Student Paper  Communication étudiante End-stage hypertrophic cardiomyopathy in a cat Andrew J.M. White Abstract — A 14-year-old Persian cat was referred for evaluation of the progression of hypertrophic cardiomyopathy (HCM) after an acute episode of congestive heart failure. The diagnosis of HCM had been made almost 13 years ago. Echocardiography and electrocardiography revealed end-stage hypertrophic cardiomyopathy and multifocal atrial tachycardia. The patient was discharged on medical management with a grave prognosis. Résumé — Cardiomyopathie hypertrophique de stade final chez un chat. Un chat Persan âgé de 14 ans a été recommandé pour l’évaluation de la progression d’une cardiomyopathie hypertrophique (CMH) après un épisode aigu d’insuffisance cardiaque congestive. Le diagnostic de CMH avait été posé il y a près de 13 ans. L’échocardiographie et l’électrocardiographie ont révélé une cardiomyopathie hypertrophique de stade final et une tachycardie atriale multifocale. Le patient a obtenu son congé avec une gestion médicale et un pronostic grave. (Traduit par Isabelle Vallières) Can Vet J 2015;56:509–511

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14-year-old, castrated male Persian cat with a history of hypertrophic cardiomyopathy (HCM) was presented to the referring veterinarian during an acute episode of left-sided congestive heart failure (CHF). The veterinarian confirmed the presence of pulmonary edema and pleural effusion on threeview thoracic radiographs. Oxygen therapy and furosemide were administered during acute treatment and the patient was prescribed furosemide and benazepril for chronic management of CHF. The patient was referred to the Cardiology Service at the Atlantic Veterinary College (AVC) for re-evaluation of the patient’s HCM and progression of the disease. On presentation the patient was bright, alert, and responsive, but was in poor body condition (body condition score = 1/5; weight = 3.7 kg) with marked sarcopenia. The patient was slightly tachypneic (40 breaths/min) with normal respiratory effort and normal broncho-vesicular lung sounds bilaterally in all fields. An irregular heart rhythm was also ausculted; however, no murmur was identified and the heart rate was within normal limits (200 beats/min). No other significant findings were present on physical examination.

Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, Prince Edward Island C1A 4P3. Address all correspondence to Andrew J.M. White; e-mail: [email protected] Dr. White will receive 50 copies of his article free of charge courtesy of The Canadian Veterinary Journal. Use of this article is limited to a single copy for personal study. Anyone interested in obtaining reprints should contact the CVMA office ([email protected]) for additional copies or permission to use this material elsewhere. CVJ / VOL 56 / MAY 2015

An electrocardiogram revealed an irregular supraventricular rhythm and multiple different P-wave morphologies consistent with multifocal atrial tachycardia (MFAT) (Figure 1). Twodimensional (2D) echocardiography revealed moderate, irregular hypertrophy of the left ventricle and the myocardium appeared stiff with decreased systolic function. The left atrium was markedly dilated (left atrial-to-aortic ratio = 3.3; normal: , 1.5) and spontaneous echocontrast (“smoke”) was present. Systolic anterior motion (SAM) of the mitral valve was not present. The right atrium was also mildly enlarged and systolic function of the right ventricle appeared to be decreased. Lastly, there was a mild amount of pericardial effusion (Figure 2). These findings confirmed end-stage hypertrophic cardiomyopathy (ES-HCM) and severe progression of the patient’s cardiac disease. A renal/electrolyte panel was unremarkable aside from a mild hypochloremia [106 mmol/L; reference interval (RI): 112 to 122 mmol/L] and mild azotemia (BUN 15.8 mmol/L, RI: 6.4 to 11.8 mmol/L; creatinine 166 mmol/L, RI: 67 to 157 mmol/L) attributed to long-term treatment with furosemide. The patient was continued on atenolol (PMS-atenolol; PharmaScience, Montreal, Quebec), 6.25 mg, PO, q12h, in an attempt to increase ventricular filling time and maintain the MFAT within the normal heart rate (160 to 240 beats/ min), as well as furosemide (Apo-furosemide; Apotex, Toronto, Canada), 2.7 mg/kg body weight (BW), PO, q12h, and benazepril (Fortekor; Novartis Animal Health Canada, Mississauga, Ontario), 0.34 mg/kg BW, PO, q24h to control the chronic CHF. Additionally, the patient was prescribed clopidogrel (Plavix; Sanofi Canada, Laval, Quebec), 5 mg/kg BW, PO, q25h, an antiplatelet drug, in order to reduce the risk of thrombus formation and thromboembolic events, as well as pimobendan (Vetmedin; Boehringer-Inglheim, Burlington, Ontario), 0.4 mg/kg BW, PO, q12h, an inodilator, in an attempt to increase systolic function and cardiac output, and the patient was discharged with a grave 509

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Figure 1.  Electrocardiogram demonstrating an irregular supraventricular heart rhythm (arrows). At least four different P-wave morphologies are discernible (*) consistent with multiple foci of premature atrial depolarization and multifocal atrial tachycardia (MFAT). 25 mm/s. 1 mm = 0.1 mV.

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RV RA

LV

LA PE

LAu

Figure 2.  Right parasternal long-axis four-chamber echocardiogram. Note the severe dilation of the left atrium (LA) and thinning of the ventricular myocardium at the apex (*). LA — left atrium; LAu — left auricle; PE — pericardial effusion; LV — left ventricular chamber; RA — right atrium; RV — right ventricular chamber.

prognosis. During a recheck telephone call, the owner reported the patient was still comfortable and had no further episodes of CHF 3 mo after discharge.

Discussion Hypertrophic cardiomyopathy is a primary myocardial disorder, and the most common feline cardiac disease (1). In humans, there are over 150 mutations identified on 10 different sarcomeric genes that can result in HCM (2). These mutations occur in genes coding for beta-myosin heavy chain, alpha-­tropomyosin, cardiac troponin T, C, and I, myosin-binding protein C, actin, titin, and regulatory light chains. In cats, point mutations in highly conserved regions of the cardiac myosin-binding protein C gene have been identified in the Maine Coon and Ragdoll breeds causing HCM in an autosomal-dominant pattern (3). Hypertrophic cardiomyopathy is characterized by an unnecessary concentric hypertrophy of primarily the left ventricle, although on occasion the right ventricle may also be affected (4). The hypertrophy may be diffuse throughout the ventricle, or may only affect the interventricular septum or ventricular free wall (termed “asymmetric” HCM) (5). Furthermore, hypertrophy may be focal and only affect a small region of the myocardium or the papillary muscles (4). Histologically, the myofibers are disorganized (myofibril disarray) and varying degrees of interstitial and interfibril fibrosis and dystrophic mineralization may be present (3). The end stage of the disease is characterized 510

by ventricular wall thinning, decreased myocardial contractility, and marked left atrial enlargement. Intracardiac thrombi or arterial thromboemboli (ATE) and CHF are consistent findings with ES-HCM (5). Coronary artery thromboemboli, small vessel coronary disease, and multifocal myocardial fibrosis (scarring) are evident histologically, and are likely responsible for decreased myocardial perfusion and the resultant cardiac changes (6). The underlying pathophysiologic mechanism of HCM is diastolic dysfunction of the heart; the thickened myocardium results in a stiff and crowded ventricle that cannot properly fill with blood during diastole leading to increased intraventricular diastolic filling pressure which can progressively cause increased left atrial and pulmonary venous pressures resulting in left atrial enlargement, and pulmonary edema and/or pleural effusion, respectively (7). Left atrial distension also increases the risk of thromboembolism and the development of supraventricular arrhythmias (5). As the disease progresses to its end-stages there may be a decrease in systolic function as the patient develops myocardial failure (6). Cats with HCM may present with an absence of clinical signs after an incidentally ausculted heart murmur, or with a history of exercise intolerance and syncope. They may also present with more serious clinical signs of dyspnea due to left-sided congestive heart failure, or acute, painful hind limb paralysis due to ATE (8). Diagnosis of HCM is typically done by echocardiographic identification of the hypertrophied ventricle, and ruling out other underlying causes of concentric hypertrophy, such as aortic stenosis, systemic arterial hypertension, and hyperthyroidism (9). N-terminal pro-brain natriuretic peptide (NT-proBNP) is a cardiac biomarker released from the ventricles when the myocardium is stretched, and can be measured when HCM is suspected. It is a sensitive marker for HCM, but other cardiac diseases may also increase NT-proBNP, making it non-specific and this marker should therefore be used to rule out cardiac disease and not diagnose HCM (10,11). Additionally, the cardiac changes seen in ES-HCM are also similar to those seen in feline restrictive cardiomyopathy (RCM): normal to increased ventricular wall thickness, diastolic dysfunction, endocardial or myocardial fibrosis, and markedly enlarged atria (6). Due to these similarities, a proper diagnosis of ES-HCM requires serial echocardiograms to demonstrate the progression of anatomical and functional changes seen between HCM and ES-HCM (6). Treatment involves medical management (typically betablockers) to reduce myocardial oxygen demand and increase diastolic filling time and coronary perfusion. Additionally, patients CVJ / VOL 56 / MAY 2015

CVJ / VOL 56 / MAY 2015

cardiac function with ES-HCM, and because it is often closely followed by CHF, as with the patient in this case, prognosis for long-term survival is grave.

Acknowledgment The author thanks Dr. Etienne Côté for editorial assistance, case supervision, and ECG and echocardiographic images. CVJ

References 1. Paige CF, Abbott JA, Elvinger F, Pyle RL. Prevalence of cardiomyopathy in apparently healthy cats. J Am Vet Med Assoc 2009;234:1398–1403. 2. Kittleson MD. Feline myocardial disease. In: Ettinger S, Feldman E, eds. Textbook of Veterinary Internal Medicine. 6th ed. St. Louis, Missouri: Saunders 2005:1087–1095. 3. Kittleson MD, Meurs KM, Munro MJ, et al. Familial hypertrophic cardiomyopathy in Maine coon cats: An animal model of human disease. Circulation 1999;93:3172–3180. 4. Kittleson MD. Hypertrophic cardiomyopathy. In: Kittleson MD, Kienle RD, eds. Small Animal Cardiovascular Medicine. 2nd ed. St. Louis, Missouri: Mosby 2005:347–362. 5. Côté E. Hypertrophic cardiomyopathy. In: Côté E, MacDonald KA, Meurs KM, Sleeper MM, eds. Feline Cardiology. 1st ed. Ames, Iowa: Wiley-Blackwell, 2011:103–176. 6. Cesta MF, Baty CJ, Keene BW, Smoak IW, Malarkey DE. Pathology of end-stage remodeling in a family of cats with hypertrophic cardiomyopathy. Vet Pathol 2005;42:458–467. 7. Hamlin RL. Pathophysiology of the failing heart. In: Fox PR, Sisson D, Moise NS, eds. Textbook of Canine and Feline Cardiology: Principles and Practice. Philadelphia, Pennsylvania: WB Saunders, 1999:205–215. 8. Rush JE, Freeman LM, Fenollosa NK, Brown DJ. Population and survival characteristics of cats with hypertrophic cardiomyopathy: 260 cases (1990–1999). J Am Vet Med Assoc 2002;220:202–207. 9. MacDonald K. Hypertrophic cardiomyopathy. In: Côté E, ed. Veterinary Clinical Advisor. 2nd ed. St. Louis, Missouri: Mosby 2011: 565–567. 10. Fox PR, Rush JE, Reynolds CA, et al. Multicenter evaluation of N-terminal probrain natriuretic peptide (NT-proBNP) as a biochemical screening test of asymptomatic (occult) cardiomyopathy in cats. J Vet Intern Med 2011;25:1010–1016. 11. Wess G, Daisenberger P, Mahling M, Hirschberger J, Hartmann K. Utility of measuring plasma N-terminal pro-brain natriuretic peptide in detecting hypertrophic cardiomyopathy and differentiating grades of severity in cats. Vet Clin Pathol 2011;40:237–244. 12. Atkins CE, Gallo AM, Kurzman ID, Cowen P. Risk factors, clinical signs, and survival in cats with a clinical diagnosis of idiopathic hypertrophic cardiomyopathy: 74 cases (1985–1989). J Am Vet Med Assoc 1992;201:613–618. 13. Baty CJ, Malarkey DE, Atkins CE, DeFrancesco TC, Sidley J, Keene BW. Natural history of hypertrophic cardiomyopathy and aortic thromboembolism in a family of domestic shorthair cats. J Vet Intern Med 2001;15:595–599.

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with left atrial distension or evidence of thrombus formation should be placed on antithrombotics (aspirin, clopidogrel, low molecular weight heparin) to reduce the risk of thromboembolic events, and those with evidence of arrhythmias should be managed with the appropriate anti-arrhythmic therapy. Cats with signs of, or presenting for, congestive heart failure should also be managed appropriately during the acute and chronic stages (diuretics, ACE inhibitors, and oxygen therapy). In the endstages of disease, systolic function may need to be increased and patients may benefit from administration of a positive inotrope such as pimobendan, or tapering the dose of atenolol (5). The prognosis for cats with HCM is highly variable, and mean survival times are determined by the cat’s presentation and clinical signs of HCM. One retrospective study reported median survival times (MST) for cats with subclinical HCM, and those presented with CHF, ATE, and syncope (8). Subclinical cats had a MST of 1129 d; however, the range has been reported from 2 d to 3778 d. Cats presenting with signs of syncope have an MST of 654 d (range: 28 to 1505 d), and those presenting with CHF and ATE carry a poorer prognosis and have a MST of 563 d (range: 2 to 4418 d) and 182 d (range: 2 to 2278 d), respectively (8). These MST of cats presenting with CHF and ATE are longer than those of 92 d, and 61 d, respectively, in an earlier report (12). Left atrial size also carries prognostic value, and cats with left atrial enlargement at the time of diagnosis progressed more rapidly into heart failure than those without. Maine coons, Ragdolls, and male cats carry a poorer prognosis as the disease manifests earlier in life and progresses more rapidly (4). This case stands out because of the longevity of the patient’s survival with the underlying disease, as well as the progression of the disease itself. The patient was initially diagnosed with HCM at 2-years of age and has survived for almost 13 y (over 4650 d); longer than the upper-ranges of previously reported survival times of cats with HCM presenting without clinical signs (3778 d) or with CHF (4418 d) (8). Furthermore, ES-HCM is a rare progression of HCM that accounts for 10% to 15% of HCM cases in humans and has been previously documented in a family of domestic shorthair cats; however, the overall prevalence in cats is unknown (13). End-stage hypertrophic cardiomyopathy is infrequently reported, and therefore MST has not been established; however, due to the deterioration of

End-stage hypertrophic cardiomyopathy in a cat.

Cardiomyopathie hypertrophique de stade final chez un chat. Un chat Persan âgé de 14 ans a été recommandé pour l’évaluation de la progression d’une ca...
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