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Background: We hypothesized that survival in implantable cardioverter defibrillator (ICD) and cardiac resynchronization therapy defibrillator (CRT-D) patients is predicted by baseline Heart Rate Score., Methods: Heart Rate Score is determined from the atrial paced and sensed histogram of a DDD ICD or CRT-D, and defined as percent of beats in the histogram in the tallest 10 beats/min range bin. It was calculated at initial remote monitoring for patients enrolled in LATITUDE® without persistent atrial fibrillation, and with pulse generators implanted in 2006-2011. Univariate, multivariate, and Kaplan-Meier analyses determined the impact of Heart Rate Score on survival., Results: Of 57,893 ICDs and 67,929 CRT-Ds followed for 2.4 ± 1.5 years, each 10% increase in Heart Rate Score was associated with decreased survival (CRT-D hazard ratio [HR] 1.07 95%, confidence interval 1.06-1.07, P < 0.0001; ICD HR 1.05, 95% confidence interval 1.04-1.06, P < 0.0001). Multivariate analysis showed survival decreased with increasing age, atrial fibrillation, presence of a shock in first-year follow-up, and increasing programmed lower pacing rate in ICD and CRT-D patients. Increased percent right ventricular pacing predicted mortality in ICD patients, while male gender and lower percent left ventricular pacing predicted mortality in CRT patients. Heart Rate Score predicted survival independent of those variables. Heart Rate Score correlates with heart rate variability (standard deviation of average R-R intervals [SDANN]) when both are obtainable, but SDANN was only present in 6% of patients with Heart Rate Score >70%., Conclusion: A simple device histogram measure, Heart Rate Score, predicts survival in ICD and CRT-D patients independent of the available variables, and even when SDANN is unavailable., (© 2017 Wiley Periodicals, Inc.)

Introduction: Cardiac resynchronization therapy (CRT) can improve clinical and cardiac structural status in heart failure patients. The role of baseline diastolic echocardiographic parameters to characterize the likelihood of positive outcomes is not well known. We explored relationships between diastolic parameters and outcomes 6 months after CRT implant in the Predictors of Response to CRT (PROSPECT) Trial., Hypothesis: We hypothesized that diastolic echocardiographic parameters were associated with clinical and structural outcomes in CRT patients., Methods: For 426 patients in PROSPECT, a prospective observational trial of CRT, baseline E/A ratio, left atrial (LA) area, isovolumic relaxation time, left ventricular inflow deceleration time, E' velocity, and E/E' ratio were evaluated and related to 6-month clinical composite score (CCS) and left ventricular end-systolic volume (LVESV) reduction using Spearman rank-order correlations. Parameters associated with outcomes were analyzed further by discrete categorization., Results: As continuous variables, only E/A ratio and LA area correlated with CCSs (P = 0.017, P = 0.045, respectively) and relative change in LVESV at 6 months (P < 0.0001, P = 0.001, respectively). As discrete variables, E/A ratio and LA area also correlated with CCSs and LVESV., Conclusion: Diastolic echo parameters E/A ratio and LA area were associated with clinical and structural outcomes in CRT patients at 6 months., (©2012, The Authors. Journal compilation ©2012 Wiley Periodicals, Inc.)

Background: Unexplained and potentially arrhythmic symptoms often lead to electrophysiology referral for evaluation. Implantable loop recorder (ILR) correlation of the symptom to the rhythm can secure a definitive arrhythmic diagnosis after a standard, yet nondiagnostic workup., Methods: This large single-center retrospective study sought to assess the role of ILR in the evaluation of potentially arrhythmic symptoms, both in terms of diagnosis of an arrhythmia as well as to rule out an arrhythmic cause. Clinical data, indications for ILR, interrogation reports, and further management strategies were collected in all 86 patients who received ILR from June 1999 to April 2008 at the University of Iowa Hospitals and Clinics. The indications for ILR were unexplained syncope (76%), palpitations (14%), and presyncope or dizziness (10%)., Results: During a mean follow-up period of 10 +/- 7 months, 53 patients (62%) had recurrent symptoms after ILR placement with the mean time to recurrence of 12 +/- 17 weeks. Of these, an arrhythmic diagnosis was established in 12 patients (14%). Forty-one patients (48%) did not have any arrhythmia during their symptoms. These patients were discharged from the electrophysiology clinic. Thirty-three patients (38%) did not have any symptoms following ILR placement. Out of these, device was explanted in 10 patients, while the rest are still being followed., Conclusions: In patients with potentially arrhythmic symptoms, ILR plays an important role not only in diagnosing an arrhythmia, but also to rule out an arrhythmic cause.

Standard training pathways in cardiac electrophysiology are being short-circuited for a "fast-track" approach to train nonelectrophysiologists (not necessarily cardiologists) to implant defibrillators in patients. This approach has been undertaken by a professional society (The Heart Rhythm Society), a society that cannot police, or properly credential. They have support from the American College of Cardiology and, perhaps, even the Combined Medicare and Medicaid Services. This issue is particularly disturbing as there are no data to support the approach taken with regard to the safety and benefit for patients. This process disrupts the standard training pathways and will have long-term implications for the field of clinical cardiac electrophysiology and for the availability of highly trained individuals qualified to implant defibrillators. This issue has broad implications with regard to medical training pathways. We discuss these issues in detail and provide the results of two surveys, including a survey from members of the Heart Rhythm Society, most of whom disagree with the "fast-track" approach. A survey of cardiologist faculty members of the American College of Cardiology yielded similar results. We are particularly concerned about the disruption of training pathways in medicine and how this can affect patient care and can influence established training pathways in medicine.

Background: Unnecessary right ventricular (RV) pacing in patients with implantable cardioverter defibrillators (ICD) may adversely affect heart failure morbidity and total mortality. Inhibition of Unnecessary RV Pacing with AV Search Hysteresis in ICDs (INTRINSIC RV) is a prospective, multicenter, randomized trial evaluating outcomes in ICD recipients programmed to single-chamber pacing (VVI) versus dual-chamber (DDDR) pacing with AV search hysteresis (AVSH)., Methods: Patients underwent ICD implant (for standard indications). The ICD was programmed to DDDR with AVSH regardless of any need for pacing. Rate-adaptive pacing was set at 60-130 ppm with dynamic AV delay from 200 to 90 ms. AVSH was programmed to search every 32 intervals and extend the AV delay by 50%. One week post-implant patients with ICDs were interrogated to assess the percentage of RV pacing with the expectation that most would have <20% RV pacing and would be randomized into INTRINSIC RV. Early analysis showed that targets for randomization were not met. AVSH parameters were modified under a protocol amendment to increase AV delay extension to 100%. We report findings related to this programming change based upon analyses of (nonrandomized) data pre- and post-amendment., Results: Twenty-one percent of patients (n = 314) were enrolled pre-amendment and 79% (n = 1,216) were enrolled post-amendment. The mean percentage of RV pacing at the 1-week visit was 41.4 +/- 29.6% pre-amendment and 14.7 +/- 22.6% post-amendment (P < 0.0001). The proportion of patients eligible for randomization (RV pacing <20% at the 1-week visit) was 31.2% pre-amendment and 76.8% post-amendment (P < 0.0001)., Conclusion: AVSH can dramatically reduce the percentage of RV pacing among ICD recipients.

Implantable cardioverter defibrillators (ICDs) reduce sudden arrhythmic death risk but when these devices are programmed DDD and pace in the right ventricle (RV), they can be associated with increased mortality and heart failure morbidity compared to an ICD programmed to back-up RV. An ideal ICD would provide effective treatment for life-threatening tachyarrhythmias, reduce unnecessary RV pacing and maintain AV synchrony. The Inhibition of Unnecessary RV Pacing with AV Search Hysteresis (AVSH) in ICDs (INTRINSIC RV) study will assess whether an ICD programmed to DDDR with AVSH is equal to an ICD programmed to VVI with regard to mortality, heart failure hospitalizations, and several predefined secondary enpoints. AVSH allows intrinsic AV conduction beyond the programmed AV delay to help minimize ventricular pacing. INTRINSIC RV, a multi-center, randomized, prospective trial will enroll >1,200 participants who receive a Guidant VITALITY AVT ICD. ICDs are programmed initially to DDDR AVSH 60-130. Then, after a week, if the %RV pacing <20%, patients are randomized to VVI-40 or DDDR 60-130 with AVSH. Those with RV pacing > or =20% are placed in an obvservational arm and programmed ad libitum by the treating physician. Patients are followed for one year. This large, randomized, controlled, clinical trial will address whether DDDR with AVSH programming is equivalent to VVI programming in an ICD with regard to mortality and heart failure hospitalization.

A patient had a dual chamber pacemaker with endocardial leads implanted chronically. The lead position on chest X ray and the ECG pattern indicated lead malposition, but a CT scan and transesophageal echocardiography were nondiagnostic. Venography indicated that both leads were in the mediastinal and pericardial space.

De novo postoperative life-threatening ventricular arrhythmias are poorly understood. Long-term benefits of, and need for, treatment is uncertain. To assess the therapeutic advantage of ICD to manage new-onset, life-threatening ventricular tachyarrhythmias after cardiac surgery. Patients included were those with an ICD implanted for de novo life-threatening ventricular tachyarrhythmias encountered 48 hours or more after cardiac surgery. Primary endpoints were total survival, time to first ICD therapy, and appropriateness of ICD therapy. Mean projected survival and projected time to first ICD therapy were calculated by the Kaplan-Meier method. Twenty-seven postoperative patients (left ventricular ejection fraction 0.22 +/- 0.07) were followed for 26 +/- 17.6 months. The index arrhythmia was sustained monomorphic ventricular tachycardia in 17 (63%) and ventricular fibrillation in 10 (37%). Electrophysiological study was positive in 22 (81%) of 27. Total survival and mean projected survival after ICD implant were 22 (81%) of 27 and 25.6 months, respectively, to end of follow-up. The majority received ICD therapy (21/27 [78%]), 20 (74%) of 27 receiving appropriate therapy. The mean time to first ICD therapy and mean projected time to first ICD therapy was 5.6 +/- 7.8 months and 10.5 months, respectively. De novo postoperative ventricular arrhythmias are associated with a high probability of late recurrence. The ICD is useful for these patients.

The determinants of high defibrillation energy requirements (DER) using nonepicardial lead systems (NELS) have not been well characterized. The goal of this study was to examine prospectively the influence of clinical, radiographic, echocardiographic, and procedural variables on DER during NELS placement. Data from 100 consecutive patients undergoing attempted NELS implantation were analyzed. Transvenous leads, subcutaneous patches, and monophasic shock devices from two manufacturers were used. Leads were successfully positioned for testing in 95% of patients. An adequate DER (< or = 25 J) was obtained in 73 of 95 (77%) of patients. Univariate analysis identified amiodarone therapy and left ventricular mass as predictors of high DER. With multivariate analysis, amiodarone therapy was the sole significant predictor of high DER (P = 0.002, odds ratio 5.46). The 22 patients with high NELS DER also had high epicardial DER (mean 24 +/- 9 J). The two patch epicardial DER was > 25 joules in 12 of 22 patients. Thus, adequate DER with monophasic shock waveforms can be obtained in most patients undergoing NELS testing. However, amiodarone therapy significantly increases the probability of obtaining high DER.

Limited data suggest that adenosine termination of atrial tachycardia is uncommon. To investigate further the effect of adenosine on atrial tachycardia, adenosine (6-12 mg) was administered during sustained atrial tachycardia in 17 patients. All patients underwent electrophysiological study to exclude other mechanisms of supraventricular tachycardia. Mean patient age was 51 +/- 20 years (range 18-82 years). Seven patients had no structural heart disease. The mean atrial tachycardia cycle length was 390 +/- 80 msecs (range 260-580). Sustained atrial tachycardia was induced with atrial extrastimuli in 8 patients, and was either incessant at baseline or developed spontaneously during isoproterenol infusion in 9 patients. Adenosine terminated atrial tachycardia in 3 patients (18%), transiently suppressed atrial tachycardia in 4 patients (23%), and produced AV block without affecting tachycardia cycle length in the remaining 10 patients. Adenosine sensitivity was observed in 3 of 8 patients with tachycardias initiated and terminated by atrial extrastimuli, and in 4 of 9 patients with spontaneous, but not inducible tachycardias including 3 of 4 patients with isoproterenol facilitated tachycardias. Of multiple clinical and electrophysiological variables examined as potential predictors of adenosine sensitivity, only isoproterenol facilitation of spontaneous or inducible sustained tachycardia predicted adenosine sensitivity (P = 0.02). These observations suggest that adenosine-sensitive atrial tachycardia may be more common than previously recognized. Adenosine sensitivity does not appear to be specific for tachycardia mechanism and cannot be predicted by response to pacing. Atrial tachycardias dependent on beta-adrenergic stimulation are most likely to be terminated by adenosine.

With the increasing flexibility allowed by implantable cardioverter defibrillators that use tiered therapy, it is important to match the therapy with the arrhythmia. In this article we present scatter diagram analysis, a new computationally efficient two-channel algorithm for distinguishing monomorphic ventricular tachycardia (VT) from polymorphic ventricular tachycardia and ventricular fibrillation (VF). Scatter diagram analysis plots the amplitude from one channel versus the amplitude from another channel on a graph with a 15 x 15 grid. The fraction (percentage) of the 225 grid blocks occupied by at least one sample point is then determined. We found that monomorphic VT traces nearly the same path in space and occupies a smaller percentage of the graph than a nonregular rhythm such as polymorphic VT or VF. Scatter diagram analysis was tested on 27 patients undergoing intraoperative implantable cardioverter defibrillator testing. Passages of 4.096 seconds were obtained from rate (bipolar epicardial) and morphology (patch) leads, and digitized at 125 Hz. Scatter diagram analysis distinguished 13 episodes of monomorphic VT (28.6% +/- 4.0%) from 27 episodes of polymorphic VT or VF (48.0% +/- 8.2%) with P < 0.0005. There was overlap in only one monomorphic VT episode and one polymorphic VT or VF episode.

Four patients with previously placed implantable defibrillators required coronary revascularization several years after the original device was inserted. Three patients had a conventional system of epicardial patches and leads, and one patient had a nonthoracotomy system placed. All four patients were successfully revascularized without evidence of perioperative infarction or significant morbidity. The patient with the nonthoracotomy device did require manipulation of the endocardial lead at a separate setting. This limited experience suggests that patients needing revascularization after placement of an implantable defibrillator can be successfully bypassed.

Atrial flutter is a common and usually benign but symptomatic supraventricular tachycardia. There is a striking similarity between patients with atrial flutter suggesting a common substrate despite the presence or absence of underlying heart disease. In man, the mechanism is a single reentrant circuit originating in the right atrium whose center appears to be functional within the anatomical constraints of the right atrium. The reentrant circuit of atrial flutter contains an area of slow conduction in the inferior right atrium but the size and exact location is uncertain. Drug therapy directed at terminating and preventing atrial flutter has been available for many years. The efficacy and safety of this therapy is not as well tested as is the same therapy for atrial fibrillation. The most effective way to terminate atrial flutter is a nonpharmacological approach. Several nonpharmacological methods provide new treatment options in the management of patients with drug resistant or hemodynamically unstable atrial flutter. The use of anticoagulation for this disorder is still evolving. There is a risk of clinically apparent thromboemboli in some patients with atrial flutter although the risk appears less than that for atrial fibrillation. In the future, refinements and improvements in therapy for atrial flutter will likely be derived from a better understanding of its mechanism.

A 65-year-old man developed incessant ventricular tachycardia following coronary artery bypass grafting while being weaned from cardiopulmonary bypass. The arrhythmia was refractory to procainamide, lidocaine, bretylium, and magnesium. Ventricular tachycardia subsided following reinitiation of cardiopulmonary bypass. Ultimately, the patient required ventricular assist devices to control his arrhythmia. This case is unique as the ventricular assist devices were used not for hemodynamic support, but for arrhythmia control. The mechanism of arrhythmia suppression may be related to contraction-excitation coupling.