Inappropriate shocks can be avoided in the following ways
Inappropriate shocks can be avoided in the following ways while using a monitoring zone: (1) not setting a monitoring zone; (2) setting the VT zone at a higher rate than that of sinus tachycardia; (3) setting the VF zone at a higher rate for evaluating PAC intervals; (4) increasing the VF detection rate; and (5) decreasing the number of sinus redetections . We changed the settings on the ICD of our patient using factors (2) through (5). We changed VT zone from 375 to 330ms for a reference using event histograms without requiring the patient to undergo a treadmill exercise test to determine factor (2). To prevent the IA from being classified as a VT, we changed the VF zone from 280 to 250ms (3). To prevent the CI from being classified as a VF, we changed the VF detection interval from 12 to 16 (4). We also extended the time to VF detection in order to promote sinus redetection, and decreased the number of sinus redetections from 5 to 3 (5). After these setting changes, we performed a 9-month follow-up, and no similar episode was recorded. The maximal order ryanodine rate obtained from the histogram was 120bpm during follow-up. We believe that the patient withheld himself from performing intense exercise and so we cannot determine whether the setting changes were effective in preventing inappropriate shock.
In a recent report, inappropriate shocks were found to be associated with a higher risk of all-cause mortality. Tzeis et al.  summarized the available tools and plans that could be followed to reduce inappropriate shocks. The total incidence of VT in Brugada syndrome is low, and a high VF zone and 1-zone configuration are effective in preventing inappropriate shocks [6–8]. Almost all patients with Brugada syndrome who receive ICD implants are young, and sinus tachycardia can easily enter the monitoring zone. Veltmann et al. reported that they did not use a monitoring zone because of the high risk of inappropriate shock [1,9].
Conflict of interest
Introduction Twiddler\'s syndrome has been described as a rare complication of pacemakers and implantable cardioverter-defibrillators (ICD), which typically leads to device malfunction [1–15]. We present a case of Twiddler\'s syndrome that was detected by the patient\'s complaint of generator rotations in the subcutaneous pocket before any ICD malfunction occurred.
Case report A 79 year-old woman (height: 154.0cm, weight: 60.6kg) with coronary artery disease received an ICD (Current DR, model CD2211-36Q, St. Jude Medical, Sylmar, CA, USA) due to hemodynamically unstable sustained ventricular tachycardia. An active fixation ventricular lead (Durata, model 2120Q; St. Jude Medical, Sylmar, CA, USA) was placed in the ventricular mid-septum and an active fixation atrial lead (Fineline, 4473-52; Boston Scientific Corp., St. Paul, MN, USA) was implanted in the right atrial anterior wall by using the cephalic vein cutdown technique (Fig. 1). Acceptable lead impedance and capture/sensing thresholds were obtained at implantation (Table 1). Five months later, the patient reported that the generator sometimes rotated in the subcutaneous pocket when she turned over in bed. Fluoroscopy showed that the generator had rotated and the leads were twisted, indicating Twiddler\'s syndrome (Fig. 2). Telemetry data did not demonstrate any lead malfunction, and no delivery of inappropriate shocks was experienced. Only a slight increase in the capture threshold of the shock lead was observed (Table 1). Therefore, the leads were untwisted and fixation of the generator to the pectoral muscle was performed (Fig. 3).
Discussion Twiddler\'s syndrome has been known to be an uncommon cause of malfunction in pacemakers, ICDs, and cardiac resynchronization therapy devices [1–15]. The prevalence of this syndrome was reported to be 0.07% in cases with a pacemaker [2,7]. This syndrome occurs if the patient consciously or unconsciously twiddles the implanted generator in the subcutaneous pocket . Twiddling of the pulse generator can result in twisting of the leads within the pocket; this usually results in dislocation or fracture of the leads, which causes loss of capture and abnormal sensing [1–15]. In these cases, the electrocardiogram shows a failure to capture and the chest radiography reveals the dislodged and twisted leads. Hypoperfusion symptoms, such as fatigue and syncope, are observed in pacing-dependent patients. In a few reports, the dislodged lead caused ipsilateral phrenic nerve stimulation leading to the sensation of diaphragmatic and abdominal pulsations [6,11,14]. Twiddler\'s syndrome is more serious and potentially life threatening in cases with a defibrillator because treatment of ventricular arrhythmias would be disabled and inappropriate shocks could be delivered due to over sensing [10,12,13].