(14.11) Thyrotoxicosis Associated with Sinus Node Dysfunction and Pulseless Arrest

Hyperthyroidism is commonly associated with cardiovascular complications such as sinus tachycardia and atrial fibrillation, while bradyarrhythmias are more commonly associated with hypothyroid states. Conduction disturbances such as sinus node dysfunction are rarely observed in hyperthyroidism and can be difficult to diagnose due to the use of negative chronotropic medication in hyperthyroid patients. Timely identification of sinus node dysfunction in patients with hyperthyroidism is important to prevent further complications such as sinus pause and arrest and avoid unnecessary pacemaker placement in patients that could otherwise be medically managed.

Case(s) Description :

The patient is a 59-year-old female who initially presented to her primary care clinic with complaints of shortness of breath, tremor, and unintentional weight loss. Laboratory evaluation revealed thyrotoxicosis with a suppressed TSH level of 0.008 mIU/L (0.350- 5.500 mIU/L) and an elevated free T4 level of 3.7 (0.8-1.8 ng/dL). Treatment was initiated with Methimazole and Propranolol. Two days later, the patient presented to the ED with acute epigastric pain and shortness of breath. An EKG confirmed the presence of atrial fibrillation at a rate of 105 beats per minute. On admission, she was noted to have a T4 level of 3.9 ng/dL and free T3 level of 9.4. Further workup was negative for acute cardiac ischemia; however, a chest x ray revealed free air under the diaphragm due to perforated duodenum so underwent an exploratory laparotomy to repair the duodenal ulcer. Postoperative recovery was complicated by persistent atrial fibrillation with rapid ventricular response despite administration of Propranolol and Cardizem. Methimazole medication was increased to 20mg every six hours rectally because she was NPO. After several days of therapy, rate was controlled but her hospital course was complicated by 5 episodes of bradycardia leading to cardiac arrest related to vagal maneuvers such as using the bedside commode and subsequently while receiving suppository medications. Due to the patient’s continued cardiac complications, inability to tolerate any vagal maneuver, and continued thyrotoxicosis, plan was made to proceed with a dual chamber permanent pacemaker implant, patient tolerated the procedure and had no further episodes of bradyarrhythmias.

Discussion :

Sinus node dysfunction in hyperthyroidism is a rare phenomenon requiring a high index of suspicion. All sinus node dysfunction patients should be screened for thyroid disturbances and treated accordingly. Traditional hyperthyroidism therapies such as beta blockers should be used with caution as to not exacerbate the rhythm disturbance, leading to worsening AV block or sinus pause. Adequate control of the patients thyroid disturbance may correct the dysrthrymia, and remove the need for further therapy. Careful consideration should also be given to which patients require pacemaker placement to manage their condition, and if these devices can be safely removed at a later time.