Abstract
Subclinical hyperthyroidism is a difficult entity to diagnose because of silent clinical features and it may be easily underdiagnosed unless it is suspected and thyroid hormone levels are examined. Although atrioventricular (AV) conduction abnormalities such as complete heart block may occasionally be seen in hyperthyroidism, its association with subclinical hyperthyroidism has not been reported previously. We report on a 50-year-old female patient who did not have any systemic or cardiovascular disease or history of drug use that could affect AV conduction and presented with presyncope and complete heart block with narrow QRS complexes. Thyroid function tests showed subclinical hyperthyroidism and an electrophysiological study showed the supra-His level as the site of complete AV block. After initiation of antithyroid treatment (propylthiouracil), the patient's rhythm improved to second-degree AV block on the third day and returned to normal sinus rhythm on the fourth day.*1
Abstract
Background: Hypothyroidism is a reversible cause of atrioventricular (AV) block. Few reports have described reversible AV block caused by hyperthyroidism. However, it is unknown whether patients with AV block are expected to have a benign course after the initiation of appropriate therapy for thyroid dysfunction.
Methods: The study group consisted of patients with II or III degree AV block and bradyarrhythmia (≤40bpm) excluding patients with myocardial infarction, electrolyte abnormalities, digitalis toxicity, and vasovagal syncope. Thyroid dysfunction is diagnosed when thyroid stimulating hormone and thyroxine levels are not in defined normal ranges. AV block was determined by surface electrocardiogram (ECG). The cause and effect relation between AV block and thyroid dysfunction was evaluated.
Results: Of 668 patients, 29 (4.3%) had hypothyroidism (19 overt) and 21 (3.1%) had hyperthyroidism (8 overt). The most frequent ECG finding was complete AV block (27 of 50 patients). Ten patients had bradyarrhythmia and 13 had second-degree AV block. Euthyroid state was achieved in 10 hypothyroidic (34%) and in 7 hyperthyroidic patients (33%) with hormone replacement and antithyroid therapy, respectively, during the follow-up period (≤21 days). Thyroid dysfunction was found to be not related with AV block in 40 patients (80%). However, in 4 of 10 patients with AV block related to thyroid dysfunction the resolution of AV block occurred after the placement of pacemaker (>21 days). Overall, 44 of 50 (88%) patients with AV block in association with thyroid dysfunction were implanted with a permanent pacemaker. Of 6 patients who did not receive a pacemaker, 2 had complete AV block and 4 had bradyarrythmia.
Conclusion: AV block associated with thyroid dysfunction needs great attention regardless of type of the thyroid disease. Patients with II and/or III degree AV block in the setting of thyroid dysfunction almost always need permanent pacemaker insertion even after normalization of thyroid status. *2
Abstract
Hyperthyroidism often causes tachyarrhythmia. Reversible atrioventricular block caused by hyperthyroidism is rare occurrence. Presently described is a case of atrioventricular block due to hyperthyroidism and recovery after antithyroid treatment.
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Abstract
The authors report the case of a 26-year old male patient who had Graves' disease with a first degree atrioventricular block (AVB) and intermittent episodes of a second degree AVB of the Lucciani-Wenckebach type. These disorders of conduction had features characteristic of a nodal block and disappeared after treatment of the hyperthyroidism. The pathogenesis of atrioventricular conduction disorders in hyperthyroidism remains controverted. The authors put forward the following hypothesis: under the influence of thyroid hormones in excessive amounts, the autonomic nervous system would act by reciprocal excitation and exacerbate a patent or latent hypervagotonia which was pre-existent to the hyperthyroidism. This hypothesis needs to be tested by intracardiac electrophysiological studies with atrial stimulation.*4
Abstract
Complete heart block developed in a 29-year-old man with hyperthyroidism and acute febrile illness. The definite cause of acute febrile illness was unknown. The results of bacteriological and viral studies were negative. Endomyocardial biopsy revealed no evidence of carditis which is the common cause of heart block. All the abnormalities resolved completely after the fever subsided and the patient was treated with an antithyroid drug. Available information indicates that a high degree of heart block can sometimes occur in hyperthyroidism in either the presence or absence of additional factors which can independently impair atrioventricular conduction. This course of events which occurred in this patient suggest that complete heartblock may have been the direct manifestation of the hyperthyroid state, however, the acute febrile illness may have been an aggravating factor in the development of abnormal atrioventricular conduction.*5
PubMed Disclaimer*5
*1 Supra-His complete atrioventricular block in a patient with subclinical hyperthyroidism]
[Article in Turkish]
Basri Amasyalı et al. Turk Kardiyol Dern Ars. 2011 Dec.
*2Atrioventricular block in patients with thyroid dysfunction: prognosis after treatment with hormone supplementation or antithyroid medication
Kazim Serhan Ozcan et al. J Cardiol. 2012 Oct.
*3 Reversible first-degree atrioventricular block due to hyperthyroidism]
*4Hyperthyroidism and atrioventricular block. Pathogenic hypothesis. Apropos of a case and review of the literature]
[Article in French]
F Toloune et al. Arch Mal Coeur Vaiss. 1988 Sep
*5Complete heart block complicating hyperthyroidism: a case report
S Sriussadaporn et al. J Med Assoc Thai. 1990 Jan.
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