A Pacemaker that was Avoided

Abstract

Objective Thyroxine is an essential hormone in human body and exerts many effects on the cardiovascular system. Low metabolic state in hypothyroidism causes bradycardia and reduced cardiac contractility leading to reduced cardiac output, severe bradycardia and Atrio-Ventricular (AV) blocks. We present a case of severe hypothyroidism causing high grade AV block which was successfully treated with thyroxine hormone replacement without requiring cardiac pacemaker placement. Method 87 years old man with past medical history of hypertension and hypothyroidism was told by his cardiologist to present to Emergency Department (ED) after he was found to have abnormal electrocardiogram (EKG) findings on Holter monitor. Patient denied chest pain, palpitations, shortness of breath, headache or dizziness at the time of presentation to ED. Physical examination findings were as follows: Pulse 36 beats /min, respiratory rate 16/ minute, Blood Pressure 180/70 mmHg, percentage oxygen saturation was 96% on room air. EKG showed New onset atrial fibrillation with slow ventricular response, frequent episodes of bradycardia to less than 40 bpm and Left Bundle branch block (figure 1). The patient was not taking any AV nodal blocking agents such as beta blockers, calcium channel blockers or digoxin. Thyroid stimulating hormone (TSH) was elevated to 74.03 IU/ml (reference range 0.39-4.08 IU/ml), with free T4 decreased to 0.53 mg/dl (0.58-1.64 mg/dl). The patient reported that he was on levothyroxine 25 mcg daily for at least 3 years and he had been taking it on an empty stomach daily. Echocardiogram showed EF 46-50%, mild diastolic dysfunction and increased pericardial fat. Patient was admitted and levothyroxine dosage was increased to 50 mcg per oral daily. Telemetry review on day one showed high degree AV block with 2.9 second sinus pause. However, subsequent telemetry review showed complete resolution of high degree AV block and pauses were no longer seen few days after increasing the dose of levothyroxine. Permanent pacemaker insertion was avoided and patient was discharged on levothyroxine 50 mcg daily, apixaban 20 mg daily for new onset atrial fibrillation and was advised to follow up with PCP for repeat thyroid function testing in 4-6 weeks. Results Cardiac dysrhythmias have been reported with hyper as well as hypothyroidism. Bradyarrhythmias are typically associated with hypothyroidism. Kazim et al. reported a study on AV blocks in patients with thyroid disease. A subgroup analysis of the study shows that 7 out of 29 patients (24%) who had hypothyroidism and AV blocks had complete resolution of AV blocks after treatment with levothyroxine. However, the sample size was too small to draw any definitive conclusion. AV blocks due to hypothyroidism in most texts is considered to be reversible, however, literature is controversial and few studies showed that most patients with AV block need permanent pacemaker placement. ACC/AHA/HRS 2008 guidelines for device based therapy of cardiac rhythm abnormalities recommend permanent pacemaker implantation in patients with advanced second degree and third degree AV blocks who have symptoms (Class I recommendation, level of evidence C). However, the guidelines also give Class III recommendation in favour of deferring a pacemaker placement in patients who are asymptomatic and have a benign reversible cause of AV blocks such as Lyme disease, drug toxicity, or transient increases in vagal tone (Level of evidence: B). There is no clear guideline regarding how to manage patients with high degree AV blocks with severe hypothyroidism and there is a lot of controversy in the literature. Our patient had a baseline first degree AV block and was found to be in new onset Atrial fibrillation with slow ventricular response and high degree AV block. AV block improved with supplementation of thyroxine. Conclusion Advanced second degree and third degree AV block with symptoms is considered to be an indication for pacemaker placement as per the latest guidelines by AHA/ ACC. However, the decision to insert a permanent pacemaker should be individualized, especially, in patients with a reversible cause of heart block such as hypothyroidism. In our patient, there was complete resolution of advanced second degree AV block within days after increasing the dose of his levothyroxine. Further studies may show better insight for role of permanent pacemaker in AV blocks in patients with thyroid dysfunction. (Figure presented).