Use of an Implantable Cardioverter Defibrillator in an Eight-Month-Old Infant with Ventricular Fibrillation Arising from a Myocardial Fibroma

We report our experience with use of a ICD in a 7-month-old infant who presented with VF. We utilized an epicardial patch and active generator in the abdomen. Development of mediastinitis required explantation and eventual replacement with a subcutaneous patch and active generator in the abdomen.     

Correlation Between the Ventricular Electrogram Amplitude in Sinus Rhythm and in Ventricular Fibrillation

During testing of implantable defibrillators, ability to sense ventricular fibrillation is assessed by observing electrograms and the emitted ECG interpretation channel during induced ventricular fibrillation. We hypothesized that ventricular electrogram amplitude in sinus rhythm could be used to predict the ventricular electrogram amplitude in ventricular fibrillation and serve as a first approximation of the "safety margin" for sensing ventricular fibrillation. We compared the peak-to-peak epicardial ventricular electrogram during sinus rhythm and ventricular fibrillation in 12 patients undergoing defibrillator implantation. The ventricular electrogram was recorded with an integrated bipolar lead and filtered at 10-50 Hz. Ventricular fibrillation was induced by alternating current and the ventricular electrogram measured from cessation of alternating current to the first countershock. The mean ventricular electrogram amplitude in sinus rhythm was 15.3 +/- 5.4 mV (range 7.1-25.5) and in 37 episodes of ventricular fibrillation was 8.3 +/- 3.6 mV (range 2.1-16.3). There was a significant relationship between the mean ventricular electrogram amplitude in sinus rhythm and in ventricular fibrillation (R = 0.7, P less than 0.001). There was wide variation among individuals in the decrease in the mean ventricular electrogram amplitude during ventricular fibrillation, with the ratio of mean ventricular electrogram in sinus rhythm to mean ventricular electrogram in ventricular fibrillation ranging from 0.29 to 1.05 (mean 0.55 +/- 0.20). This suggests that up to a fourfold decrease may be expected in the mean ventricular electrogram amplitude during ventricular fibrillation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Experience with a New Implantable Pacer-, Cardioverter-Defibrillator for the Therapy of Recurrent Sustained Ventricular Tachyarrhythmias: A Step Toward a Universal Ventricular Tachyarrhythmia Control Device

Ten consecutive patients (mean age 57.9 +/- 7.6 years) were treated with an investigational tachyarrhythmia control device, the implantable Medtronic Pacer-, Cardioverter-, Defibrillator model 7216A or 7217B. All patients had coronary artery disease with old myocardial infarctions and presented hemodynamically significant sustained ventricular tachyarrhythmias not suppressed by antiarrhythmic drug therapy and unrelated to acute myocardial infarction. In two patients a nonthoracotomy lead system was implanted. Lowest effective defibrillation energy ranged from 5 to 18 joules (mean 12.2 +/- 4 joules) for the epicardial bielectrode systems and were 15 and 18 joules for the nonthoracotomy lead system implants. The postoperative periods were unremarkable. Follow-up ranged from 7 to 19 months (mean 13.8 +/- 4.5 months). Spontaneous tachyarrhythmia episodes were detected and treated by the device in six patients, five of them received staged therapies. No deaths occurred and no hospital admissions were necessary for device related or ventricular tachyarrhythmia related complications. In conclusion, this integrated device represents a major step toward the development of a universal ventricular arrhythmia control device.     

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.     

Total Pectoral Implantation: A New Technique for Implantation of Transvenous Defibrillator Lead Systems and Implantable Cardioverter Defibrillator

We describe a new approach to tolal pectoral implantation of cardioverter defibrillators with an endocardial defibrillation lead system. Endocardial lead configuration used was an FDA approved right atrial-superior vena cavo defibriliation spring electrode, right ventricular bipolar sensing electrode, and a pectoral patch. Endocardial leads were implanted via a cephalic or an axillary venesection. Pectoral patch was placed in a sabmuscular position. In case of failure to obtain satisfactory thresholds, a small intercostal thoracofomy was performed via fhe same skin incision and patch placed over the epicardium instead of submuscular position and used with Ihe right atrial spring electrode. The device was implanted in the pectoral region, submuscularly, over the patch. Sixteen consecutive patients underwent this approach. With a submascular patch, adequate defibrillation thresholds (< 15 joules [J]) were obtained in 14 (87.5%) patients. In the other two, defibrillation thresholds of ≤ 15) were obtained with a epicardial patch. Pectoral implantation of the device was feasible in all 16 patients and none needed repositioning. Average postimplant hospital stay was 5 days. During follow-up period (average 5 months), none of the patients reported any major local symptoms and no problems have been encountered in device interrogation. Thus, total pectoral implantation of the cardioverter defibrillator including the patch, leads, and the device is feasible. Furthermore, in case of foilure to obtain adequate defibrillotjon thresholds with submuscular patch, an epicardial patch can easily be implanted and allows 100% successful defibrillation at energy levels of ≤ 15 J with right atrial patch configuration.     

Does Dual Chamber or Atrial Pacing Prevent Atrial Fibrillation? The Need for a Randomized Controlled Trial

Partially due to recent reports that cardiac antiarrhythmic therapy may have adverse effects on patient survival, clinicians have become more interested in the nonpharmacological prevention of atrial fibrillation. There is a large body of literature that suggests that the rate of development of atrial fibrillation in paced sick sinus syndrome patients is much lower in those patients who have received an atrial-based system, rather than a VVI system. However, all the published studies to date are retrospective, and fraught with potential bias favoring the AAI or DDD group. The authors strongly believe that the only way to determine if these suggestive but uncertain retrospective analyses are correct is to apply the same scientific rigor to this problem as has been applied to many other problems in cardiovascular medicine and perform a prospective randomized trial. A proposed trial design is discussed.     

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.     

Idiopathic Ventricular Fibrillation in Out-of-Hospital Cardiac Arrest Survivors

This study examined diagnostic and therapeutic roles of electrophysiological testing and long-term clinical outcome after out-of-hospital cardiac arrest due to idiopathic ventricular fibrillation. This is defined as ventricular fibrillation occurring in the absence of detectable underlying heart disease or metabolic or electrolyte disturbance. Out-of-hospital cardiac arrest resulting from idiopathic ventricular fibrillation is uncommon. Records of all patients who underwent electrophysiological testing between June 1979 and June 1992 were reviewed. Patients with out-of-hospital cardiac arrest due to idiopathic ventricular fibrillation were identified. Follow-up information was obtained by telephone interview in June 1992. Of 194 patients who underwent electrophysiological study after out-of-hospital cardiac arrest not associated with acute myocardial infarction, only six (4 male and 2 female) had idiopathic ventricular fibrillation. It was induced in only two patients by programmed ventricular stimulation. No sustained ventricular arrhythmias were induced in the remaining four patients. Four patients received implantable cardioverter defibrillators, one was treated with a β-adrenergic blocker, and one received no treatment. All patients were alive at a mean follow-up of 50 months. Two of the four patients without inducible sustained ventricular arrhythmias had events during follow-up. Of the two patients with inducible ventricular fibrillation, one experienced a cardiac arrest and documented ventricular fibrillation at 41 months after the index event and the other had had no recurrence at 15-month follow-up. All four patients with implantable cardioverter defibrillators were alive at last follow-up, and two had device discharges. In survivors of out-of-hospital cardiac arrest due to idiopathic ventricular fibrillation: (1) programmed electrical stimulation is of limited value for evaluating cause and guiding therapy; (2) a high rate of recurrent events is observed (50%); and (3) an implantable cardioverter defibrillator is effective for preventing a fatal outcome.     

A Prospective, Randomized Evaluation of a Nonthoracotomy Implantable Cardioverter Defibrillator Lead System

Nonthoracotomy lead systems for ICDs have been developed that obviate the need for a thoracotomy and reduce the morbidity and mortality associated with implantation. However, an adequate DFT cannot be achieved in some patients using transvenous electrodes alone. Thus, a new subcutaneous "array" electrode was designed and tested in a prospective, randomized trial that compared the DFT obtained using monophasic shock waveforms with a single transvenous lead alone that has two defibrillating electrodes, the transvenous lead linked to a subcutaneous/submuscular patch electrode, and the transvenous lead linked to the investigational array electrode. There were 267 patients randomized to one of the three nonthoracotomy ICD lead systems. All had DFTs that met the implantation criterion of ≤ 25 J. The resultant study population was 82% male and 18% female, mean age of 63 ± 11 years. The indication for ICD implantation was monomorphic VT in 70%, VF in 19%, monomorphic VT/VF in 6%, and polymorphic VT in 4% of the patients, respectively. The mean LVEF was 0.33 ± 0.13. The mean DFT obtained with the transvenous lead alone was 17.5 ± 4.9 J as compared to 16.9 ± 5.5 J with the lead linked to a patch electrode (P = NS), and 14.9 ± 5.6 with the lead linked to the array electrode (array versus lead alone, P = 0.0001; array versus lead/patch, P = 0.007). The results of this investigation suggest that the subcutaneous array may be superior to the standard patch as a subcutaneous electrode to lower the DFT and increase the margin of safety for successful nonthoracotomy defibrillation.     

Transcutaneous T Wave Shock: A Universal Method for Ventricular Fibrillation Induction

Our objective was to develop a universal noninvasive method for VF induction. ICD implantation requires VF induction. Conventional rapid ventricular stimulation may fail to induce VF. Some ICDs can deliver low energy shocks on the T wave to induce VF. We hypothesized that an external dual chamber pacemaker and an external defibrillator could be configured to allow reliable VF induction with any ICD system. A surface ECC signal was delivered to the atrial channel of an external dual chamber DDD pacemaker. The 'AV' delay was adjusted so that the ventricular output of the pacemaker was delivered to an external defibrillator synchronized to deliver 5–50 J. Twenty-six patients at ICD implant or follow-up had VF induced in native rhythm (sinus rhythm or atrial fibrillation), or during a ventricular pacing train (3–8 beats at cycle length 500–880 ms). VF was successfully induced in 14 of 25 (56%) patients in native rhythm; and in 16 of 17 (94%) patients during pacing (P = 0.013). VF induction success rate was 36% in native rhythm (31/86 attempts) and 88% during pacing (69/78 attempts) (P < 0.001). The 'R' to shock interval was 269 ± 31 ms in native rhythm and 257 ± 48 ms during pacing. Energy delivered from the external defibrillator was 19 ± 3 J in native rhythm and 21 ± 6 J during pacing. We concluded that VF induction by synchronizing a small external shock to the T wave is a fast, effective way to reliably ensure arrhythmia induction with any ICD at implant or follow-up. This method is more successful during pacing than in sinus rhythm.     

Ventricular Fibrillation Induction Using Nonsynchronized Low Energy External Shock During Rapid Ventricular Pacing: Method of Induction When Fibrillation Mode of ICD Fails

Third-generation implantable cardioverter defibrillators (ICD) are frequently implanted with non-thoracotomy systems and provide noninvasive methods for electrical stimulation and ventricular fibrillation induction. These modalities facilitate postoperative testing of the ICD. Rapid right ventricular burst pacing via the defibrillator is commonly used for initiation of ventricular tachyarrhythmias. However, with the available third-generation devices, ventricular fibrillation (VF) induction may be impossible in up to 19% of the patients. In these cases, transvenous placement of a right ventricular catheter has been required to generate VF and appropriately evaluate the device. We report a new technique of noninvasive induction of VF using a low energy external nonsynchronized shock delivered during ICD fibrillation induction pacing. In three patients, after all efforts to induce VF by the Ventritex Cadence V-100 had failed, a 20 J nonsynchronized shock was delivered during rapid RV pacing. This resulted in VF on the first attempt in all patients. This noninvasive technique of VF initiation may provide a useful clinical approach to ICD testing that eliminates the costs and risks of an invasive procedure.     

Pacing Induced Ventricular Fibrillation in Internal Cardioverter Defibrillator Patients: A New Form of Proarrhythmia

Current model internal cardioverter defibrillators (ICDs) have cardioversion, defibrillation, pacemaker, and telemetry function. Telemetry documents arrhythmia and facilitates therapeutic adjustments. We report two cases of pacing induced VF terminated by the defibrillator, with the device responsible for both initiation and correction of the arrhythmia.     

The Mean Ventricular Fibrillation Cycle Length: A Potentially Useful Parameter for Programming Implantable Cardioverter Defibrillators

In programming the implantable cardioverter defibrillator (ICD), the ventricular tachycardia (VT) detection cycle length (CL) is based on the CL of the documented tachycardia but the ventricular fibrillation (VF) detection CL is set arbitrarily. Appropriate programming of VF detection may not only reduce the incidence of inappropriate ICD shocks for non-VF rhythms but can also avoid the fatal underdetection of VF. The mean VFCL may provide a useful parameter for optimal ICD programming for VF detection if it is reproducible. This study examined the intrapatient reproducibility and interpatient variation of the mean VFCL in 30 ICD patients (25 men and 5 women, mean age 63 ± 13 years). A total of 210 VF episodes (7 ± 4 per patient, range 3–17) induced by T-wave shocks (166) or AC (44) at the ICD implant (30 patients) and the predischarge test (12 of 30 patients) were analyzed. The mean VFCL was calculated from the stored V-V intervals in the ICDs. Although the mean VFCL varied significantly from 171 ± 6 to 263 ± 11 ms (P < 0.01) among different patients, it was reproducible among different VF episodes in an individual patient (maximal variation 4–50 ms, P > 0.05). The mean VFCL was not significantly different between patients with and without antiarrhythmic drugs (210 ± 32 vs 210 ± 23 ms, P > 0.05) and was correlated with the ventricular effective refractory period (r = 0.5, P < 0.05). The mean VFCL varies greatly among different patients but remains reproducible in an individual patient, suggesting that the mean VFCL may serve as a reference for ICD programming of VF detection.     

Ventricular Tachycardia/Fibrillation: Therapeutic Alternatives

It is now clear that no single therapy is appropriate for a consecutive series of patients with ventricular tachycardia or ventricular fibrillation (VT/VF). Drug responders by electrophysiological studies, patients who are not inducible following surgery, and patients treated with an implantable cardioverter defibrillator (ICD) all can have similarly low sudden death rates and virtually identical long-term mortality. However, many patients fail to respond to drugs, and surgical risks are excessive in others, and always higher than for an ICD implant. Nevertheless, overall survival in each of these groups (and probably for patients treated with antitachycardia pacers and ablation) is about 60% at 60 months. Major challenges now are: (1) choosing therapy to maximize risk-benefit ratio; and (2) treatment of the pump failure and progressive disease that now accounts for most cardiac mortality.     

Systolic Arterial Pressure Recovery After Ventricular Fibrillation/Flutter in Humans

Although the elective induction of cardiac arrest for implantable defibrillator insertion under general anesthesia is widely used, the hemodynamics of recovery of arterial blood pressure after cardiac arrest is not well-defined. Accordingly, the time course of recovery of systolic arterial pressure was studied in seven patients during the repetitive induction of ventricular fibrillation (n = 6) or ventricular flutter (n = 1). The mean number of episodes of cardiac arrest was 7 ± 2, and the mean drop in systolic pressure was 84 ± 16mmHg. The mean recovery time for systolic pressure was 10 ± 6 seconds, the average systolic pressure recovery rate was 13 ± 14 mmHg/sec, and the mean percent systolic pressure recovery was 94%± 9%. A negative logarithmic relation was found to exist between the rate of systolic arterial pressure recovery and the duration of ventricular fibrillation or flutter with a correlation coefficient of 0.68 to 0.97 (P < 0.05) in five of the seven patients. A linear relation between the time for systolic pressure recovery and duration of asystole was also defined. These results are consistent with the view that prolongation of ventricular fibrillation or flutter increases the duration of arterial pressure recovery through a negative effect on left ventricular contractility. Increased understanding of these relations may lead to increased safety of implantable defibrillator insertion.     

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.     

Failure of a Second and Third Generation Implantable Cardioverter Defibrillator to Sense Ventricular Tachycardia: Implications for Fixed-Gain Sensing Devices

Failure to sense ventricular tachycardia and/or ventricular fibrillation by implantable cardioverter defibrillators (ICDs) is rare. We report a case in which persistent undersensing of monomorphic and polymorphic ventricular tachycardia occurred with a second and third generation ICD using fixed-gain sensing. This occurred despite adequate R wave sensing during sinus rhythm. The use of an endocardial sensing lead did not correct the problem. Failure to sense ventricular tachycardia in the third generation device with fixed-gain sensing occurred late after implantation and was discovered only at follow-up electrophysiology testing of the ICD. This problem could not be corrected by reprogramming of the device, and was not related to lead dislodgement. Placement of a new device with an automatic-gain sensing algorithm and use of previously implanted epicardial leads with better sensing characteristics provided appropriate sensing of ventricular tachyarrhythmias. The case illustrates the importance of testing the sensing of all ventricular arrhythmias in patients with fixed-gain ICD's. Follow-up electrophysiology testing and evaluation of epicardial and endocardial leads may be necessary in certain cases to ensure adequate sensing of ventricular tachyarrhythmias late after implantation.     

Left Ventricular Malposition of a Transvenous Cardioverter Defibrillator Lead: A Case Report

A case of left ventricular endocardial malposition of a transvenous implantabie cardioverter defibrillator (ICD) lead through a patent foramen ovale is presented. Diagnostic modalities include lateral chest radiography, echocardiography, and electrocardiographic analysis during lead placement. The operative therapy consists of open lead replacement. Measures to avoid lead misplacement are suggested.