Third-generation Implantable Cardioverter-defibrillator Research Articles

Usefulness of procainamide challenge for electrophysiologic arrhythmia risk stratification

Among 58 consecutive patients who underwent electrophysiologic testing for risk assessment and who subsequently received a third-generation implantable cardioverter-defibrillator, 39 had ventricular tachycardia induced in the baseline state and 19 had ventricular tachycardia induced only after administration of intravenous procainamide, increasing the yield of electrophysiologic risk assessment by 49%. At follow-up, ventricular arrhythmias requiring implantable cardioverter-defibrillator termination occurred in 14 of 39 patients inducible in the baseline state and in 7 of 19 patients inducible only with intravenous procainamide. The provocative use of intravenous procainamide during electrophysiologic risk assessment increases the detection rate for risk of sustained ventricular arrhythmias with no loss of positive predictive value.

Effect of sensing system on the incidence of myopotential oversensing during bradycardia pacing in implantable cardioverter-defibrillators

Oversensing during bradycardia pacing, sometimes leading to spurious tachyarrhythmia detection and inappropriately delivered shocks, has been reported with Ventritex (St. Jude Corporation, Sunnyvale, California) Cadence (models V-100 and V-110) implantable cardioverter-defibrillators (ICDs). 1 Kelly P.A. Mann D.E. Damle R.S. Reiter M.J. Oversensing during ventricular pacing in patients with a third-generation implantable cardioverter-defibrillator. J Am Coll Cardiol. 1994; 23: 1531-1534 Abstract Full Text PDF PubMed Scopus (47) Google Scholar , 2 Rosenthal M.E. Paskman C. Noise detection during bradycardia pacing with a hybrid nonthoracotomy implantable cardioverter defibrillator system. PACE. 1998; 21: 1380-1386 Crossref Scopus (9) Google Scholar , 3 Peters W. Kowallik P. Wittenberg G. Scholl C. Meesmann M. Inappropriate discharge of an implantable cardioverter defibrillator during atrial flutter and intermittent ventricular antibradycardia pacing. J Cardiovasc Electrophysiol. 1997; 8: 1167-1174 Crossref PubMed Scopus (15) Google Scholar One cause of this problem is sensing of diaphragmatic or abdominal myopotentials in the setting of the high sensitivity that automatically occurs during bradycardia pacing. 2 Rosenthal M.E. Paskman C. Noise detection during bradycardia pacing with a hybrid nonthoracotomy implantable cardioverter defibrillator system. PACE. 1998; 21: 1380-1386 Crossref Scopus (9) Google Scholar Ventritex ICDs use a stepwise automatic amplifier gain control, and amplifier gain is continuously maximal during bradycardia pacing, with a minimal sensed signal of approximately 0.2 mV. 4 Reiter M.J. Mann D.E. Sensing and tachyarrhythmia detection problems in implantable cardioverter-defibrillators. J Cardiovasc Electrophysiol. 1996; 7: 542-558 Crossref PubMed Scopus (60) Google Scholar Newer Ventritex devices, Cadet, Contour, and Angstrom (models V-115, V-145, V-180, and V-190) use a similar automatic gain control, although gain changes occur more rapidly than in the Cadence models. 5 Mann D.E. Damle R.S. Kelly P.A. Landers M. Otto L. Reiter M.J. Comparison of oversensing during bradycardia pacing in two types of implantable cardioverter-defibrillator systems. Am Heart J. 1998; 136: 658-663 Abstract Full Text Full Text PDF PubMed Scopus (20) Google Scholar Other ICDs use different sensing algorithms. Medtronic (Minneapolis, Minnesota) and CPI Guidant (St. Paul, Minnesota) devices automatically adjust sensitivity or gain on a beat-by-beat basis. Sensitivity or gain is adjusted according to the amplitude of each sensed complex. Between complexes, sensitivity or gain exponentially increases, eventually reaching a maximum level that in some devices is programmable. In Medtronic and CPI devices, sensitivity or gain during bradycardia pacing is maximal for less of the cardiac cycle than in Ventritex devices, and thus the propensity to oversense could be less in these devices. 4 Reiter M.J. Mann D.E. Sensing and tachyarrhythmia detection problems in implantable cardioverter-defibrillators. J Cardiovasc Electrophysiol. 1996; 7: 542-558 Crossref PubMed Scopus (60) Google Scholar To assess the effect these differences in sensing function may have on oversensing of myopotentials, we performed the following prospective study.

Interaction of septadian and circadian rhythms in life-threatening ventricular arrhythmias in patients with implantable cardioverter-defibrillators

Previous studies have shown that life-threatening ventricular arrhythmias display both circadian and septadian (day of the week) periodicity. We hypothesized that assessing the relation between these circadian and septadian rhythms may provide important pathophysiologic information about the mechanism of sudden cardiac death. Using the database from a population of 683 consecutive patients with a third-generation implantable cardioverter-defibrillator (ICD), we examined the time pattern of ICD activations for rapid (prospectively defined as cycle length <280 ms) tachycardias for each day of the week. A total of 5,270 arrhythmic episodes were analyzed. Despite the fact that event distribution was significantly nonuniform (p <0.001) for both circadian and septadian analyses, the circadian pattern was strikingly similar for each day of the week with a relatively broad peak between 9 a.m. and 6 p.m. and a long nadir between 9 p.m. and 6 a.m. We conclude that the trigger factors responsible for the daily circadian distribution of life-threatening ventricular arrhythmias in a population with ICDs are similar throughout the week and may thus be unrelated to the standard work week. These data suggest that the physiologic modulators of circadian and septadian rhythms may be different.

Is inappropriate therapy a resolved issue with current implantable cardioverter defibrillators?

Patients with an implantable cardioverter defibrillator (ICD) can undergo inappropriate therapies if electrical activity not originating in the ventricle is wrongly recognized as ventricular by the device. Inappropriate therapy can be the result of detection of supraventricular tachycardias or over-sensing of other artifacts by the device. Enhanced detection criteria in third-generation ICD have been implemented to recognize fast supraventricular arrhythmias. Analysis of the use of these criteria in patients with an ICD has shown that arrhythmias detected in the ventricular tachycardia zone are frequently supraventricular (193 supraventricular of 690 tachycardia episodes in 23 of 59 patients). Use of sudden onset was very effective in detecting sinus tachycardia (65 of 67 episodes) and stability was very useful in detecting atrial fibrillation (31 of 32 episodes). However, sensitivity in detecting ventricular tachycardia was only 90% (451 of 497 episodes). Application of the sustained, rate duration criteria allowed appropriate treatment of all ventricular tachycardia episodes, increasing sensitivity to 100%; however, specificity in appropriate nontreatment of supraventricular episodes decreased from 96% to 83%. Subsequent analysis of different algorithms showed that sudden onset >9% and stability <40 msec was the algorithm with the best specificity and sensitivity. Programming sudden onset and stability detection criteria with a sustained, rate duration safety net for triggering tachycardia therapy results in appropriate device management in most patients with supraventricular and relatively slow ventricular tachycardia.

Sudden death in implantable cardioverter-defibrillator recipients: clinical context, arrhythmic events and device responses.

We sought to investigate the nature of terminal events and potential contributory clinical and nonclinical (e.g., device-related) factors associated with sudden death (SD) in recipients of an implantable cardioverter-defibrillator (ICD). The ICD is very effective in terminating ventricular tachycardia (VT) or ventricular fibrillation (VF), but protection against SD is not absolute. Little is known about the nature and potential causes of SD in patients with ICDs. We analyzed 25 cases of out-of-hospital SD among patients enrolled in the clinical investigation of the Cadence Tiered-Therapy Defibrillator System. All patients (24 men and 1 woman, mean age 62+/-10 years) received epicardial lead systems. The majority (92%) had coronary artery disease and a previous myocardial infarction (MI), with a mean left ventricular ejection fraction 0.25+/-0.07. At device implantation, the mean defibrillation threshold was 13+/-5 J. Sudden death occurred 13+/-11 months later. Twenty patients (80%) had received appropriate ICD therapies before death, and 18 (72%) were receiving > or = 1 antiarrhythmic drugs at the time of death. Sudden death was tachyarrhythmia-associated in 16 patients (64%), non-tachyarrhythmia-associated in 7 (28%) and indeterminate in 2 (8%). In the 16 patients with tachyarrhythmia-associated SD, the overall first therapy success rate in tachycardia and fibrillation zones was 60% and 67%, respectively. However, despite protracted therapies (> or = 2 shocks) in 7 (66%) of 12 patients who received fibrillation therapies, the final tachyarrhythmic episode was ultimately terminated by the ICD in 15 (94%) of the 16 patients, whereas 1 patient died after multiple (initially successful) internal and external shocks for intractable VT/VF during exercise. In 10 patients (40%) one or more, primarily clinical, factors potentially contributory to SD were identified: heart failure (n=8), angina (n=2), hypokalemia (n=1), adverse antiarrhythmic drug treatment (n=1) and acute MI (n=1). An additional 10 patients (40%) had experienced an increase in frequency of ICD shocks within 3 months of SD. Appropriate battery voltages and normal circuitry function were found in all devices interrogated and analyzed after death. In this select group of patients receiving a third-generation ICD, SD was associated with VT or VF events in nearly two-thirds of patients, and death occurred despite ultimately successful, although often protracted, device therapies. These observations, along with evidence of recent worsening clinical status, suggest acute cardiac mechanical dysfunction as a frequent terminal factor. In recipients with ICDs, SD directly attributable to device failure seems to be rare.

Cardiac death and stored electrograms in patients with third-generation implantable cardioverter-defibrillators

Objectives. We sought to utilize terminal stored intracardiac electrograms (EGMs) to study the electrophysiologic events that accompany mortality in patients with third-generation implantable cardioverter-defibrillators (ICDs).Background. Despite their ability to effectively terminate ventricular tachyarrhythmias, cardiac mortality in patients with ICDs remains high. The mechanisms and modes of death in these patients are not well understood.Methods. We retrospectively analyzed clinical data and stored EGMs from patients enrolled in the clinical trial of the Ventritex Cadence ICD. Of the 1,729 patients 119 died during 6 years of follow-up. The final recorded EGM was reviewed. Postimplant EGMs as well as 50 control EGMs were used to define normal EGM characteristics.Results. There were 36 noncardiac deaths (30%) and 83 cardiac deaths (70%). Of the cardiac deaths, 55 (66%) were nonsudden and 28 (34%) were sudden. When cardiac deaths were analyzed, 46 (55%) had no stored EGMs within 1 h of death, implying that the deaths were not directly related to tachyarrhythmias. In 37 cardiac deaths (18 nonsudden, 19 sudden), stored EGMs were present within 1 h of death. In these 37 deaths, the final EGM recorded was wide (>158 ms) in 33 (89%). Wide EGMs were interpreted as ventricular tachycardia in 27 and ventricular fibrillation in 6. In 13 of the 33 patients (39%) with wide EGMs, therapy was not delivered by the ICD, as it incorrectly detected a spontaneous termination of the arrhythmia. EGMs were significantly wider if recorded within 1 h, as compared with those recorded from 1 to 48 h before death (261 ± 124 vs. 181 ± 93 ms, p = 0.04).Conclusions. Only 37 patients (31%) who died after placement of an ICD had a stored EGM within 1 h of the time of death, suggesting that the majority of deaths (69%) were not the immediate result of a tachyarrhythmia. When EGMs were recorded, they were wide in 89% of patients. These wide EGMs most likely represent intracardiac recordings of electromechanical dissociation. Thus, of the 119 deaths, 112 (94%) were not the immediate result of a tachyarrhythmia.

Predischarge Arrhythmia Induction Testing of Implantable Defibrillators May Be Unnecessary in Selected Cases

Complete postoperative evaluation of implantable cardioverter-defibrillators (ICDs) before discharge, including arrhythmia induction, has been the standard since their introduction. Whereas the original ICDs provided little telemetered information and used separate pace-sense and defibrillation leads, modern, third-generation devices provide pace-sense function information in addition to other data and are used in conjunction with integrated transvenous endocardial leads that combine pace-sense and defibrillation function. Changes in lead position, which can potentially result in either an inability to detect fibrillation or to terminate it, should be mirrored by changes in resting pace-sense function. Thus, for newer ICDs implanted with integrated endocardial lead systems, it is possible that in at least some cases predischarge arrhythmia inductions can be avoided. Two hundred patients receiving third-generation ICDs in conjunction with integrated transvenous leads were evaluated before discharge. Defibrillation detection or termination problems were seen in 8. Declines in resting R-wave amplitude and pacing impedance were significantly associated with such complications (−7 ± 5 vs −0.3 ± 2.3 mV [p <0.0001] and −158 ± 138 vs −93 ± 76 Ω [p <0.05], for those with vs without complications, respectively), as were gross right ventricular lead migrations on chest x-ray. No patient with a defibrillation complication had an R-wave change of <3 mV. However, 13% of patients without complications had R-wave changes of >3 mV. It is concluded that a pace-sense evaluation of ICDs may be a satisfactory screen to determine those who need to go on to complete testing with arrhythmia induction in selected cases.

Caring for patients with third-generation implantable cardioverter defibrillators: from decision to implant to patient's return home

Caring for patients with third-generation implantable cardioverter defibrillators: from decision to implant to patient's return home

Enhanced Detection Criteria in Implantable Cardioverter-Defibrillators to Avoid Inappropriate Therapy

The aim of this prospective study was to evaluate the efficacy and safety of enhanced detection criteria, stability and sudden onset, for ventricular tachycardia (VT) in the therapy of implantable cardioverter-defibrillators (ICDs). These detection enhancements ensure a high specificity in detecting VT, thereby avoiding inappropriate therapy delivery due to supraventricular tachycardia. However, delayed sensing or even undersensing of VT may lead to a problematic, even fatal, outcome. In our study, the stability detection enhancement was programmed to discriminate atrial fibrillation (AF) in 84 of 124 patients with implanted ICDs and the sudden-onset detection enhancement in 47 of the 124 patients to discriminate sinus tachycardia. Using these enhancements in 124 patients with third-generation ICDs, 13 patients (11%) had inappropriate therapy during 20 months of follow-up. AF caused shock delivery in 6 patients (5%) and antitachycardia pacing in 4 patients, atrial flutter triggered shock therapy in 1 patient, and sinus tachycardia caused shock delivery in 2 patients. In 3 of the 13 patients inappropriate therapy recurred despite reprogramming the detection enhancements. The stability parameter of 241 spontaneous VT episodes as measured by the devices was 8 ± 7 msec. Only 10 (4%) VTs had a stability parameter >25 msec. In 46 patients a combination of both detection enhancements, stability and/or sudden onset, were programmed. The use of detection enhancements proved safe and no patient had suffered negative side effects due to prolonged detection time or therapy delay. Inappropriate shock delivery due to AF, a major complication in ICD therapy, was reduced to 5% of patients. The use of the stability enhancement is recommended for patients with intermittent or chronic AF. Selected patients profit from programming both the stability and sudden onset criteria. (Am J Cardiol 1996;78(suppl 5A):42–50)

CIRCADIAN PATTERNS AND TRIGGERS OF SUDDEN CARDIAC DEATH

Sudden cardiac death and other acute cardiovascular events have been demonstrated to occur in certain temporal patterns. The study of these patterns may yield important clues to the pathophysiology of the disease process. Most studies of the timing of onset of sudden cardiac death have revealed a prominent midmorning peak, thought to be related to a surge in catecholamines associated with arising and assuming the upright posture, that is blunted or eliminated by beta blockers. In addition, some studies have also shown a secondary peak in late afternoon or early evening of uncertain cause. The development of third-generation implantable cardioverter defibrillators with memory capabilities offers a unique opportunity to accurately define event chronology.

960-83 A Prospective Study of Tested versus Nontested Antitachycardia Pacing in Implantable Cardioverter-Defibrillators

The value of testing antitachycardia pacing (ATP) for the termination of ventricular tachycardias (VT) in implantable defibrillators was evaluated in a prospective trial. Pre-discharge testing of antitachycardia pacing was attempted in 66 consecutive patients (pts) with non-thoracotomy third-generation implantable cardioverter-defibrillators (ICD). VT's could be induced in 18 pts (group A: 14 CAD, 3 DCM, 1 other) and were terminated by ATP at the pre-discharge testing at least twice. In 48 pts (group B: 30 CAD, 9 DCM, 9 others) the effectivity of ATP could not be tested due to non-inducible VT ATP was programmed in both groups as an autodecremental ramp with 81% of the tachycardia cycle length and up to 4 sequences with 8 to 11 stimuli. The mean follow-up was 10 months. Results: group A group B ATP-tested yes no patients (n) 18 48 VT episodes 532 491 ATP-termination 468 430 ATP unsuccessfull 29 41 VT-acceleration 35 (6.6%) 20 (4.7%) ATP-success rate 88% 88% The autodecremental ramp is a safe and effective antitachycardia pacing mode for terminating spontaneous ventricular tachycardias in 88% regardless of the result of the pre-discharge test.

Results of delivered therapy for VT or VF in patients with third-generation implantable cardioverter defibrillators.

Third-generation implantable cardioverter defibrillators (ICDs) offer tiered therapy and can provide significant advantage in the management of patients with life-threatening arrhythmias. Three different types of ICDs were implanted in 21 patients with ventricular tachycardia (VT) or ventricular fibrillation (VF). Arrhythmia presentation was VT (76%), VF (10%), or both (14%). The mean left ventricular ejection fraction for the group was 32.4 +/- 7%. No surgical mortality occurred. Prior to discharge individual EPS determined the final programmed settings of the ICDs. During a mean follow-up of 13 +/- 1.4 months (range 2-20) the overall patient survival was 85.7%. No sudden arrhythmic or cardiac death occurred. Twenty of 21 patients (95%) received therapy by their device. In 14 patients (67%) antitachycardia pacing (ATP) was programmed "on," 13 of which was self-adaptative autodecremental mode. There were 247 VT episodes, 231 of which were subjected to ATP with 97% success and 3% acceleration or failure. Low energy shocks reverted all other VT episodes. VF episodes were successfully reverted by a single shock (93%), two shocks (6%), or three shocks (1%). We conclude that ATP therapy of VT is successful in the large majority of episodes with rare failures, and that VF episodes are generally terminated by a single ICD shock.

Clinical benefits of third-generation implantable cardioverter-defibrillators

Clinical benefits of third-generation implantable cardioverter-defibrillators

Third generation antitachycardia pacing implantable cardioverter-defibrillators.

With advanced third-generation implantable cardioverter-defibrillator (ICD) technology, patients receiving electrical therapy may only be aware of symptoms such as palpitations, or may be completely unaware of the event. Third-generation ICDs provide bradycardia back-up pacing, antitachycardia pacing (ATP), cardioversion, and defibrillation therapy. Additional benefits are noninvasive electrophysiologic testing capabilities and enhanced diagnostic features. An alternative surgical approach with a nonthoracotomy lead system is now also available.

Effectiveness of noninvasive programmed stimulation for initiating ventricular tachyarrhythmias in patients with third-generation implantable cardioverter defibrillators.

Previous generations of implantable cardioverter defibrillators (ICDs) required invasive electrophysiological testing to assess defibrillator function. Newer third-generation ICDs include the capability for performing noninvasive programmed stimulation (NIPS) and may reduce the need for invasive studies to assess tachycardia recognition and antitachycardia therapy algorithms. The effectiveness of ICD-based NIPS for the induction of ventricular arrhythmias has not, however, been formally assessed. Third-generation ICDs were implanted in 79 patients, who underwent a total of 166 postoperative defibrillator tests. NIPS with rapid ventricular pacing was performed in all patients in an attempt to induce ventricular fibrillation. In patients with prior sustained uniform ventricular tachycardia, programmed stimulation with up to three extrastimuli was performed in order to attempt to initiate the clinical ventricular tachcardia. Ventricular fibrillation was induced with NIPS in 146 of 166 studies (88%). Ventricular tachycardia was initiated with NIPS in 104 of 123 studies (85%). The type of defibrillator and the use of endocardial or epicardial rate sensing/pacing leads did not influence the efficacy of NIPS. NIPS with third-generation ICDs is generally effective at inducing ventricular fibrillation and clinically relevant ventricular tachycardias, and reduces the need to perform invasive electrophysiological testing following device implantation. In a minority of patients temporary transvenous pacing catheters must still be used to facilitate arrhythmia induction.

Oversensing during ventricular pacing in patients with a third-generation implantable cardioverter-defibrillator

Objectives. The purpose of this study was to identify the causes of oversensing during ventricular pacing in patients with a thirdgeneration implantable cardioverter-defibrillator.Background. Third-generation implantable cardioverterdefibrillators have the capability for bradycardia pacing as well as antitachycardia pacing and defibrillation. With the Ventritex Cadence Tiered Therapy Defibrillator System, the pulse generator sensitivity is increased during bradycardia pacing to prevent undersensing of an arrhythmia with small amplitude signals.Methods. Records from 85 consecutive patients who underwent implantation of a Cadence device for treatment of ventricular tachyarrhythmias were reviewed.Results. Four patients required continuous pacing for bradyarrhythmias. In three of these patients, ventricular pacing was accomplished using the bradycardia pacing feature of the Cadence device. All three experienced spurious device discharges or had aborted shocks for oversensing. Analysis of real-time and stored electrograms revealed intermittent high frequency, large amplitude noise in two patients and oversensing of maximally gained R and T waves in the remaining patient. No evidence of lead fracture was found in any patient. The problem was solved by implantation of a separate permanent pacemaker in two patients and was partially solved by reprogramming of the device in the remaining patient.Conclusions. Although the Cadence implantable cardioverterdefibrillator has the capability for ventricular pacing in patients with bradyarrhythmias, certain features of its automatic gain control circuit limit its utility in this instance. Oversensing occurs commonly, leading to device discharges or aborted shocks. Implantation of a separate permanent pacemaker may be required in patients who have a Cadence device for tachyarrhythmia control and who also need pacing for bradycardia.

Clinical outcome of patients with malignant ventricular tachyarrhythmias and a multiprogrammable implantable cardioverter-defibrillator implanted with or without thoracotomy: An international multicenter study

Objectives. The long-term efficacy and safety of a thirdgeneration implantable cardioverter-defibrillator implanted with thoracotomy and nonthoracotomy lead systems was evaluated in a multicenter international study.Background. The clinical impact of transvenous leads for nonthoracotomy implantation and pacing for bradyarrhythmias and tachyarrhythmias in implantable cardioverter-defibrillator systems is not well defined.Methods. The safety of the implantation procedure and clinical outcome of 1,221 patients with symptomatic and life-threatening ventricular tachyarrhythmias who underwent implantation of a third-generation cardioverter-defibrillator using either a thoracotomy approach with epicardial leads (616 patients) or a nonthoracotomy approach with endocardial leads (605 patients) in a nonrandomized manner was analyzed. The implantable cardioverter-defibrillator system permitted pacing, cardioversion, defibrillation, arrhythmia event memory and noninvasive tachycardia induction.Results. Successful implantation of an endocardial lead system was achieved in 665 (88.2%) of 686 patients and an epicardial system in 614 (99.7%) of 616 (p < 0.05). Perioperative 30-day mortality rate was 0.8% (1.8% including crossover) in endocardial implant recipients compared with 4.2% (p < 0.001) in epicardial implant recipients (3.6% without crossovers, p < 0.05, respectively). Implantation mortality risk was significantly lower for noathoracotomy systems irrespective of left ventricular ejection fraction or New York Heart Association functional class. Pacing therapies prevented need for cardioversion or defibrillation shocks in 89% of all ventricular tachycardia episodes and were comparably effective for both lead systems. Total survival rate at 2 years was significantly higher in endocardial (87.6%) than epicardial (81.9%) lead recipients (p < 0.001). Elimination of perioperative mortality from the analysis demonstrated comparable survival in both groups (p > 0.2).Conclusions. Third-generation cardioverter-defibrillators with monophasic waveforms can be successfully implanted with epicardial (99.7%) and endocardial (88.2%) lead systems. We conclude that endocardial leads should be the implant technique of first choice. Improved patient management and tolerance for device therapy is achieved with the addition of antitachycardia pacemaker capability in these systems.

Changes in cerebral perfusion during third-generation implantable cardioverter defibrillator testing

Third-generation implantable cardioverter defibrillators (ICDs) are designed to provide tiered therapy for ventricular tachycardia and ventricular fibrillation. At present, however, therapy prescription does not take into account the hemodynamic consequences of ventricular dysrhythmias. Design of “intelligent” devices depends on their ability to assess hemodynamic consequences of tachyarrhythmias and end-organ perfusion. Quantitative electroencephalography (QEEG) and transcranial Doppler flow provide sensitive and specific measures of cerebral perfusion during ICD testing and programming. In response to prolonged hypotension (> 15 seconds), transient loss of α power (i.e., increase in δ power) in the EEG spectrum, accompanied by impaired cerebrovasomotor reactivity (CVR), was observed in 25 of 91 hypotensive episodes in 15 patients, ages 36 to 72 years, predicting intolerance to the programmed ICD therapy. Conversely, intact CVR prevented ischemia, slowing in the EEG, and predicted tolerance to the therapy prescription. These changes were exaggerated in the erect posture during tilt-table ICD testing. During ventricular tachycardia, signs of cerebral hypoxia detected by QEEG and Doppler techniques were accompanied by a fall in transcranial oxyhemoglobin saturation measured by near-infrared spectroscopy. We conclude that transcranial Doppler and QEEG are sensitive indicators of cerebral perfusion. These techniques could be used as indexes of perfusion against which hemodynamic sensors for future ICDs could be evaluated.

Unique sensing errors in third-generation implantable cardioverter-defibrillators

Objectives. Third-generation cardioverter-defibrillators appear to be susceptible to unique sensing errors. This study was performed to determine the incidence and types of sensing errors in combination therapy implantable devices.Background. One of the advantages offered by third-generation implantable cardioverter-defibrillators is the combination of bradycardia and antitachycardia pacing and cardioversion-defibrillation capabilities in a single device. The potential for unique sensing errors, those caused by the conflicts presented by combining bradycardia and tachycardia sensing and therapy algorithms in the same device, has not been previously addressed.Methods. To determine the incidence of important sensing errors, 61 patients with a combination therapy device (Cadence [Ventritex] and PCD [Medtronic]) were studied for a 25-month period. In addition to surface electrocardiography recordings during implantation and routine device testing, real-time and stored electrograms recorded from the rate-sensing ieads (Cadence) and real-time marker channel recordings (PCD) were reviewed to diagnose sensing errors that resulted in symptoms, device inefficacy or delivery of inappropriate therapy. After recognition, specific reprogramming steps were performed in an attempt to avoid recurrent sensing errors.Results. A total of 13 sensing errors were diagnosed in 12 patients (19.7%); the incidence was similar in both devices. Five distinct categories of sensing errors were identified. After device reprogramming, only one recurrent error occurred in 98 patientmonths of follow-up.Conclusions. Important sensing errors occur in approximately 20% of patients with third-generation combination therapy cardioverter-defibrillators. Prompt diagnosis of sensing errors can lead to specific reprogramming steps to avoid recurrent errors.

Utility of transtelephonic ECG monitoring in evaluating discharges from a third-generation implantable cardioverter defibrillator

The authors report the case of a 60-year-old man with a third-generation implantable cardioverter defibrillator whose rate-sensing lead malfunction was diagnosed only after surface loop electrocardiographic (ECG) monitor recording. The stored R-R intervals suggested an irregular ventricular rhythm, but the loop ECG monitor demonstrated inappropriate shocks delivered during sinus rhythm.