A 74-year-old woman (height, 156 cm; weight, 58 kg) was scheduled to undergo thoracoscopic thymectomy for MG associated with thymoma. The symptoms of MG included ptosis and muscle weakness, for which at 1.5 months preoperatively, she was administered a 1-week course of ambenonium and methylprednisolone pulse therapy that markedly improved the symptoms by the time of the surgery. She also had a history of tachyarrhythmia; however, on initiating treatment with metoprolol, the palpitations subsided and no further episodes of bradycardia or syncope occurred. Dyslipidemia was another comorbidity. Her blood test results were positive for thyroglobulin, acetylcholine receptor, and thyroid peroxidase antibodies, but no electrolyte imbalance was noted. Preoperative electrocardiogram (ECG) showed a first-degree AVB (PR interval of 0.204 s) (Fig. 1a). Transthoracic echocardiography showed mild to moderate aortic regurgitation and mitral regurgitation, but the ejection fraction was preserved.
The surgery was performed under combined general and epidural anesthesia. An epidural catheter was inserted at the T5–6 interspace. No bradycardia was observed during the procedure or at the time of administration of the test dose. In addition to the standard parameters, including blood pressure, pulse oximetry, and ECG, invasive blood pressure was also monitored. Neuromuscular blockade was monitored via visual observation of the train-of-four count. Anesthesia was induced via intravenous administration of fentanyl, propofol, and rocuronium, and maintained using desflurane (EtDes, 3–5%) and remifentanil (0.2–0.3 mcg/mg/min). At 15 min before the end of the surgery, thoracic epidural catheter infusion of 0.2% ropivacaine and fentanyl was initiated with an initial dose of 5 mL. No bradycardia or other arrhythmias were noted during the surgery that lasted for 3 h 52 min. The train-of-four count throughout the surgery was 0–1. Extubation was performed without difficulty. However, she complained of chills and started shivering; therefore, pethidine (35 mg) was administered. Although she was mildly sedated after pethidine administration, she did not complain of pain, and her respiratory status was stable. Therefore, she was returned to the intensive care unit after adequate observation.
At 2 h postoperatively, she was awake and had no complaints of pain. However, her heart rate (HR) dropped to 15 bpm, and she suddenly became nauseous at 5 h postoperatively. After vomiting, her HR improved, and she did not lose consciousness during this episode of bradycardia. At 9 h postoperatively, severe bradycardia for 22 s with a 10-s-long pause due to complete AVB was observed on the ECG (Fig. 1b). After the event, 12-lead ECG was performed, but no complete AVB was detected. Moreover, transthoracic echocardiography did not reveal any wall motion abnormalities. Her high-sensitivity troponin T level was slightly elevated at 0.042 ng/mL, but no electrolyte imbalance was noted.
Based on the previously mentioned symptoms and the ECG, our cardiologist diagnosed complete AVB, and implanted a temporary pacemaker programmed to VVI 40 via the right jugular vein. Subsequently, emergency coronary angiography was performed to investigate ischemic heart disease, but no significant stenosis was observed in the coronary arteries. During coronary angiography, her HR dropped with nausea and cardiac pacing started, but returned to sinus rhythm within a few seconds.
At 19 h postoperatively on postoperative day 1, her HR dropped again with nausea and cardiac pacing started that lasted approximately 30 s (Fig. 1c). Thoracic epidural administration was discontinued at 21 h postoperatively because of its adverse effect on her HR. Thereafter and until postoperative day 2, no further complete AVB was observed. On postoperative day 3, atrial fibrillation appeared and the HR increased to 110–170 bpm; therefore, bisoprolol tape administration was initiated. After the initiation of bisoprolol, the HR decreased, and she developed tachycardia-bradycardia syndrome. Because of this syndrome, complete AVB, and after considering her request, we implanted a permanent pacemaker and programmed it to manage the ventricular pacing (MVP™; Medtronic, Minneapolis, MN, USA) mode on postoperative day 8. She was discharged from the hospital on postoperative day 17. Pacemaker checks were performed at 1 and 6 months after the implantation and showed no atrial fibrillation or complete AVB.