Inappropriate rate response in a leadless pacemaker due to automatic rate profile optimization.

A three-axis accelerometer sensor is incorporated in a leadless pacemaker (MicraTM , MedtronicInc ) for rate adaptation. Three sensor setpoints at lower rate (LR), activity of daily living rate (ADLR), and upper rate (UR) are used to convert detected acceleration to a desired rate response. We describe inappropriate rate acceleration at rest and during chest physiotherapy in a sedentary elderly patient with leadless pacemaker. The underlying mechanism and various programming options are discussed.

One stage atrioventricular nodal ablation and leadless pacemaker implantation for refractory atrial fibrillation.

Atrioventricular nodal (AVN) ablation and right ventricular (RV) pacing is recommended for refractory atrial fibrillation (AF) and tachycardia-bradycardia syndrome. Three AF patients (mean age 83, range 79-89 years) underwent AVN ablation and transvenous leadless pacemaker Micra™ implantations using the same venous access without anticoagulation interruption. Satisfactory pacing 0.59 (0.50-0.63) V at 0.24 ms and sensing 11.2 (6.3-15.6) mV were achieved within 1-3 deployments. There were no vascular complications nor device dislodgment. Durable pacemaker parameters and VVIR pacing were achieved. Combined AVN ablation and leadless pacemaker implantation is feasible and safe, and avoids pacemaker pocket hematoma and bleeding complications in patients on uninterrupted anticoagulation.

Continuous optimization of cardiac resynchronization therapy reduces atrial fibrillation in heart failure patients: Results of the Adaptive Cardiac Resynchronization Therapy Trial.

BACKGROUND: Data from randomized trials have suggested a modest or no effect of conventional cardiac resynchronization therapy (convCRT) on the incidence of atrial fibrillation (AF). AdaptivCRT (aCRT, Medtronic, Mounds View, MN) is a recently described algorithm for synchronized left ventricular (LV) pacing and continuous optimization of cardiac resynchronization therapy (CRT). OBJECTIVE: We compared the long-term effects of aCRT with convCRT pacing on the incidence of AF. METHODS: The Adaptive CRT trial randomized CRT-defibrillator (CRT-D)-indicated patients (2:1) to receive either aCRT or convCRT pacing. The aCRT algorithm evaluates intrinsic conduction every minute, providing LV-only pacing during normal atrioventricular (AV) conduction and AV and ventriculoventricular timing adjustments during prolonged AV conduction. The primary outcome of this subanalysis was an episode of AF >48 consecutive hours as detected by device diagnostics. RESULTS: Over a follow-up period with a mean and standard deviation of 20.2 ± 5.9 months, 8.7% of patients with aCRT and 16.2% with convCRT experienced the primary outcome (hazard ratio [HR] = 0.54; 95% confidence interval [CI] = 0.31-0.93; P = .03). In patients with prolonged baseline AV, the incidence of the primary outcome was 12.8% in patients randomized to aCRT compared with 27.4% in convCRT patients (HR = 0.45; 95% CI = 0.24-0.85; P = .01). Also, patients with AF episodes adjudicated as clinical adverse events were less common with aCRT (4.3%) than with convCRT (12.7%) (HR = 0.39; 95% CI = 0.19-0.79; P = .01). CONCLUSION: Patients receiving aCRT had a reduced risk of AF compared with those receiving convCRT. Most of the reduction in AF occurred in subgroups with prolonged AV conduction at baseline and with significant left atrial reverse remodeling.

Asystole in focal epilepsy complicating a traumatic subdural hematoma.

Ictal asystole due to sinus node suppression is a cause of sudden unexplained death in epilepsy. Here, for the first time, we describe a complete atrioventricular nodal block in a patient with non-compressive traumatic subdural hematoma, who developed ictal asystole as a delayed presentation. A leadless VVI pacemaker (ventricular paced, ventricular sensed, and pacing inhibited in response to a sensed beat) was implanted as a preventive measure against seizure-related heart block.

Transcatheter Leadless Cardiac Pacing in Renal Failure with Limited Venous Access.

Entirely leadless cardiac pacemakers that are delivered transvenously required the use of large-diameter delivery sheath and femoral venous approach. The complexity of external femoral and iliac venous anatomy may limit their implantation. We describe a hemodialysis patient without subclavian venous access and a conventional pacemaker with a failed right ventricular lead, who had difficult iliac venous anatomy that was also compressed by an external endovascular abdominal aortic stent. Successful leadless pacing using a Micra™ (Medtronic Inc., Minneapolis, MN, USA) was accomplished with a strong support wire, hydrophilic delivery sheath, and guided by venography.

Subclinical atrial fibrillation and stroke: insights from continuous monitoring by implanted cardiac electronic devices.

Nearly one out of five strokes is associated with atrial fibrillation (AF). Atrial fibrillation is often intermittent and asymptomatic. Detection of AF after cryptogenic stroke will likely change therapy from antiplatelet to oral anticoagulation agents for secondary stroke prevention. A critical step is to convert 'covert' AF into electrocardiogram documented AF. External rhythm recording devices have registered a high incidence of AF to occur after a cryptogenic stroke, but are limited by short duration of continuous recordings. Invasive cardiac monitoring using insertable leadless cardiac monitors are sensitive means to identify subclinical AF (SCAF) after cryptogenic stroke, and AF has been reported to occur in 8.9% of these patients by 6 months in one study. It will be more attractive to identify SCAF before a stroke occurs. Recent series in pacemaker and implantable cardioverter-defibrillator (ICD) recipients showed that short episodes of SCAF increased stroke risk, with odds ratio ∼2.2-3.1 compared with those without SCAF recorded. However, temporal sequence of recorded SCAF and stroke occurrence was uncertain, and the overall stroke risk was lower compared with patients with clinical AF at similar risk scores. This article reviews the incidence and clinical role of using implanted devices to detect SCAF and discusses the implication of SCAF so detected in primary and secondary stroke prevention.

Clinical outcomes with synchronized left ventricular pacing: analysis of the adaptive CRT trial.

BACKGROUND: Acute studies have suggested that left ventricular pacing (LVP) may have benefits over biventricular pacing (BVP). The adaptive cardiac resynchronization therapy (aCRT) algorithm provides LVP synchronized to produce fusion with the intrinsic activation when the intrinsic atrioventricular (AV) interval is normal. The randomized double-blind adaptive cardiac resynchronization therapy trial demonstrated noninferiority of the aCRT algorithm compared to echocardiography-optimized BVP (control). OBJECTIVE: To examine whether synchronized LVP (sLVP) resulted in better clinical outcomes. METHODS: First, stratification by percent sLVP (%sLVP) and multivariate Cox proportional hazards model was used to assess the relationship between %sLVP and clinical outcomes. Second, outcomes were compared between patients in the aCRT arm (n = 318) and control patients (n = 160) stratified by intrinsic AV interval at randomization. RESULTS: In the aCRT arm, %sLVP ≥50% (n = 142) was independently associated with a decreased risk of death or heart failure hospitalization (hazard ratio 0.49; 95% confidence interval 0.28-0.85; P = .012) compared with %sLVP <50% (n = 172). A greater proportion of patients with %sLVP ≥50% improved in Packer's clinical composite score at 6-month (82% vs. 68%; P = .002) and 12-month (80% vs. 62%; P = .0006) follow-ups compared to controls. In the subgroup with normal AV (n = 241), there was a lower risk of death or heart failure hospitalization (hazard ratio 0.52; 95% confidence interval 0.27-0.98; P = .044) with the aCRT algorithm. A greater proportion of patients in the aCRT arm improved in the clinical composite score at 6-month (81% vs. 69%; P = .041) and 12-month (77% vs. 66%; P = .076) follow-ups compared to controls. CONCLUSIONS: Higher %sLVP was independently associated with superior clinical outcomes. In patients with normal AV conduction, the aCRT algorithm provided mostly sLVP and demonstrated better clinical outcomes compared to echocardiography-optimized BVP.

Investigation of a novel algorithm for synchronized left-ventricular pacing and ambulatory optimization of cardiac resynchronization therapy: results of the adaptive CRT trial.

BACKGROUND: In patients with sinus rhythm and normal atrioventricular conduction, pacing only the left ventricle with appropriate atrioventricular delays can result in superior left ventricular and right ventricular function compared with standard biventricular (BiV) pacing. OBJECTIVE: To evaluate a novel adaptive cardiac resynchronization therapy ((aCRT) algorithm for CRT pacing that provides automatic ambulatory selection between synchronized left ventricular or BiV pacing with dynamic optimization of atrioventricular and interventricular delays. METHODS: Patients (n = 522) indicated for a CRT-defibrillator were randomized to aCRT vs echo-optimized BiV pacing (Echo) in a 2:1 ratio and followed at 1-, 3-, and 6-month postrandomization. RESULTS: The study met all 3 noninferiority primary objectives: (1) the percentage of aCRT patients who improved in their clinical composite score at 6 months was at least as high in the aCRT arm as in the Echo arm (73.6% vs 72.5%, with a noninferiority margin of 12%; P = .0007); (2) aCRT and echo-optimized settings resulted in similar cardiac performance, as demonstrated by a high concordance correlation coefficient between aortic velocity time integrals at aCRT and Echo settings at randomization (concordance correlation coefficient = 0.93; 95% confidence interval 0.91-0.94) and at 6-month postrandomization (concordance correlation coefficient = 0.90; 95% confidence interval 0.87-0.92); and (3) aCRT did not result in inappropriate device settings. There were no significant differences between the arms with respect to heart failure events or ventricular arrhythmia episodes. Secondary end points showed similar benefit, and right-ventricular pacing was reduced by 44% in the aCRT arm. CONCLUSIONS: The aCRT algorithm is safe and at least as effective as BiV pacing with comprehensive echocardiographic optimization.

A novel algorithm for individualized cardiac resynchronization therapy: rationale and design of the adaptive cardiac resynchronization therapy trial.

BACKGROUND: The magnitude of benefit of cardiac resynchronization therapy (CRT) varies significantly among its recipients; approximately 30% of CRT patients do not report clinical improvement. Optimization of CRT pacing parameters can further improve cardiac function, both acutely and chronically. Echocardiographic optimization is used in clinical practice, but it is time and resource consuming. In addition, optimal settings at rest may change later with activity or cardiac remodeling. The adaptive CRT (aCRT) algorithm was designed to provide automatic ambulatory adjustment of CRT pacing configuration (left ventricular or biventricular pacing) and device delays based on periodic measurement of electrical conduction intervals. METHODS: The aCRT algorithm is currently undergoing evaluation in a prospective, randomized, double-blinded, worldwide clinical trial. The trial enrolled 522 patients, who satisfied standard clinical indications for a CRT device. Within 2 weeks after the implant, the patients were randomized to aCRT versus echo-optimized biventricular pacing (Echo) settings in 2:1 ratio and followed up at 1-, 3-, 6-, and 12-month postrandomization. The noninferiority primary trial objectives at 6-month postrandomization are to demonstrate that (a) the percentage of aCRT patients who improved in their clinical composite score is at least as high as the percentage of Echo patients; (b) cardiac performance as assessed by echocardiography is similar when using aCRT settings versus echo-optimized settings; and (c) aCRT does not result in inappropriate device settings. First and last patient enrollments occurred in November 2009 and December 2010, respectively. CONCLUSIONS: The safety and efficacy of the aCRT algorithm will be evaluated in this ongoing clinical trial.

Alleviation of pulmonary hypertension by cardiac resynchronization therapy is associated with improvement in central sleep apnea.

BACKGROUND: Recent studies have demonstrated that cardiac resynchronization therapy (CRT) reduces sleep apnea in heart failure (HF); however, the mechanism of benefit remains unclear. METHODS: Overnight polysomnography (PSG) was performed in consecutive HF patients who were scheduled for CRT implant. Patients with sleep apnea defined by an apnea-hypopnea index (AHI) of >10/hour were recruited and underwent echocardiogram examination at baseline and 3 months after CRT. RESULTS: Among 37 HF patients screened, 20 patients (54%) had sleep apnea and 15 of them consented for the study. After 3 months of CRT, there was a significant improvement in New York Heart Association functional class (3.1+/-0.1 vs 2.1+/-0.1, P<0.01), quality-of-life (QoL) score (62.9+/-3.3 vs 56.1+/-4.5, P=0.02), left ventricular ejection fraction (LVEF, 28.8+/-2.5% vs 38.1+/-2.3%, P<0.01), and reduction in pulmonary artery systolic pressure (PASP, 41.0+/-2.7 vs 28.6+/-2.2 mmHg; P<0.01) compared with baseline. Repeated PSG after CRT demonstrated a reduction in the duration of arterial oxygen desaturation

Emerging trends of community acquired infective endocarditis.

BACKGROUND: To obtain epidemiological information and to evaluate the emerging trend of incidence and clinical features of community acquired infective endocarditis (IE) in Hong Kong. METHODS: Population-based survey in a regional hospital in Hong Kong which served 0.55 million population over an 11-year period was conducted. 172 patients diagnosed to have IE between 1995 and 2005 were analyzed. Incidence, underlying heart disease, causative microorganisms and clinical outcomes of IE were studied. RESULTS: The standardized annual incidence of community acquired IE was 2.8 cases per 100,000 person-year and remain stable over the past 10 years in Hong Kong (P=0.57 for trends). The most common underlying heart diseases for IE were intravenous drug addict (30%), followed by chronic rheumatic heart disease (18%). There was a time trend of increasing age in patients suffered from IE, both in patients with or without intravenous drug abuse (overall P=0.004). Although there were no significant changes in the overall proportion of IE patients with different underlying etiologies, site of IE involvement and types of microorganisms, non-addict patients showed an increasing trend of staphylococcal IE during the study period (P=0.01). The adverse clinical outcome of IE during the study period remained unchanged (P=0.71). CONCLUSIONS: The results of this study have demonstrated that IE continued to be an important disease with stable incidence and high morbidity and mortality over time in Asia. Furthermore, our study also highlighted that IE is an emerging disease with continuously changing clinical and microbiologic patterns, and significant differences are still present between different countries.

Advances in devices for cardiac resynchronization in heart failure.

Patients with advanced heart failure have a high mortality and morbidity despite medical therapy. Depending on the underlying heart disease and severity of heart failure, 3.7 to 52.8% of patients have a QRS complex > or =120 ms who may have interventricular and intraventricular dyssynchrony correctible by cardiac resynchronization therapy (CRT). The latter is usually achieved with biventricular pacing, with the left ventricular lead placed in a tributary of the coronary sinus (CS), with a reported success rate between 88-92%. The technical advances for implantation include preformed guide sheaths to cannulate the CS, over the wire leads with passive fixation mechanism, and surgical placement methods. Device-specific CRT features include optimizing heart failure through insurance of a high percentage of pacing, heart failure monitoring, atrioventricular and interventricular timing, and avoiding double ventricular sensing. Furthermore, arrhythmic co-morbidities of heart failure such as atrial fibrillation and ventricular tachyarrhythmias can also be managed. Recent prospective trials suggest that there is a 30% reduction in heart failure hospitalization with CRT, and preliminary results suggest a survival benefit with CRT and implantable cardioverter defibrillator over optimal medical therapy.

Pulmonary vein isolation using transvenous catheter cryoablation for treatment of atrial fibrillation without risk of pulmonary vein stenosis.

OBJECTIVES: We sought to evaluate the efficacy and safety of pulmonary vein (PV) isolation using transvenous cryoablation for the treatment of atrial fibrillation (AF). BACKGROUND: Although electrical isolation of PVs with radiofrequency energy for the treatment of AF is feasible, it is associated with a significant risk of PV stenosis. Cryoablation is a new alternative therapy allowing ablation of tissue while preserving its underlying architecture. METHODS: In 52 patients with paroxysmal (n = 45) or persistent (n = 7) AF, PV isolation using the CryoCor cryoablation system (CyroCor Inc., San Diego, California) with a 10F deflectable transvenous catheter was performed as guided by ostial PV potentials. Cryoablation was applied twice at each targeted site (2.5 to 5 min/application). Computed tomography (CT) of the thorax was performed at baseline and at 3 and 12 months to evaluate for PV stenosis. RESULTS: All targeted PVs were completely isolated in 49 (94%) of 52 of patients. Of 152 PVs targeted, 147 (97%) were successfully isolated (mean 3.0 PVs isolated per patient). After a mean period of 12.4 +/- 5.5 months of follow-up, 37 (71%) of 52 patients had no recurrence of AF or were clinically improved, including 29 patients (56%) who had no recurrence of AF with (n = 11) or without the use of anti-arrhythmic drugs. At 3 and 12 months, the CT scan showed no evidence of PV stenosis associated with cryoablation in any patients. CONCLUSIONS: Transvenous catheter cryoablation is an effective method to create PV electrical isolation for the treatment of AF. A clinically satisfactory result can be achieved in 71% of patients with AF, without the risk of PV stenosis.

Acute results of transvenous cryoablation of supraventricular tachycardia (atrial fibrillation, atrial flutter, Wolff-Parkinson-White syndrome, atrioventricular nodal reentry tachycardia).

INTRODUCTION: Radiofrequency (RF) catheter ablation currently is used for treatment of cardiac arrhythmias. Although the success rate is high for almost all supraventricular tachycardias (SVT), this technique has some drawbacks, especially when pulmonary veins (PV) are targeted for treatment of atrial fibrillation (AF). Additionally, new techniques for isolation of the PVs have the drawback that they can be used only for PV isolation and not for routine treatment of other SVTs. The aim of this study was to report on the safety and efficacy of a new cryoablation system for treatment of all SVTs. METHODS AND RESULTS: Forty-nine patients with SVT (38 men; age 48 years, range 23-76) were enrolled in the study. Five patients were withdrawn from the study before they underwent cryoablation. The remaining 44 patients were treated with cryoablation (22 AF, 15 atrial flutter, 3 accessory pathway, 2 AV nodal reentrant tachycardia, 1 AV junction ablation for permanent AF, 1 atrial tachycardia). Cryoablation was performed with the CryoCor cryoablation system, which uses a precooling system and N2O as a refrigerant. The number of freezes applied varied according to the index arrhythmia treated. Successful isolation of PVs was performed in 20 of (96%) 21 AF patients and 53 of 55 veins. The overall acute success was 98% (43/44). Fifty-three PVs were isolated (2.5/patient). The success rate was 100% (23/23) for right-sided procedures. The average and nadir temperatures reached in right-sided and left-sided procedures were -77 degrees C and -80 degrees C and -75 degrees C and -78 degrees C, respectively. No acute PV stenosis was seen. CONCLUSION: This novel cryoablation system appears to be safe and can successfully treat different types of SVTs, including AF. Isolation of PVs is possible without producing stenosis. Despite the high blood flow in the right atrial isthmus and PVs, bidirectional conduction block can be achieved.

New Bayesian discriminator for detection of atrial tachyarrhythmias.

BACKGROUND: Accurate, rapid detection of atrial tachyarrhythmias has important implications in the use of implantable devices for treatment of cardiac arrhythmia. Currently available detection algorithms for atrial tachyarrhythmias, which use the single-index method, have limited sensitivity and specificity. METHODS AND RESULTS: In this study, we evaluated the performance of a new Bayesian discriminator algorithm in the detection of atrial fibrillation (AF), atrial flutter (AFL), and sinus rhythm (SR). Bipolar recording of 364 rhythms (AF=156, AFL=88, SR=120) at the high right atrium were collected from 20 patients who underwent electrophysiological procedures. After initial signal processing, a column vector of 5 features for each rhythm were established, based on the regularity, rate, energy distribution, percent time of quiet interval, and baseline reaching of the rectified autocorrelation coefficient functions. Rhythm identification was obtained by use of Bayes decision rule and assumption of Gaussian distribution. For the new Bayesian discriminator, the overall sensitivity for detection of SR, AF, and AFL was 97%, 97%, and 94%, respectively; and the overall specificity for detection of SR, AF, and AFL was 98%, 98%, and 99%, respectively. The overall accuracy of detection of SR, AF, and AFL was 98%, 97% and 98%, respectively. Furthermore, sensitivity, specificity, and accuracy of this algorithm were not affected by a range of white Gaussian noises with different intensities. CONCLUSIONS: This new Bayesian discriminator algorithm, based on Bayes decision of multiple features of atrial electrograms, allows rapid on-line and accurate (98%) detection of AF with robust anti-noise performance.