Long-term impact of intrathoracic impedance findings on survival and heart failure hospitalizations after cardiac resynchronization therapy in ICD Registry patients.

Aims: To determine adjusted associations among OptiVol® threshold crossings, long-term survival, and hospitalizations among heart failure (HF) patients with Medicare coverage in the United States. Methods and results: A cohort with OptiVol®-enabled cardiac resynchronization therapy defibrillators (CRT-D) devices from the Implantable Cardioverter Defibrillator Registry was linked to both Medicare claims/summary data and Medtronic's CareLink® Network data. An extended multivariable Cox model was used to analyse associations among OptiVol® threshold crossings (treated as time-dependent covariates), mortality, and HF-related hospitalizations (HFH). We analysed N = 1565 patients with OptiVol®-enabled CRT-D devices (mean age 72.8, 28% women). The median follow-up was 6.3 years. Patients with >15.1% of days above OptiVol® threshold (highest quartile) had more than a 4-fold increase in mortality [hazard ratio (HR) 4.2, 95% confidence interval (CI): 3.3-5.3] and more than a 3-fold increase in HFH (HR 3.2, 95% CI: 2.4-4.2) compared with patients having <4.1% of days above threshold (lowest quartile) after adjustment for key covariates. In addition, a single OptiVol® crossing was associated with significantly increased rates of both mortality (HR 1.87, 95% CI: 1.27-2.75) and HFH (HR 1.70, 95% CI: 1.28-2.27). Conclusion: In a CRT-D cohort with over 6 years of follow-up, both single OptiVol® crossings and time above OptiVol® threshold were associated with increased rates of mortality and hospitalization, which has important implications for clinical care. This is the first study integrating device data with Medicare outcomes to validate the long-term significance of OptiVol® findings.

Real-World Experience with Insertable Cardiac Monitors to Find Atrial Fibrillation in Cryptogenic Stroke.

BACKGROUND: The characteristics of atrial fibrillation (AF) episodes in cryptogenic stroke patients have recently been explored in carefully selected patient populations. However, the incidence of AF among a large, real-world population of patients with an insertable cardiac monitor (ICM) placed for the detection of AF following a cryptogenic stroke has not been investigated. METHODS: Patients in the de-identified Medtronic DiscoveryLink™ database who received an ICM (Reveal LINQ™) for the purpose of AF detection following a cryptogenic stroke were included. AF detection rates (episodes ≥2 min) were quantified using Kaplan-Meier survival estimates at 1 and 6 months and compared to the CRYSTAL AF study at 6 months. The time to AF detection and maximum duration of AF episodes were also analyzed. RESULTS: A total of 1,247 patients (age 65.3 ± 13.0 years) were followed for 182 (IQR 182-182) days. A total of 1,521 AF episodes were detected in 147 patients, resulting in AF detection rates of 4.6 and 12.2% at 30 and 182 days, respectively, and representing a 37% relative increase over that reported in the CRYSTAL AF trial at 6 months. The median time to AF detection was 58 (IQR 11-101) days and the median duration of the longest detected AF episode was 3.4 (IQR 0.4-11.8) h. CONCLUSIONS: The real-world incidence of AF among patients being monitored with an ICM after a cryptogenic stroke validates the findings of the CRYSTAL AF trial and suggests that continuous cardiac rhythm monitoring for periods longer than the current guideline recommendation of 30 days may be warranted in the evaluation of patients with cryptogenic stroke.

Threshold crossing of device-based intrathoracic impedance trends identifies relatively increased mortality risk.

AIMS: Threshold crossings of impedance trends detected by implanted devices have been associated with clinically relevant heart failure events, but long-term prognosis of such events has not been demonstrated. The aim of this study is to examine the relationship between alterations in intrathoracic impedance and mortality risk in patients with implantable devices. METHODS AND RESULTS: We reviewed remote monitoring data in the de-identified Medtronic CareLink(®) Discovery Link that captured intrathoracic impedance trends for >6 months. The initial 6 months of the cardiac and impedance trends were used as the observation period to create the patient groups and cross-referenced with the Social Security Death Index for mortality data. In our study cohort of 21 217 patients, 36% experienced impedance threshold crossing within the initial 6 months of monitoring (defined as the 'early threshold crossing' group). Patients with early threshold crossings demonstrated an increased risk of age- and gender-adjusted all-cause mortality [hazard ratio (HR) 2.15, 95% confidence interval (CI) 1.95-2.38, P< 0.0001]. Increased mortality risk remained significant when analysed in subgroups of patients without defibrillator shock (HR 2.10, 95% CI 1.90-2.34, P< 0.0001, n= 1621) or within those patients without device-detectable atrial fibrillation (AF) during the initial 6 months of monitoring (HR 2.09, 95% CI 1.86-2.34, P< 0.0001, n= 17 235). Both the number and the duration of early threshold crossings of impedance trends detectable by implanted devices were associated with increased mortality risk. Furthermore, the improvement of altered impedance trends portends more favourable prognosis. CONCLUSIONS: Threshold crossing of impedance trends detectable by implanted devices is associated with relatively increased mortality risk even after adjusted for demographic, device-detected AF, or defibrillator shocks.

Burden of atrial fibrillation and poor rate control detected by continuous monitoring and the risk for heart failure hospitalization.

INTRODUCTION: Atrial fibrillation (AF) on electrocardiogram has been identified as a risk factor for hospitalizations in patients with heart failure (HF). We investigated whether continuous AF monitoring can identify when patients with HF are at risk for hospitalization. METHODS: In this retrospective analysis of data from 4 studies enrolling patients with HF with cardiac resynchronization therapy defibrillator devices with ≥90 days of follow-up (n = 1561), patients were identified as having AF if they had ≥1 day of >5 minutes of AF and >1 hour of total AF during entire follow-up. In patients with AF, device recorded AF burden (AFb) and ventricular rate during AF (VRAF) over the last 30 days was classified on a monthly basis into 3 evaluation groups: (1) ≥1 day of high burden of paroxysmal AF (≥6 hours) or persistent AF (all 30 days with AFb >23 hours) with poor rate control (VRAF >90 beats/min), (2) ≥1 day of high burden of paroxysmal AF with good rate control (VRAF ≤ 90 beats/min), and (3) no days with high burden of AF (AFb <6 hours) or persistent AF with good rate control. Each group was compared with monthly evaluations in patients without AF using an Anderson-Gill model for occurrence of HF hospitalizations in the next 30 days. RESULTS: Patients with AF (n = 519, 33%) have a greater risk (hazard ratio [HR] 2.0, P < .001) for impending HF hospitalizations during entire follow-up compared with patients with no AF. One day of high burden of paroxysmal AF with good rate control in the last 30 days increases risk for HF hospitalization in the next 30 days (HR 3.4, P < .001). The risk increases further (HR 5.9, P < .001) with 1 day of poor rate control during persistent AF or high burden paroxysmal AF in last 30 days. CONCLUSION: Evaluation of AFb and rate control information on a monthly basis can identify patients at risk for HF hospitalization in the next 30 days.

INTERVENE-HF: feasibility study of individualized, risk stratification-based, medication intervention in patients with heart failure with reduced ejection fraction.

AIMS: Determine the feasibility of implementing a heart failure (HF) management strategy that (i) uses a device-based, remote, dynamic, multimetric risk stratification model to predict the risk of HF events and (ii) uses a standardized, centrally administered, ambulatory medication intervention protocol to reproducibly and safely decrease elevated risk scores. METHODS AND RESULTS: Prospective, non-randomized, single-arm, multicenter feasibility study (Intervene-HF) was conducted in HF patients implanted with a cardiac resynchronization therapy with implantable cardio defibrillator (CRT-D) with TriageHF risk score feature. Certified HF nurses (CHFN) in the Medtronic Care Management Services Program implemented an ambulatory medication intervention strategy by following a standardized guided action pathway triggered by risk-based alert. When CHFN received notification of increased risk score (HF care alert), they implemented a 3 day course of diuretic up-titration (PRN) previously prescribed by a physician. Safety was monitored daily. Recovery after PRN was defined as ≥70% recovery of impedance toward baseline levels. Sixty-six patients followed for 8.2 ± 3.9 months had 49 HF care alerts. Twenty-three of 49 alerts did not receive PRN due to protocol-mandated criteria. Twenty-six of 49 alerts received PRN, 22 were completed, and 19 led to impedance recovery. Four interventions were stopped for safety without leading to an adverse event (AE). One of 26 PRNs was followed by a HF event. Eighty-five per cent (22/26) of PRNs were completed without an AE; 69% (18/26) met the recovery criteria. CONCLUSIONS: The Intervene-HF study supports the feasibility of testing, in a large randomized clinical trial, an ambulatory medication intervention strategy that is physician-directed, CHFN-implemented, and based on individualized device risk stratification.

Improved 30 day heart failure rehospitalization prediction through the addition of device-measured parameters.

AIMS: This study aimed to improve in-person clinical evaluation on the day of heart failure (HF) hospitalization discharge by adding device-measured parameters to predict 30 day HF rehospitalization risk in cardiac resynchronization therapy-defibrillator (CRT-D) patients. METHODS AND RESULTS: In a cohort of Medicare patients with CRT-Ds, the independent prognostic value of four device-measured parameters was assessed relative to typical clinical parameters associated with rehospitalization risk. Medicare registry, claims, and Medtronic CareLink® Network data for these patients were analysed using logistic regression modelling and net reclassification methods. Among 1563 CRT-D patients, 411 patients had 607 HF hospitalization events during a median 6.3 years of follow-up. Compared with clinical variables alone, impedance measurements resulted in a 28% improvement between the predicted probabilities of having vs. not having a 30 day HF rehospitalization (relative integrated discrimination improvement = 0.28) and a net 42% improvement in the classification of 30 day HF rehospitalization events and non-events after an index HF hospitalization (net reclassification index = 0.42; 95% CI: 0.10, 0.74). CONCLUSIONS: In CRT patients, intrathoracic impedance measurements improve prediction of 30 day HF rehospitalization over clinical characteristics alone. The present study provides supportive data for the routine evaluation of intrathoracic impedance prior to discharge in patient with CRT devices. Furthermore, the models developed in this study could be used to design interventions to improve compliance with Medicare reimbursement guidelines regarding 30 day HF rehospitalization.

Incremental Value of Implantable Cardiac Device Diagnostic Variables Over Clinical Parameters to Predict Mortality in Patients With Mild to Moderate Heart Failure.

Background Heart failure remains a leading cause of morbidity and mortality. Clinical prediction models provide suboptimal estimates of mortality in this population. We sought to determine the incremental value of implantable device diagnostics over clinical prediction models for mortality. Methods and Results RAFT (Resynchronization/Defibrillation for Ambulatory Heart Failure Trial) patients with implanted devices capable of device diagnostic monitoring were included, and demographic and clinical parameters were used to compute Meta-Analysis Global Group in Chronic Heart Failure (MAGGIC) heart failure risk scores. Patients were classified according to MAGGIC score into low (0-16), intermediate (17-24), or high (>24) risk groups. Mortality was evaluated from 6 months postimplant in accordance with the RAFT protocol. In a subset of 1036 patients, multivariable analysis revealed that intermediate and high MAGGIC scores, fluid index, atrial fibrillation, and low activity flags were independent predictors of mortality. A device-integrated diagnostic parameter that included a fluid index flag and either a positive atrial fibrillation flag or a positive activity flag was able to significantly differentiate higher from lower risk for mortality in the intermediate MAGGIC cohort. The effect was more pronounced in the high-risk MAGGIC cohort, in which device-integrated diagnostic-positive patients had a shorter time to death than those who were device-integrated diagnostic negative. Conclusions Device diagnostics using a combination of fluid index trends, atrial fibrillation burden, and patient activity provide significant incremental prognostic value over clinical heart failure prediction scores in higher-risk patients. This suggests that combining clinical and device diagnostic parameters may lead to models with better predictive power. Whether this risk is modifiable with early medical intervention would warrant further studies. Clinical Trial Registration URL : http://www.clinicaltrials.gov . Unique identifier: NCT00251251.

Prediction of All-Cause Mortality Based on the Direct Measurement of Intrathoracic Impedance.

BACKGROUND: Intrathoracic impedance-derived OptiVol fluid index calculated using implanted devices has been shown to predict mortality; direct measurements of impedance have not been examined. We hypothesized that baseline measured impedance predicts all-cause mortality; changes in measured impedance result in a change in the predicted mortality; and the prognostic value of measured impedance is additive to the calculated OptiVol fluid index. METHODS AND RESULTS: A retrospective analysis of 146,238 patients within the Medtronic CareLink database with implanted devices was performed. Baseline measured impedance was determined using daily values averaged from month 6 to 9 after implant and were used to divide patients into tertiles: group L = low impedance, ≤ 65 ohms; group M = medium impedance, 66 to 72 ohms; group H = high impedance, ≥ 73 ohms. Change in measured impedance was determined from values averaged from month 9 to 12 post implant compared with the 6- to 9-month values. OptiVol fluid index was calculated using published methods. All-cause mortality was assessed beginning 9 months post implant; changes in mortality was assessed beginning 12 months post implant. Baseline measured impedance predicted all-cause mortality; 5-year mortality for group L was 41%, M was 29%, and H was 25%, P < 0.001 among all groups. Changes in measured impedance resulted in a change in the predicted mortality; the prognostic value of measured impedance was additive to the OptiVol fluid index. CONCLUSIONS: Direct measurements of intrathoracic impedance using an implanted device can be used to stratify patients at varying mortality risk.

Real-world performance of an enhanced atrial fibrillation detection algorithm in an insertable cardiac monitor.

BACKGROUND: Insertable cardiac monitors (ICMs) are used for long-term ECG monitoring. The Reveal LINQ ICM has an improved atrial fibrillation (AF) detection algorithm. OBJECTIVE: The purpose of this study was to investigate the algorithm's real-world performance in patients with syncope, cryptogenic stroke, and known AF. METHODS: Consecutive patients with implanted ICM and AF detection parameters automatically set and maintained depending on the indication for monitoring were included. A single reviewer annotated all stored episodes after ICM implant. A second reviewer annotated a random sample of 10% of all detected AF episodes. The episode detection positive predictive value as well as true and false detection rates were determined for AF episodes of different durations. RESULTS: The study enrolled 3759 patients (1604 [43%] with syncope, 1049 [28%] with known AF, 1106 [29%] with cryptogenic stroke). Overall, 20,659 AF episodes were detected in 1020 patients. The gross episode detection positive predictive value was 84%, 73%, and 26% for all episodes (≥2 minutes) and improved to 97%, 95%, and 91% for detected AF episodes ≥1 hour in the syncope, known-AF, and cryptogenic stroke patient cohorts, respectively. The true (and false) detection rate was 0.23 (0.05), 3.8 (1.4), and 0.23 (0.65) per patient-month of monitoring for the syncope, known-AF, and cryptogenic stroke patient cohorts, respectively. Limiting ECG storage to the longest detected AF episode significantly reduced the burden of episode adjudication without significantly compromising the identification of patients with true AF. CONCLUSION: The performance of LINQ ICM is dependent on the AF incidence rate in the population being monitored, the programmed sensitivity of AF algorithm, and the duration of detected AF episodes.

Early recurrence of atrial fibrillation after ambulatory shock conversion.

OBJECTIVES: We sought to gain insights into the early recurrence of atrial fibrillation (ERAF) after cardioversion shocks delivered by permanently implanted rhythm management systems. BACKGROUND: Several reports have characterized ERAF, but these reports used a limited definition and did not evaluate an association between clinical or device variables and ERAF. METHODS: A total of 144 patients with recurrent, drug-resistant, symptomatic atrial fibrillation (AF) underwent implantation of an atrial rhythm management system (Medtronic Jewel AF, Model 7250, Minneapolis, Minnesota). The device was programmed to deliver cardioversion shocks automatically and/or on patient command. The incidence of ERAF was evaluated after 1,092 successful shocks among 97 patients. Three different ERAF definitions were used: recurrence within 1 min, 1 h or 1 day. Multiple clinical and device variables were assessed for their relationship with ERAF. RESULTS: The per-patient incidences of ERAF were 44%, 61% and 70% for ERAF within 1 min, 1 h and 1 day, respectively. The per-episode incidences of ERAF were 17%, 30% and 43% for ERAF within 1 min, 1 h and 1 day, respectively. Variables that were independently associated with ERAF included AF duration <3 h before termination, more than one shock required to cardiovert and the absence of a previous myocardial infarction. The most potent variable was AF duration <3 h, associated with a threefold increase in the incidence of ERAF. CONCLUSIONS: Recurrence of AF early after ambulatory shock cardioversion is common. In this retrospective study, both clinical and device variables were predictive.

New-generation atrial antitachycardia pacing (Reactive ATP) is associated with reduced risk of persistent or permanent atrial fibrillation in patients with bradycardia: Results from the MINERVA randomized multicenter international trial.

BACKGROUND: Atrial fibrillation (AF) is a frequent comorbidity in patients with pacemaker and is a recognized cause of mortality, morbidity, and quality-of-life impairment. The international MINimizE Right Ventricular pacing to prevent Atrial fibrillation and heart failure trial established that atrial preventive pacing and atrial antitachycardia pacing (DDDRP) in combination with managed ventricular pacing (MVP) reduce permanent AF occurrence in comparison with standard dual-chamber pacing (DDDR). OBJECTIVE: We aimed to determine the role of new-generation atrial antitachycardia pacing (Reactive ATP) in preventing AF disease progression. METHODS: Patients with dual-chamber pacemaker and with previous atrial tachyarrhythmias were randomly assigned to DDDR (n = 385 (33%)), MVP (n = 398 (34%)), or DDDRP+MVP (n = 383 (33%)) group. The incidence of permanent AF, as defined by the study investigator, or persistent AF, defined as ≥7 consecutive days with AF, was estimated using the Kaplan-Meier method, while its association with patients' characteristics was evaluated via multivariable Cox regression. RESULTS: At 2 years, the incidence of permanent or persistent AF was 26% (95% confidence interval [CI] 22%-31%) in the DDDR group, 25% (95% CI 21%-30%) in the MVP group, and 15% (95% CI 12%-20%) in the DDDRP+MVP group (P < .001 vs. DDDR; P = .002 vs. MVP). Generalized estimating equation-adjusted Reactive ATP efficacy was 44.4% (95% CI 41.3%-47.6%). Multivariate modeling identified high Reactive ATP efficacy (>44.4%) as a significant predictor of reduced permanent or persistent AF risk (hazard ratio 0.32; 95% CI 0.13-0.781; P = .012) and episodes' characteristics, such as long atrial arrhythmia cycle length, regularity, and the number of rhythm transitions, as predictors of high ATP efficacy. CONCLUSION: In patients with bradycardia, DDDRP+MVP delays AF disease progression, with Reactive ATP efficacy being an independent predictor of permanent or persistent AF reduction.

Sample size estimates for atrial fibrillation endpoints.

This article reviews the current sample size requirements for studies evaluating the efficacy of atrial therapies. Sample sizes for several study designs and endpoints are presented. However, emphasis is given to studies conducted in patients with implantable devices in the light of new available data from recent trials involving such patients. Studies utilizing mortality require >5,000 patients followed for at least 2 years. Symptomatic episode recurrence represents a possible alternate endpoint but still requires >400 patients followed for 1 year. Parallel design studies for device atrial fibrillation (AF) burden and frequency endpoints were found to be of little value because they would require thousands of patients. In contrast, cross-over studies utilizing device AF burden or AF frequency endpoints provide the best option in terms of sample size and study duration. A 30% therapy efficacy (reduction in AF burden or frequency) can be detected with just a little over 100 patients followed for 6 months. Therefore, cross-over studies with device-based endpoints are a viable option to evaluate and screen possible new rhythm control treatments before evaluating their effect on clinical outcome variables that may require larger trials with longer follow-up times.

Implantable device diagnostics on day of discharge identify heart failure patients at increased risk for early readmission for heart failure.

AIMS: We hypothesized that diagnostic data in implantable devices evaluated on the day of discharge from a heart failure hospitalization (HFH) can identify patients at risk for HF readmission (HFR) within 30 days. METHODS AND RESULTS: In this retrospective analysis of four studies enrolling patients with CRT devices, we identified patients with a HFH, device data on the day of discharge, and 30-day post-discharge clinical follow-up. Four diagnostic criteria were evaluated on the discharge day: (i) intrathoracic impedance>8 Ω below reference impedance; (ii) AF burden>6 h; (iii) CRT pacing<90%; and (iv) night heart rate>80 b.p.m. Patients were considered to have higher risk for HFR if ≥2 criteria were met, average risk if 1 criterion was met, and lower risk if no criteria were met. A Cox proportional hazards model was used to compare the groups. The data cohort consisted of a total of 265 HFHs in 175 patients, of which 36 (14%) were followed by HFR. On the discharge day, ≥2 criteria were met in 43 (16% of 265 HFHs), only 1 criterion was met in 92 (35%), and none of the four criteria were met in 130 HFHs (49%); HFR rates were 28, 16, and 7%, respectively. HFH with ≥2 criteria met was five times more likely to have HFR compared with HFH with no criteria met (adjusted hazard ratio 5.0; 95% confidence interval 1.9­13.5, P=0.001). CONCLUSION: Device-derived diagnostic criteria evaluated on the day of discharge identified patients at significantly higher risk of HFR.

Development of a method to risk stratify patients with heart failure for 30-day readmission using implantable device diagnostics.

The aim of the present study was to evaluate whether diagnostic data collected after a heart failure (HF) hospitalization can identify patients with HF at risk of early readmission. The diagnostic data from cardiac resynchronization therapy defibrillator (CRT-D) devices can identify outpatient HF patients at risk of future HF events. In the present retrospective analysis of 4 studies, we identified patients with CRT-D devices, with a HF admission, and 30-day postdischarge follow-up data. The evaluation of the diagnostic data for impedance, atrial fibrillation, ventricular heart rate during atrial fibrillation, loss of CRT-D pacing, night heart rate, and heart rate variability was modeled to simulate a review of the first 7 days after discharge on the seventh day. Using a combined score created from the device parameters that were significant univariate predictors of 30-day HF readmission, 3 risk groups were created. A Cox proportional hazards model adjusting for age, gender, New York Heart Association class, and length of stay during the index hospitalization was used to compare the groups. The study cohort of 166 patients experienced a total of 254 HF hospitalizations, with 34 readmissions within 30 days. Daily impedance, high atrial fibrillation burden with poor rate control (>90 beat/min) or reduced CRT-D pacing (<90% pacing), and night heart rate >80 beats/min were significant univariate predictors of 30-day HF readmission. Patients in the "high"-risk group for the combined diagnostic had a significantly greater risk (hazard ratio 25.4, 95% confidence interval 3.6 to 179.0, p = 0.001) compared to the "low"-risk group for 30-day readmission for HF. In conclusion, device-derived HF diagnostic criteria evaluated 7 days after discharge identified patients at significantly greater risk of a HF event within 30 days after discharge.

Isolated atrial segment pacing: an alternative to His bundle pacing after atrioventricular junctional ablation.

OBJECTIVES: This study was designed to investigate a practical alternative to His bundle pacing after atrioventricular (AV) junctional ablation by pacing a small area of isolated atrial tissue surrounding the AV node. BACKGROUND: His bundle pacing is preferred after AV junctional ablation in patients with refractory atrial fibrillation. However, it is technically difficult and not clinically useful at the present time. METHODS: This study was conducted in an isolated working swine heart model (n = 5), with real-time imaging capabilities. A small area of atrial tissue surrounding the AV node and the His bundle was isolated using sequential radiofrequency ablation lesions. RESULTS: Complete AV block created by segmental atrial isolation was achieved in 5 of 5 experiments. The isolated atrial segment was bordered by the ablation lines, the tricuspid annulus, and the AV node-His bundle. The AV conduction was characterized using a pacing electrode implanted into the isolated atrial segment. Pacing from the atria, the ventricles, and the isolated atrial segment at different rates confirmed complete bidirectional block between the atria and isolated area, whereas antegrade and retrograde AV nodal conduction between the isolated atrial segment and the ventricles remained intact. Pacing from the isolated area produced minimal changes in systolic left ventricular pressure compared with baseline sinus rhythm (mean -2 mm Hg). CONCLUSIONS: Isolation of a small area of atrial tissue surrounding the AV node is feasible by transcatheter radiofrequency ablation. This procedure may be a useful alternative to conventional AV junctional ablation because it can create complete AV block, while in effect permitting the equivalent of His bundle pacing after AV junctional ablation.

Recurrence of atrial tachyarrhythmias in implantable cardioverter-defibrillator recipients.

BACKGROUND: Because the natural history of atrial tachyarrhythmia (AT) is not known in patients with implantable cardioverter-defibrillators (ICDs) but without device-based atrial therapies, we aimed to describe the characteristics and recurrence of AT in such patients. METHODS: In this multicenter trial, 269 patients with standard indications for ICD placement and 2 episodes of AT in the preceding year received a dual-chamber ICD capable of logging AT. Patients were randomly assigned to 3-month periods of atrial therapies "on" or "off." This analysis considered only the 118 patients with atrial therapies programmed off at ICD placement. RESULTS: Fifty-eight patients (49%) had at least 1 AT episode longer than 1 minute, and 21 (18%) had at least 1 prolonged episode (>24 hours). The median episode frequency for each patient (episodes per month) was 1.8 episodes longer than 1 minute, 0.8 longer than 1 hour, and 0 longer than 24 hours. The median AT burden was 12.2 hours per month. CONCLUSIONS: Patients with standard ICD indications and history of AT have infrequent episodes, frequent short episodes, or prolonged episodes of AT-atrial fibrillation. However, the clinical characteristics examined did not distinguish among the groups. Improved diagnostic tools may help identify patients at risk for development of AT, thereby allowing specific therapies to be targeted to each group of patients.

Determinants of first-shock success for atrial implantable cardioverter defibrillators.

INTRODUCTION: The aim of this study was to identify determinants of first-shock success for defibrillation of spontaneous atrial fibrillation (AF) in ambulatory patients with an atrial implantable cardioverter defibrillator (ICD). The determinants of first-shock success in ambulatory patients with atrial ICDs are unknown. METHODS AND RESULTS: We used the generalized estimating equation method to analyze determinants of first-shock success in 50 consecutive atrial ICD recipients in whom DFT+ (weakest shock that defibrillates on two consecutive trials) was determined at implant and spontaneous AF was shocked with shock strength > or = 2 x DFT+. DFT+ was 6.2 +/- 3.1 J. Of 470 first shocks, 407 were successful (generalized estimating equation 85%, confidence interval 79% to 90%). Determinants of first-shock success were use of coronary sinus electrode (univariate P = 0.02; multivariate P < 0.001, relative risk 5.0), absence of a Class III antiarrhythmic drug (univariate P = 0.06; multivariate P < 0.001, relative risk 3.2), absence of early recurrence of atrial fibrillation (ERAF; univariate P = 0.06; multivariate P = 0.02, relative risk 2.9), and longer duration of AF prior to shock > or = 3 hours (univariate: P = 0.02; multivariate P = NS). Sinus rhythm >1 minute persisted after 93% of first shocks in patients without documented ERAF but after only 58% of shocks in patients with documented ERAF (P < 0.001). CONCLUSION: Reducing ERAF is critical to achieving a clinically acceptable rate of persistent sinus rhythm after first shocks. For first shocks > or = 2 x DFT +, success is not increased by programming stronger shocks. Early cardioversion does not increase first-shock success.

Atrial pacing lead location alters the effects of atrioventricular delay on atrial and ventricular hemodynamics.

The combined role of atrial pacing lead location and AV timing on cardiovascular performance has not been defined. This study tested the hypothesis that atrial pacing lead location can change the dependence of LA and LV hemodynamics on AV timing in vivo. Dogs anesthetized with isoflurane (n = 8) were instrumented for measurement of hemodynamics including LA pressure, LA volume, and pulmonary venous bloodflow. Data were recorded during normal sinus rhythm, and atrial overdrive pacing from the right atrial appendage (RAA), proximal coronary sinus (CS), and LA lateral wall (LAW). The AV node was then ablated and measurements repeated during synchronous ventricular pacing and during dual chamber pacing from each atrial lead location at various AV delays (20, 60, 120, 180, 240, and 350 ms). Hemodynamics during intrinsic sinus rhythm and overdrive atrial pacing from different sites were similar. In contrast, ventricular or dual chamber pacing caused significant (P < 0.05) changes in cardiac output with different AV timing during RAA (3.5 +/- 0.2 vs 2.9 +/- 0.2 L/min at 120 and 350 ms, respectively) and LAW pacing but not CS pacing. A significant interaction between atrial lead location and AV delay was observed for changes in stroke volume, pulmonary venous blood transport, LA volume, and LV preload. The results indicate that the atrial contribution to cardiac output depends on AV timing and atrial lead location in isoflurane-anesthetized dogs with AV nodal conduction block.