Phantom shocks in patients with an implantable cardioverter defibrillator

Phantom shock is the sensation of shock in the absence of an actual implantable cardioverter-defibrillator (ICD) discharge. The ICD is now the first-line therapy for patients with ventricular tachycardia and fibrillation. There has been a significant increase in the number of patients with an ICD and patients presenting to the Emergency Department (ED) after a shock for evaluation and device interrogation. Phantom shock is more likely to be nocturnal in the first 6 months after implantation, and patients are more likely to be clinically depressed and have higher levels of anxiety. There is no specific treatment. We report 3 patients who presented to the ED with the sensation of ICD discharges, however, on device interrogation had no shocks and no dysrhythmias.     

Effect of Antiarrhythmic Drug Therapy on the Incidence of Shocks in Patients who Receive an Implantable Cardioverter Defibrillator after a Single Episode of Sustained Ventricular Tachycardia/Fibrillation

Seventy-four patients (16 women, 58 men, age 58 ± 21 years, mean ± standard deviation) who received an implantable Cardioverter de/ibrillator (ICD) after experiencing a single episode of ventricular tachycardia or ventricular fibrillation were followed to determine if antiarrhythmic drug therapy affects the incidence of ICD discharges. Thirty-three patients (group A) were treated with an antiarrhythmic drug that was either untested or previously demonstrated during electropharmacological testing to be ineffective in suppressing the induction of ventricular tachycardia. Forty-one patients (group B) were not treated with an antiarrhythmic drug. There were no significant differences between the two groups in regards to age, sex, incidence of coronary artery disease, left ventricular function or the type of ICD pulse generator used. During a mean follow-up of 14 months for the entire cohort, 15 patients (46%) in group A and 18 patients (44%) in group B experienced at least one ICD shock. The time to the first appropriate shock (5 ± 5 months in both groups) and the frequency of ICD shocks (0.3 ± 0.2/month in group A vs 0.4 ± 0.5/month in group B) were similar in both groups. The incidence of syncope at the time of ICD discharge was higher in group A than group B patients (31% vs 5%, P < 0.05). In conclusion, antiarrhythmic drugs that are untested or have failed electropharmacological testing do not appear to reduce the probability of ICD discharge over a short-term (mean 14 months) follow-up in patients who have had only one clinical episode of VT/VF and may increase the risk of syncope during ICD discharge. Studies with a larger sample size and longer follow-up period will be needed to confirm these findings.     

Electromagnetic interference in implantable pacemakers.

The inhibited pacemaker (VVI or AAI) has become the most popular in recent years because of its ability to combine a physiological advantage with economical current consumption in cases with spontaneous activity. One of its disadvantages is its sensitivity to external electromagnetic interference. Though today's pacemakers possess effective protection against most interference signals there may be instances in which patients are subjected to uncomfortable or even life-threatening situations. This is the case of "amplitude modulated" or "pulsed" fields with modulation frequencies in the physiological range. Fields of that sort have been found in the vicinity of a welder, an electric steel plant, and in medical practice where therapeutic currents were applied. Even touch-actuated switches may influence a demand pacemaker. However, these situations may be overcome by a device within the pacemaker for simple time analysis which can be carried out with few components. If electromagnetic fields of diathermy equipment are applied, today's pacemakers may react with intolerably high or low rates. They should, therefore, be avoided.     

Implantation of Automatic Cardioverter-Defibrillators Via Median Sternotomy

Nous avons implané 15 défibrillateurs automatiques (Model B) chez 10 patients. La voie chirurgicale préferée est la sternotomie médiane. Nous préferons utiliser une électrode "patch" sur l'oreillette droite, une électrode "patch" sur l'apex du ventricule gauche et deux épicardiques pour le recueil du potentiel bipolaire. Alternativement, les "patch" peuvent être placés sur les faces antérieure du ventricule droit el postérieure du ventricule gauche si les seuils sont favorables. La période de surveillance représente 109 patients-mois et tous survivent. Les défibrillateurs ont choqué la tachycardie ventriculaire, flutter ventriculaire, et fibrillation ventriculaire. Des chocs ont été délivrés egalement pour tachycardie sinusale et pour la fibrillation auriculaire au dessus de la fréquence cible dans 3 cas. L'épuisement prématurée de la pile s'est produit dans 4 stimulateurs Model B, trois à 18 mois après implantation et parait être dûà un défaut de la pile originale. Les chocs pour tachycardie supraventriculaire resteront un problème jusqu'à ce que l'on obtienne une meilleure différentiacion entre tachycardies ventriculaires et tachycardies supraventriculaires. Le défibrillateur semble prévenir la mort subite suivant les tachyarythmies ventriculaires.     

Anxiety and Depression in Patients with Life-Threatening Ventricular Arrhythmias: Impact of the Implantable Cardioverter-Defibrillator

In order to assess the psychological responses to the automatic implantable cardioverter-defibrillator (AICD), 18 patients with a history of life-threatening ventricular arrhythmias were requested to complete the Spielberger State-Trait Anxiety Inventory and the Beck Depression Inventory. The patients were divided into three groups of six and matched for age, sex, underlying cardiac disease, ejection fraction, and NYHA Functional Classification. Group I had experienced conscious discharges from the AICD, group II had the AICD but without discharges, and group III without the AICD were treated with antiarrhythmic medications alone based on electrophysiological guided testing. Patients with the AICD were also requested to complete a questionnaire directed specifically at their experiences with the AICD. All of the 18 patients completed the study responses and results were analyzed by blinded review. There were no significant differences in anxiety and depression scores in the three groups studied, nor any significant differences in responses to the questionnaire in group I versus group II. One patient in group I reported experiencing adverse psychological responses to the AICD. Although there appears to be no significant differences in psychological responses as a result of the AICD implantation in patients with life-threatening ventricular arrhythmias, further study with larger patient groups is needed to identify and support patients who may develop adverse responses to the AICD.     

Patient Discomfort Following Pectoral Defibrillator Implantation Using Conscious Sedation

Background: The miniaturization of implantable cardioverter defibrillators (ICDs) has made pectoral implantation possible. However, postoperative pain following the procedure has not been systematically studied. The aim of the current study was to prospectively assess patient discomfort and identify factors influencing pain perception during follow-up. Methods: Pain related to device implantation was quantified in 21 consecutive patients (age, 61 ± 11 years; 17 men and 21 women; 16 of 21 had coronary artery disease; left ventricular ejection fraction, 32%± 15%) undergoing pectoral ICD implantation with conscious sedation (fentanyl 118 ± 72 μg, midazolam 14 ± 9 mg). Patients completed the Visual Analogue Scale (VAS, 0–100) and the McGill Pain Questionnaire 24 hours and 1 month postoperatively. Regression analysis was used to define clinical and procedure related variables affecting patient discomfort and frequency of postoperative analgesic use. Results: The mean VAS score was 34 ± 20 24 hours postoperatively. A single (4.8%) patient described postoperative pain as severe. Pain was reported to be moderate by 10 (47.6%) patients and mild by 10 (47.6%) patients. Intraoperative fentanyl requirement was a predictor of postoperative pain (R = 0.51, P = 0.036), and procedural duration was a strong predictor of postoperative analgesic use (R = 0.75, P < 0.001). Pain at 1 month decreased to a VAS score of 19 ± 18 (P = 0.002 vs 24 hours) and was rated to be severe, moderate, and mild by 1, 3, and 17 patients, respectively. Late pain was related to a VAS score at 24 hours (R = 0.67, P = 0.004). Conclusions: (1) Pectoral ICD implantation using conscious sedation is well tolerated. (2) Postoperative discomfort correlates with longer procedural times and larger intraoperative narcotic requirements.     

Echocardiographic Assessment of Epicardial Defibrillator Patch Electrodes

We performed a blinded controlled analysis of transthoracic echocardiograms on IK patients before and after epicardial defibrillator patch electrode placement to determine the accuracy of echocardiography in identifying defibrillator patches and to determine possible echocardiographic findings that may correlate with defibrillator function or perioperative complications. The sensitivity of two-dimensional echocardiography in detecting defibrillator electrodes was 72% by one observer and 39% by a second observer. Corresponding specificities were 67% and 83%, respectively. The discordance rate was 27%. The echocardiographic finding of patch buckling was not observed, and echocardiographic estimates of the distance from patch to epicardium did not correlate with defibrillator threshold at the time of surgery. We conclude that: echocardiography is only moderately sensitive and specific in identifying epicardial defibrillator electrodes; significant interobserver variability does exist; and echocardiography therefore cannot be used reliably to assess for pericardia] changes or possible complications of patch electrode placement.     

Potential Hazards of Fixed Gain Sensing and Arrhythmia Reconfirmation for Implantable Cardioverter Defibrillators

Appropriate sensing of ventricular tachycardia (VT) and ventricular fibrillation (VF)is of paramount importance for safety of patients with implanted cardioverter defibrillators (ICDs). Recently, the Guardian^R ATP 4210, a new third generation ICD that uses programmable but fixed sensing during sinus rhythm and doubles its sensitivity settings when VF is detected, to a maximum programmable sensitivity of 1 mV, has been tested in phase I and II clinical trials. A reconfirmation algorithm of this ICD confirms the presence of VT or VF prior to therapy. This case report describes undersensing of VF in a patient with the Guardian^R ATP 4210 at the maximum programmed sensitivity of 1 mV. Inappropriate episodes of asystole and prolonged bradycardias were also observed in this patient due to shortcomings in the reconfirmation algorithm design. Reoperation was required, with positioning of a new endocardial sensing lead to correct the undersensing of VF. This, however, did not correct asystolic pauses following antitachycardia pacing or spontaneous tachycardio termination prior to therapy. This case report highlights the hazards of fixed gain sensing for implantable ICDs and a potential limitation of a specific tachyarrhythmia reconfirmation algorithm used in this device.     

A Report Using a Hybrid ICD System: The Need for Compatibility Among Implanted Defibrillator Components

The successful implantation of an ICD system with hardware from three different manufacturers is described. This case exemplifies the need for compatibility of components among different manufacturers. This is most relevant at a time when rapidly changing technology and hardware availability may require a mixing, by informed practitioners, of ICD system components. The parallel to the development of the uniform IS-1 standard for bradycardia devices is made.     

Modified Magnet Test for a Reversed Automatic Implantable Cardioverter Defibrillator

We present the case of a 55-year-old man with atrial septal defect and cardiomyopathy who underwent implantation of an automatic cardioverter defibrillator (AICD) for ventricular tachycardia resulting in collapse. This case demonstrates multiple unusual complications related to AICD, including rotation of the pulse generator unit about its long axis requiring a "left-handed" magnet test to determine the appropriate counts.     

A Technique for the Prevention of Automatic Implantable Cardioverter Defibrillator Generator Migration

In order to prevent AICD generator migration in nine patients and correct chronic painful generator migration in three patients, we placed the AICD generator in an absorbable microfibrillar collagen pouch at the time of implant to facilitate fibrous capsule formation. Over a mean follow-up period of 14 +/- 2 months for the new implants, there have been no episodes of generator erosion, migration or infection. The three patients who suffered from generator migration have been symptom free for 12 +/- 2 months. We conclude that use of a microfibrillar collagen pouch at the time of AICD implant is a safe, inexpensive, and effective method for preventing generator migration.     

AutoCapture with Dual-Coil Leads of Implantable Cardioverter Defibrillator

AutoCapture™ (AC) can confirm ventricular capture with true bipolar single coil leads of implantable cardioverter defibrillators (ICD). The compatibility of AC with a new, true bipolar, dual-coil ICD lead needed to be evaluated. This multicenter study enrolled 46 patients (69 ± 10 years, 37 men) undergoing ICD implantation. All patients received a true bipolar, dual-coil lead. Evoked response (ER) sensitivity and AC threshold tests were performed using a pulse generator with the AC algorithm. Mean capture threshold was 0.85 ± 0.67 V, pacing impedance 612 ± 225 Ω, R wave amplitude 13.85 ± 6.17 mV, and defibrillation threshold 14.4 ± 5.1 J. AC was recommended in 45 patients (97.8%) with ER and polarization values of 14.86 ± 7.32 mV and 0.87 ± 0.69 mV, respectively. The AC algorithm was highly compatible with true bipolar, dual-coil ICD leads. An AC algorithm specifically designed for an ICD may improve the generator longevity. Further examination of AC compatibility with other leads is warranted.     

Implantable cardioverter defibrillator in a 4-month-old infant with cardiac arrest associated with a vascular heart tumor

A previously healthy male infant was resuscitated after spontaneous ventricular fibrillation at 9 weeks of age. Echocardiography revealed three tumors in the left ventricle not amenable to complete resection. Despite treatment with antiarrhythmic agents the ventricular arrhythmias continued. When the child was 4 months old and weighed 7 kg an ICD system was implanted using epicardial sense-pacing leads and a superior vena caval lead as a subcutaneous defibrillator coil placed posterior on the left thorax. Shocks were delivered between the subcutaneous coil lead and the intraabdominally placed ICD can. This ICD array system has not been reported previously.     

Radiofrequency Catheter Ablation of the AV Node to Improve the Function of an Antitachycardia Implantable Defibrillator

A case of coexisting atrial fibrillation and ventricular tachycardia in a patient with an implantable cardioverter defibrillator is described. Despite careful reprogramming, the device was not always able to distinguish between the two arrhythmias and continued to deliver inappropriate antitachycardia therapy including DC shocks. Attempts to pharmacologically control the atrial fibrillation were unsuccessful so radiofrequency ablation of the atrioventricular node was performed. Following successful ablation, there have been no further false detections nor episodes of further ventricular tachycardia.     

Effects of Extracorporeal Shock Wave Lithotripsy on Tiered Therapy Implantable Cardioverter Defibrillators

The effects of extracorporeal shock wave lithotripsy (ESWL) were tested on four advanced generation implantable cardioverter-defibrillators (ICDs) in vitro and in vivo in two patients. During in vitro testing, advancement of nonsustained episode counters occurred in one device, and a set screw and power source cell loosened in another, which was connected to an external power source. No arrhythmias occurred during in vivo procedures, but programmed parameters were reset and elective replacement indicated after one procedure. ESWL can be performed safely in selected patients with ICDs, but testing should be performed afterwards to confirm satisfactory function and component continuity.     

Accuracy of Rhythm Classification Using a Data Log System in Implantable Cardioverter Defibrillators

Because the presence or absence of symptoms alone may be insufficient to correctly diagnose the rhythm for which implantable Cardioverter defibrillator therapy is delivered, we hypothesized that the addition of data Jog information available in Telectronics ATP 4210 may improve the accuracy of rhythm classification. With this system the recorded ventricular electrogram cycle length is reported on a beat-to-beat basis immediately before, during, and after the tachyarrhythmia is detected. Using this information recorded from the data log in 32 separate tachyarrhythmia episodes in 20 patients, we compared the sensitivity, specificity, and predictive accuracy of rhythm classification on the basis of symptoms alone, data Jog alone, and data Jog combined with symptoms. While classification based on symptoms alone is highly specific (10/10 episodes), it is insensitive and has an overall predictive accuracy of 53%. By contrast, data log is sensitive (90%) and specific (91%) with better predictive accuracy (94%) than symptoms alone (P = 0.002). The addition of symptoms to information on beat-to-beat cycle length from data log resulted in a slight increase in predictive accuracy.