Revised Implantation Procedure for Programmable Automatic Implantable Cardioverter Defibrillator: Don''t Discard the Magnet

The newest implantable defibrillator (Ventak 1550 AICD) introduces radiofrequency telemetric communication that obviates the need for activation and deactivation of the device by a magnet during implantation. We present three of our first ten cases of implantation in which difficulties in intraoperative sensing would have been undetected without use of the magnet for audible evaluation of sensing. Based on this experience, we recommend a revised implantation protocol in which audible confirmation of sensing for 30 to 60 seconds by means of a sterile magnet is performed twice (with a pacemaker, if present in DOO or VOO mode): at the time of system test before induction of arrhythmia with testing cables connected to permit recording of rate, morphology, and ECG interpretation channel signals; and after final connection of the leads to the AICD. This simple additional maneuver is a powerful troubleshooting tool during implantation that permits prompt identification of sensing problems.     

Serum Creatine Kinase Activity And Sensing Characteristics After Intraoperative Arrhythmia Induction Using Implantable Defibrillator Rate Sensing Leads

In 29 patients (24 men, 5 woman, mean age 57 +/- 14 years) we evaluated the effect of intraoperative arrhythmia induction during implantable defibrillator (ICD) placement using alternating current (AC) applied through the epicardial rate sensing leads on acute and chronic pacing thresholds, electrogram amplitudes, slew rates and serum creatine kinase levels. In 15 patients undergoing new ICD implantation, pacing thresholds, electrogram amplitudes, slew rates, and resistances were measured before and following at least three inductions of ventricular fibrillation (VF) using AC applied through the epicardial rate sensing leads. Fourteen patients who underwent VF induction using AC through the epicardial leads during initial implant (mean time of 31 months previously) underwent ICD pulse generator replacement only with parameters measured as above before and after at least two inductions, and these compared to the values at initial implant. In all 29 patients serum creatine kinase levels were obtained before, immediately following, and at 8, 16, and 24 hours after surgery. No significant change in acute pacing threshold, electrogram amplitude, slew rate or resistance occurred. Chronically there was an expected 154% increase in pacing threshold but no significant change in electrogram amplitude or resistance. Serial serum creatine kinase and MB isoenzyme determinations demonstrated no evidence of myocardial necrosis. We conclude that intraoperative arrhythmia induction during ICD implantation using AC applied through the rate sensing leads is a safe and effective technique.     

A Randomized Controlled Clinical Trial Comparing Ventricular Fibrillation Detection Time Between Two Transvenous Defibrillator Models

The Ventak AV is an implantable cardioverter defibrillator with dual chamber pacing capability. Features include detection and treatment of ventricular arrhythmias, detection of atrial arrhythmias, as well as dual chamber pacing. The objective of the investigation was to verify the efficacy of the Ventak AV in detecting ventricular fibrillation in the presence of dual chamber pacing. Thirty-three patients, who were to receive an implantable defibrillator were randomized (1:1) in a paired comparison study to the Ventak AV (study device) and the Ventak Mini (control) during defibrillation threshold testing. In order to create a "worst case scenario" for sensing of ventricular fibrillation, pacing was performed at high lower rate limit values (Ventak AV DDD pacing at 150/min, Ventak Mini at VVI 100/min). Ventricularfibrillation was induced and the randomized device was allowed to detect and treat the arrhythmia. This test was repeated for each patient using the alternate device in a randomized order, such that all patients were tested with both devices. The mean ventricular fibrillation detection time for the Ventak AV was 2.0+/-0.11 seconds and for the control device the detection time was 1.8+/-0.11 seconds (P = 0.26). Appropriate tachyarrhythmia therapy decision was documented in all episodes for both devices. The study patient population demonstrated equivalent ventricular fibrillation detection time between the Ventak AV and the Ventak Mini. The Ventak AV demonstrated effectiveness in detecting ventricular fibrillation in the presence of high rate dual chamber pacing.     

Distortion of Intracardiac Electrograms Following Defibrillator Shocks for Atrial Tachyarrhythmias

In three patients with a defibrillator system consisting of a Ventak P2 pulse generator and an Endotak C transvenous lead, we observed distortion of introcardiac electrograms following defibrillator shocks for atrial arrhythmias. There was a transient marked widening of the intracardiac ventricular complexes resembling ventricular tachycardia. This phenomenon should be recognized when evaluating arrhythmic episodes.     

Automatic implantable cardioverter-defibrillator: early experience at Wilford Hall USAF Medical Center.

Fifteen patients with malignant ventricular arrhythmias were treated with the automatic implantable cardioverter-defibrillator (AICD) over a 22-month period. The cause of the arrhythmia was coronary artery disease in 13 of the patients (87%), sarcoid cardiomyopathy in one (7%), and a primary electrical abnormality in one (7%). The mean ejection fraction was 29%, with a range of 15% to 70%. Fourteen of the patients had inducible ventricular tachycardia using program stimulation. Defibrillating and rate-sensing leads were inserted through a lateral thoracotomy in 13 patients and through a median sternotomy in two patients in conjunction with other cardiac procedures. The generators were positioned in a subcutaneous pocket beneath the left costal cartilage. There was one early and one late death, both due to congestive heart failure. Neither was related to a ventricular tachyarrhythmia, and in each patient the AICD was functioning properly at the time of death. The mean follow-up period was 11.5 months, with five patients receiving a total of 17 shocks. We conclude that the AICD is a highly effective, low-risk treatment for malignant ventricular tachyarrhythmias.     

Use of the Elective Replacement Indicator in Predicting Time of Automatic Implantable Cardioverter-Defibrillator Battery Depletion

The elective replacement indicator (ERI) of an automatic implantable cardioverter-defibrillator (AICD) is intended to be utilized as strict criteria for the appropriate timing of pulse generator replacement. The manufacturer's newest recommendations suggest replacement within 3 months post-ERI attainment and this applies to both AID-B units and the latest Ventak models currently being implanted with expectations or increased battery longevity. Twelve patients with the AID-B model were prospectively evaluated in regard to (a) time from attainment of ERI to generator exchange and (b) total battery life with respect to the presence or absence of spontaneous discharges. In the overall group, the ERI was reached at 18.9 +/- 3.9 months (mean +/- standard deviation). The time from ERI attainment to generator exchange due to battery depletion was 8.1 +/- 5.1 months, and total battery life was 27.3 +/- 3.1 months. In the group with spontaneous discharges, the duration of time (months) post-ERI to generator exchange was 5.7 +/- 2.6 but was 11.4 +/- 6.1 in the others (P = 0.052); battery life was 25.7 +/- 2.4 and 29.4 +/- 2.7, respectively (P = 0.03). We conclude that the current ERI recommendation seems overly conservative in planning generator exchange for patients without the occurrence of spontaneous discharges and appropriate for patients with such discharges.     

The challenge of endocardial right ventricular pacing in patients with a tricuspid annuloplasty ring and severe tricuspid regurgitation

On occasion, patients with a tricuspid annuloplasty ring may require permanent cardiac pacing. Although it is technically possible to pass a ventricular transvenous lead through a tricuspid valve with an annuloplasty ring, the procedure is complicated by considerable chamber enlargement and mechanical distortion of the tricuspid valve often with severe residual tricuspid regurgitation. Over a 25-month period, transvenous ventricular lead placement following insertion of a tricuspid annuloplasty ring was successfully performed in five patients (three women). The patient mean age was 66 years (range 55-77 years). Four cases had slow atrial fibrillation and another paroxysmal atrial fibrillation requiring His-bundle ablation. Two patients had mitral valve replacement and two aortic and mitral valve replacements. All patients had residual severe to torrential tricuspid regurgitation. Seven ventricular steroid-eluting screw-in leads were used. Single leads were used in three cases, whereas in two others, two ventricular leads were attached to a dual chamber pulse generator. Although technically difficult, ventricular lead placement was successful using standard guidewires with broad curvatures. Satisfactory acute and follow-up stimulation thresholds and sensing were obtained with the only complication being an intraoperative lead dislodgement, prompting a second ventricular lead. Successful transvenous lead placement across a tricuspid annuloplasty ring is possible.     

The Performance of the Probability Density Function in Differentiating Supraventricular from Ventricular Rhythms

The ability of the probability density function (PDF) of an automatic implantable cardioverter defibrillator (AICD) to reject supraventricular arrhythmias being recognized as ventricular was evaluated in 12 patients who were treated with an AICD (Ventak P 1600). The PDF criterion was monitored via telemetry with the sinus rate during exercise test. PDF was satisfied in seven patients at a rate of 75-144/min (mean 109/min), and not in the remaining five patients (mean rate 141/min). PDF was fulfilled in five of ten patients at a lower heart rate than predicted by the duty cycle index, derived from the ventricular patch lead electrogram at the implantation. Thus PDF is often fulfilled already at a moderately elevated sinus rate. If used to prevent inadvertent AICD discharges during rapid supraventricular rhythms, its performance should be tested in the individual patient.     

Magnet Application, a Cause of Persistent Arrhythmias in Physiological Pacemakers. Report of 2 Cases

Report of 2 cases. Magent application during routine pacemaker check-up induced persistent arrhythmias in two patients with physiological pacemakers. One patient had received an atrial synchronous ventricular demand pacemaker (VDD) because of alternating second-and third-degree atrio-ventricular block. During routine pacemaker follow-up, a magnet was applied over the pulse generator to measure the pacemaker rate. This converted the system to fixed rate ventricular pacing at a rate of 65 bpm which resulted in retrograde atrial activation. When the magnet was removed the retrograde conducted P-waves were sensed by the atrial amplifier and the ventricular output was triggered again, causing a re-entry pacemaker tachycardia with a rate of 175 bpm. The tachycardia could be suppressed by applying a magnet once more, but the pulse generator had to be programmed in the VVI-mode to prevent induction of the tachycardia again. A second patient had complete atrioventricular block and left heart failure. After three years of ventricular demand pacing, we decided to implant a DDD pacemaker because of persisting left heart failure and poor exercise tolerance. During a routine visit io the pacemaker clinic a magnet was applied over the pulse generator to measure the basic rate. The system was thus converted to fixed rate A-V-sequential pacing (DOO) which resulted in atrial flutter. When the magnet was removed and the pulse generator returned to its DDD mode, the atrial flutter was partially sensed by the atrial amplifier, resulting in a tachycardia with a variable rate up to 125 bpm. Fortunately we were able to terminate the atrial arrhythmia by applying the magnet again. In this patient fixed rate underdrive pacing stopped the atrial arrhythmia. (PACE, Vol. 5, September-October, 1982)     

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.     

Far-field QRS complex sensing: prevalence and timing with bipolar atrial leads

Sensing of far-field QRS complex through the atrial pacemaker lead may cause a number of pacemaker function disturbances, most of which are rarely seen with modern pulse generators. However, certain pulse generator algorithms will still be jeopardized by far-field QRS complex sensing. Intracardiac electrograms with markers were obtained by telemetry in 30 patients following implantation of a permanent bipolar atrial lead and a DDDR pulse generator. The occurrence and timing of far-field QRS complex sensing was studied at different atrial amplifier sensitivity settings. With paced ventricular complexes, QRS sensing was documented in all 30 cases at the maximum atrial sensitivity (0.1 mV). The median QRS complex sensing threshold was 0.3 mV, and the sensing window at high atrial sensitivities was 67-202 ms following the ventricular pacing impulse. In one case, QRS complex sensing was seen up to an atrial sensitivity of 1.5 mV. In 12 of 13 patients with 1:1 AV conduction, atrial sensing of spontaneously conducted ventricular complexes was seen (median sensing threshold 0.2 mV; the sensing window was -23 to 114 ms relative to the ventricular amplifier sensing event). Far-field QRS complex sensing was also found in all 12 patients in whom ventricular fusion complexes were obtained (median sensing threshold 0.2 mV; the window of sensing was 64-187 ms after the ventricular pacing impulse). Constant or intermittent QRS complex sensing via the atrial bipolar lead was thus universally demonstrable. It occurred in only a minority (20%) of patients at a sensitivity of 0.5 mV or less. Knowledge regarding the timing of the oversensing as related to the atrial sensitivity setting may aid in the design of algorithms of future pacemakers and cardioverter defibrillators.     

Combination of Antitachycardia Pacemaker and Automatic Implantable Cardioverter/Defibrillator for Ventricular Tachycardia

Antitachycardia pacing for ventricular tachycardia (VT) is associated with the possibility of fibrillating the heart; on the other hand, the frequency of VT and patient discomfort can limit treatment with the automatic implantable cardioverter/defibrillator (AICD). To contribute to the further development of a universal pacemaker, we evaluated the combined use of the antitachycardia pacemaker ("tachylog") and the AICD in five patients with recurrent VT. In the automatic mode, the "tachylog" worked as a bipolar VVI pacemaker. For antitachycardia pacing, a burst of rapid ventricular pacing was delivered at about 80% of the cycle length. During a follow-up period of 5 +/- 2 months (range, 3 to 8) two to 291 successful interventions of antitachycardia pacing were counted from diagnostic data which had been collected by the pulse generator during the course of treatment. When the antitachycardia pacemaker failed to terminate VT, the AICD was activated. In the individual case, between 0 and 41 discharges of the AICD were delivered. The high pulse energy of the AICD did not damage the antitachycardia pacemaker; no interference of the two devices was observed. Future antitachycardia systems should be more flexible with regard to detection and termination modes, combining antitachycardia pacing with back-up defibrillation.     

Preliminary Experience with the Helifix Electrode for Transvenous Atrial Implantation

A Helifix electrode was inserted transvenously in the right atrial appendage for temporary atrial stimulation in three patients. The low stimulation threshold as well as the excellent stability of the electrode encouraged us to proceed to permanent implantation of this lead in thirteen patients. The lead was introduced through the saphenous vein in twelve patients and through the cephalic vein in one patient. Five patients had sinoatrial dysfunction and five had bradycardia-tachycardia syndrome; they received atrial demand pacemakers. Two patients had atrioventricular block and received atrial synchronous ventricular pacemarkers. Our last patient had restrictive cardiomyopathy, heart failure and a drug-refractory atrial arrhythmia. She received a dual-chamber sequential pacing device. Atrial electrode displacement occurred in one patient soon after implantation. The lead was promptly repositioned without difficulty. Partial sensing of spontaneous P waves was observed in two patients. One recovered spontaneously, the second after substituting a pulse generator with a higher input sensitivity. Our clinical experience during the period from November 1977 to January 1979 has shown that the Helifix electrode is suitable for transvenous atrial implantation.     

Clinical Performance of the Implantable Cardioverter Defibrillator: Electrocardiographic Documentation of 101 Spontaneous Discharges

Records of 105 patients, who received an automatic implantable Cardioverter defibrillator (AICD), were studied to investigate the causes of spontaneous AJCD discharges and to correlate the symptoms with the arrhythmias triggering AJCD discharges. During a follow-up period of 13 ± 8 months, 46/105 (44%) patients had 566 spontaneous AICD discharges. A total of 101 discharges were documented with Holter monitoring in 23 patients. In this study group, there were 8 (8%) AICD discharges for 5 episodes of ventricular fibrillation, and 68 (67%) discharges for 63 episodes of sustained ventricular tachycardia. Patients lost consciousness in all episodes of ventricular fibrillation, but were symptomatic prior to only 36 (53%) discharges in ventricular tachycardia. Non-sustained ventricular tachycardia persisting for a period of 7,5 ± 2 seconds resulted in 20 AICD discharges; patients were symptomatic prior to 13 (65%) discharges. Supraventricular tachycardias triggered three discharges. One patient had two spurious discharges during sinus rhythm. In conclusion, most of the spontaneous AICD discharges were appropriate for the detected rhythms, but only clinically appropriate for the management of arrhythmias in 75% of the cases. A significant portion of the patients with sustained or nonsustained ventricular tachycardias triggering AICD discharges were asymptomatic prior to discharge, which requires further assessment of the physiology of the arrhythmia as a component of the detection algorithm.     

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.     

Implantation of the Automatic Implantable Cardioverter Defibrillator (AICD): Practical Aspects

Most patients who are resuscitated from an episode of sudden cardiac death or one of sustained ventricular tachycardia (VT) can now be treated using serial electrophysiologic testing as a guide to drug therapy. Recurrence rates are low if an antiarrhythmic regimen can be found which prevents induction of VT. Patients failing serial drug testing have a high recurrence rate (approximately 50%/year). Most clinicians now refer such patients for either experimental antiarrhythmic therapy or electrical intervention. The most promising of the electrical interventions (including tachycardia converting pacemakers and intraoperative mapping)has been the automatic implantable cardioverter defibrillator (AICD). Only recently has the AICD been released from investigative status by the Food and Drug Administration. It can be implanted safely and with favorable clinical outcome if the techniques of implantation are well understood and used often. The text incorporates the authors' experience in implanting nearly 200 devices and is intended as a practical guide to the use of the AICD.     

The Noise Sampling Period: A New Cause of Apparent Sensing Malfunction of Demand Pacemakers

Two patients with Omni-Stanicor pulse generators presented an apparent sensing problem characterized by intermittent reversion to fixed-rate pacing only during atrial fibrillation with a very rapid ventricular rate. Every fixed-rate cycle contained two unsensed beats. The first unsensed beat fell in the noise sampling period (the last 1/6 of the pacemaker refractory period) and, therefore, disabled the demand function of the pulse generator for a single timing cycle. The presence of two consecutively unsensed beats within one timing cycle (automatic or escape interval) during tachycardia suggests normal function of the noise sampling period of this particular pulse generator, rather than a true sensing problem. The diagnosis becomes evident if the sensing problem disappears when abbreviation of the refractory period occurs by reprogramming the pulse generator at a higher rate.     

Tachycardia Sensing Failure of an Implantable Cardioverter Defibrillator in a Patient with Hypertrophic Cardiomyopathy

A 17-year-old white male was found to have nonobstructive hypertrophic cardiomyopathy after suffering three severe syncopal episodes. He experienced an episode of sustained polymorphic ventricular tachycardia during exercise tolerance testing that required cardioversion. Electrophysiological studies were able to reproduce sustained polymorphic ventricular tachycardia that was unresponsive to standard pharmacotherapy. An automatic implantable defibrillator was placed. However, during implantation with the rate sensing electrodes on the left ventricle, it was found that the extremely polymorphic nature of the tachycardia caused such rapid fluctuations in the sensed R wave signal that the device could not properly detect the tachycardia. This was felt to be due to the automatic gain control circuit of the Ventak 1550. The problem was solved by moving the rate sensing electrodes to the lateral right ventricle. This case suggests that the unique arrhythmic substrate of hypertrophic cardiomyopathy may present sensing difficulties during automatic implantable defibrillator insertion.     

Use of the contralateral subclavian vein for placement of atrial electrodes in chronically VVI paced patients

Two patients with documented pacemaker syndrome were referred for AV sequential pacing and were found to have inaccessible venous systems on the side of their original transvenous pacemaker placement. The contralateral subclavian vein was subsequently catheterized with an atrial electrode using the sheath-set technique. Then the proximal aspect of the atrial endocardial lead was tunneled to the original pacemaker pocket. Once accomplished, both (atrial and ventricular) leads were connected to an AV sequential pulse generator. The united pulse generator and lead were reinserted in the original pacemaker pocket.     

A prospective randomized-controlled trial of ventricular fibrillation detection time in a DDDR ventricular defibrillator. Ventak AV II DR Study Investigators

Implantable cardioverter defibrillators (ICDs) with dual chamber and dual chamber rate responsive pacing may offer hemodynamic advantages for some ICD patients. Separate ICDs and DDDR pacemakers can result in device to device interactions, inappropriate shocks, and underdetection of ventricular fibrillation (VF). The objectives of this study were to compare the VF detection times between the Ventak AV II DR and the Ventak AV during high rate DDDR and DDD pacing and to test the safety of dynamic ventricular refractory period shortening. Patients receiving an ICD were randomized in a paired comparison to pacing at 150 beats/min (DDD pacing) or 175 beats/min (DDDR pacing) during ICD threshold testing to create a "worst case scenario" for VF detection. The VF detection rate was set to 180 beats/min, and VF was induced during high rate pacing with alternating current. The device was then allowed to detect and treat VF. The induction was repeated for each patient at each programmed setting so that all patients were tested at both programmed settings. Paired analysis was performed. Patient characteristics were a mean age of 69 +/- 11 years, 78% were men, coronary artery disease was present in 85%, and a mean left ventricular ejection fraction of 0.34 +/- 0.11. Fifty-two episodes of VF were induced in 26 patients. Despite the high pacing rate, all VF episodes were appropriately detected. The mean VF detection time was 2.4 +/- 1.0 seconds during DDD pacing and 2.9 +/- 1.9 seconds during DDDR pacing (P = NS). DDD and DDDR programming resulted in appropriate detection of all episodes of VF with similar detection times despite the "worst case scenario" tested. Delays in detection may be seen with long programmed ventricular refractory periods which shorten the VF sensing window and may be avoided with dynamic ventricular refractory period shortening.