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  • Rate dependent RBBB is not commonly

    2019-05-30

    Rate-dependent RBBB is not commonly observed during routine clinical exercise testing [8]. In the S-ICD, when new RBBB arises, the QRS-T wave morphology recorded by the device may also change. In this case, the R/T wave ratio may decrease to a threshold where the T wave is above the sensing decay curve following R wave detection and is therefore counted by the device׳s detection algorithm. In our case, analysis of the stored event indicated a change in QRS-T wave morphology and TWOS prior to the inappropriate shock, a phenomenon that was reproduced in the subsequent exercise test but not in the first exercise test, as the patient was unable to achieve maximal exercise capacity. This case highlights the difficulties in preventing oversensing due to dynamic changes in the QRS-T wave morphology and the importance of performing a full exercise test as part of the screening, ensuring that the patient reaches the maximal exercise level they may achieve in daily life. Recently, a case of S-ICD TWOS resulting from the development of RBBB after alcohol septal ablation in a patient with hypertrophic cardiomyopathy was reported. In this case, as RBBB was persistent and R wave amplitude was low in all three sensing vectors, the authors chose to implant a new T-ICD [9]. In our case, TWOS was resolved by reprogramming the sensing vector to one unaffected by the rate-dependent RBBB.
    Conflict of interest Dr. Maria João Sousa is awaiting approval to receive educational grants from Boston Scientific. Dr. Betts has received honoraria from Boston Scientific for teaching and speaker fees.
    Funding sources Dr Betts׳ salary is part funded by the Oxford Biomedical Research Centre.
    Introduction Derived from the foxglove plant, cardiac glycosides have been used for the treatment of Zebularine failure for more than 200 years and are continued to be used today for patients with atrial fibrillation and heart failure. Currently, cardioactive steroid toxicity has become a well-known entity that even now, continues to be an issue. According to the National Poison Data System, in 2013, there were 26 deaths in the U.S. directly attributable to digoxin overdose, with many more non-fatal cases reported [1]. Bufadienolides are a group of cardioactive steroids with a chemical structure similar to digoxin. They are used in multiple traditional Chinese medications and aphrodisiacs. Because they are structurally similar to digoxin, they also display a similar toxicity profile. There have been multiple case reports of overdose with clinical presentations similar to digoxin toxicity [2], with death occurring owing to arrhythmia. Currently, the only available treatment is the same digoxin-specific antibody fragments used to treat digoxin overdose. In this paper, we will discuss the clinical and electrocardiographic similarities between digoxin and bufadienolide-containing substances.
    Case A 39-year-old man presented to the emergency department with vomiting and diaphoresis after eating a half block of “Piedra China”, an aphrodisiac intended to be applied topically. Vital signs at the time were within normal limits; heart rate was 65BPM and regular, blood pressure was 157/66mmHg, and respiratory rate was 20breaths/min. Shortly after arrival, ECG revealed sinus rhythm at 100BPM with complete heart block (Fig. 1). Potassium was 4.6mEq/L and digoxin concentration was 1.14ng/mL (normal=0.5–0.8ng/mL). He had acute hemodynamic decompensation with immediate ECG changes. Fig. 2 shows a QRS complex that is mildly wider than baseline, with 3:2 grouped beating; this would indicate supraventricular tachycardia (atrial or junctional with 3:2 block) or bidirectional ventricular tachycardia (VT) with 3:2 exit block. Ultimately, he deteriorated to ventricular fibrillation and underwent 90min of resuscitation. Treatment included defibrillation, epinephrine, atropine, amiodarone, procainamide, and three repeated boluses of digoxin-specific antibody fragments. After each dose of antibody fragments (10 vials, 12 vials, and 11 vials respectively; 38mg/vial), his rhythm converted to normal sinus with heart rate 70–80BPM. These improvements were transient and, despite aggressive care, the patient repeatedly deteriorated to ventricular fibrillation, which eventually led to asystole.