Holter Functions of the Implantable Cardioverter Defibrillator: What is Still Missing?

The technology of the implantable Cardioverter defibrillator (ICD) offers the opportunity to overcome the present limits of the invasive and noninvasive approaches of clinical electrophysiology. The invasive approach enables us to reproduce severe arrhythmias if they are inducible, but does not give information concerning the way they spontaneously arise. The noninvasive approach (Holter) gives this information, but it usually concerns only trivial arrhythmias with different therapeutic targets. One hopes in the future, by means of an important extension to ICD technology, which is not technically possible for the time being, to have access to pertinent information and to a better understanding of the circumstances leading to severe spontaneous arrhythmias, potentially lethal. For the moment, we only have the diagnostic certainty leading to the therapeutic intervention. It is based on an ECG and on the sequence of cardiac cycles preceding the rhythmic controlled accident. These data allow verification of but not explanation of the events. To have a chance to be understood and explained, these "events" must be replaced in the context of the "nonevents." Ideally, one should have all the gross information concerning the last 24 hours and subsequently analyze them. It is already a big step, thanks to the defibrillators the right to therapeutic error has been gained, a unique and fatal accident has been transformed into a repeatable event, and therefore, access is gained to the evolution of the responsible disease. I PACE 1995; 18[Pt. II].560–568)     

Transtelephonic Interrogation of the Implantable Cardioverter Defibrillator

Third generation implantable cardioverter defibrillators (ICDs) have extensive memory capability to store data about the patient's arrhythmias and the effect of therapies delivered by the ICD. However, this data has so far been accessible only when the patient attends the pacing clinic. Two Medtronic 9421 PCD TeletraceR transmitters have been used to interrogate Medtronic 7216A and 7217B PCD S at distances of up to 300 miles from our hospital and transmit the data to a 9420 PCD TeletraceR receiver. Successful transmission of data has been obtained on 50 occasions with 100% data concordance with repeat transmission. The system can reduce the number of unscheduled clinic visits, reduce delay in making a diagnosis following unexpected delivery of a shock therapy, and reassure patients about to be discharged following ICD implantation. The benefits are magnified where patients reside far away from the implanting center.     

Electrocardiographically Documented Unnecessary, Spontaneous Shocks in 241 Patients With Implantable Cardioverter Defibrillators

The incidence and cause of electrocardiographically documented spontaneous implantuble Cardioverter defibrillator (ICD) discharges for a rhythm other than ventricular tachycardia (VT) or fibrillation (VF) (unnecessary shocks) were determined in 241 patients who underwent ICD implantation between March 1983 and November 1991. During follow-up of 24 ± 20 months, 54 of 241 patients (22%) received a total of 132 unnecessary ICD shocks confirmed by Holler or telemetry monitoring or stored electrograms (Egs) from the ICD. The rhythm preceding these unnecessary ICD shocks was atrial fibrillation in 30 patients, sinus or supraventricular tachycardia (SVT) in 11 patients, antitachycardia pacing triggered by atrial fibrillation or SVT resulting in VT in 5 patients, nonsustained VT in 3 patients, and normal sinus or pacemaker rhythm in 10 patients. Unnecessary ICD discharges occurred most frequently during the first week after implantation or generator replacement (18 of 54 patients [33%]). Unnecessary ICD discharges could be documented more often by stored Egs in patients with devices with Eg storage capability (Ventritex Cadence(tm), 19 of 54 patients [35%]) than by Holter or telemetry monitoring in patients with devices without Eg storage capabilities (34 of 193 patients [18%], P < 0.01), despite a shorter mean follow-up duration of 14 ± 9 months versus 26 ± 21 months, respectively. Only six of 54 patients (11%) in whom unnecessary ICD discharges occurred had recurrent unnecessary shocks during 22 ± 20 months of follow-up after treatment directed at the cause of the first episode or device reprogramming to preclude non-VT rhythm detection. In conclusion, unnecessary ICD shocks are a frequent complication of ICD therapy occurring in at least 22% of patients. The cause of these shocks is most frequently atrial fibrillation with a rapid ventricular response. The availability of Eg storage capabilities facilitates the diagnosis of the electrical event precipitating inappropriate ICD shocks. Diagnosis of the cause of unnecessary shocks allows for the institution of therapy that may reduce the risk for subsequent events.     

Complications of Third-Generation Implantable Cardioverter Defibrillator Therapy

To determine the incidence of complications of third-generation implantable cardioverter defibrillator (ICD) therapy, 144 patients were prospectively studied who underwent first implant of third-generation devices (i.e., ICD systems with biphasic shocks, ECC storage capability, and nonthoracotomy lead systems). During 21 ± 15 months of follow-up, 41 (28%) patients had one or more complications. No patient died perioperatively (30 days) and no ICD infection was observed during follow-up. Complications included bleeding or pocket hematoma (hemoglobin drop > 2 g/dL) in 5 (3%) patients, prolonged reversible ischemic neurological deficit in 1 (1%) patient, postoperative deep venous thrombosis of leg in 1 (1%) patient, pneumothorax in 2 (1%) patients, difficulty to defibrillate ventricular fibrillation intraoperatively in 2 (1%) patients, generator malfunction in 1 (1%) patient, arthritis of the shoulder in 3 (2%) patients, and allergic reaction to prophylactic antibiotics in 2 (1%) patients. A total of seven lead related complications were observed in six (4%) patients including endocardial lead migration in four (3%) patients. Twenty-three (16%) patients received inappropriate shocks for supraventricular tachyarrhythmias (n = 13), non-sustained ventricular tachycardia (VT) (n = 7), or myopotential oversensing (n = 3). We conclude that serious complications such as perioperative death or ICD infection are rare in patients with third-generation ICDs. Lead-related problems and inappropriate shocks during follow-up are the most frequent complications of third-generation ICD therapy. Recognition of these complications should promote advances in ICD technology and management strategies to avoid their recurrence.     

Infections in Implantable Cardioverter Defibrillator Patients

Implantable cardioverter de;fibrillators fICDsj have been documented as an effective modality in reducing arrhythmic mortality. A serious complication associated with implantation of the device is infection. Few studies have addressed this issue. Two hundred seven patients with refractory ventricular arrhythmias underwent 207 ICD implantations, and 56 subcutaneous generator changes at our institution. Eight patients developed wound infections, four following ICD implantation (4 out of 207 or 1.9%), and four following a generator change (4 out of 56 or 7.1%). Wound cultures most commonly revealed Staphylococcus aurous and Staphylococcus epidermidis. Infections treated with antibiotics alone, or with only generator removal, frequently recurred (four out of five attempts). There were no recurrences following total patch/lead and generator system removal. In jive patients, the same generator unit was successfully emplaned following ethylene oxide sterilization without infection recurrence. We conclude that treatment of device-associated infection generally requires total generator and patch/lead system removal, and that generator units can be successfully reimplanted yielding substantial cost savings.     

Infection of Implantable Cardioverter Defibrillator Systems: A Preventable Complication?

In a consecutive series of 164 patients undergoing primary implantation of an impJantable cardioverter defibrillator (ICD), two patients died in the hospital (1.2%) and early system infection developed in one patient requiring expJantation of the device (0.61%). Late infection developed in one additional patient (0.61%) 7 months after transvenous ICD implantation, and was thought to be due to a recent intravascular catheterization. Symptomatic generator pocket hematomas developed in three patients, two of which were treated by simple evacuation and one with temporary generator explantation and subsequent reimplantation of the unit in a new pocket. No infection developed in these three patients during follow-up. Generator erosion without obvious system infection developed in a fourth patient. Guidelines for the prevention of infection in ICD systems are presented.     

Implantable Cardioverter Defibrillator Proarrhythmia: Case Report and Review of the Literature

A 31-year-old man who received an automatic cardioverter defibrillator subsequently underwent exercise testing. During exercise, a sinus tachycardia resulted above his device detect rate prompting two shocks, the second of which produced an unstable polymorphous ventricular tachycardia. In this article, we review the literature on automatic cardioverter defibrillator-induced ventricular tachyarrhythmias as well as the management of exercise testing in patients with these devices.     

The Impact of the Implantable Cardioverter Defibrillator on Quality-of-Life

The implantable Cardioverter defibrillator (ICD) is an established treatment for patients with life-threatening ventricular arrhythmias. While it clearly reduces the incidence of death from recurrent arrhythmia, little is known about the impact on patients' quality-of-life. In this prospective study, quality-of-life was assessed by questionnaire before and after ICD implantation. The "Sickness Impact Profile" (SIP), which evaluates physical, psychosocial, and other activities, as well as functions of daily life, was used. Employment and rehospitalization rates were also examined. Twenty-one of 23 consecutive patients, aged 58 ± 11 years, undergoing ICD implantation at Royal Perth Hospital were studied. During the 14 ± 8 month follow-up, 4 patients died. Functional capacity was unchanged in all but one of the survivors in whom it improved from New York Heart Association Class III to II. Four of 8 survivors employed before implant have since retired. Six patients required rehospitalization on 13 occasions, problems related to arrhythmias or the ICD. Overall SIP scores preimplant (11.2 ± 9.3; P < 0.05) were significantly worse at 6-month follow-up (21.7 ± 18.2), but returned to preimplant levels by 12-month follow-up (8.8 ± 10.8; NS). This was primarily due to transient problems in the areas of emotional behavior, alertness, and social interaction. SIP psychosocial dimension scores: preimplant: 7.2 ± 9.0; 6-month: 17.8 ± 18.1 (P < 0.05); and 12-month: 8.6 ± 10.3 (NS). Early retirement and hospitalizations due to arrhythmias may still be expected even after implantation of an ICD; however, quality-of-life appears only to temporarily decline.     

Implantable Cardioverter Defibrillator Lead Technology: Improved Performance and Lower Defibrillation Thresholds

The performance of an ICD system depends, in part, on the effectiveness with which the lead system functions. Engineering trade-offs are made during the design of a lead to optimize one or more performance characteristics: e.g., lead handling, fatigue life, size, and optimized therapy delivery. To assure low defibrillation thresholds, careful attention must be taken during the design process to prevent these trade-offs from hampering the lead's therapy effectiveness. Four basic design rules are described that capture many of the engineering concepts that will enhance a lead's efficacy: (1) minimize electrode pullback, (2) deliver current to the apex, (3) minimize energy loss in the lead, and (4) use large, efficient electrodes. These rules speak to optimizing delivery of current to the heart and efficiency of the lead and electrode interface. When the lead performs its function well, the complete ICD system of the heart, lead, and implantable pulse generator will provide optimal safety margins for device implant and an increased number of patients that can be implanted with a single-lead system.     

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.     

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.     

Inappropriate Discharges of an Implantable Cardioverter Defibrillator Secondary to Automatic Adjustable Gain of Atrial Tachycardia

Third generation implantable cardioverter defibrillators are capable of complex arrhythmia detection using sensing algorithms with automatic adjustable gain settings. We report a unique case where inappropriate sensing of atrial tachycardia in a patient with a His bundle ablation lead to satisfaction of ventricular fibrillation detection criteria.     

Implantable Cardioverter Defibrillator: Data Storage and Retrieval with Patientlog

A pacemaker management system (Patientlog), implemented on a IBM personal computer (AT), was adapted for the control and the administrative management of patients with an implantable cardioverter defibrillator (ICD). Several parameters used for pacemakers were also suitable for ICDs, while some fields were defined within the available frame of the database, to cope with the specific technical information of ICDs. "Intervention-cards" display diagnostic (threshold) as well as complex surgical information (approach, lead systems, etc.). "Follow-up-cards" present charge time and the number of shocks in such a way that decision making is very easy. Fourteen patients were followed with a total of 21 interventions, six different types of devices, and more than 150 follow-ups. A correct control of ICD functions is easy. The system is adapted for programmable ICDs. Updated reports containing necessary information are generated immediately after each procedure or follow-up.     

Sudden Death Mortality in Implantable Cardioverter Defibrillator Patients

Implanfable Cardioverter defibrillator (ICD) prevention of sudden cardiac death (SCD) is not absolute and our experience was reviewed to determine the frequency and nature of SCO in this population. The incidence and cause of mortality in 56 consecutive patients, who underwent ICD implantation beginning May 1982 with follow-up through May 19, 1990 were analyzed. Twenty-one patients died, 33% of the mortality was due to SCD, and 52% of deaths may be considered arrhythmic. The cumulative 1, 3, and 5 year SCD survivals were 93%, 89%, and 75%. All seven patients dying of SCD presented initially with SCD, all received previous shocks prior to SCD, and two of the seven patients had devices that were probably inactive at the time of death. We conclude that ICDs reduce but by no means eliminate arrhythmic death, particularly in those at highest risk for SCD. Arrhythmic death remained the most common cause of death in this population.     

Combined Third-Generation Implantable Cardioverter Defibrillator with Permanent Unipolar Pacemakers: Preliminary Observations

As implantable Cardioverter defibrillators (ICDs) are strictly contraindicated in the presence of unipolar pacemakers, currently available options in patients having such chronic pacing systems include: abandoning the implanted pacemaker and selecting an ICD with ventricular demand (VVI) pacing; or replacing the chronic (dual chamber) unipolar pacing system with a dedicated bipolar version prior to ICD implantation. In three patients with previously implanted unipolar pacemakers, we challenged the premise that all ICD systems are incompatible by combining with a third-generation transvenous ICD system (Medtronic 7217B PCD® incorporating true bipolar sensing, a self-limiting auto-adjusting sensitivity, and a tolerant VF detection algorithm. The potential for pace-maker-ICD interaction was minimized by separating the tip of the ICDs transvenous right ventricular pace/sense-defihrillation coil lead from that of the chronic pacemaker lead by > 2–3 cm, and by performing “worst case” intraoperative testing. Although ICD double-counting of the dual chamber pacemaker's atrial and ventricular pacing spikes could be provoked at extreme high output settings, it did not occur at clinically appropriate settings. More importantly, continuous high output asynchronous pacing during ventricular fibrillation (VF) did not interfere with ICD detection. During a mean follow-up period of 18 months, one patient has had VF appropriately terminated bv the ICD. In the remaining two patients, proper VF detection and ICD function was reassessed at 3 months and/or at 1 year during noninvasive testing. Conclusion: These preliminary findings demonstrate that this transvenous ICD system's VF sensing and detection features combined with careful implant technique, rigorous “worst case” testing for possible pacemaker-ICD interaction with regular follow-up, may permit implantation of this ICD system in patients with chronic unipolar pacing systems. Further studies are needed to validate the long-term clinical safety of this promising revised approach to a currently contraindicated device combination.     

Evaluation of Outpatients Experiencing Implantable Cardioverter Defibrillator Shocks Associated with Minimal Symptoms

Patients receiving minimally symptomatic shocks from their implantable cardioverter defibrillators were studied prospectively using transtelephonic ECC loop monitoring. The time course to the first subsequent shock was evaluated. Twenty-nine consecutive patients who received a shock preceded by mild palpitations or no symptoms were given a transtelephonic ECG loop monitor and instructed to activate the monitor if a subsequent shock occurred. Kaplan-Meier analysis was used to quantitate the time to first shock during the study period. The point estimate ± standard error of patients receiving a shock during the study period was 31%± 9% at 30 days, 41%± 9% at 60 days, and 60%± 9% at 120 days. The ECG was successfully transmitted in 7 of 13 patients who had shocks in the 60-day monitoring period, and demonstrated inappropriate shocks in 6 of 7. Determination of the cause of shock led to a change in subsequent management in all 7 patients. We conclude that the incidence of inappropriate shocks may be higher than estimated previously in patients with minimal symptoms prior to the shock. There are thousands of patients with implantable cardioverter defibrillators that have no storage function for treated tachycardias; transtelephonic ECG loop monitoring can determine the cause of implantable cardioverter defibrillator discharge in these patients, and the diagnosis is invaluable in their management.     

Multiple Inappropriate Shocks Precipitated by Interrogation of an Implantable Cardioverter Defibrillator

A 57-year-old man suffered multiple inappropriate shocks from an implantable cardioverter defibrillator that could not be inactivated because the magnet switch feature was deactivated. Attempts to interrogate the defibrillator caused shocks to be delivered. Emergent explantation was performed and a loose sensing lead was discovered. Sensing and defibrillation leads functioned normally, and testing of the explanted generator demonstrated no abnormalities. A new generator was put in place and the patient has been without shocks for 6 months. This case illustrates the need for robust methods of attenuating electromagnetic interference and the importance of multiple methods of device inactivation.