Electrophysiological relation between the superior vena cava and right superior pulmonary vein in patients with paroxysmal atrial fibrillation.

INTRODUCTION: The superior vena cava (SVC) is a main source of nonpulmonary vein (PV) ectopies initiating atrial fibrillation (AF). Empiric SVC isolation may improve rhythm outcomes after catheter ablation of AF. Because the SVC passes immediately adjacent to the right superior PV (RSPV), an electrophysiological relation could be present between the two structures. The present study aimed to estimate the interrelation between the SVC and RSPV by evaluating arrhythmogenic activities observed during catheter ablation of AF. METHODS AND RESULTS: Study subjects comprised 121 consecutive patients referred for catheter ablation of paroxysmal AF. Isoproterenol infusion was used to induce ectopies and AF. Patients were divided into two groups depending on the presence of arrhythmogenic SVC: arrhythmogenic-SVC (A-SVC) and nonarrhythmogenic SVC (Non-A-SVC) groups. The prevalence of females was higher and body surface area was smaller in the A-SVC group (N = 22) than Non-A-SVC group (N = 99). Arrhythmogenic activities were observed in 60 (49%) RSPVs, 24 (20%) right inferior PVs, 72 (59%) left superior PVs, and 31 (25%) left inferior PVs. Arrhythmogenic RSPVs were more prevalent in the A-SVC group than Non-A-SVC group (86% vs. 41%, P = 0.0001), whereas these prevalences in the other three PVs were not different between groups (P >0.3). In multivariable analysis, arrhythmogenic RSPV was the only independent predictor of arrhythmogenicity of the SVC (OR, 8.53; 95% CI 2.31-31.46; P = 0.001). CONCLUSIONS: An electrophysiological interrelation may be present between the SVC and RSPV in patients with paroxysmal AF. Semiempiric SVC isolation limited to patients with an arrhythmogenic RSPV may be a more efficient treatment strategy.

Atrial Tachycardia Originating in the Vicinity of the Noncoronary Sinus of Valsalva: Report of a Series Including the First Case of Ablation-Related Complete Atrioventricular Block.

BACKGROUND: A few series of focal atrial tachycardia (AT) originating from the noncoronary sinus of Valsalva (NCSV) have been reported in the literature during the last decade. METHODS AND RESULTS: Of 147 patients with AT referred for radiofrequency ablation (RFA), we identified nine (6%) originating in the vicinity of the NCSV. Clinical AT was induced during electrophysiological study in all patients without (n = 6) and with (n = 3) isoproterenol infusion. Mean cycle length of the induced tachycardia was 399 ± 85 ms. Mapping of the right atrium and of the left atrium (LA) was initially performed in all nine patients and in four patients, respectively. Earliest tachycardia activation occurred at the His bundle area in all cases. Earliest activations in the LA were at the low paraseptal regions. In two patients with antegrade dual atrioventricular (AV) node physiology that rendered difficult accurate distinction between atrial and ventricular activation, slow pathway ablation was necessary. A retrograde aortic approach was used for mapping the aortic cusps. The earliest local atrial activation in the NCSV preceded the atrial activation in the His area in all patients by 27 ± 8 ms. RFA was performed in all nine patients and was acutely successful in eight. Two patients required radiofrequency (RF) energy outputs of 50 W in order to terminate the arrhythmia. In one patient, successful AT ablation was associated with complete AV block requiring implantation of permanent pacemaker. CONCLUSIONS: Focal AT can be successfully mapped and ablated in the NCSV. Higher than usual RF energy levels are sometimes required. Complete AV block is a possible complication.

Overdrive pacing from downstream sites on multielectrode catheters to rapidly detect fusion and to diagnose macroreentrant atrial arrhythmias.

BACKGROUND: Entrainment criteria for macroreentrant arrhythmias are based on detecting fusion between tachycardia and paced wavefronts, but this is often difficult for atrial tachycardias (AT) after ablation of atrial fibrillation. METHODS AND RESULTS: With the use of a multipolar catheter, pacing was performed from electrodes within the coronary sinus showing activation later than adjacent electrodes (downstream overdrive pacing) during 66 ATs in 62 patients: 20 cavotricuspid isthmus-dependent ATs, 20 perimitral ATs, 13 focal ATs with sequential coronary sinus activation, and 13 other macroreentrant left atrial ATs. The paced cycle length was 10 to 30 milliseconds below the tachycardia cycle length (TCL), and activation at the neighboring upstream electrodes was assessed. Downstream overdrive pacing at 48 sites close to a macroreentrant circuit (PPI-TCL <40 milliseconds, where PPI is postpacing interval) produced constant fusion demonstrated by a long stimulus to upstream atrial electrogram interval (S-Au) >75% TCL and was consistent with orthodromic activation of the upstream site despite its close proximity to the pacing site. In contrast, downstream overdrive pacing at 18 sites during focal AT or remote from the macroreentrant AT circuit (PPI-TCL >40 milliseconds) always demonstrated a comparatively short S-Au <25% of TCL (12±4% versus 89±4% of TCL; P<0.001), consistent with direct activation. CONCLUSIONS: Selection of a downstream activation site for overdrive pacing can facilitate rapid recognition of macroreentry and proximity to the reentry circuit using a single multielectrode catheter by recognizing a PPI-TCL <40 milliseconds and S-Au >75% of TCL. Recognition of intracardiac constant fusion with this method is a novel criterion for transient entrainment.

Failed anti-tachycardia pacing can be used to differentiate atrial arrhythmias from ventricular tachycardia in implantable cardioverter-defibrillators.

BACKGROUND: Atrial fibrillation/tachycardia (AF/AT) may result in inappropriate therapies in implantable cardioverter-defibrillators (ICDs). The post-pacing interval (PPI) and tachycardia cycle length difference (PPI - TCL) has been previously demonstrated to indicate the proximity of the pacing site to a tachycardia origin. AIMS: We postulated that the PPI and PPI - TCL would be greater in AT/AF vs. ventricular tachycardia (VT) after episodes of failed anti-tachycardia pacing (ATP). METHODS AND RESULTS: This was a single-centre, retrospective study evaluating consecutive patients implanted with dual (DR)/biventricular (BIV) ICDs. Stored electrograms were used to determine whether the ATP captured the arrhythmia and the arrhythmia did not present with primary or secondary termination. Measurements were done using manual calipers. A total of 155 patients were included. There were 79 BIV and 76 DR devices. In total, 39 episodes were identified in 20 patients over a 23-month follow-up period. A total of 76 sequences of ATP (burst/ramp) were delivered, 28 (37%) of them inappropriate. Fifty-one events (18 AT/AF and 33 VT) were compared. The mean PPI was 693 ± 96 vs. 512 ± 88 ms (P < 0.01) and the mean PPI - TCL was 330 ± 97 vs. 179 ± 103 ms (P < 0.01) for AT/AF and VT, respectively. Cut-offs of 615 ms for the PPI [area under curve (AUC) 0.93; 95% confidence interval (CI): 0.84-1.00; P < 0.01] and 260 ms for PPI - TCL (AUC 0.86; 95% CI: 0.74-0.98; P < 0.01) were identified. CONCLUSION: The PPI and PPI - TCL after failed ATP differs significantly between AF/AT and VT and are therefore useful indices to discriminate between supraventricular tachycardia and VT in ICDs.

Radiofrequency catheter ablation of atrial tachyarrhythmias after an atrial switch operation in a patient with univentricular heart combined with transposition of the great arteries.

A 31-year-old patient previously underwent a Mustard operation presented with palpitations. Atrial tachycardia and paroxysmal atrial fibrillation were documented on the surface electrocardiogram. Under the guidance of a three-dimensional electroanatomic mapping system, ablation of the isolated left-sided pulmonary vein and a cavo-tricuspid isthmus-dependent intra-atrial macro re-entry circuit eliminated atrial tachycardia and paroxysmal atrial fibrillation without the recurrence of atrial tachyarrhythmia.

Atrial tachycardia mimicking atrioventricular nodal reentry tachycardia.

BACKGROUND: The term supraventricular tachycardia (SVT) is used to describe tachydysrhythmias that require atrial or atrioventricular nodal tissue for their initiation and maintenance. SVT can be used to describe atrioventricular nodal reentry tachycardia, atrioventricular reentry tachycardia, and atrial tachycardia (AT). AT is the least common of these SVT subtypes, accounting for only 10% of cases. Although the suggested initial management of each SVT subtype is different, they all can present with similar symptoms and electrocardiographic findings. OBJECTIVE: Discuss the pathophysiology, diagnosis, and treatment of AT as compared with other types of SVT. CASE REPORT: We report a 56-year-old woman with symptoms and electrocardiographic findings consistent with SVT. Although standard treatment with intravenous adenosine failed to convert the SVT, it revealed AT as the cause of the tachydysrhythmia. The AT was successfully terminated with beta-blockade and the patient eventually underwent successful radioablation of three separate AT foci. CONCLUSIONS: AT frequently mimics other more common forms of SVT. AT might be recognized only when standard treatment of SVT has failed. Identification of AT in this setting is crucial to allow for more definitive therapy.

Continuous low-level vagus nerve stimulation reduces stellate ganglion nerve activity and paroxysmal atrial tachyarrhythmias in ambulatory canines.

BACKGROUND: We hypothesize that left-sided low-level vagus nerve stimulation (LL-VNS) can suppress sympathetic outflow and reduce atrial tachyarrhythmias in ambulatory dogs. METHODS AND RESULTS: We implanted a neurostimulator in 12 dogs to stimulate the left cervical vagus nerve and a radiotransmitter for continuous recording of left stellate ganglion nerve activity, vagal nerve activities, and ECGs. Group 1 dogs (N=6) underwent 1 week of continuous LL-VNS. Group 2 dogs (N=6) underwent intermittent rapid atrial pacing followed by active or sham LL-VNS on alternate weeks. Integrated stellate ganglion nerve activity was significantly reduced during LL-VNS (7.8 mV/s; 95% confidence interval [CI] 6.94 to 8.66 versus 9.4 mV/s [95% CI, 8.5 to 10.3] at baseline; P=0.033) in group 1. The reduction was most apparent at 8 am, along with a significantly reduced heart rate (P=0.008). Left-sided low-level vagus nerve stimulation did not change vagal nerve activity. The density of tyrosine hydroxylase-positive nerves in the left stellate ganglion 1 week after cessation of LL-VNS were 99 684 µm(2)/mm(2) (95% CI, 28 850 to 170 517) in LL-VNS dogs and 186 561 µm(2)/mm(2) (95% CI, 154 956 to 218 166; P=0.008) in normal dogs. In group 2, the frequencies of paroxysmal atrial fibrillation and tachycardia during active LL-VNS were 1.4/d (95% CI, 0.5 to 5.1) and 8.0/d (95% CI, 5.3 to 12.0), respectively, significantly lower than during sham stimulation (9.2/d [95% CI, 5.3 to 13.1]; P=0.001 and 22.0/d [95% CI, 19.1 to 25.5], P<0.001, respectively). CONCLUSIONS: Left-sided low-level vagus nerve stimulation suppresses stellate ganglion nerve activities and reduces the incidences of paroxysmal atrial tachyarrhythmias in ambulatory dogs. Significant neural remodeling of the left stellate ganglion is evident 1 week after cessation of continuous LL-VNS.

Radiofrequency ablation for atrial tachycardia and atrial flutter.

Atrial tachycardia is a generic term for a range of tachyarrhythmias with their origin in the atria. These can be broadly divided by mechanism into macro-reentrant, focal and small circuit re-entry. "Atrial flutter" is a term which, today, should be restricted to those classical circuits around the tricuspid annulus dependent on the cavo-tricuspid isthmus. The advent of sophisticated mapping solutions has rendered the vast majority of these atrial circuits curable with catheter ablation, with high success rates and very low incidence of complications.

Optimization of initial energy for cardioversion of atrial tachyarrhythmias with biphasic shocks.

OBJECTIVE: Recommendations for optimal first-shock energies with biphasic waveforms are conflicting. We evaluated prospectively the relation between type and duration of atrial tachyarrhythmias and the probability of successful cardioversion with a specific biphasic shock waveform to develop recommendations for the initial energy setting aiming at the lowest total cumulative energy with 2 or less consecutive shocks. METHODS: We analyzed 453 consecutive patients undergoing their first transthoracic electrical cardioversion, including 358 attempts for atrial fibrillation (AF) and 95 attempts for atrial flutter (AFL) or atrial tachycardia (AT). A step-up protocol with a truncated exponential biphasic waveform starting at 50 J was used. Total cumulative energies were estimated under the assumption of a 2-tiered escalating shock protocol with different initial energy settings and a "rescue shock" of 250 J for AFL/AT or 360 J for AF. The initial energy setting leading to the lowest total cumulative energy was regarded as the optimal first-shock level. RESULTS: Cardioversion was successful in 448 patients (cumulative efficacy, 99 %). In patients with AFL/AT, the lowest total cumulative energy was attained with an initial energy setting of 50 J. In patients with AF, lowest values were achieved with an initial energy of 100 J for arrhythmia durations of 2 days or less and an initial energy of 150 J for arrhythmia durations of more than 2 days. CONCLUSION: We recommend an initial energy setting of 50 J in patients with AFL/AT, of 100 J in patients with AF 2 days or less, and of 150 J with AF more than 2 days.

Reversal of global apoptosis and regional stress kinase activation by cardiac resynchronization.

BACKGROUND: Cardiac dyssynchrony in the failing heart worsens global function and efficiency and generates regional loading disparities that may exacerbate stress-response molecular signaling and worsen cell survival. We hypothesized that cardiac resynchronization (CRT) from biventricular stimulation reverses such molecular abnormalities at the regional and global levels. METHODS AND RESULTS: Adult dogs (n=27) underwent left bundle-branch radiofrequency ablation, prolonging the QRS by 100%. Dogs were first subjected to 3 weeks of atrial tachypacing (200 bpm) to induce dyssynchronous heart failure (DHF) and then randomized to either 3 weeks of additional atrial tachypacing (DHF) or biventricular tachypacing (CRT). At 6 weeks, ejection fraction improved in CRT (2.8+/-1.8%) compared with DHF (-4.4+/-2.7; P=0.02 versus CRT) dogs, although both groups remained in failure with similarly elevated diastolic pressures and reduced dP/dtmax. In DHF, mitogen-activated kinase p38 and calcium-calmodulin-dependent kinase were disproportionally expressed/activated (50% to 150%), and tumor necrosis factor-alpha increased in the late-contracting (higher-stress) lateral versus septal wall. These disparities were absent with CRT. Apoptosis assessed by terminal deoxynucleotide transferase-mediated dUTP nick-end labeling staining, caspase-3 activity, and nuclear poly ADP-ribose polymerase cleavage was less in CRT than DHF hearts and was accompanied by increased Akt phosphorylation/activity. Bcl-2 and BAD protein diminished with DHF but were restored by CRT, accompanied by marked BAD phosphorylation, enhanced BAD-14-3-3 interaction, and reduced phosphatase PP1alpha, consistent with antiapoptotic effects. Other Akt-coupled modulators of apoptosis (FOXO-3alpha and GSK3beta) were more phosphorylated in DHF than CRT and thus less involved. CONCLUSIONS: CRT reverses regional and global molecular remodeling, generating more homogeneous activation of stress kinases and reducing apoptosis. Such changes are important benefits from CRT that likely improve cardiac performance and outcome.

Bi-atrial and right atrial activation times help to differentiate focal from macroreentrant right atrial tachycardias.

OBJECTIVE: The objective was to study atrial activation intervals and their relation to the tachycardia cycle length (TCL) as electrophysiologic parameters differentiating focal (FAT) from macroreentrant atrial tachycardias (MRAT) originating in the right atrium. METHODS: In 21 patients (8 men) with 30 successfully ablated right atrial tachycardias (15 focal) the endocardial activity during tachycardia was registered using multipolar catheters in the right atrium and the coronary sinus. Using this catheter configuration we measured the tachycardia cycle length (TCL), biatrial activation (BAA), right atrial activation (RAA), left atrial activation (LAA), as well as the proportion of those intervals to TCL. In 14 patients, the measurements were repeated in sinus rhythm as well. The diagnostic accuracy of the ratio of BAA to TCL was assessed. RESULTS: TCL was longer, but all other intervals and ratios were significantly shorter in FAT compared to MRAT (P < 0.05 for all parameters, except for LAA - P = NS). During sinus rhythm, patients with MRAT had prolonged RAA (P = 0.003), but not BAA and LAA (P = NS), compared to patients with FAT. A discriminating value of 40% for the ratio of BAA to TCL, compared to 50% and 30%, was found to have the best sensitivity, specificity, positive and negative predictive values for MRAT, as well as for FAT. CONCLUSIONS: BAA, RAA, LAA and their relation to the TCL are significantly shorter in FATs compared to MRATs arising from the right atrium. The ratio of BAA to TCL obtained using a simple 2-catheter configuration, allows a rapid and reliable differentiation between FAT and MRAT.

Variability in post-pacing intervals predicts global atrial activation pattern during tachycardia.

INTRODUCTION: Knowledge of the global atrial activation pattern is critical to ablation of an atrial arrhythmia. We hypothesized that the variability in post-pacing intervals (PPIs) with pacing at different cycle lengths (CLs) from the same pacing site, regardless of distance to the circuit, can be used to identify atrial activation patterns during tachycardia. METHODS AND RESULTS: Consecutive patients referred for ablation of organized atrial arrhythmias were included (n = 28, 31 total tachycardias). The variability in PPIs (PPIV) was calculated by comparing the difference in PPIs after overdrive pacing with 5-second trains 10, 20, and 30 ms shorter than the tachycardia cycle length (TCL). The global activation pattern was defined as circuitous (macroreentrant atrial circuit) or centrifugal (focal origin with centrifugal radiation) by electroanatomic mapping. Except for one case, all pacing was performed from the proximal coronary sinus bipole. Circuitous tachycardias (n = 17, all macro-reentrant) exhibited minimal variability with pacing at 10 ms and 30 ms shorter than TCL (6.0 +/- 2.5 ms), whereas centrifugal tachycardias (n = 14, 8 microreentrant) displayed a high degree of variability (56.5 +/- 20.6 ms). Rank sum analysis of PPIV suggests that the two groups are indeed distinct (P < 0.001). Using PPIV cutoffs of or=30 ms, circuitous and centrifugal activation patterns could be distinguished with a high degree of sensitivity (94% circuitous, 92.8% centrifugal) and 100% specificity. CONCLUSIONS: Our data support the use of PPIV to rapidly and accurately predict the global activation pattern during atrial arrhythmia.

Successful catheter ablation of atrial tachycardia originating from the non-coronary aortic sinus.

We report a rare case of atrial tachycardia originating from the non-coronary aortic sinus. After failed radiofrequency (RF) energy applications at right His-bundle region, the complete elimination of atrial tachycardia was achieved with an RF energy application in the non-coronary aortic sinus. With the review of other papers, this report emphasizes the importance of mapping in the non-coronary aortic sinus in focal atrial tachycardia near the atrioventricular node or near the His-bundle.

A novel pacing maneuver to localize focal atrial tachycardia.

BACKGROUND: Although focal atrial tachycardias cannot be entrained, we hypothesized that atrial overdrive pacing (AOP) can be an effective adjunct to localize the focus of these tachycardias at the site where the post-pacing interval (PPI) is closest to the tachycardia cycle length (TCL). METHODS: Overdrive pacing was performed in nine patients during atrial tachycardia, and in a comparison group of 15 patients during sinus rhythm. Pacing at a rate slightly faster than atrial tachycardia in group 1 and sinus rhythm in group 2 was performed from five standardized sites in the right atrium and coronary sinus. The difference between the PPI and tachycardia or sinus cycle length (SCL) was recorded at each site. The tachycardia focus was then located and ablated in group 1, and the atrial site with earliest activation was mapped in group 2. RESULTS: In both groups the PPI-TCL at the five pacing sites reflected the distance from the AT focus or sinus node. In group 1, PPI-TCL at the successful ablation site was 11 +/- 8 msec. In group 2, PPI-SCL at the site of earliest atrial activation was 131 +/- 37 msec (P < 0.001 for comparison). In groups 1 and 2, calculated values at the five pacing sites were proportional to the distance from the AT focus or sinus node, respectively. CONCLUSIONS: The PPI-TCL after-AOP of focal atrial tachycardia has a direct relationship to proximity of the pacing site to the focus, and may be clinically useful in finding a successful ablation site.

Catheter ablation for cardiac arrhythmias: a 14-year experience with 5330 consecutive patients at the Quebec Heart Institute, Laval Hospital.

BACKGROUND: Catheter ablation is a curative treatment with excellent success and minimal complication rates for patients with supraventricular or ventricular arrhythmias. METHODS: The acute outcomes and complications of all catheter ablation procedures for supraventricular and ventricular arrhythmias performed at the Quebec Heart Institute (Sainte-Foy, Quebec) during a 14-year period from January 1, 1993, to December 31, 2006, were prospectively assessed. The ablation procedures were classified according to the arrhythmias induced using standard electrophysiological techniques and definitions. Immediate success and complication rates were prospectively included in the database. RESULTS: A total of 5330 patients had catheter ablation performed at the Institute during the period assessed. The mean (+/- SD) age of patients was 50 +/- 18 years (range four to 97 years), and 2340 patients (44%) were men. Most of the patients were younger than 75 years (group 1), and 487 (9%) were 75 years of age and older (group 2). Indications for ablations were as follows: atrioventricular nodal re-entry tachycardia (AVNRT) in 2263 patients, accessory pathways in 1147 patients, atrioventricular node ablation in 803 patients, typical atrial flutter in 377 patients and atrial tachycardia in 160 patients; 580 patients had other ablation procedures. The overall success rates were 81% for atrial tachycardia, 92% for accessory pathways or flutter, and 99% for AVNRT or atrioventricular node ablation. There was no difference in the success rates of the younger (group 1) and older (group 2) patients. Seventy-seven patients (1.4%) had complications, including 11 major events (myocardial infarction in one patient, pulmonary embolism in three patients and permanent pacemaker in seven patients). In patients undergoing AVNRT ablation, two had a permanent pacemaker implanted immediately after the procedure and three had a permanent pacemaker implanted at follow-up. CONCLUSIONS: The results confirm that radiofrequency ablation is safe and effective, supporting ablation therapy as a first-line therapy for the majority of patients with cardiac arrhythmias.

[Atrial tachycardia ablated from the non-coronary aortic cusp]. / Ablacja czestoskurczu przedsionkowego w niewiencowej zatoce aorty.

We present a case of a patient with drug resistant atrial tachycardia which was ablated from the noncoronary aortic cusp. Tachycardia was adenosine-sensitive and was characterized by a long RP' interval and low amplitude P waves (biphasic in II, III, aVF and V1-V2 leads, and positive in aVL). The earliest atrial activation during tachycardia was recorded at His region and from non-coronary aortic sinus of Valsalva. RF ablation at this area terminated tachycardia and did not impair atrio-ventricular conduction.

Reduction of atrial tachyarrhythmia episodes during the overdrive pacing period using the post-mode switch overdrive pacing (PMOP) algorithm.

BACKGROUND: Early recurrences within 10 minutes after termination of an atrial tachyarrhythmia, such as atrial tachycardia (AT), atrial flutter, or atrial fibrillation (AF) episodes, account for a large part of paroxysmal AT/AF episodes. It is unclear whether these arrhythmias can be suppressed by overdrive pacing. OBJECTIVE: We set out to prove that overdrive pacing is effective in preventing early recurrences of AT/AF. METHODS: This AT500 (DDDRP device, Bakken Research Center Medtronic, Maastricht, The Netherlands) post-mode switch overdrive pacing (PMOP) study is a randomized controlled trial designed to test the efficacy of overdrive pacing on the suppression of early recurring AT/AF episodes. With the PMOP feature, overdrive pacing is activated 12 ventricular beats after device-confirmed termination of an AT/AF episode with a programmed duration and rate. If at least four episodes of 1 minute in duration occurred within the run-in period of 1 month, patients were randomized to one of the three settings (PMOP off and PMOP 10 minutes at 90 bpm or 120 bpm) for 2 months. At 2 and 4 months, patients were crossed over to another arm. At 6 months, all patients were programmed with PMOP on at 90 bpm for 30 minutes. RESULTS: We enrolled 122 and randomized 50 patients. Sixty percent of all stored AT/AF episodes occurred within 10 minutes after a previous episode; 31% occurred after device-determined termination and before the device reached the overdrive rate (17-27 ventricular beats after termination), and 29% of the episodes occurred while the device was pacing at the programmed overdrive rate. Thirty-seven percent of the average percentage of episodes during the overdrive period was prevented by the randomized settings of PMOP 90 bpm/10 min (P = .01, paired t-test, n = 39) and 120 bpm/10 min (P = .03, n = 35). In addition, for the nonrandomized setting of PMOP 90 bpm/30 min, the average number of episodes during the overdrive period was significantly smaller than the percentage of episodes occurring during the corresponding off period of 30 minutes (P = .05, n = 33). No significant differences in burden and episodes were found between the PMOP settings and the corresponding off periods. CONCLUSIONS: This is the first randomized controlled clinical trial to prove that overdrive pacing is effective in preventing early recurrences of AT/AF. However, shortcomings of the PMOP algorithm, such as late activation, need further improvement.