Circadian Variation in Atrial Fibrillation in Patients with Frequent Paroxysms

Determinants of the duration of episodes of atrial fibrillation (AF) in patients with paroxysmal atrial fibrillation (PAF) are poorly understood. However, autonomic tone shows circadian variation and is known to affect atrial electrophysiology. We therefore compared the duration of episodes of AF with an onset during the day (08:00 - 22:00) to those with an onset during the night in a database of 24-hour ECG recordings in patients with frequent symptomatic PAF. The heart rate in the 30 seconds prior to AF onset was also compared. From 42 recordings, 296 episodes of AF > 30 seconds duration and preceded by > 60 seconds sinus rhythm were identified. The 165 nocturnal episodes tended to be shorter (median =1.15 min) than the 131 diurnal episodes (median =1.5 min) and the distribution of nocturnal and diurnal durations was significantly different (P = 0.007; Kolgomorov-Smirnov test). This was also true in recordings containing at least 1 diurnal and at least 1 nocturnal episode. The mean heart rate prior to AF onset was lower at night (62.2 ± 11.8 vs 75.6 ± 16.4 beats/min; P < 0.0001 Wilcoxon test). These findings suggest that in patients with frequent symptomatic PAF, autonomic influences affect the duration of episodes of AF and has pathphysiohgical and therapeutic implications.     

Age and Gender Influences on Rate and Duration of Paroxysmal Atrial Fibrillation

The influence of age and gender on the character of paroxysmal atrial fibrillation (PAF) has not been described. Methods: The heart rate (HR) during PAF in patients receiving placebo or antiarrhythmic therapy was analyzed. Data from 177 24-hour Holter recordings were analyzed to mark the onset and termination of PAF and converted into RR interval files. PAF episodes lasting at least 2 minutes and containing ± 20% noise were included. HR during the first 30-second segment versus during the remainder of the episode, and the duration of PAF episodes were compared among groups of different ages and sex (Wilcoxon test). Results: 236 episodes from 55 recordings in 32 patients (all patients: 61.4 ± 12.8 years; men (19): 58.5 ± 12.6 years; women (13) 65.5 ± 12.4 years, P = ns for difference in age) fulfilled the inclusion criteria. Women had a higher mean heart rate at AF onset (123 ± 35 beats/min vs 115 ± 20 beats/min, P = 0.02) and during the remainder of the episode (120 ± 25 beats/min vs 112 ± 22 beats/min at the start, P = 0.01, and 116 ± 26 beats/min vs 108 ± 18 beats/min subsequently, P = 0.01). Episodes tended to be longer in women (mean 89.8 min vs 50.5 min, P = NS) and in the aged (mean 83.8 min vs 46.9 min, P = NS). Conclusion: PAF episodes are associated with faster heart rates and last longer in women, which may reflect differing autonomic responses to AF. A slower ventricular rate during PAF in older patients probably reflects an increasing prevalence of impaired atrioventricular conduction.     

Remote, Wireless, Ambulatory Monitoring of Implantable Pacemakers, Cardioverter Defibrillators, and Cardiac Resynchronization Therapy Systems: Analysis of a Worldwide Database

Study Objective: To describe the daily routine application of a new telemonitoring system in a large population of cardiac device recipients.
Methods: Data transmitted daily and automatically by a remote, wireless Home Monitoring™ system (HM) were analyzed. The average time gained in the detection of events using HM versus standard practice and the impact of HM on physician workload were examined. The mean interval between device interrogations was used to compare the rates of follow-up visits versus that recommended in guidelines.
Results: 3,004,763 transmissions were made by 11,624 recipients of pacemakers (n = 4,631), defibrillators (ICD; n = 6,548), and combined ICD + cardiac resynchronization therapy (CRT-D) systems (n = 445) worldwide. The duration of monitoring/patient ranged from 1 to 49 months, representing 10,057 years. The vast majority (86%) of events were disease-related. The mean interval between last follow-up and occurrence of events notified by HM was 26 days, representing a putative temporal gain of 154 and 64 days in patients usually followed at 6- and 3-month intervals, respectively. The mean numbers of events per patient per month reported to the caregivers for the overall population was 0.6. On average, 47.6% of the patients were event-free. The mean interval between follow-up visits in patients with pacemakers, single-chamber ICDs, dual chamber ICDs, and CRT-D systems were 5.9 ± 2.1, 3.6 ± 3.3, 3.3 ± 3.5, and 1.9 ± 2.9 months, respectively.
Conclusions: This broad clinical application of a new monitoring system strongly supports its capability to improve the care of cardiac device recipients, enhance their safety, and optimize the allocation of health resources.     

Continuous versus intermittent monitoring of ventricular rate in patients with permanent atrial fibrillation

Background: Ventricular rate control (VRC) is an important treatment strategy for patients with permanent atrial fibrillation (AF). We assessed the prevalence of poor VRC and the adequacy of various intermittent monitoring regimens to accurately characterize VRC during permanent AF. Methods: We retrospectively analyzed data from dual chamber implantable cardioverter defibrillator (ICD) and cardiac resynchronization therapy defibrillator (CRT‐D) patients in the Medtronic Discovery? Link having permanent AF (AF burden >23 hours/day) and ≥365 consecutive days of device data. Poor VRC was defined as a day with the mean ventricular rate during AF >100 beats/minute (bpm) for ICD patients and >90 bpm for CRT‐D patients. Intermittent monitoring regimens were simulated from continuous device data by randomly selecting subsets of days in which data were available for analysis. Assessments of poor VRC were computed after replicating 1,000 simulations. Results: ICD (n = 1,902, age = 71 ± 10) and CRT‐D (n = 3,397, age = 72 ± 9) patients were included and followed for 365 days. The prevalence of poor VRC was 24.8% among ICD patients and 28.6% among CRT‐D patients. Significantly more patients were identified as having poor VRC with continuous monitoring compared to all intermittent monitoring regimens (sensitivity range = 8%–31%). Furthermore, 11.6% of ICD patients and 17.9% of CRT‐D patients experienced ≥7 days with poor VRC, to which the sensitivities of annual 7‐ and 21‐day recordings were <7% and <20%, respectively. Conclusions: A significant proportion of permanent AF patients experience poor VRC that would be missed with random intermittent monitoring. Whether improved knowledge of VRC with continuous monitoring will lead to improved outcomes compared to intermittent monitoring requires further study. (PACE 2012;1–7)     

Sinus and paced P wave duration and dispersion as predictors of atrial fibrillation after pacemaker implantation in patients with isolated sick sinus syndrome

The aim of this study was to prospectively evaluate the sinus and the paced P wave duration and dispersion as predictors of AF after pacemaker implantation in patients with isolated sick sinus syndrome (SSS). The study included 109 (69 women, mean age 72 +/- 11 years) patients with SSS, 59 with bradycardia-tachycardia syndrome (BTS). A 12-lead ECG was recorded before pacemaker implantation and during high right atrial and septal right atrial pacing at 70 and 100 beats/min. The ECGs were scanned into a computer and analyzed on screen. The patients were treated with AAIR (n = 52) or DDDR pacing. The P wave duration was measured in each lead and mean P wave duration and P wave dispersion were calculated for each ECG. AF during follow-up was defined as: AF in an ECG at or between follow-up visits; an atrial high rate episode with a rate of > or =220 beats/min for > or =5 minutes, atrial sensing with a rate of > or =170 beats/min in > or =5% of total counted beats, mode-switching in >/=5% of total time recorded, or a mode switching episode of > or =5 minutes recorded by the pacemaker telemetry. The ECG parameters were correlated to AF during follow-up. Mean follow-up was 1.5 +/- 0.9 years. None of the ECG parameters differed between patients with AF and patients without AF during follow-up, nor was there any difference between groups after correction for BTS and age. BTS was the strongest predictor of AF during follow-up (P < 0.001). P wave duration and dispersion measured before and during pacemaker implantation were not predictive of AF after pacemaker implantation in patients with isolated SSS.     

Analysis of 57,148 Transmissions by Remote Monitoring of Implantable Cardioverter Defibrillators

Introduction: Remote monitoring of implantable cardioverter defibrillators (ICD) is designed to decrease the number of ambulatory visits and facilitate the early detection of adverse events. We examined the impact of remote monitoring on clinical workload by a comprehensive analysis of transmitted events.
Methods: The study population consisted of 146 recipients of ICD capable of remote monitoring. Data were transmitted daily or in case of pre-specified events (e.g., arrhythmia, out-of-range lead and/or shock impedance). Transmitted events were classified as clinical (disease-related) or system-related. Event rates/patient/month were calculated and compared according to events classification and clinical groups.
Results: During a mean follow-up of 22 ± 16 months, a total of 57,148 remote transmissions were recorded. Of these transmissions, 1009 (1.8%) were triggered by a pre-specified event, including induced ventricular fibrillation (VF) episodes during defibrillation threshold testing. The median number of events/patient/month was 0.14. Event rates were similar in patients with primary and secondary prevention indications for ICD (0.15 vs. 0.11). After exclusion of the induced VF episodes, 5.6% of transmitted events were classified as system-related and 94.4% as clinical. The median number of clinical events/patient/month was 0.023. The clinical event-free rates were 62% and 45%, at 1 and 4 years, respectively.
Conclusion: Remote monitoring of ICD patients is feasible. Despite the large number of data transmissions, remote monitoring imposed a minimal additional burden on the clinical workload. The rate of triggered data transmissions by critical events was, relatively, very low.     

Efficacy of Dronedarone Versus Propafenone in the Maintenance of Sinus Rhythm in Patients With Atrial Fibrillation After Electrical Cardioversion

Purpose

Our objective was to compare the efficacy of dronedarone and propafenone in maintaining sinus rhythm in patients with atrial fibrillation (AF) after electrical cardioversion.

Methods

In this single-center, open-label, randomized trial, we randomly assigned patients with AF after electrical cardioversion to receive dronedarone 400 mg BID or propafenone 150 mg TID.Follow-up clinical evaluations were conducted at 1, 2, 3, and 6 months of treatment. The primary end point was the time to the first recurrence of AF.

Findings

A total of 98 patients were enrolled (79 men; mean age, 59.2 years; n = 49 per group). The median times to first recurrence of AF were 31 days in the dronedarone group and 32 days in the propafenone group (P = 0.715). The median (interquartile range) ventricular rates at first recurrence of AF were 76.5 (67.3–86.5) beats/min in the dronedarone group and 83.0 (71.0–96.0) beats/min in the propafenone group (P = 0.059).

Implications

Dronedarone and propafenone had similar efficacies in maintaining sinus rhythm in patients with AF after electrical cardioversion. The ventricular rate at the first recurrence of AF was numerically but not statistically significantly lower in the dronedarone group than in the propafenone group. ClinicalTrials.gov identifier: NCT01991119.     

Prevalence of Cancelled Shock Therapy and Relationship to Shock Delivery in Recipients of Implantable Cardioverter-Defibrillators Assessed by Remote Monitoring

Background: Cancelled shock therapy (CxTx) may presage shock delivery and shorten battery longevity of implantable cardioverter-defibrillators (ICDs). However, it is silent and has received little attention. Remote home monitoring (HM) with continuous surveillance and automatic daily data archiving allows investigation of CxTx.
Methods and Results: We retrospectively analyzed a database of 4,960 recipients of HM ICD, from 2002 to 2007. Over a mean follow-up of 445 ± 253 days, CxTx occurred in 1,392 (28%) patients, mostly as single episodes (n = 1,120). However, 142 patients (10% of patients with CxTx, 2.9% of the whole ICD population) had >10 CxTx. CxTx was followed by shock delivery in 432 patients, in 239 (55%) of whom CxTx occurred >10 days prior to shock delivery. In 113 patients (26%), CxTx occurred in the 72-hour period preceding the shock. A single CxTx preceded the shock in 74 of these 113 patients, and only eight patients had >3 CxTx.
Conclusion: CxTx was highly prevalent in unselected ICD recipients, though the intraindividual density of episodes was low. In 2.9% of the overall population, the number of CxTx was sufficient to shorten the battery longevity. A high number of CxTx usually did not predict the delivery of shocks.     

Efficacy of Ventricular Rate Stabilization by Right Ventricular Pacing During Atrial Fibrillation

To assess the effect of right ventricular pacing on rate regularity during exercise and daily life activities, 16 patients with sinoatrial disease and chronic atrial fibrillation (AF) were studied. Incremental ventricular pacing was commenced at 40 beats/min until > 95% of ventricular pacing were achieved during supine, sitting, and standing. Thirteen patients also underwent randomized paired submaximal exercise tests in either a fixed rate mode (VVI) or a ventricular rate stabilization (VRS) mode in which the pacingrate was set manually at 10 beats/min above the average AF rate duringthe last minute of each exercise stage. The pacing interval for rate regularization was shortest during standing (692 ± 26 ms) compared with either supine or sitting (757 ± 30 and 705 ± 26 ms, respectively, P < 0.05). During exercise, VRS pacing significantly increased the maximum rate (119 ± 5.2 vs 106 ± 4.2 ms, P < 0.05), percent of ventricular pacing (85%± 5% vs 23%± 7%, P < 0.05), rate regularity index (5.8%± 1.6% vs 13.4%± 1.9%, P < 0.05), and maximum level of oxygen consumption (12.4 ± 0.5 vs 11.3 ± 0.5 ml/kg, P < 0.05) compared with VVI pacing. There was no change in oxygen pulse or difference in symptom scores in this acute study between the two pacing modes. It is concluded that right ventricular pacing may significantly improve rate regularity and cardiopulmonary performance in patients with chronic AF. This may be incorporated in a pacing device for rate regularization of AF using an algorithm that is rate adaptive to postural and exercise stresses.     

Mechanism of Atrial Fibrillation:

Atrial fibrillation (AF) has been associated with premature beats and decreased atrial conduction velocity. This study examined a new index of dynamic inter-atrial conduction time (iaCT) in patients with paroxysmal AF (PAF). We compared 42 consecutive patients with paroxysmal AF (mean age = 52 ± 16 years) without structural heart disease with 39 age-matched patients (mean age = 49 ± 15 years) who underwent ablation of junctional tachycardias. Prior to investigation, all antiarrhythmic drugs were discontinued for an appropriate period of time. The following measurements were made: baseline iaCT (iaCTb) between high right atrium (HRA) and distal coronary sinus, iaCT during HRA pacing S1S1 600 ms (iaCTS1), maximum prolongation of iaCT during S2 and S3 delivery (iaCTS2, iaCTS3). We then derived the decremental index (DI), the maximum percent prolongation of iaCT = iaCT S3-iaCTS1/iaCTS1%. In patients with PAF, iaCTb was 81.3 ± 24 ms versus 59.5 ± 14 ms in controls (P = 0.0001). Atrial fibrillation was reproducibly and easily induced with a prominent increase in iaCT in 11 patients with AF. In this subgroup DI was 92 ± 17%, compared to 45 ± 21% in the other patients with AF (P = 0.0001) and 21 ± 15% in the control group (P = 0.0001). Spontaneous isolated or repetitive ectopic activity was observed in 11 patients with AF (26%), and decremental atrial conduction was observed in 76% of patients with AF. This study supports the role of dynamic inter-atrial conduction disturbances in patients with lone PAF. The DI may be a new index of vulnerability to paroxysmal AF.     

Epicardial and Nonthoracotomy Defibrillation Lead Systems Combined with a Cardioverter Defibrillator

The intraoperative and long-term results were reviewed in 67 patients who underwent implantation of the Ventritex Cadence defibrillator with either epicardial patch (EPI, 25 patients) or nonthoracotomy CPI Endotak (ENDO, 42 patients) defibrillation lead systems. In the ENDO group, 35 patients (83 %) had a defibrillation threshold (DFT) of ≤ 20 joules and did not require a subcutaneous patch. Intraoperatively, the DFT was 13 ± 9 joules (mean ± SD) for EPI and 15 ± 8 joules for ENDO (P = NS). There was no perioperative death in either group. During a mean follow-up of 12 ± 8 months, there was no sudden death, and four patients died from congestive heart failure (3 EPI, 1 ENDO). During follow-up, 875 spontaneous arrhythmia episodes (AE) occurred in 15 of 25 EPI patients (60%). versus 652 in 28 of 42 ENDO patients (67%; P = NS). Ventricular tachycardia at a rate ≥ 222 beats/min or ventricular fibrillation represented 167 AE for EPI (19%) and 182 AE for ENDO (28%), and was terminated by the first shock in 76% and 75% of attempts, respectively. Ventricular tachycardia at a rate ≥ 222 beats/min represented a total of 1,178 AE and antitachycardia pacing was successful in 660 of 708 AE (93%) with EPI and 414 of 470 AE (88%) with ENDO lead systems (P= NS). Therefore, a nonthoracotomy approach using the Cadence V-100 is safe and effective and has clinical results that are not significantly different from epicardial defibrillation lead systems.     

Acute Testing of the Rate-Smoothed Pacing Algorithm for Ventricular Rate Stabilization

We evaluated the capability of a new pacemaker-based rate-smoothing algorithm (RSA) to reduce the irregular ventricular response of AF. RSA prevents sudden decreases in rate using a modified physiological band and flywheel feature. Twelve patients (51 ± 21 years) with hemodynamically tolerated AF of 4 months to 20 years duration were studied. Atrial and ventricular leads were connected to the external pacemaker device in the electrophysiology laboratory. Consecutive RR intervals during AF were measured at baseline and after ventricular pacing with RSA ON. Ventricular pacing with the rate smoothing algorithm reduced maximum RR intervals (1,207 ± 299 vs 855 ± 148 ms, P = 0.0005), with no significant change in the minimum RR interval (401 ± 55 vs 393 ± 74 ms, P = 0.292). A small shortening of the mean RR interval (634 ± 153 vs 594 ± 135 ms, P = 0.007) was seen with no change in the median RR interval (609 ± 153 vs 595 ± 143 ms, P = 0.388). There was a 43% reduction in RR standard deviation (145 ± 52 vs 82 ± 28, P = 0.0005), 49% reduction in mean absolute RR interval difference (MAD) (152 ± 64 vs 77 ± 34, P = 0.0005) and MAD/mean RR ratio (0.23 ± 0.05 vs 0.13 ± 0.04, P = 0.0005). We conclude that rate-smoothed pacing effectively reduces RR variability of AF in the acute setting.     

Importance of the Site of Ventricular Tachycardia Origin on Left Ventricular Hemodynamics in Humans

Experimental animal data have indicated that the site of ventricular tachycardia origin and, hence, the degree of asynchronous contraction, may influence the hemodynamic tolerance during sustained ventricular tachycardia. However, data in man are scarce. We studied patients with preserved left ventricular function and absence of significant coronary artery disease. Ventricular tachycardia was simulated with rapid pacing (at 120 and 150 beats/min), performed randomly, from the right ventricular apex or the right ventricular outflow tract. Following pacing from one site, it was repeated from the alternate site. Compared to outflow tract pacing, QRS duration was significantly longer during rapid pacing from the apex. Left ventricular pressure was recorded using a micromanometer-tipped catheter. During sinus rhythm, peak systolic pressure was 142 ± 14 mmHg: at 120 beats/min, it decreased to 109 ± 12 mmHg during pacing from the apex and to 127 ± 21 mmHg during pacing from the outflow tract (P = 0.008). This difference diminished at 150 beats/min (101 ± 16 mmHg vs 112 ± 16 mmHg, respectively, P = 0.21). During sinus rhythm end-diastolic pressure was 13 ± 1 mmHg, which did not change significantly during pacing at 120 beats/min. During pacing at 150 beats/min, end-diastolic pressure increased to 21 ± 3 mmHg during pacing from the apex and to 16 ± 2 mmHg during pacing from the outflow tract (P = 0.005). Changes in first derivative of pressure and in isovolumic relaxation time constant were comparable during pacing from the two sites. Thus, it seems that tachycardias originating from the right ventricular outflow tract result in more favorable left ventricular hemodynamics, compared to those from the right ventricular apex     

Management of Atrial Tachyarrhythmias: Benefits of Pacemaker Diagnostics

FAUCHIER, L., et al.: Management of Atrial Tachyarrhythmias: Benefits of Pacemaker Diagnostics. The aim of this prospective multicenter study was to assess the clinical benefits of the Selection (Vitatron) pacemaker diagnostic functions (AF 1.0) in the management of AF. Forty patients (   71 ± 9  years   of age), with documented AF and conventional pacing indications, received a Selection. The AF 1.0 function of the pacemaker was programmed to document the AF burden, onset, daily distribution, duration, premature atrial beats before onset, and mode of onset of the last 12 episodes for AF episodes exceeding 180 beats/min. By comparing patients' symptoms records, patient conventional assessment at follow-up and AF 1.0 data, the investigators evaluated the usefulness of AF 1.0 in AF management at 3- and 6-month follow-ups. Usefulness was defined as a change in arrhythmia management prompted by the disclosure of AF 1.0 data. AF recurrences were recorded in 71% of the follow-ups with symptoms reported by patients in only 16%. Thirty-nine percent of therapeutic changes based on conventional assessment were confirmed by AF 1.0 data, and in 61% of instances, the initial changes were modified by AF 1.0 data. Changes included pacing parameters in 56% of cases, AF prevention with pacing algorithms in 37%, and medical treatment in 7%. All investigators indicated that AF 1.0 was useful in all patients. The AF 1.0 diagnostic functions offered a unique documentation of AF in asymptomatic patients, and allowed therapeutic adjustments impossible otherwise. (PACE 2003; 26[Pt. II]:233–238)     

A Prospective Multicenter Study Demonstrating Clinical Benefit with a New Accelerometer-Based DDDR Pacemaker

From November 1994 to October 1995, 63 patients (average age 66 years; 41 men) from 15 centers implanted with the Biotronik Dromos DR and Ergos TC 03 pulse generators were prospectively screened with an exercise test in the DDD mode for the presence of chronotropic incompetence (CI). Both pulse generators incorporate an identical accelerometer-based motion sensor. CI was defined as a maximum heart rate < 60% of age predicted maximum heart rate or 100 beats/min. Twenty-five patients (40%) met the criteria for CI. Two weeks later, CI patients were required to complete paired metabolic exercise testing in the DDD and DDDR modes on consecutive days with a 24-hour rest period. The order of testing was randomized and performed double blinded to minimize potential biases. Three patients who did not reach the anaerobic threshold (AT) and one patient who was unable to perform the metabolic testing were excluded from the analysis. Compared to the DDD mode, there were statistically significant improvements in the DDDR mode for all five endpoints: heart rate (84 ± 3.6 vs 113 ± 3.5 beats/min; P < 0.0001); total exercise time (8.23 ± 0.71 vs 9.15 ± 0.65 min; P = 0.0005); maximum VO₂ (17.76 ± 1.36 vs 20.43 ± 1.75 mL/kg per min; P = 0.0001); V0₂ at AT (13.1 ± 0.87 vs 14.59 ± 0.79 mL/kg per min; P < 0.01); and exercise time to AT (5.65 ± 0.61 vs 6.33 ± 0.53 min; P = 0.02). In conclusion, the results of paired metabolic exercise tests with the Dromos DR and Ergos TC 03 pulse generators demonstrate a clear clinical benefit using the accelerometer-based sensor in the CI patient     

Exercise Chronotropy in Patients with Normal and Impaired Sinus Node Function After Cardiac Transplantation

The chronotropic response during graded, symptom limited exercise was investigoted in 32 cardiac transplant recipients a mean of 49 ± 18 days after transplantation. All patients had systematic evaluation of postoperative donor sinus node (SN) function and the cardioacceleratory response was compared according to the SN function. Twenty-one patients had normal postoperative SN studies (corrected SN recovery time < 520 msec, group I) while the SN function was impaired postoperatively in the remainder (n = 11, group II; corrected SN recovery time 4,149 ± 6,283 msec in 5 patients, junctionai escape rhythm in 6 patients). All patients had regained sinus rhythm at time of the exercise test Patients in group II had lower basal sinus rates at the beginning of exercise (91.5 ± 11 vs 101.4 ± 7 beats/min, P < 0.02). This lower chronotropy was maintained over every incremental step (F_{rato between groups}= 30, P = 0.0001, F_{rate vs workload}= 15, P = 0.0001 by two-way ANOVAJ and resulted in a significantly lower heart rate at individual peak exercise (108.3 ± 20 vs 124.2 ±13 beats/min, P < 0.02). A total of 14/16 patients in group I but only 2/16 patiejils in group 11 accomplished a peak heart rate ± 120 beats/min (P = 0.009). The workload achieved did not differ between the groups (107 ± 29 vs 102 ± 32 watts, P > 0.5). These data show a lower SN chronotropy during rest and at peak exercise in cardiac transplant recipients with postoperative SN deficiency and apparent normalization of SN fundion.     

Effects of Systolic Atrial Function on Plasma Renin Activity and Natriuretic Peptide Secretion after High Rate Atrial and Ventricular Pacing in Dogs

Rapid atrial rates cause electrical, structural remodeling, and neuro-humoral changes. This study compares the effects of mechanical remodeling on plasma renin activity (PRA) and atrial natriuretic peptide (ANP) secretion. Eight beagles were subjected to rapid atrial pacing (AP) at 400 beats/min for 16 days. After complete recovery of left ventricular function, they underwent rapid ventricular pacing (VP) at 240 beats/min of equal duration. Left atrial systolic maximal dimension (LAmax) and left atrial appendage (LAA) peak late emptying velocity (LAA-E) were assessed by echocardiography. Blood samples were taken from the right atrium and from the peripheral vein. LAmax after AP and VP enlarged significantly (2.16 ± 0.21 cm vs 2.41 ± 0.23 cm, P = 0.002). Compared with baseline, LAA-E velocities were significantly reduced (0.65 ± 0.12 m/s vs 0.26 ± 0.16 m/s, P = 0.001) after AP only. AP caused a significant elevation of PRA in right atrial (9.28 ± 4.23 nmol/L per hour) and peripheral samples compared with baseline values (4.82 ± 2.53 nmol/L per hour, P = 0.04). ANP levels increased after AP (1117.12 ± 252.21 fmol/L) with respect to baseline values (824.37 ± 159.08 fmol/L, P = 0.001). There was no difference in PRA and ANP levels between atrial and peripheral samples. Atrial size and impaired systolic appendage function play an important role in secretion of PRA and ANP. Both neuro-humoral pathways may be therapeutic targets in the treatment of patients with AF.     

Safety of Antitachycardia Pacing in Patients with Implantable Cardioverter Defibrillators and Severely Depressed Left Ventricular Function

The purpose of this study was to investigate the efficacy and safety of antitachycardia pacing (ATP) in third-generation implantable Cardioverter defibrillators (ICDs) for terminating spontaneously occurring ventricular tachycardias (VTs) in patients with severely depressed left ventricular (LV) function. Ninety-one patients with active ATP were followed for 16 ± 13 months. During this period, 775 VT episodes occurring in 36 patients were treated by ATP. The patients were divided into two groups according to their LV ejection fraction (LVEF): group A with LVEF ± 30% (n = 20), and group B with LVEF ± 30% (n = 16). There were no differences between both groups in age, gender, underlying heart disease, indication for ICD therapy, or drug therapy. The VT rates were comparable (group A: 183 ± 16 beats/min; group B: 180 ± 21 beats/min; P = NS). Eighty-three percent of all episodes (n = 332) in group A and 93% of the VTs (n = 443) in group B were ATP terminated (P ± 0.01). Ten percent of VTs in group A were accelerated by ATP into the ventricular fibrillation zone versus 2% in group B (P ± 0.01). The individual termination rate and acceleration rate per patient were comparable in both groups. All VT episodes unresponsive to ATP were converted by backup shocks. The efficacy of first-shock therapy was similar in both groups (group A: 89%; group B: 97%; P = NS). The proportion of patients who needed at least one backup shock for unsuccessful ATP was comparable in both groups (group A: 65%; group B: 56%; P= NS). We conclude that ATP is effective and safe in patients with recurrent VTs and severely depressed LV function, and it can be safely programmed in this group of patients to minimize the use of shock therapy.     

Ventricular Proarrhythmic Effects of Atrial Fibrillation are Modulated by Depolarization and Repolarization Anomalies in Patients with Left Ventricular Dysfunction

Background: Atrial fibrillation (AF) may have a ventricular proarrhythmic effect, particularly in the setting of heart failure. We assessed whether AF predicts appropriate implantable cardioverter-defibrillator (ICD) shocks in patients with left ventricular dysfunction and explored modulators of risk.
Methods and Results: A retrospective cohort study was conducted on 215 consecutive patients with ICDs for primary prevention having a left ventricular ejection fraction ≤ 35%. Mean age at ICD implantation was 61.0 ± 9.7 years and 17% were women. Overall, 22 patients (10.2%) experienced appropriate ICD shocks over a follow-up of 1.3 ± 0.7 years, corresponding to an actuarial event-rate of 5.8% per year. In univariate analysis, AF was associated with a 3.6-fold increased risk of appropriate shocks (P = 0.0037). Annual rates of appropriate ICD shocks in patients with and without AF were 12.9% and 3.5%, respectively (P = 0.0200). In multivariate stepwise Cox regression analyses controlling for baseline imbalances, demographic parameters, underlying heart disease, and therapy, history of AF independently predicted appropriate shocks (hazard ratio 2.7, P = 0.0278). Prolonged QRS duration (>130 ms) and QTc (>440 ms) modulated the effect of AF on appropriate shocks. Patients with both AF and QRS > 130 ms were more than five times more likely to receive an appropriate ICD shock (hazard ratio 5.4, P = 0.0396). Patients with AF and QTc > 440 ms experienced a greater than 12-fold increased risk of appropriate shocks (hazard ratio 12.7, P = 0.0177).
Conclusion: In prophylactic ICD recipients with left ventricular dysfunction, AF is associated with increased risk for ventricular tachyarrhythmias, particularly when combined with conduction and/or repolarization abnormalities.     

Analysis of the Corrected QT Before the Onset of Nonsustained Ventricular Tachycardia in Patients with Hypertrophic Cardiomyopathy

BARANOWSKI, R., et al .: Analysis of the Corrected QT Before the Onset of Nonsustained Ventricular Tachycardia in Patients with Hypertrophic Cardiomyopathy. This study examined ventricular repolarization before the onset of 37 episodes of nonsustained ventricular tachycardia (NSVT) in 26 untreated patients with hypertrophic cardiomyopathy (HCM). Fourteen episodes were recorded in patients with a history of cardiac arrest or patients who died suddenly during follow-up. The QT interval was measured beat-by-beat on 24-hour ambulatory electrocardiograms. Mean 24-hour, hourly QTc and QTc of the last 10 beats prior to NSVT, consisted of 4–50 cycles (mean   9 ± 10   ), at the fastest rates of 100–175 beats/min (mean 122 ± 22) were analyzed. NSVT was more prevalent during nighttime (23 episodes), than during daytime (14 episodes,   P < 0.05   ). No significant differences were observed between mean 24-hour, mean hourly QTc during the hour with NSVT, and QTc of the last 10 cycles prior to onset of NSVT. QTc was significantly longer in patients with a history of sudden cardiac death (SCD) or who died suddenly during follow-up than in survivors. The 24-hour QT variability was higher in nonsurvivors than in survivors (   -39 ± 6   vs   33 ± 6 ms, P = 0.03   ). Episodes of NSVT in untreated patients with hypertrophic cardiomyopathy were more frequent during the nighttime. The 24-hour QT variability was higher in nonsurvivors than in survivors. (PACE 2003; 26[Pt. II]:387–389)