Effect of cardiac resynchronisation therapy on occurrence of ventricular arrhythmia in patients with implantable cardioverter defibrillators undergoing upgrade to cardiac resynchronisation therapy devices.

BACKGROUND: Cardiac resynchronisation therapy (CRT) improves outcomes in selected patients with heart failure and left ventricular dysfunction. One mechanism of benefit is believed to be favourable ventricular remodelling. Whether CRT also decreases the frequency of ventricular arrhythmias and risk of sudden death is unknown. OBJECTIVE: To determine the effect of CRT on frequency of ventricular arrhythmias and appropriate ICD therapies. DESIGN: Retrospective cohort study. SETTING: Single-centre, tertiary care facility (Mayo Clinic). PATIENTS: 52 patients (46 male), aged 70 (SD 10) years, who underwent upgrade from an implantable cardioverter defibrillator (ICD) to a CRT-defibrillator were included. INTERVENTIONS: Upgrade of ICD to CRT-defibrillator. MAIN OUTCOME MEASURES: Frequency of ventricular arrhythmias prior to and following upgrade to CRT device. RESULTS: Ejection fraction increased from 22% (SD 8%) to 27% (SD 11%) following CRT. However, the frequency of non-sustained ventricular arrhythmias, sustained ventricular arrhythmias, and ventricular fibrillation was not significantly changed prior to and following CRT (2.38 (SD 9.78) vs 58.51 (SD 412.73) per patient per month, p = 0.66; 0.07 (SD 0.17) vs 0.16 (SD 0.52), p = 0.70; 0.05 (SD 0.12) vs 0.25 (SD 1.40), p = 0.12). CONCLUSIONS: CRT is not associated with a decrease in the frequency of ventricular arrhythmia or appropriate device therapy. Thus, use of CRT alone is not beneficial in decreasing the frequency of ventricular arrhythmias or the risk of appropriate ICD therapies.

Triboelectric simulation of pacemaker malfunction.

We report the occurrence of a triboelectric phenomenon (static electricity) that mimicked malfunction of a contemporary pacemaker by creating an electrocardiograpic artifact virtually identical to the pacemaker stimuli. The diagnosis was established by observing a subtle overshoot of the questionable deflection that was absent from pacemaker stimuli.

Breath-holding spells associated with significant bradycardia: successful treatment with permanent pacemaker implantation.

OBJECTIVE: To determine whether children with pallid breath-holding spells associated with bradycardia can be treated safely and successfully with permanent pacemaker implantation. METHODS: The records of pediatric patients who had apparent breath-holding spells and associated bradycardia and were treated with permanent pacemaker implantation were reviewed. RESULTS: Ten pediatric patients with apparent breath-holding spells associated with bradycardia were treated with a permanent ventricular demand pacemaker at the Mayo Clinic between 1985 and 1995. Patients had onset of symptoms between ages 6 days and 12 months and presented for evaluation between ages 12 months and 5 years. Duration of spells was 15 seconds to 10 minutes. Medications to prevent spells were unsuccessful. Electrocardiograms documented asystolic pauses of 1.7 to 24 seconds (mean: 11.9 seconds). Permanent ventricular demand pacemakers were implanted at 10 months to 5 years of age (median: 14.5 months): 9 endocardial and 1 epicardial. Three patients required pacemaker revision. At follow-up of 38 to 170 months (median: 65.5), 5 patients had complete resolution of spells, 2 had only mild color change without loss of consciousness or seizure activity, and 3 continued to have minor brief spells. CONCLUSIONS: Permanent pacemaker therapy for children with pallid breath-holding spells associated with severe bradycardia is safe, efficacious, and warranted.

Radiofrequency treatment of hepatic neoplasms in patients with permanent pacemakers.

Clinicians who provide care for patients with implantable devices for rhythm management, ie, pacemakers and internal cardioverter defibrillators, must be aware of sources of interference that could affect device function. Intracardiac radiofrequency is a recognized source of potential interference. However, radiofrequency to extracardiac sites that are relatively close to the implanted device has not been investigated thoroughly. We present 2 patients with permanent pacemakers undergoing intrahepatic radiofrequency for the treatment of metastatic disease. No interference was documented in either patient. Additional in vitro and in vivo studies are needed to determine definite clinical guidelines for such patients.

Left ventricular and biventricular pacing in congestive heart failure.

Dual-chamber pacing improved hemodynamics acutely in a subset of patients with left ventricular (LV) dysfunction but conveyed no long-term symptomatic benefit in most. More recently, LV pacing and biventricular (multisite) pacing have been used to improve systolic contractility by altering the electrical and mechanical ventricular activation sequence in patients with severe congestive heart failure (CHF) and intraventricular conduction delay or left bundle branch block (LBBB). Intraventricular conduction delay and LBBB cause dyssynchronous right ventricular and LV contraction and worsen LV dysfunction in cardiomyopathies. Both LV and biventricular cardiac pacing are thought to improve cardiac function in this situation by effecting a more coordinated and efficient ventricular contraction. Short-term hemodynamic studies have shown improvement in LV systolic function, which seems more pronounced with monoventricular LV pacing than with biventricular pacing. Recent clinical studies in limited numbers of patients suggest long-term clinical benefit of biventricular pacing in patients with severe CHF symptoms. Continuing and future studies will demonstrate whether and in which patients LV and biventricular pacing are permanently effective and equivalent and which pacing site within the LV produces the most beneficial hemodynamic results.

Evaluation of the coronary venous system using electron beam computed tomography.

New therapeutic strategies in interventional cardiology and electrophysiology involve the coronary veins. This study examines the potential usefulness of electron beam computed tomography to obtain detailed noninvasive definition of the coronary venous anatomy and of arteriovenous relationships. Electron beam computed tomography allows acquisition and three-dimensional reconstruction of tomographic images of the beating heart with high spatial and temporal resolution. Contrast-enhanced, thin-section electron beam computed tomographic coronary arteriographic images of 34 patients (21 men and 13 women, age 60+/-10 years) were analyzed. The visibility of the coronary veins and their spatial relationship to the coronary arteries were assessed qualitatively on two- and three-dimensional displays. The coronary sinus was visible in 91%, the great cardiac vein in 100%, the middle cardiac vein in 88%, at least one vein overlying the lateral surface of the left ventricle in 97%, the anterior interventricular vein in 97%, and the small cardiac vein in 68%. A left marginal and a left posterior vein were seen in 44%, one of the two in 38%, and neither in 3%. The course of the anterior interventricular vein was parallel to the left anterior coronary artery in 79% and a crossover between the two vessels at an obtuse angle occurred in 12%. Contrast-enhanced electron beam computed tomography imaging of the heart noninvasively provides information on the coronary venous system and arteriovenous relationships that may help guide new interventional procedures.

Unexpected ICD pulse generator failure due to electronic circuit damage caused by electrical overstress.

Because it is a lifesaving device, the unexpected failure of an ICD can be catastrophic. We report ICD electronic circuit failure due to electrical overstress damage (EOS) to the high voltage hybird circuit and other electronic components in a series of ICD pulse generator models. Data were obtained from the Multicenter Registry of Pacemaker and ICD Pacemaker and Lead Failures, and from the manufactures' adverse event reports, that were in the FDA's Manufacturer and User Facility Device Experience (MAUDE) database. Of 16 nonbattery Guidant/CPI ICD pulse generator failures reported to the registry, 6 (38%) have been confirmed by the manufacturer to be EOS related, and Guidant/CPI has reported 273 such failures to the FDA as of 12/29/00. The signs of failure included loss of telemetry and inability to deliver therapy, and some patients have experienced serious adverse events. Hybrid circuit damage may have occurred during capacitor charging or reform, and the majority appears to have happened during normal ICD function. While the incidence of this problem is unknown, a management strategy should be adopted that includes routine follow-up every 3 months and device evaluation after a shock or exposure to external defibrillation or electrosurgical devices. This study suggests that additional data are needed to determine the incidence of this problem, and that our present methods for monitoring the performance of ICD's following market release are inadequate.

Use of a transurethral microwave thermotherapeutic device with permanent pacemakers and implantable defibrillators.

OBJECTIVE: To determine whether a device (Urologix Targis system) used for transurethral microwave treatment interferes with sensing, pacing, and arrhythmia detection by permanent pacemakers and implantable cardioverter-defibrillators (ICDs). METHODS: We tested 13 pacemakers in both bipolar and unipolar sensing configurations and 8 ICDs in vitro. Pacemakers and ICDs were programmed to their most sensitive settings. Energy outputs of the microwave device were typical of those used clinically. The probe of the microwave device was anchored 1.2 cm from the pacemaker or ICD being tested. RESULTS: No sensing, pacing, or arrhythmic interactions were noted with any ICD or any pacemaker programmed to the bipolar configuration. One pacemaker (Guidant Vigor 1230) showed intermittent tracking when programmed to the unipolar configuration. CONCLUSIONS: Most patients with permanent pacemakers or ICDs can safely undergo transurethral microwave therapy using the device tested. Pacemakers and ICDs should be programmed to the bipolar configuration (if available) during therapy. The pacemaker or ICD should be interrogated before and after therapy to determine whether programming changes occurred as a result of treatment. However, our findings suggest that this is unlikely.

Cardiac pacing. A review.

Pacing is a field of rapid clinical progress and technologic advances. Clinical progress in the 1990s included the refinement of indications for pacing as well as the use of pacemakers for new, nonbradycardiac indications, such as the treatment of cardiomyopathies and CHF and the prevention of atrial fibrillation. Important published data and studies in progress are shedding new light on issues of pacing mode selection, and they may influence future practice significantly. Important technologic advances include development of new rate-adaptive sensors and sensor combinations and the evolution of pacemakers into sophisticated diagnostic devices with the capability to store data and ECGs. Automatic algorithms monitor the patient for appropriate capture, sensing, battery status, and lead impedance, providing better patient safety and pacemaker longevity.

Cellular phone interference with external cardiopulmonary monitoring devices.

OBJECTIVES: To determine the potential effect (electromagnetic interference) of cellular telephones on external cardiopulmonary monitoring devices. METHODS: For this study, we tested 17 different medical devices with 5 portable telephones (4 digital, 1 analog) to assess the potential for electromagnetic interference. The telephones were tested in a normal operating mode to simulate a typical hospital environment with patients or their families using their cellular phones. The medical devices were connected to the appropriate simulators for proper operation while the tests were under way. The screens and alarms of the medical devices were monitored while the telephones were maneuvered in the y and z planes near the devices. Clinically important interference was defined as interference that may hinder interpretation of the data or cause the equipment to malfunction. RESULTS: Any type of interference occurred in 7 (41%) of the 17 devices tested during 54.7% of the 526 tests. The incidence of clinically important interference was 7.4%. CONCLUSIONS: Cellular telephones may interfere with the operation of external cardiopulmonary monitoring devices. However, most of the test results showed that the interference would rarely be clinically important.

Second-degree atrioventricular block: a reappraisal.

In this review, we discuss the various forms and causes of second-degree atrioventricular (AV) block and the reasons they remain poorly understood. Both type I and type II block characterize block of a single sinus P wave. Type I block describes visible, differing, and generally decremental AV conduction. Type II block describes what appears to be an all-or-none conduction without visible changes in the AV conduction time before and after the blocked impulse. Although the diagnosis of type II block is possible with an increasing sinus rate, absence of sinus slowing is an important criterion of type II block because a vagal surge (generally a benign condition) can cause simultaneous sinus slowing and AV nodal block, which can superficially resemble type II block. The diagnosis of type II block cannot be established if the first postblock P wave is followed by a shortened PR interval or is not discernible. A pattern resembling a narrow QRS type II block in association with an obvious type I structure in the same recording (e.g., Holter) effectively rules out type II block because the coexistence of both types of narrow QRS block is exceedingly rare. Concealed His bundle or ventricular extrasystoles confined to the specialized conduction system without myocardial penetration and depolarization can produce electrocardiographic patterns that mimic type I and/or type II block (pseudo-AV block). All correctly defined type II blocks are infranodal. A narrow QRS type I block is almost always AV nodal, whereas a type I block with bundle branch block barring acute myocardial infarction is infranodal in 60% to 70% of cases. A 2:1 AV block cannot be classified in terms of type I or type II block, but it can be nodal or infranodal. Infranodal blocks require pacing regardless of form or symptoms. The widespread use of numerous disparate definitions of type II block appears primarily responsible for many of the problems surrounding second-degree AV block. Adherence to the correct definitions provides a logical and simple framework for clinical evaluation.

Is there an adverse outcome from abandoned pacing leads?

BACKGROUND: Indications for extraction of an abandoned pacemaker lead (APL) are controversial. The purpose of this study was to determine whether or not APLs should be extracted in the absence of pacemaker-related problems. METHODS AND RESULTS: We retrospectively reviewed, from 1977 through 1998, all patients with retained, non-functional leads and identified 433-266 males and 167 females. Mean age at initial pacemaker implantation was 68[emsp4 ]years. These patients received a total of 259 atrial and 948 ventricular leads. Of the total of 1,207 leads, 611 became non-functional. A total of 531 non-functional leads were abandoned, of which 18 were later extracted: one APL in 345 patients, two in 78, and three in 10. Indications for new lead placement when non-functional leads were abandoned included capture and/or sensing failure (243), lead recall (177), lead fracture (86), pacing system replacement to the contralateral side (11), accommodating patient growth (5), pacemaker function upgrade (5), replacement with implantable cardioverter defibrillator (ICD, 2), interference with ICD (1), and unknown (1). Complications that were associated with pacemakers were found in 24 patients (5.5%)-pacemaker system infection (8 patients) and venous occlusion at the time of a subsequent procedure of new lead placement when APLs had already been in place (16) which resulted in APL extraction (7) or transfer of the pacemaker system to the contralateral side (9). Neither venous thrombosis nor other complications were found in the remaining 409 patients (94.5%). The incidence of complications was higher in patients with three APLs than in patients with two or fewer APLs (40% vs. 4.7%, P=1x10(-6)), in patients with four or more total lead implantations than in patients with three or fewer total lead implantations (26.2% vs. 0. 6%, P<1x10(-10)), and in patients with three or more procedures of new lead placements than in patients with two or fewer procedures of new lead placements (36.4% vs. 3.9%, P=1x10(-10)). Patients with complications were younger than those without complications both at the time of initial pacemaker implantation (59+/-16 vs. 68+/-17 y, P=0.01) and when non-functional leads were abandoned (63+/-15 vs. 71+/-16 y, P=0.04). Mean numbers of APLs, total leads implanted, and procedures of new lead placement were significantly larger in patients with complications than in those without complications (1.58+/-0.78 vs. 1.2+/-0.44, 4.96+/-1.23 vs. 2.66+/-0.8, and 2.13+/-0.85 vs. 1.25+/-0.53, P=0.03, 4x10(-9) and 4x10(-5), respectively). CONCLUSIONS: 1. With only 5.5% of patients having had pacemaker-related complications, the adverse outcome of APL is small. 2. Clinical clues to the possible occasion for pacemaker-related complications include three or more APLs, four or more total leads, three or more procedures of new lead placement, and a younger age at initial pacemaker implantation. 3. Patients with a large number of APLs, total lead implantations, and procedures of new lead placement should be carefully observed to detect possible pacemaker-associated complications.

Factors affecting the frequency of subcutaneous lead usage in implantable defibrillators.

Subcutaneous leads (SQ) add complexity to the defibrillation system and the implant procedure. New low output devices might increase the requirement for SQ arrays, although this might be offset by the effects of active can and biphasic technology. This study sought to assess the impact of these technologies on SQ lead usage, and to determine if clinical variables could predict the need for an SQ lead. Patients receiving nonthoracotomy systems (n = 554) at our institution underwent step-down-to-failure DFT testing with implant criteria of a 10-J safety margin. SQ leads were used only after several endovascular configurations failed. Use of biphasic waveforms significantly lowered the frequency of use of SQ leads from 48% to 3.7% (P < 0.000001). SQ leads were required in 4.4% of patients with cold can devices and 2.6% of patients with active can devices (P = NS). There was no increase in SQ lead usage with low energy (< 30-J delivered energy) devices. Clinical variables (including EF, heart disease, arrhythmia, and prior bypass) did not predict the need for an SQ lead. The implant DFT using SQ arrays (14.5 +/- 6.5 J) was not significantly lower than that for SQ patches (16.6 + 6.0 J). We conclude that biphasic waveforms significantly reduce the need for SQ leads. Despite this reduction, 3.7% of implants still use an SQ lead to achieve adequate safety margins. The introduction of lower output devices has not increased the need for SQ leads, and when an SQ lead is required, there is not a significant difference in the implant DFT of patches versus arrays. Clinical variables cannot predict which patients require SQ leads.

Recommendations for extraction of chronically implanted transvenous pacing and defibrillator leads: indications, facilities, training. North American Society of Pacing and Electrophysiology Lead Extraction Conference Faculty.

The procedure of lead removal has recently matured into a definable, teachable art with its own specific tools and techniques. It is now time to recognize and formalize the practice of lead removal according to the current methods of medicine and the health care industry. In addition, since at this time the only prospective scientific study of lead extraction is the PLEXES trial, we suggest that studies relating to the techniques of and indications for lead extraction be designed. Recommendations for a common set of definitions, for a framework of training and reviewing physicians in the art, for general methods of reimbursement, and for consistency among clinical trials have been made. Implementation of these recommendations will require additional effort and cooperation from practicing physicians, medical societies, hospital administrations, and industry.

Monitoring equipment induced tachycardia in patients with minute ventilation rate-responsive pacemakers.

Minute ventilation-sensing pacemakers enable the paced heart to respond to an increased workload. Two patients with such a pacemaker developed pacemaker-driven tachycardia when connected to an electrocardiogram (ECG) monitor also capable of documenting ventilatory frequency and ECG lead disconnection. This tachycardia stopped when the ECG leads were removed. These pacemakers and monitors emit a low-amplitude electrical current and measure the resultant impedence signal across the chest. When patients are connected to the monitor the pacemaker sensor summates both impedence signals and the paced heart rate is increased as a result.

Determination of pacing capture in implantable defibrillators: benefit of evoked response detection using RV coil to can vector.

Automatic detection of capture in ICDs would be useful for ensuring normal pacing function and lead integrity and may increase device longevity. Evoked response detection can be difficult due to postpace polarization. Polarization on the RV coil to can vector, however, should be absent when pacing with a true bipolar lead (pace tip to ring). Polarization on the RV coil to can vector should be low in an integrated bipolar lead due to the large surface area of the coil. Ventricular-paced responses were prospectively recorded in 20 patients during ICD implantation or replacement. Capture and loss of capture responses were noted during threshold searches with electrograms recorded between the RV coil and can. A detector was designed to discriminate between capture and noncapture-paced responses using data from the first 11 patients and validated on the remaining 9. The detector had a sensitivity of 99.9% (detected capture on capture beats), and had a specificity of 100% (detected no capture on noncapture beats) for all lead configurations. There was no measurable polarization with true bipolar leads. In integrated bipolar leads, maximum polarization ranged from 0.0 to 16.7 mV. In conclusion, paced evoked responses can be detected in ICDs using the RV coil to can vector using standard pacing waveforms. Special polarization reducing pacing waveforms are not required. These observations could be used to design ICDs with automatic pacing threshold detection.

Permanent pacing in patients with univentricular heart.

Patients with one of several varieties of malformation designated as "univentricular hearts" may be especially challenging when permanent pacing is required. Our objective was to review our experience in this subset of patients that had undergone permanent pacing and thus determine the optimal approach. A retrospective chart review was done of 32 patients with some variety of "univentricular" malformation who had required permanent pacing at our institution. Although technically challenging, permanent pacing in this group of patients can be successful through several approaches. The various approaches, as well as consideration of the differences that exist between patients undergoing septation and those undergoing a Fontan procedure are discussed. Although long-term permanent pacing is possible in this group of patients, before pacing begins, a thorough understanding of the anatomy and prior surgical procedures is necessary. Use of a combined atrial transvenous and ventricular epicardial pacing system may work well for some patients. With the development of newer and more reliable coronary sinus leads, dual chamber transvenous pacing with ventricular stimulation via the coronary sinus could become the approach of choice in some patients with "univentricular hearts."