyopathy dogs

Table . 2
. Left Ventricle dimensions and Indices of DCM dogs