Ventricular Fibrillation: Potential Deadly Consequence of Discontinuation of Methimazole Prior to Radioiodine Ablation

Figures

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  Figure 1. QTc Improvement With Methimazole Treatment Image shows improving QTc interval after treatment with high-dose methimazole (30 mg every 6 hours). After >24 hours of treatment, QTc interval improved from 607 to 431 and after >48 hours of treatment QTc improved to 399. QTc: corrected QT interval for heart rate.

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  Figure 2. Relationship Between QTc and Free T4 Image shows a positive correlation between QTc interval and the patient’s free thyroxine (T4). In March 2019, free T4 was 2.08 and QTc was 297 ms. In November 2019, free T4 increased to 4.70 and QTc increased to 437 ms.

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  Figure 3. Ventricular Fibrillation on AICD Interrogation AICD interrogation revealed VF, which can be seen on the ventricular electrogram (V) on the AICD (black box). The onset of the VF is labeled with the blue arrow and the red arrow signifies the 40-Joule defibrillation shock, which converted the patient to sinus rhythm. VF: ventricular fibrillation; FF: far-field electrogram; AV: marker channel; V: ventricular electrogram; A: atrial electrogram; AICD: automatic implantable cardioverter-defibrillators.

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  Figure 4. PVCs Prior to Ventricular Fibrillation: R-on-T Phenomena AICD detected PVCs prior to VF. PVCs (red arrows) can be seen on the ventricular electrogram (V). These PVCs supports the assumption that along with QTc prolongation, the PVCs could have resulted in the “R on T” phenomena, which triggered the VF. FF: far-field electrogram; AV: marker channel; V: ventricular electrogram; A: atrial electrogram; PVC: premature ventricular contraction.