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Recent studies have shown that transvenous atrial cardioversion is feasible with lead configurations primarily designed for implantable cardioverter defibrillators (ICD). The purpose of this study was to examine the influence of an active pectoral ICD can on the atrial cardioversion threshold (ADFT). Forty consecutive patients received a transvenous single lead system (Endotak DSP 0125, CPI, St. Paul, MN, USA) in combination with a left subpectoral ICD (Ventak Mini, CPI) for treatment of malignant ventricular tachyarrhythmias. Patients were randomized into two groups: 21 received a Hot Can 1743 and 19 patients a Cold Can 1741. Step-down testing of the ventricular defibrillation threshold (VDFT) was performed intraoperatively and evaluation of the ADFT for induced atrial fibrillation (AF) at predischarge. After testing, each patient received a 2-J shock and was asked to quantify discomfort on a numerical scale ranging from 0 to 10. Both groups were comparable with regard to all clinical parameters studied. The mean VDFT in patients with a Hot Can device was significantly lower than in patients with a Cold Can (7.5 +/- 2.3 J vs 9.8 +/- 3.8 J; P < 0.03). The mean ADFT in the Hot Can group tended to be lower than in the group with Cold Cans (3.4 +/- 1.4 J vs 4.5 +/- 2.4 J; P = 0.07), and the proportion of patients in whom atrial cardioversion was accomplished at low energies (< or = 3 J) was higher in patients with active compared with patients with inactive pulse generators (57% vs 26%; P < 0.04). The mean discomfort reported after delivery of a 2-J shock was comparable in both groups (Hot Can 5.2 +/- 1.9; Cold Can: 5.3 +/- 2.1; P = NS). We conclude that the inclusion of an active left subpectoral can in the defibrillation vector of a ventricular ICD seems to reduce the energy requirements for atrial cardioversion without increasing the discomfort caused by low energy shocks.

The prevalence and clinical significance of sleep-related breathing disorders (SRBDs) in patients with cardiac disease and a history of life-threatening ventricular tachyarrhythmias is unclear. Forty consecutive recipients of implantable cardioverter defibrillators (ICDs) with cardiac disease and a documented history of spontaneous, life-threatening, ventricular tachyarrhythmias underwent full night polysomnography. SRBDs were diagnosed if the apnea/hypopnea index was > 10. SRBD were diagnosed in 16 of 40 patients (40%): central sleep apnea (CSA) was present in 9 of these 16 patients (56%), 8 of whom had associated Cheyne-Stoke respiration. Seven of the 16 patients with SRBD (44%) had obstructive sleep apnea (OSA). Patients with and without SRBDs were comparable with respect to left ventricular ejection fraction, NYHA classification, underlying heart disease, ICD indications, and concomitant antiarrhythmic drug and beta-blocker therapy. Patients were followed prospectively for 2 years. ICD-treated ventricular tachyarrhythmias occurred in 10 of 24 patients (42%) without SRBD, in 4 of 9 patients (44%) with CSA, and in 3 of 7 patients (44%) with OSA (NS). The numbers and circadian distributions of episodes recorded during follow-up in patients without SRBD versus with CSA or OSA were not significantly different (14 +/- 25, median = 4 vs 4 +/- 5, median = 2.5 vs 15 +/- 15, median = 7, respectively). The 2-year mortality, which was entirely attributable to nonsudden cardiac events, was highest in patients with CSA (4/9 [44%], vs 0/7 [0%] with OSA, vs 3/24 patients (12.5%) without SRBD; P < 0.05).

The analysis of endocardial signals obtained from an electrode located in the right atrium enabled by new dual chamber implantable cardioverter defibrillators may be helpful to provide additional therapies such as overdrive pacing or low energy atrial cardioversion for the treatment of concomitant atrial flutter (AFL) or atrial fibrillation (AF). Algorithms for discrimination of atrial tachyarrhythmias based on rate counting are of limited efficacy. The aim of this study was to assess the intersignal variability by using fast discrete wavelet transforms (FDWT) as a new method of discrimination of AF from AFL. Patients with spontaneous episodes of AF/AFL or patients who developed AF/AFL during an electrophysiological study were studied. The endocardial signals were recorded from the high right atrium using a transvenous 5 Fr bipolar electrode catheter (interelectrode spacing: 1 cm). The signals were digitized (2 kHz, 12-bit resolution) after amplification and filtering (40-500 Hz). Within data segments of 10-second duration, 25 consecutive signals were selected and normalized and FDWT was applied. Standard deviations of the wavelet coefficients (SD) from coarse scales (scale 4-8) were calculated. A total of 94 data segments (AF: 52, AFL: 42) from 28 patients were analyzed. SD at each considered scale was higher for AF than for AFL (P < 0.001). SD at scale 8 discriminated between AF from AFL with 100% sensitivity and specificity. We conclude that assessment of intersignal variability of bipolar endocardial recordings using FDWT is an effective method for the discrimination of AF from AFL. The implementation of this tool in a discrimination algorithm of an implantable device may help provide the appropriate differential therapy for atrial tachyarrhythmias.

The purpose of our study was to determine the prevalence of sleep related breathing disorders (SRBD) in patients with an implantable cardioverter-defibrillator (ICD) and to evaluate prospectively the possible influence of SRBD on arrhythmia recurrence and circadian arrhythmia variation as well as on cardiac mortality during long-term follow-up. Forty consecutive ICD recipients with cardiac disease and a documented history of spontaneous, life-threatening, ventricular tachyarrhythmias underwent full-night polysomnography and were followed for 2 years. In 16 of 40 patients (40%), SRBD were diagnosed (Apnea/Hypopnea Index (AHI) > 10); in 9 of these 16 patients (56%) central sleep apneas (CSA) occurred (in 8 of these 9 patients in combination with Cheyne-Stokes respiration). Seven of the 16 patients with SRBD (44%) revealed obstructive sleep apneas (OSA). AHI was 32 +/- 15 (12-60) in patients with CSA and 32 +/- 27 (11-86) in patients with OSA. Patients with and without SRBD were comparable concerning left ventricular ejection fraction, NYHA classification, cardiac disease, ICD indication, and concomitant medication. ICD registered ventricular tachyarrhythmias occurred in 10 of 24 patients (42%) without SRBD, in 4 of 9 patients (44%) with CSA, and in 3 of 7 patients (44%) with OSA. The numbers and circadian variation of episodes registered during follow-up in patients without SRBD, with OSA or CSA were comparable (14 +/- 25, median 4 vs 15 +/- 15, median 7 vs 4 +/- 5, median 2.5). The 2-year cardiac mortality was highest in patients with CSA (4/9 (44%) vs. 0/7 patients (0%) with OSA vs 3/24 patients (12.5%) without SRBD. Thus, the prevalence of SRBD in patients with chronic heart failure and a history of malignant ventricular tachyarrhythmias is high (40%) and the occurrence of CSA seems to be predictive for cardiac mortality in these patients. An influence of moderate SRBD on arrhythmia recurrence and circadian variation of spontaneous sustained tachyarrhythmic events could not be demonstrated.

We studied retrospectively 60 consecutive recipients of an implantable cardioverter-defibrillator and identified 16 patients who were temporarily on and off beta-blockers (further medication unchanged). An intraindividual analysis revealed that 56% of the patients experienced more arrhythmic episodes during follow-up off beta-blockers compared to 44% while being on beta-blockers. Also, the mean episode frequency during follow-up time on and off beta-blockers was comparable (0.4+/-0.6 vs. 0.5+/-0.5, ns).

We analyzed spontaneous ventricular tachycardias treated by antitachycardia pacing during long-term follow-up in 138 recipients of an implantable cardioverter-defibrillator. An inverse circadian variation of the antitachycardia pacing termination and acceleration rates with the worst antitachycardia pacing success during the time period with the highest episode frequency (morning hours) was demonstrated.

Aims of the present study were (1) to investigate the clinical significance of short-term recurrent tachyarrhythmias (STRTs) in ICD recipient, (2) to identify basic characteristics of the subgroup of patients with STRTs and (3) to compare the frequency and circadian pattern of single arrhythmic events and STRTs. We reviewed data from 119 consecutive patients with late generation ICD. All registered spontaneous ventricular tachyarrhythmias were divided into STRTs (defined as two or more consecutive episodes separated by < or =1 h of sinus rhythm) and single events. During a mean follow up of 36+/-18 months (range 2-67 months) 1849 ventricular arrhythmic events were detected in 57 out of 119 ICD recipients (48%). 202 STRTs consisting of 1128 single detection (6+/-7/STRT, range 2-52) occurred in 34/57 patients (60%; 6+/-6 per patient, range 1-21). Recurrent ventricular tachycardias before device implantation and a high number of single arrhythmic events during follow-up distinguished patients with STRTs. Cardiac mortality was significantly higher in patients with STRTs (26 vs. 4%, P<0.05). The majority of both single episodes and STRTs were registered between 8 a.m. and noon and in the evening. This study reveals a high incidence of STRTs in ICD recipients with spontaneous tachyarrhythmias during follow-up and identifies STRTs as prognostic significant events. Comparable circadian variations suggest that similar triggering factors may be involved in the genesis of STRTs and single tachyarrhythmias.

We studied the possible relation between the frequency of ventricular tachyarrhythmic events and thermal stress in patients with an implantable cardioverter-defibrillator (ICD) living in a locally limited area under homogeneous climatic conditions. The frequency of tachyarrhythmic events was correlated with the thermal stress level according to the "Klima Michel Model," a complete thermophysiologic model that calculates "felt-temperature" values on the basis of the outdoor temperature and further meteorologic data. During a mean follow-up time of 40 +/- 17 months (range 4 to 72), 761 ventricular tachyarrhythmic events occurred in 50 of 138 consecutive ICD recipients. Analysis of the monthly felt-temperature levels and the mean circannual variation of the registered ventricular arrhythmias suggested that very cold and very hot conditions may be associated with an increased frequency of ventricular tachyarrhythmias. This finding was confirmed by calculation of the sum of tachyarrhythmias on all 2,039 days of the follow-up period divided into 5-degree-step felt-temperature classes. Thus, thermal stress may be 1 factor triggering the occurrence of ventricular tachyarrhythmias in patients with cardiac disease and suppressed cardiac function. Part of the increase in cardiac mortality under above-average hot and cold atmospheric conditions may be attributed to ventricular arrhythmic events.

The purpose of this study was to investigate the efficacy and safety of atrial cardioversion using an endocardial single lead system presently used for ventricular defibrillation. The study population consisted of 26 recipients of an ICD in combination with a conventional endocardial single lead system with the proximal spring electrode as anode in the SVC and the distal as cathode in the apex of the RV. Atrial tachyarrhythmias were induced by right atrial burst pacing. If the arrhythmia sustained > 1 minute, biphasic shocks synchronized with the R wave were delivered using the implanted device, beginning with an energy of 4 J. If 4 J failed to terminate the arrhythmia, energy was increased stepwise, if the first shock was successful, a step-down testing was performed after reinduction of atrial tachyarrhythmias. The mean atrial defibrillation threshold was 2.3 +/- 1.2 J (range, 0.5-5 J). A total of 154 shocks were delivered and no adverse effects were observed. The mean defibrillation threshold for atrial flutter was somewhat lower than that for AF (1.8 +/- 1 J vs 2.7 +/- 1.4 J, P = 0.08). There was no correlation between the atrial defibrillation threshold and a history of previously occurring atrial tachyarrhythmias, the kind of the underlying heart disease, a prescription of antiarrhythmic drugs, the dimension of the LA, the LVEF, or the ventricular DFT. Internal atrial cardioversion of short duration atrial tachyarrhythmias using a transvenous single lead system designed for ventricular defibrillation is feasible and safe at low energies, and may have important clinical applications.

The purpose of this study was to determine the termination and acceleration rates for 1 to 6 attempts of antitachycardia pacing [ATP] delivered by ICD in order to terminate spontaneously occurring VTs. Twenty-four ICD recipients with active ATP programs, including a maximum of six ATP sequences and spontaneously occurring VTs during follow-up, were investigated. During a mean follow-up of 42 +/- 15 months (range, 17-63 months) 413 spontaneous VT episodes (17 +/- 14; range, 1-49 per patient) resulting in appropriate ATP delivery by the ICD occurred. ATP successfully terminated 328 episodes (80%) with a mean number of 1.6 +/- 1.1 pacing sequences. Eighty episodes (19%) were accelerated by ATP and 5 (1%) were unresponsive to ATP. The ATP success decreased until the third ATP sequence (59%-->31%-->24%), but increased again in the fourth to sixth attempt (46%-->46%-->29%). The acceleration rate increased from sequence one to sequence three (8%-->13%-->28%), but decreased significantly in further ATP attempts (19%-->0%-->0%). The mean time delays until redetection or termination after 4, 5, and 6 attempts of ATP were 22 +/- 5 seconds, 37 +/- 2 seconds, and 41 +/- 9 seconds, respectively. Nine patients (37%) used > or = 3 ATP attempts during follow-up and all of them had a therapeutic benefit from it. Five out of 13 VTs (38%) treated with > or = 4 attempts could ultimately be terminated by ATP. The results of this study demonstrate that the first ATP sequence is the most effective and that > 4 ATP attempts may be useful in a minority of patients. There seems to be a low risk of VT acceleration by the fourth to sixth ATP sequence. Because of the associated time delay, a high number of ATP attempts should only be programmed in patients with hemodynamically well-tolerated stable VTs.

Atrial fibrillation (AF), the most common arrhythmia resulting in hospital admission, is a major health problem. The limited efficacy of antiarrhythmic drugs to control this rhythm disorder and their potential proarrhythmic risk led to the development of new techniques to ameliorate the treatment of AF. Transvenous atrial defibrillation using endocardial electrodes has been shown to be effective at low energy levels. An implantable atrial defibrillator could be a potentially valuable treatment option for patients with paroxysmal AF that is medically refractory. Research is currently under way to investigate several critical issues concerning this new therapeutic concept: long-term efficacy, safety, patient's tolerance, and an acceptable cost/benefit ratio. It is well known that AF often complicates the use of the implantable cardioverter-defibrillator (ICD) for ventricular tachyarrhythmias. Therefore, it would seem desirable to implement the capability for atrial defibrillation into current ICD systems. It has been shown that atrial defibrillation, using endocardial lead configurations specifically designed for ventricular defibrillation, is feasible at energies well within the capabilities of current ICD technology. Further research is needed to evaluate if some enhancement of the lead configuration in combination with possible advanced technology could reduce the atrial defibrillation threshold to a well tolerated level as a prerequisite for automated atrial defibrillation, in ICD recipients with concomitant paroxysmal AF.

Objective: To determine the prevalence of sleep-related breathing disorders (SRBD) on patients who, because of malignant ventricular tachyarrhythmias associated with cardiac disease, have an implanted cardioverter-defibrillator (ICD). It was also investigated whether the frequency and circadian distribution of spontaneous ventricular tachycardia and (or) fibrillation (VTF) can be influenced by SRBD., Patients and Methods: 29 consecutive ICD patients (28 men, one woman; mean age 64 +/- 8 years) were investigated by multifunction recordings. 22 patients had coronary heart disease, and seven dilated cardiomyopathy. For each patient the number of VIF episodes per month were recorded, as well as the percentage distribution of the episodes during the day per hour and after grouping into four time periods., Results: SRBDs were recorded in 13 of the 29 patients (45%) (apnoea-hypopnea index [AHI] > 10). The other 16 patients had normal findings (AHI < or = 10). Mean frequency of the registered VTF attacks was similar in both groups (0.41/month with AHI < or = 10 vs 0.44/month with AHI > 10; difference not statistically significant). Averaged percentage distribution pattern showed a maximum frequency in both groups between 6 o'clock and 12 o'clock a.m. There was no significant increase of VTF during the night (10 o'clock p.m.-6 o'clock a.m.) in the group with SRBD (19% with AHI > 10 vs 18.2% with ATF < or = 10; difference not significant)., Conclusion: There was a high prevalence of SRBD in the patients with ICD and underlying cardiac disease. No influence of SRBD on frequency and circadian distribution of VTF was demonstrated in patients with ICD during long-term observation.

The purpose of this study was to analyze temporal patterns of spontaneous ventricular tachyarrhythmias in patients (p) with implantable cardioverter-defibrillator (ICD). By reading out the ICD-data logs 725 arrhythmic episodes (e) from 43 patients were investigated. After grouping the episodes into four defined time periods (period 1: midnight to 6 a.m., period 2: 6 a.m. to noon, period 3: noon to 6 p.m., period 4: 6 p.m. to midnight) according to the data stored by the device, the percentage of episodes per time period has been calculated for each patient who experienced at least 10 arrhythmic events (n = 22). A significant peak occurrence (mean 34%) could been demonstrated for the morning hours (period 2). Analyzing patients individually, 4 subgroups could be identified: group 1 with an episode peak in period 2 (9 p, 277 e, p < 0.01), group with an episode peak in period 3 (4 p, 83 e, p < 0.01), group 3 with a peak occurrence in period 4 (3 p, 110 e, p < 0.01) and group 4 with an equal episode distribution over all four time periods (6 p, 187 e). Comparing sustained and nonsustained tachyarrhythmias, the nonsustained episodes were found to be distributed much more equally, meanwhile the circadian variation for fast (HR > or = 240/min) and slower (HR < 240/min) arrhythmias was identical. Regarding episodes of patients on beta-blocker or class III-antiarrhythmic therapy the same circadian variation has been found. There was no significant difference between the subgroups of patients with an episode peak in period 2 and the other patients concerning age, sex, cardiac disease, left ventricular ejection fraction, clinical arrhythmia, beta-blocker or class III-antiarrhythmics, number of recorded episodes or follow-up time. Further studies are needed to determine a possible correlation between these findings and different circadian variations in individual psychovegetative activity.