Patricia A. Kelly

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 third-generation implantable cardioverter-defibrillator. BACKGROUND Third-generation implantable cardioverter-defibrillators 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 cardioverter-defibrillator 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.

Low Dose Disopyramide Often Fails to Prevent Neurogenic Syncope During Head‐Up Tilt Testing

Low dose disopyramide has been used to prevent neurally‐mediated syncope during head‐up tilt testing but a correlation between blood levels and efficacy has not been described. We measured disopyramide levels in 15 patients with recurrent syncope and positive 70° head‐up tilt tests who underwent one or more repeat tests on the drug. There were 9 males and 6 females, age range 15–78 years. Fourteen of the 15 patients had structurally normal hearts. The daily disopyramide dose was 645 ± 165 mg (mean ± SD). Patients developed syncope during 9 tests and had no syncope during 12 tests. The mean disopyramide level in patients with positive tests was significantly lower than the level in patients with negative tests (2.4 ± 0.15 μ/mL vs 3.2 ± 0.22 μ/mL, P = 0.018). Six patients were tested twice on different disopyramide doses. Five of these six patients had syncope during head‐up tilt testing on the lower dose and negative tests on the higher dose (disopyramide levels 2.2 μ 0.17 μ/mL vs 3.2 μ0.17 fi/mL, P = 0.004). Thus, disopyramide is effective in preventing neurogenic syncope during head‐up tilt testing, but higher blood levels are often necessary for efficacy. In a given patient, failure to respond to low dose disopyramide does not preclude success on higher doses.

Palpitations Occur Frequently Following Radiofrequency Catheter Ablation for Supraventricular Tachycardia, But Do Not Predict Pathway Recurrence

Radiofrequency ablation of extranodal pathways is an effective treatment for supraventricular tachycardia, but late recurrences of pathway conduction do occur. To determine if recurrence of palpitations following ablation predicts pathway recurrence, we interviewed 77 patients who were at Jeast 4 weeks status‐post successful ablation of an accessory pathway (43 overt, 11 concealed)or a slow pathway (23)for AV nodal reentrant tachycardia. Palpitations were reported by 45 (58%)patients postablation, and 28 (36%)patients reported palpitations lasting ≥10 seconds and/or felt their symptoms represented recurrent tachycardia (major palpitations). Repeat electrophysiological testing was performed 3 months postablation in 53 patients, including 34 patients with palpitations (22 with major symptoms). Eight (10%)patients had recurrent pathway conduction demonstrated on repeat testing: two had no symptoms prior to restudy and six had major symptoms. One patient had major symptoms, but was found to have inducible atrial tachycardia and not pathway recurrence on restudy. Thus, 15 (68%)of 22 patients with major symptoms who were restud‐ied had no pathway recurrence or inducible arrhythmia to explain their symptoms. Of the 24 patients not restudied, none has had documented recurrent tachycardia or overt pathway conduction by electrocardiogram over a mean follow‐up of 335 ± 138 (range 132–616)days. Thus, palpitations, including palpitations reminiscent of preablation symptoms, are common following radiofrequency ablation and often do not predict pathway recurrence. Repeat electrophysiological testing is frequently required to document long‐term success of radiofrequency ablation for supraventricular tachycardia in patients with recurrence of major symptoms.

Tachycardia-induced cardiomyopathy in a cardiac transplant recipient: treatment with radiofrequency catheter ablation.

Tachycardia‐Induced Cardiomyopathy. Introduction: Two years after orthotopic cardiac transplantation, a 60‐year‐old man presented with unexplained congestive heart failure and an incessant atrial tachycardia.

Undersensing During Ventricular Tachyarrhythmias in a Third-Generation Implantable Cardioverter Defibrillator: Diagnosis Using Stored Electrograms and Correction with Programming

Third‐generation implantable cardioverter defibrillators with stored electrograms allow diagnosis of various sensing problems that may lead to an inappropriate device response. Undersensing of ventricular tachyarrhythmias is a potentially serious problem, as it may lead to failure to deliver therapy. To determine the incidence of this problem, we reviewed 98 patients with Ventritex Cadence defibrillator systems and found 2 patients in whom defibrillation therapy was delayed or aborted because of undersensing during induced ventricular tachyarrhythmias. In both cases, examination of stored electrograms revealed variation in electrogram amplitude, which presumably resulted in failure of the autogain feature to increase its sensitivity enough to count each complex. During charging, criteria for redetection of sinus rhythm were met because of this undercounting, leading to failure to deliver defibrillation therapy. This problem was detected in both patients 4–6 weeks following device implant during device testing, and both patients had been started on antiarrhythmic drug therapy prior to this testing. Programming the sinus redetection parameter from nominal to slow, increasing the number of beats necessary to confirm resumption of sinus rhythm, corrected the problem in both patients. Device testing in the electrophysiology laboratory, routinely postoperatively and following initiation of antiarrhythmic drug therapy, and the ability to retrieve stored electrograms are useful in detecting such sensing anomalies

Atrial Fibrillation After Implantable Cardioverter Defibrillator Implantation

Atrial fibrillation is a reported complication of automatic defibrillator implantation. Its incidence, risk factors, time‐course, and complications have not been well‐defined. Accordingly, data from 117 patients who underwent defibrillator implantation via a thoracotomy (n = 71) or nonthoracotomy (n = 46) approach were reviewed. To identify risk factors, 15 variables of potential predictive value were chosen and analyzed. Atrial fibrillation developed in 26/117 patients (22%) during the early postoperative period and all but one of these 26 patients had undergone thoracotomy (P < 0.001). Patients who developed atrial fibrillation tended to be older than those who did not (63 ± 2 vs 58 ± 2 years, P = 0.04) and more frequently had a prior history of paroxysmal atrial fibrillation (31 % vs 10%, P = 0.02). They were also less likely to be taking Class I or III antiarrhythmic drugs (1/26 vs 24/91, P = 0.01). By multivariate analysis, operative approach (P < 0.001), the absence of antiarrhythmic drug therapy (P = 0.006), and a prior history of atrial fibrillation (P = 0.003) were significant independent variables. Digoxin neither prevented the occurrence of atrial fibrillation nor slowed the maximal ventricular response. The mortality and complication rates did not differ between the two groups. The major adverse effect of postimplant atrial fibrillation was automatic defibrillator discharge; six patients received between 1 and 11 discharges for atrial fibrillation with rapid ventricular rates.

Developing a cardiology-oncology clinical practice guideline.

Clinical Practice Guidelines (CPG) have become an increasingly common method to assist practitioner and patient decisions about health care for specific medical problems. CPGs generally address a single medical diagnosis or syndrome leaving practitioners and patients with little guidance when two major medical diagnoses exist such as in the case of heart disease and cancer. As cancer and heart disease are both diseases of the elderly and share many common risk factors it is likely they will coexist in many patients. Thus screening for and preventing and treating heart disease in the cancer patient assumes increasing importance as aggressive cancer therapies are applied to older patients and as a growing number of cardiovascular side effects of anti-cancer therapy are described. Careful evaluation of heart disease in the cancer patient will likely improve quality of life but may also improve mortality as the presence or development of heart disease may significantly limit life-saving cancer therapies. The rationale, potential problems, and important steps in developing a cardiology-oncology guideline are discussed.

Inappropriate Shock Therapy for Nonsustained Ventricular Tachycardia in a Dual Chamber Pacemaker Defibrillator

We report a patient who Received a CPI Ventak AV II DR ICD for ventricular tachycardia and complete heart block without an escape rhythm. During induced nonsustained ventricular tachycardia, the device, although programmed to deliver noncommitted shocks, acted like a committed device. This phenomenon is due to undocumented behavior that is likely to occur in any patient who is pacemaker dependent and has nonsustained ventricular tachycardia.

Significant differences in charge times among currently available implantable cardioverter defibrillators.

Capacitor charging accounts for most of the delay between arrhythmia detection and therapy delivery in ICDs. Long capacitor charge times may increase the risk of syncope in patients with poorly tolerated arrhythmias. To determine if there are clinically important differences in charge time among currently available devices, we analyzed charge times at various delivered energy levels in three manufacturers’devices: Medtronic, CPI, and Ventritex, Charge times were measured for shocks delivered for spontaneous or induced arrhythmias occurring from time of implant to 4 months after implant. A total of 343 shocks were assessed in 63 patients with ICDs: 16 Medtronic (Microfewel II, model 7223Cx). 14 CPI (Mini II, model 1762), and 33 Ventritex (Cadet and Contour, models V‐115 and V‐145). The curves of the relationship between charge time and delivered energy for the three types of devices were significantly different, with Medtronic charge times shorter than CPI or Ventritex (P < 0.0001), and CPI charge times shorter than Ventritex (P ‐ 0.002). The difference in mean charge times between the Ventritex and Medtronic devices ranged from 1.7 seconds at a delivered energy of 10 ± 2.5 J to 8,0 seconds at a delivered energy of 30 ± 2.5 J. Thus, clinically important differences in charge time exist among the three types of defibrillators studied. These results should be considered in selecting an ICD for patients with poorly tolerated arrhythmias.

Implantation of an Automatic Defibrillator Using a New Nonthoracotomy Approach

Most current nonthoracotomy systems for defibrillator implantation use monophasic devices. To determine the safety and efficacy of a new nonthoracotomy lead configuration when used in conjunction with a device that used biphasic waveforms, 38 consecutive patients were taken to the operating room for implantation of a Cadence tiered therapy defibrillator system. The lead system consisted of a transvenous coil electrode positioned at the right atrial‐superior vena caval junction, a bipolar endocardial right ventricular lead, and a large patch placed subcutaneously near the cardiac apex. Of the 38 nontboracotomy defibrillator implantations attempted, 36 (95%) were completed with adequate defibriliation thresholds. The mean defibriliation threshold in these 36 patients was ± 563 ± 10 V (± 20 ± 1 J). There was no perioperative mortality. Complications included coil lead migration (5). sensing lead migration (1), infection (3), pneumothorax (2), arterial embolism (1), and folding of the subcutaneous patch with an increase in defibriliation threshold (1). No patient died during a median follow‐up period of 22 weeks. Fourteen patients (39%) had spontaneous sustained ventricular tachyarrhythmias, which were all successfully terminated by the implanted device. Shocks for nonsustained arrhythmias were aborted in eight patients (22%). Spurious discharges for sinus tachycardia or atrial fibrillation occurred in six patients (17%) and were readily diagnosed by examination of the stored electrograms. Thus, implantation of a biphasic tiered therapy defibrillator system using this nonthoracotomy approach is feasible in the majority of patients. The major complication associated with this procedure is lead dislodgment. The clinical course of these patients compares favorably with that of patients who have undergone defibrillator implantation via an epicardial approach.