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Severe complications of H arise from cardiovascular involvement: tachyarrhythmias,
associated thromboembolism, and heart failure. AF occurs in approximately
15% of H patients overall; H accounts for 15% of all patients with newly
diagnosed AF; and thyrotoxic AF is complicated by thromboembolism in 15%
of cases (76). In the older patient, symptoms of overt heart failure or
exacerbation of symptoms of an established cardiac disease such as angina
pectoris may be dominant. Myocardial oxygen utilisation increases about
34% per unit mass of myocardium in the average H patient (5). Heart failure
frequently develops in H patients with AF, mainly because a rapid ventricular
rate impairs diastolic filling and cardiac performance but possibly also
from abnormal intrinsic left ventricular performance. Of 31 deaths over
10 yr with a primary diagnosis of H, AF was documented in 61% and 26% presented
with a major arterial embolus (77). In 262 patients with H and AF, 26 (10%)
episodes of arterial embolism were noted (78). Three patients in this series
were <55 yr at the time of the embolic event, whereas 13 were >65 yr.
Arterial embolism was noted in 12 out of 30 H patients in AF, compared
with no embolic episodes in 121 patients in sinus rhythm (79). The risk
of embolism was higher in older patients, in males and in those with coexisting
hypertensive heart disease.
The risk of cerebrovascular events, with special attention to the first year after the diagnosis of H, was retrospectively studied in 610 patients with initially untreated H, 91 (15%) of whom had AF, with the highest frequency in the elderly patients (80). In 46% of the AF patients sinus rhythm developed after treatment of H, but the frequency of reversion to sinus rhythm varied from 100% in the youngest patients to 25% in the elderly. A total of 27 (4.4%) cerebrovascular events occurred, 12 (13%) in those having AF and 15 (3%) in patients with sinus rhythm. Thirteen patients had stroke and 14 had TIA. There were significantly more strokes in patients with AF compared to those in sinus rhythm. Using logistic regression methods, only age was an important risk factor, whereas AF was not significant as independent risk factor. From this study, the indication for prophylactic treatment with anticoagulants for prevention of stroke in thyrotoxic AF seems doubtful, especially as no controlled studies of such treatment in patients with AF are currently available. Nevertheless, the risk of arterial thromboembolism in elderly patients with H and AF warrants the consideration of anticoagulant therapy. Prophylactic anticoagulant therapy with warfarin reduces the frequency of embolic events in patients with AF in general (81), but it also entails a finite risk of hemorrhagic complications that may exceed the risk of thromboembolism, especially in the elderly. Since increased sensitivity to warfarin in H has been observed, the loading dose should, therefore, be reduced and therapy monitored closely. |
