ICD hardware failure associated with multiple internal shocks

The delivery of 37 shocks by an ICD within 20 minutes, in response to T wave oversensing during atrial flutter, resulted in several manifestations of undesirable device behavior. The generator reverted to backup mode, and disabled automatic capacitor reformation, therapy delivery, and automatic gain control. Postexplant analysis of the device revealed damage to the high voltage output section of the circuitry consistent with excessive electrical stress. In rare circumstances, multiple internal discharges can result in serious clinical anomalies in ICD behavior, and possibly in an increase in susceptibility to circuitry damage.     

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.     

The Use of Beep-O-Grams in the Assessment of Automatic Implantahle Cardioverter Defibrillator Sensing Function

Noninvasive assessment of sensing performance in the automatic implantable cardioverter defibrillator is limited by the absence of telemetry or memory functions. The adaptation of the electrophysiological test mode into a "beep-o-gram" recording, with simultaneous audible tones and a surface electrocardiogram, was used in the confirmation of sensing malfunction. Eleven of 13 recordings in patients with documented or clinically suspected inappropriate defibrillator discharges (group 1) demonstrated evidence of definite oversensing. Nonspecific oversensing or undersensing was present in 77% of 27 randomly selected asymptomatic patients without known sensing malfunction (group 2). The sensitivity and specificity for identifying definite oversensing was 85% and 60%, respectively. The beep-o-gram system is a reliable, noninvasive means of confirming sensing malfunction in the automatic implantable cardioverter defibrillator. Its specificity is limited by the detection of subclinical sensing aberrations, to some degree related to the device's automatic gain control sensing algorithm.     

Improved Sensing Signals After Endocardial Defibrillation with a Redesigned Integrated Sense Pace Defibrillation Lead

Adequate sensing is a basic requirement for appropriate therapy with ICDs. Integrated sense pace defibrillation leads, which facilitate ICD implantation, show a close proximity of sensing and defibrillation electrodes that might affect the sensing signal amplitude by the high currents of internal defibrillation. In 99 patients, we retrospectively examined two integrated sense pace defibrillation leads, eitherboth with a distance of 6 mm between the tip of the lead (sensing cathode) and the right ventricular defibrillation electrode (sensing anode) or one with a distance of 12 mm. Three seconds after a shock of 20 J, mean sensing signal amplitude during sinus rhythm (SR) decreased from 10.5 ± 4.3 mVto 5.1 ± 3.7 mV (P < 0.001) for the 6-mm lead, but showed no significant decrease for the 12-mm lead. The degree of signal reduction was inversely related to the time passed since defibrillation. Significant differences in reduction of sensing signal amplitude concerning monophasic and biphasic shocks could not be observed. Mean sensing signal amplitude of VF after shocks that failed to terminate it decreased in the same order as during SR (from 8.3 ± 4.1 mV to 4.1 ± 3.2 mV), but resulted in no failure of redetection during ongoing VF. DFTs did not differ for the 6-mm and the 12-mm lead. In conclusion, close proximity of the right ventricular defibrillation coil to the sensing tip of an integrated sense pace defibrillation lead causes energy and time related reductions in sensing signal amplitude after defibrillation, and might cause undersensing in the postshock period. A new lead design with a more proximal position of the right ventricular defibrillation coil avoids these problems without impairing DFTs.     

Sensing Failure in a Tiered Therapy Implantable Cardioverter Defibrillator: Role of Auto Adjustable Gain

WASE A., et.al .: Sensing Failure in a Tiered Therapy Implantable Cardioverter Defibrillator: Role of Auto Adjustable Gain . Implantable cardioverter defibrillators have an established role in the management of life-threatening tachyarrhythmias. These devices use sophisticated sensing circuitry to detect and promptly treat a vast majority of these arrhythmias. However, they are not foolproof. We report one case where the device failed to sense every other QRS complex during induced ventricular fibrillation due to marked electrical alterans. Thus, undersensing can be a potentially fatal problem despite the use of auto adjustable gain.     

R wave undersensing caused by an algorithm intended to enhance sensing specificity in an implantable cardioverter defibrillator

This article reports on a case of ventricular undersensing despite normal R wave amplitudes during sinus rhythm in an ICD patient. Undersensing of ventricular signals was noted without any evidence of lead dislocation or variation in signal amplitude. Undersensing was due to an exceptionally small R wave signal width and a feature of the Biotronik sensing algorithm designed to avoid oversensing. This algorithm, intended to enhance the sensing specificity of the device, requires registration of two consecutive points above the maximum programmed sensitivity for a ventricular sense event. After modifying the algorithm to a single point registration undersensing disappeared.     

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.     

Paced Beats Following Single Nonsensed Complexes in a "Codependent" Cardioverter Defibrillator and Bradycardia Pacing System: Potential for Ventricular Tachycardia Induction

Patients with implantable defibrillators often require bradycardia pacemakers. Adverse interactions between separate defibrillator and bradycardia pacing units have occurred, including failure to detect ventricular fibrillation due to persistent bradycardia pacing during the arrhythmia. A device with combined bradycardia pacing and antitachycardia therapy capability may obviate adverse device interactions. We describe a previously unrecognized phenomenon that may occur in a combined device when the algorithms for sensing bradycardia and tachycardia are "codependent"; that is, the circuitry for brady- and tachyarrhythmia detection relies on the same automatic gain sense amplifier. Three of 37 patients in whom the device was implanted had ventricular tachycardia initiated when bradycardia pacing stimuli were delivered by the device after probable nonsensed sinus beats. In each case, nonsensed beats appeared to have a markedly diminished amplitude, occurred after ventricular premature depolarizations that produced large amplitude electrograms, and had an electrogram morphology that matched that of sinus rhythm. In each case, the bradycardia pacing interval was at least 1,200 msec (range 1,200 to 1,714 msec). In two of the three patients, large amplitude ventricular premature depolarizations or nonsustained ventricular tachycardia caused an adjustment of the gain control that potentiated the failure to sense the subsequent lower amplitude signal. In all three patients, the induced arrhythmia was rapidly terminated by pacing or cardioversion. Decreasing the bradycardia pacing interval by 110-514 msec has prevented recurrence during short-term follow-up. Our findings suggest that codependent bradycardia and antitachycardia devices may have their own unique potential difficulties in adapting to rapid changes in rate and signal amplitude.     

Retromammary Implantation of an ICD Using a Single Lead System: An Alternative Approach to Pectoral Implantation in Women

Pectoral ICD implantation, although feasible with the release of smaller devices, can be cosmetically disturbing to some patients due to the device protruding under the skin. An ICD was implanted using the retromammary approach in a 25-year-old female patient. Retromammary implantation of an ICD is feasible and offers an alternative approach in women.     

Undersensing of VF in a Patient With Optimal R Wave Sensing During Sinus Rhythm

We describe a case of potentially fatal undersensing of VF by a third generation ICD with predetermined automatic gain control. In this patient, ventricular sensing was optimal, as R wave amplitudes during sinus rhythm were at least 16 mV. Cyclical, high amplitude signals during VF elevated the sensing floor to such an extent that complete undersensing of subsequent lower amplitude local electrograms occurred. This led to bradypacing and complete ICD therapy failure. Therefore, high R wave amplitudes during sinus rhythm do not warrant flawless sensing during VF. (PACE 2004; 27[Pt. I] 833–834)     

A Multicenter, Randomized Trial Comparing an Active Can Implantable Defibrillator with a Passive Can System

Replacing one defibrillation electrode lead by the defibrillator can may simplify implantation of the ICD. In this multicenter study, 304 patients were randomized to receive either the biphasic active can (AC) (model 7219C system, Medtronic, Inc.) or the passive can (PC) (model 7219D system). The AC and PC systems were compared with respect to their ability to meet the implant defibrillation criterion and to defibrillate VF, and to DFTs, implant time, patient adverse events, and survival rates. A higher percentage fulfilled the implant defibrillation criterion on the first configuration with the AC (86.3% vs 75.9% for PC; P = 0.023), and the first shock success for terminating induced VF was 94% for AC compared to 89% for PC (P = 0.026). DFTs were significantly lower (10.9 vs 12.7 J; P = 0.031), and implant time was significantly shorter for the AC patients (99.2 vs 112.0 min; P = 0.002). The two groups showed no significant differences in 3-month adverse event rates, 3-month survival, and hospital stay.     

Comparison of a Unipolar Defibrillation System with a Dual Lead System Using an Enlarged Defibrillation Anode

The unipolar system for transvenous defibrillation, consisting of a single right ventricular lead as the cathode and the device shell as anode, has been shown to combine low de- fibrillation thresholds (DFTs) and simple implantation techniques. We compared the defibrillation efficacy of this system with the defibrillation efficacy of a dual lead system with a 12-cm long defibrillation anode placed in the left subclavian vein. The data of 38 consecutive patients were retrospectively analyzed. The implantation of an active can system was attempted in 20 patients (group 1), and of the dual lead system in 18 patients (group 2). Both groups had comparable demographic data, cardiac disease, ventricular function, or clinical arrhythmia. The criterion for successful implantation was a DFT of > 24 J. This criterion was met in all 18 patients of group 2, The active can system could not be inserted in 3 of the 20 group 1 patients because of a DFT > 24 J. In these patients, the implantation of one (n = 2) or two (n = 1) additional transvenous leads was necessary to achieve a DFT ≤ 24). The DFTs of the 17 successfully implanted group 1 patients were not significantly different from the 18 patients in group 2 (12.3 ± 5.7 f vs 10.8 ± 4.8 J). The defibrillation impedance was similar in both groups (50.1 ± 6.1 ± 48.9 ± 5.2 Ω). In group 1, both operation duration (66.8 ± 17 min vs 80.8 ± 11 min; P < 0.05) and fluoroscopy time (3.3 ± 2.1 min vs 5.7 ± 2.9 min; P < 0,05) were significantly shorter. Thus, the active can system allows reliable transvenous defibrillation and a marked reduction of operation duration and fluoroscopy time. The dual lead system, with an increased surface area defibrillation anode, seems to he a promising alternative for active can failures.     

Temporal and geographical trends in indications for implantation of cardiac defibrillators in Europe 1993-1998. Medtronic ICD System Investigators

Despite the demonstrated efficacy of implantable cardioverter defibrillators (ICDs) in reducing sudden and total mortality in selected populations, their implantation rates vary greatly between countries. The aim of our study was to analyze temporal and geographical trends in ICD implantations in countries with similar health related expenditure in Western Europe. A total of 2,257 patients from ten European evaluation studies of Medtronic defibrillators and defibrillation electrodes, conducted between 1993 and 1998, representing 12 countries, was included in this analysis. Rates of implantation and clinical characteristics were compared between countries and years of implantation. Rates of implantation differed greatly between Western European countries and did not correlate with indices of health related expenditure (i.e., number of patients per physician and number of patients per hospital bed). However, there was a strong and statistically significant negative correlation between the use of amiodarone and the rates of implantation (r = -0.66, P = 0.02). Temporal trends showed a significant increase in the age of the patients receiving an ICD between 1993 and 1998 (57 +/- 14 vs 61 +/- 12 years, mean +/- SD, P < 0.001). There was also a temporal trend towards an increased incidence of coronary artery disease and a significant decrease in the incidence of cardiomyopathy. There was a temporal increase in implantations in patients with a history of ventricular tachycardia. Despite a general scientific agreement that ICDs are a first line treatment for patients at high risk of sudden cardiac death, their acceptance remains low in several developed countries. This low acceptance may not be entirely related to budget constraint but may also be related to their perceived efficacy by physicians and health authorities.     

Energy Steering of Biphasic Waveforms Using a Transvenous Three Electrode System

The optimal electrode configuration for endocardial defibrillation is still a matter of debate. Current data suggests that a two pathway configuration using the right ventricle (RV) as cathode and a common anode constituted by a superior vena cava (SVC) and a pectoral can (C) is the most effective combination. This may be related to the more uniform voltage gradient created by shocks delivered using this configuration. We hypothesized that more effective waveforms could be obtained by varying the distribution of the shock current between the two pathways of a three electrode endocardial defibrillation system. In 12 pigs, we compared the characteristics and the defibrillation efficacy of six biphasic waveforms discharged using either a two (RV → C) or a three (RV → SVC + C) electrode combination with the following configurations: Configuration 1 (W1): the RV apical coil was used as a cathode and the subcutaneous C as anode (RV → C). Configuration 2 (W2): The RV was used as cathode and the combination of the atriocaval coil (SVC) and the subcutaneous C as anode (RV → SVC + C). Configuration 3 (W3): The RV → C was used for the first 25% off + and RV → SVC + C for the remainder of the discharge including f 2. Configuration 4 (W4): The RV → C was used for the first 50% off + and RV → SVC + C for the remainder of the discharge including f 2. Configuration 5 (W5): The R V → C was used for the first 75% off + and RV → SVC + C for the remainder of the discharge including f 2. Configuration 6 (W6): The RV → C was used for f + and RV → SVC + C for f2. As an increasing fraction of the waveform was discharged using the RV → SVC + C pathways, the impedance and the pulse width decreased while the tilt, the peak, and the average current significantly increased. The waveforms delivered using the RV → SVC + C configuration for 100% or 75% of their duration had significantly lower stored energy DFT than the other waveform. Current distribution between three endocardial electrodes can be altered during the shock and generates waveforms with different characteristics. Shocks with 75% or more of the current flowing to the RV → SVC + C required the lowest stored energy to defibrillate. This method of energy steering could be used to optimize current delivery in a three electrodes system.     

Implantation of a Cardioverter/Defibrillator in the Subpectoral Region Combined with a Nonthoracotomy Lead System

An implantable cardioverter defibrillator was placed into a sub-pectoral pocket via the incision for cephalic venotomy during implantation of a nonthoracotomy lead system. The approach obviated another incision and subcutaneous tunneling of the leads. There were no perioperative complications and after 6 months of follow-up, the patient continues to tolerate the device satisfactorily.