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Mechanisms and Management of Thyroid Disease and Atrial Fibrillation: Impact of Atrial Electrical Remodeling and Cardiac Fibrosis. Cells 2022; 11:cells11244047. [PMID: 36552815 PMCID: PMC9777224 DOI: 10.3390/cells11244047] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2022] [Revised: 12/08/2022] [Accepted: 12/13/2022] [Indexed: 12/23/2022] Open
Abstract
Atrial fibrillation (AF) is the most common cardiac arrhythmia associated with increased cardiovascular morbidity and mortality. The pathophysiology of AF is characterized by electrical and structural remodeling occurring in the atrial myocardium. As a source of production of various hormones such as angiotensin-2, calcitonin, and atrial natriuretic peptide, the atria are a target for endocrine regulation. Studies have shown that disorders associated with endocrine dysregulation are potential underlying causes of AF. The thyroid gland is an endocrine organ that secretes three hormones: triiodothyronine (T3), thyroxine (T4) and calcitonin. Thyroid dysregulation affects the cardiovascular system. Although there is a well-established relationship between thyroid disease (especially hyperthyroidism) and AF, the underlying biochemical mechanisms leading to atrial fibrosis and atrial arrhythmias are poorly understood in thyrotoxicosis. Various animal models and cellular studies demonstrated that thyroid hormones are involved in promoting AF substrate. This review explores the recent clinical and experimental evidence of the association between thyroid disease and AF. We highlight the current knowledge on the potential mechanisms underlying the pathophysiological impact of thyroid hormones T3 and T4 dysregulation, in the development of the atrial arrhythmogenic substrate. Finally, we review the available therapeutic strategies to treat AF in the context of thyroid disease.
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Bekiaridou A, Kartas A, Moysidis DV, Papazoglou AS, Baroutidou A, Papanastasiou A, Giannakoulas G. The bidirectional relationship of thyroid disease and atrial fibrillation: Established knowledge and future considerations. Rev Endocr Metab Disord 2022; 23:621-630. [PMID: 35112273 DOI: 10.1007/s11154-022-09713-0] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 01/28/2022] [Indexed: 11/24/2022]
Abstract
Atrial fibrillation (AF) tends to occur frequently in patients with thyroid disease, primarily hyperthyroidism. In hyperthyroidism, increased levels of thyroid hormones, via intra- and extranuclear mechanisms, have profound effects on cardiac electrophysiology. Hypothyroidism carries a lower risk for AF and is mainly associated with the overtreatment of hypothyroid patients. New-onset AF is frequently the only manifestation of thyroid disease, which renders screening for thyroid dysfunction in that scenario clinically useful. Managing thyroid disease and comorbid AF is essential. This includes thyroid hormones control along with conventional AF therapy. However, there are several open issues with this comorbid duo. The optimal management of thyroid disease and its impact on AF burden remains obscure. There is scanty information on clear-cut benefits for therapy of subclinical thyroid disease and screening of asymptomatic patients. Furthermore, the immunogenetic overlap between the autoantibodies in Graves' disease and AF genesis may lead to novel therapeutic implications. The objective of this review is to summarize the up-to-date epidemiology, pathogenesis, pathophysiology and management of interacting thyroid disease and AF.
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Affiliation(s)
- Alexandra Bekiaridou
- First Department of Cardiology, AHEPA University Hospital, Aristotle University of Thessaloniki, St. Kiriakidi 1, 54636, Thessaloniki, Greece
| | - Anastasios Kartas
- First Department of Cardiology, AHEPA University Hospital, Aristotle University of Thessaloniki, St. Kiriakidi 1, 54636, Thessaloniki, Greece
| | - Dimitrios V Moysidis
- First Department of Cardiology, AHEPA University Hospital, Aristotle University of Thessaloniki, St. Kiriakidi 1, 54636, Thessaloniki, Greece
| | - Andreas S Papazoglou
- First Department of Cardiology, AHEPA University Hospital, Aristotle University of Thessaloniki, St. Kiriakidi 1, 54636, Thessaloniki, Greece
| | - Amalia Baroutidou
- First Department of Cardiology, AHEPA University Hospital, Aristotle University of Thessaloniki, St. Kiriakidi 1, 54636, Thessaloniki, Greece
| | - Anastasios Papanastasiou
- First Department of Cardiology, AHEPA University Hospital, Aristotle University of Thessaloniki, St. Kiriakidi 1, 54636, Thessaloniki, Greece
| | - George Giannakoulas
- First Department of Cardiology, AHEPA University Hospital, Aristotle University of Thessaloniki, St. Kiriakidi 1, 54636, Thessaloniki, Greece.
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Association between dilated cardiomyopathy and hypothyroidism in dogs. ACTA VET BRNO 2022. [DOI: 10.2754/avb202291020201] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
It is a known fact that thyroid hormones have an influence on the heart function. Opinions on hypothyroidism and its effect on dilated cardiomyopathy (DCM) development are controversial and often contradictory. This prospective study examined the potential association between hypothyroidism and DCM in dogs. A total of 35 dogs with DCM were included in the study. Preclinical DCM was diagnosed in 18 patients, and clinical DCM was diagnosed in 17 patients, four of which were also diagnosed with hypothyroidism. There was a positive correlation between the thyroid-stimulating hormone and body weight, left atrium size and the serum NT-proBNP concentration in patients with preclinical DCM. Euthyroid dogs with DCM had higher total thyroxine values and more ventricular premature complexes than hypothyroid dogs. Although our study did not confirm a direct relationship between hypothyroidism and DCM as a possible cause, other correlations were detected that had not yet been described in veterinary medicine.
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Pedro B, Fontes-Sousa AP, Gelzer AR. Canine atrial fibrillation: Pathophysiology, epidemiology and classification. Vet J 2020; 265:105548. [PMID: 33129553 DOI: 10.1016/j.tvjl.2020.105548] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2020] [Revised: 09/20/2020] [Accepted: 09/21/2020] [Indexed: 12/14/2022]
Abstract
Atrial fibrillation (AF) is the most common non-physiological arrhythmia in dogs and humans. Its high prevalence in both species and the impact it has on survival time and quality of life of affected patients, makes it a very relevant topic of medical research. Significant developments in understanding the mechanisms underlying this arrhythmia in humans has occurred over the last decades and some of this knowledge is being applied to veterinary medicine, despite the many differences between species. This article reviews the current understanding of the pathophysiology of AF. The epidemiology and classification of AF in dogs will also be discussed.
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Affiliation(s)
- Brigite Pedro
- Willows Veterinary Centre and Referral Service, Highlands Road, Solihull, West Midlands B90 4NH, UK.
| | - Ana Patrícia Fontes-Sousa
- Laboratório de Farmacologia e Neurobiologia, Centro de Investigação Farmacológica e Inovação Medicamentosa (MedInUP), Instituto de Ciências Biomédicas Abel Salazar, Universidade do Porto (ICBAS-UP), Porto, Portugal
| | - Anna R Gelzer
- Department of Clinical Sciences and Advanced Medicine, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA, USA
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Guglielmini C, Berlanda M, Fracassi F, Poser H, Koren S, Baron Toaldo M. Electrocardiographic and echocardiographic evaluation in dogs with hypothyroidism before and after levothyroxine supplementation: A prospective controlled study. J Vet Intern Med 2019; 33:1935-1942. [PMID: 31468615 PMCID: PMC6766517 DOI: 10.1111/jvim.15600] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2019] [Accepted: 08/07/2019] [Indexed: 12/25/2022] Open
Abstract
Background Improvement in cardiac function has been demonstrated after thyroxine treatment in humans with hypothyroidism using the myocardial performance index (MPI). Cardiac changes after thyroxine supplementation are poorly documented in dogs with spontaneous hypothyroidism and comparison with clinically healthy dogs is lacking. Objectives To evaluate the electrical activity and mechanical function of the heart in dogs with primary hypothyroidism at baseline (T0) and after thyroxine supplementation (T60). Animals Forty client‐owned dogs with hypothyroidism and 20 clinically healthy dogs. Methods Prospective cohort study. Selected electrocardiographic and echocardiographic variables, including the MPI, were measured in all dogs at T0 and in 30 hypothyroid dogs at T60. Results Hypothyroid dogs had significantly decreased median or mean heart rate (HR), P wave amplitude, and R wave amplitude (P = .04, P = .002, and P = .003, respectively) and E‐point‐to‐septal separation normalized to body weight (EPSSn) and trans‐mitral E wave velocity (E max; P < .001 and P = .025, respectively) at T0 compared to control dogs. At T60, significantly increased median or mean HR, P wave amplitude, fractional shortening, and E max (P < .001, P = .004, P = .002, and P = .009, respectively) and significantly decreased left ventricular end‐diastolic volume index, and normalized systolic diameter and EPSSn (P = .03, P = .03, and P = .001, respectively) were found. Conclusions and Clinical Importance Hypothyroidism in dogs induces mild and reversible changes of electromechanical cardiac function. The MPI does not have clinical importance in identifying cardiac dysfunction in affected dogs.
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Affiliation(s)
- Carlo Guglielmini
- The Department of Animal Medicine, Production and Health, University of Padua, Padua, Italy
| | - Michele Berlanda
- The Department of Animal Medicine, Production and Health, University of Padua, Padua, Italy
| | - Federico Fracassi
- The Department of Veterinary Medical Sciences, Alma Mater Studiorum-University of Bologna, Bologna, Italy
| | - Helen Poser
- The Department of Animal Medicine, Production and Health, University of Padua, Padua, Italy
| | - Shani Koren
- The Department of Veterinary Medical Sciences, Alma Mater Studiorum-University of Bologna, Bologna, Italy
| | - Marco Baron Toaldo
- The Department of Veterinary Medical Sciences, Alma Mater Studiorum-University of Bologna, Bologna, Italy
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Blake RR, Longo M, Santarelli G, Liuti T, Martinez-Pereira LdaVet Y. Coronary arteriovenous malformation in a dog with a complex arrhythmia and hypothyroidism. J Vet Cardiol 2019; 23:38-44. [PMID: 31174728 DOI: 10.1016/j.jvc.2019.01.005] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2018] [Revised: 01/18/2019] [Accepted: 01/25/2019] [Indexed: 01/26/2023]
Abstract
A four-year-old Japanese Akita was referred for investigation of lethargy, exercise intolerance, and an irregular heart rhythm. He was diagnosed with atrial fibrillation, a complex ventricular arrhythmia, and hypothyroidism. Echocardiography identified a nest of anomalous vessels surrounding the heart and shunting into the pulmonary artery. Computed tomography confirmed a coronary arteriovenous malformation consisting of a coronary-to-pulmonary arterial communication and an associated complex nest of tortuous vessels, which was thought to be an incidental finding. Clinical signs improved with levothyroxine and antiarrhythmic treatment. Describing an unusual coronary artery anomaly as well, this case serves as a reminder to critically evaluate the hemodynamic significance of structural cardiac disease and to screen for systemic disease in patients with arrhythmias.
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Affiliation(s)
- R R Blake
- Cardiopulmonary Service, Hospital for Small Animals, Royal (Dick) School of Veterinary Studies & The Roslin Institute, The University of Edinburgh, Roslin, Midlothian, EH25 9RG, UK.
| | - M Longo
- Diagnostic Imaging Service, Hospital for Small Animals, Royal (Dick) School of Veterinary Studies & The Roslin Institute, The University of Edinburgh, Roslin, Midlothian, EH25 9RG, UK
| | - G Santarelli
- Cardiopulmonary Service, Hospital for Small Animals, Royal (Dick) School of Veterinary Studies & The Roslin Institute, The University of Edinburgh, Roslin, Midlothian, EH25 9RG, UK
| | - T Liuti
- Diagnostic Imaging Service, Hospital for Small Animals, Royal (Dick) School of Veterinary Studies & The Roslin Institute, The University of Edinburgh, Roslin, Midlothian, EH25 9RG, UK
| | - Y Martinez-Pereira LdaVet
- Cardiopulmonary Service, Hospital for Small Animals, Royal (Dick) School of Veterinary Studies & The Roslin Institute, The University of Edinburgh, Roslin, Midlothian, EH25 9RG, UK
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Seo J, Singh MK. Electrical cardioversion in a dog with atrial fibrillation and hypothyroidism. VETERINARY RECORD CASE REPORTS 2018. [DOI: 10.1136/vetreccr-2017-000583] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Affiliation(s)
- Joonbum Seo
- Royal Veterinary CollegeNorth MymmsUK
- Small Animal Specialist HospitalNorth RydeNew South WalesAustralia
| | - Manreet K Singh
- Small Animal Specialist HospitalNorth RydeNew South WalesAustralia
- Veterinary Cardiac ReferralsTerrey HillsNew South WalesAustralia
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Chow B, French A. Conversion of atrial fibrillation after levothyroxine in a dog with hypothyroidism and arterial thromboembolism. J Small Anim Pract 2014; 55:278-82. [DOI: 10.1111/jsap.12184] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/02/2014] [Indexed: 11/27/2022]
Affiliation(s)
- B. Chow
- Animal Health Center, College of Veterinary Medicine; Mississippi State University; P.O. Box 6100 Starkville MS 39762-6100 USA
| | - A. French
- Animal Health Center, College of Veterinary Medicine; Mississippi State University; P.O. Box 6100 Starkville MS 39762-6100 USA
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Zhang Y, Dedkov EI, Teplitsky D, Weltman NY, Pol CJ, Rajagopalan V, Lee B, Gerdes AM. Both hypothyroidism and hyperthyroidism increase atrial fibrillation inducibility in rats. Circ Arrhythm Electrophysiol 2013; 6:952-9. [PMID: 24036190 DOI: 10.1161/circep.113.000502] [Citation(s) in RCA: 69] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
BACKGROUND Evidence indicates that cardiac hypothyroidism may contribute to heart failure progression. It is also known that heart failure is associated with an increased risk of atrial fibrillation (AF). Although it is established that hyperthyroidism increases AF incidence, the effect of hypothyroidism on AF is unclear. This study investigated the effects of different thyroid hormone levels, ranging from hypothyroidism to hyperthyroidism on AF inducibility in thyroidectomized rats. METHODS AND RESULTS Thyroidectomized rats with serum-confirmed hypothyroidism 1 month after surgery were randomized into hypothyroid (N=9), euthyroid (N=9), and hyperthyroid (N=9) groups. Rats received placebo, 3.3-mg l-thyroxine (T4), or 20-mg T4 pellets (60-day release form) for 2 months, respectively. At the end of treatment, hypothyroid, euthyroid, and hyperthyroid status was confirmed. Hypothyroid animals showed cardiac atrophy and reduced cardiac systolic and diastolic functions, whereas hyperthyroid rats exhibited cardiac hypertrophy and increased cardiac function. Hypothyroidism and hyperthyroidism produced opposite electrophysiological changes in heart rates and atrial effective refractory period, but both significantly increased AF susceptibility. AF incidence was 78% in hypothyroid, 67% in hyperthyroid, and the duration of induced AF was also longer, compared with 11% in the euthyroid group (all P<0.05). Hypothyroidism increased atrial interstitial fibrosis, but connexin 43 was not affected. CONCLUSIONS Both hypothyroidism and hyperthyroidism lead to increased AF vulnerability in a rat thyroidectomy model. Our results stress that normal thyroid hormone levels are required to maintain normal cardiac electrophysiology and to prevent cardiac arrhythmias and AF.
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Affiliation(s)
- Youhua Zhang
- Department of Biomedical Sciences, New York Institute of Technology College of Osteopathic Medicine, Old Westbury, NY
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Bilotta F, Pizzichetta F, Fiorani L, Paoloni FP, Delfini R, Rosa G. Risk index for peri-operative atrial fibrillation in patients undergoing open intracranial neurosurgical procedures. Anaesthesia 2009; 64:503-7. [PMID: 19413819 DOI: 10.1111/j.1365-2044.2008.05833.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The aim of this prospective study was to determine the prevalence of pre-operative atrial fibrillation and the incidence of postoperative atrial fibrillation in patients undergoing elective or emergency intracranial neurosurgical procedures and the relation to survival and neurological outcome at 6-months follow-up compared to patients with sinus rhythm. A total of 2020 patients were enrolled; 1540 patients underwent elective procedures and 480 underwent emergency procedures. Prevalence of pre-operative atrial fibrillation was 3.7% in elective and 7.2% in emergency procedures (p = 0.0012). In patients undergoing elective cerebral procedures with pre-operative atrial fibrillation, compared to patients with sinus rhythm, 6-month neurological outcome and survival rate are similar. In patients undergoing emergency neurosurgical cerebral procedures, the presence of pre-operative atrial fibrillation is related to an increased risk of poor neurological outcome but with similar survival rate.
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Affiliation(s)
- F Bilotta
- Department of Anaesthesiology, Critical Care and Pain Medicine, La Sapienza University of Rome, Italy.
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Scott-Moncrieff JC. Clinical Signs and Concurrent Diseases of Hypothyroidism in Dogs and Cats. Vet Clin North Am Small Anim Pract 2007; 37:709-22, vi. [PMID: 17619007 DOI: 10.1016/j.cvsm.2007.03.003] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Canine hypothyroidism may present with a wide range of clinical signs. The most common clinical signs are those of a decreased metabolic rate and dermatologic manifestations; however, many other clinical signs have been associated with hypothyroidism. There is strong evidence for a causal relation between hypothyroidism and a variety of neurologic abnormalities; however, the association between hypothyroidism and other manifestations, such as reproductive dysfunction, clinical heart disease, and behavioral abnormalities, is less compelling. Further studies are necessary to determine the full spectrum of disorders caused by hypothyroidism.
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Affiliation(s)
- J Catharine Scott-Moncrieff
- Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Purdue University, VCS/LYNN, 625 Harrison Street, West Lafayette, IN 47907-2026, USA.
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Abstract
Atrial fibrillation (AF) is one of the most frequent complications of cardiac surgery, affecting more than one third of patients. The mechanism of this arrhythmia is believed to be reentry. The electrophysiologic substrate may be preexisting or may develop due to heterogeneity of refractoriness after surgery. Multiple perioperative factors have been proposed to contribute to the latter, including operative trauma, inflammation, elevations in atrial pressure (including that due to left ventricular diastolic dysfunction), autonomic nervous system imbalance, metabolic and electrolyte imbalances, or myocardial ischemic damage incurred during the operation. Whether ectopic beats originating in the pulmonary veins explain at least some episodes of postoperative AF, as has been shown for nonsurgical patients with the arrhythmia, is of current interest as such sites could easily be isolated at the time of surgery. The development of postoperative AF is associated with a higher risk of operative morbidity, prolonged hospitalization, and increased hospital cost compared with that in patients remaining in sinus rhythm. Many factors have been identified as being associated with postoperative AF, but the most consistent variable across studies is increasing patient age. It is speculated that age-related pathologic changes in the atrium contribute to arrhythmia susceptibility. An important modifiable risk factor for postoperative AF is the failure to resume therapy with beta-adrenergic receptor blockers after surgery. The stratification of patients who are at higher risk for AF would focus preventative strategies on patients who are most likely to benefit from such therapy. Nonetheless, since postoperative AF often develops in patients with comorbidities who are predisposed to other complications and prolonged hospitalization, it is presently unclear whether the prevention of postoperative AF will result in improved patient outcomes, particularly shorter hospitalizations.
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Affiliation(s)
- Charles W Hogue
- Department of Anesthesiology, Washington University School of Medicine, 660 South Euclid Ave, Box 8054, St. Louis, MO 63110, USA.
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Hess RS, Kass PH, Van Winkle TJ. Association between diabetes mellitus, hypothyroidism or hyperadrenocorticism, and atherosclerosis in dogs. J Vet Intern Med 2003; 17:489-94. [PMID: 12892299 DOI: 10.1111/j.1939-1676.2003.tb02469.x] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
The objective of this study was to determine whether dogs with atherosclerosis are more likely to have concurrent diabetes mellitus, hypothyroidism, or hyperadrenocorticism than dogs that do not have atherosclerosis. A retrospective mortality prevalence case-control study was performed. The study group included 30 dogs with histopathological evidence of atherosclerosis. The control group included 142 dogs with results of a complete postmortem examination, a final postmortem examination diagnosis of neoplasia, and no histopathological evidence of atherosclerosis. Control dogs were frequency matched for age and year in which the postmortem examination was performed. Proportionate changes in the prevalence of diabetes mellitus, hypothyroidism, and hyperadrenocorticism were calculated by exact prevalence odds ratios (POR), 95% confidence intervals (95% CI), and P values. Multiple logistic regression analysis was used to examine the combined effects of prevalence determinants while controlling for age and year of postmortem examination. Dogs with atherosclerosis were over 53 times more likely to have concurrent diabetes mellitus than dogs without atherosclerosis (POR = 53.6; 95% CI, 4.6-627.5; P = .002) and over 51 times more likely to have concurrent hypothyroidism than dogs without atherosclerosis (POR = 51.1; 95% CI, 14.5-180.1; P < .001). Dogs with atherosclerosis were not found to be more likely to have concurrent hyperadrenocorticism than dogs that did not have atherosclerosis (POR = 1.8; 95% CI, 0.2-17.6; P = .59). Diabetes mellitus and hypothyroidism, but not hyperadrenocorticism, are more prevalent in dogs with atherosclerosis compared to dogs without atherosclerosis on postmortem examination.
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Affiliation(s)
- Rebecka S Hess
- Department of Clinical Studies, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104-6010, USA.
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Abstract
A definitive diagnosis of hypothyroidism can be difficult because of the many clinical abnormalities associated with thyroid hormone deficiency, and the lack of readily available diagnostic tests with high sensitivity and specificity. Thyroid function tests should be performed only in dogs with clinical findings consistent with hypothyroidism. Measurement of serum total thyroxine (T4) concentration is a useful initial screening test since most hypothyroid dogs have values below the reference range. Serum free T4 concentration measured by equilibrium dialysis is a more sensitive and specific test of thyroid function than total T4 and is particularly useful in dogs with non-thyroidal illness or atypical clinical signs. Measurement of serum endogenous thyroid-stimulating hormone concentration is also helpful, but many hypothyroid dogs have normal results. The gold standard for diagnosis of hypothyroidism remains the thyroid-stimulating hormone response test. It should be used to confirm hypothyroidism when other tests do not agree with the clinical impression or if atypical signs or non-thyroidal illness exist or there has been administration of drugs known to alter thyroid function tests. Ultimately, a positive response to treatment is expected in hypothyroid dogs treated appropriately with levothyroxine.
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Affiliation(s)
- D L Panciera
- Department of Small Animal Clinical Sciences, Virginia-Maryland Regional College of Veterinary Medicine, Virginia Tech University, Blacksburg 24061-0442, USA
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