Stratifying patients at the risk of heart failure hospitalization using existing device diagnostic thresholds

Background

Heart failure hospitalizations (HFHs) cost the US health care system ~$20 billion annually. Identifying patients at risk of HFH to enable timely intervention and prevent expensive hospitalization remains a challenge. Implantable cardioverter defibrillators (ICDs) and cardiac resynchronization devices with defibrillation capability (CRT-Ds) collect a host of diagnostic parameters that change with HF status and collectively have the potential to signal an increasing risk of HFH. These device-collected diagnostic parameters include activity, day and night heart rate, atrial tachycardia/atrial fibrillation (AT/AF) burden, mean rate during AT/AF, percent CRT pacing, number of shocks, and intrathoracic impedance. There are thresholds for these parameters that when crossed trigger a notification, referred to as device observation, which gets noted on the device report. We investigated if these existing device observations can stratify patients at varying risk of HFH.

Methods

We analyzed data from 775 patients (age: 69 ± 11 year, 68% male) with CRT-D devices followed for 13 ± 5 months with adjudicated HFHs. HFH rate was computed for increasing number of device observations. Data were analyzed by both excluding and including intrathoracic impedance. HFH risk was assessed at the time of a device interrogation session, and all the data between previous and current follow-up sessions were used to determine the HFH risk for the next 30 days.

Results

2276 follow-up sessions in 775 patients were evaluated with 42 HFHs in 37 patients. Percentage of evaluations that were followed by an HFH within the next 30 days increased with increasing number of device observations. Patients with 3 or more device observations were at 42× HFH risk compared to patients with no device observation. Even after excluding intrathoracic impedance, the remaining device parameters effectively stratified patients at HFH risk.

Conclusion

Available device observations could provide an effective method to stratify patients at varying risk of heart failure hospitalization.

Nocturnal peak in atrial tachyarrhythmia occurrence as a function of arrhythmia burden

INTRODUCTION

We examined circadian periodicity of atrial tachyarrhythmias (AT/AF) in a large group of patients with implantable devices, which allow continuous collection of the event data over prolonged periods of time.

METHODS AND RESULTS

A total of 16,130 AT/AF events were recorded in 236 patients (age: 63 ± 12 years, 27% female, 90% had a history of cardiovascular disease, 33% ischemic, LVEF: 49 ± 18%) over a period of 12 months. To exclude interactions with therapy, the patterns of arrhythmia occurrence were examined for all events and for those episodes that were preceded by at least 1, 6, and 24 hours of sinus rhythm. To prevent biasing toward patients with more frequent episodes, the patterns of AT/AF onset were analyzed both in absolute and patient-normalized (i.e., divided by the total number of events in each patient) units per hour per patient and then summarized for the entire group. In patients with <4 AT/AF events, the onset times were randomly distributed over 24-hour period. However, as the number of AT/AF events increased, a nocturnal pattern of occurrence (determined by the occurrence of a trough around noon) gradually emerged and became highly statistically significant (P < 10(-4) ). The magnitude of nocturnal peak of AT/AF events was well explained by a single-exponential function (R(2) = 0.97, P < 10(-2) ).

CONCLUSION

Patients with more frequent atrial tachyarrhythmias are more likely to develop AT/AF at night. Knowledge of patient-specific circadian patterns of arrhythmia occurrence can be useful for personalized management of individuals with significant arrhythmia burden.

Management of atrial tachyarrhythmias. Rhythm control using implantable devices

Presently, most devices with atrial diagnostic and therapeutic features are implanted in patients for electrical treatment of bradyarrhythmias and ventricular tachyarrhythmias. The painless electrical strategies for prevention and termination of ATa have not demonstrated significant clinical effectiveness in the general population with ATa. The effectiveness of ATP in reducing burden may be significantly higher in a subgroup of patients with a high incidence of stable ATa, but this needs to be evaluated prospectively. Smart sensing and detection schemes will also help provide accurate information and determine when ATa can be terminated with ATP. Although electrical defibrillation is effective, the discomfort associated with atrial shocks has limited the widespread use of this technology. Recent technological advances have increased the capabilities of implantable devices to store large amounts of diagnostic information. In the near future, implantable devices without transvenous leads may be implanted to monitor a variety of physiologic signals. This could help improve clinical outcomes and determine which therapies (pharmacologic, ablative, or electrical) would be most effective as well as monitor their safety and efficacy. Frequent monitoring from home and the availability of this data to the physician/nurse on the Internet can potentially improve the management of patients' ATa at a much lower cost.

Impact of atrial fibrillation duration on postcardioversion recurrence

BACKGROUND

"Begetting," a mechanistic tenet of atrial fibrillation (AF), stipulates that the rate of recurrence of AF after cardioversion is proportional to the preceding arrhythmia duration. However, recent reports suggest that, for brief durations, the incidence of early recurrence of AF (ERAF) is inversely proportional to duration. These reports were based on potentially biased data.

OBJECTIVES

We performed a prospective study to examine the impact of AF duration on postcardioversion recurrence.

METHODS

Forty-four patients underwent placement of an implantable cardioverter-defibrillator (ICD) capable of delivering patient-elicited AF cardioversion shocks. Subsequently, in the ambulatory setting, the timing of shocks in relationship to perceived AF onset was randomly assigned within individuals to early (as soon as possible) or delayed (1 day later).

RESULTS

During a follow-up averaging 199 days per patient, a total of 61 AF episodes among 17 patients occurred for which a patient-elicited cardioversion shock was delivered. Twenty-three shocks were delivered using early protocol (mean 6.8 hours after AF onset), and 38 shocks were delivered using delayed protocol (mean 34.7 hours after AF onset). The incidence of ERAF was significantly lower using the delayed protocol.

CONCLUSION

A strategy of approximately 24-hour delay in cardioversion shock timing decreased the incidence of ERAF, relative to a shock delivered within a few hours of AF onset. This observation has important mechanistic and therapeutic implications.

Quantification of atrial tachyarrhythmia burden with an implantable pacemaker before and after pulmonary vein isolation

Long-term efficacy of pulmonary vein (PV) ostial isolation for paroxysmal atrial fibrillation is difficult to assess. We evaluated the net duration of atrial tachyarrhythmia episodes (burden), atrial tachyarrhythmia episode frequency, and quality-of-life (QOL) before and after PV isolation in patients with an existing pacemaker featuring extensive diagnostic capabilities. Due to frequent recurrences of paroxysmal atrial fibrillation, PV isolation was performed 21 +/- 10 months following pacemaker implantation on 12 patients (57 +/- 5 years) with normal left ventricular function. Atrial tachyarrhythmia burden (ATB) and episode frequency were monitored daily by the device both pre- and postablation. QOL questionnaires were collected at ablation and 1, 3, and 6 months thereafter. Patients were followed for 20 +/- 9 and 11 +/- 9 months pre- and postablation, respectively. Membrane-active antiarrhythmic medications were discontinued after ablation in 8 of 12 patients. PV isolation resulted in a significant reduction of ATB from a median of 3.2 hours/day (preablation) to 0.2 hours/day (postablation, P < 0.01, Wilcoxon signed-rank test). The median tachyarrhythmia frequency was 6.4 episodes/day (preablation) and 0.3 episodes/day (postablation, P = 0.09). QOL measures significantly improved over the data collection intervals (P < 0.05). Tachyarrhythmia burden was positively associated with Symptom Checklist frequency and severity (P < 0.01). Significant long-term reductions in total ATB (symptomatic and asymptomatic) were observed. Furthermore, reductions in ATB were associated with improvements in QOL measures. Extensive monitoring capabilities in implantable devices help provide complete disclosure on the effect of PV isolation in paroxysmal atrial fibrillation patients.

Temporal variability of atrial tachyarrhythmia burden in bradycardia–tachycardia syndrome patients

AIMS

Several studies have tested non-pharmacological therapies for atrial tachyarrhythmias (ATs) by measuring the cumulative time (burden) the patient spends in arrhythmia. Contradictory results questioned either therapy efficacy or statistical power of the trials. We studied AT burden variability in patients paced for sinus node disease (SND) in order to interpret currently published data appropriately and to evaluate reliable sample sizes.

METHODS AND RESULTS

One hundred and five patients with AT and SND received a dual chamber pacemaker with antitachyarrhythmia-pacing capability, and were followed for 13 months. Seventy-eight patients (74%) suffered AT recurrences. Device-gathered diagnostic measures were used to simulate results of randomized studies both with crossover and parallel design. The sample size required for statistically significant results was calculated as a function of the expected therapy-induced burden reduction. AT burden intra-patient variability was high: 43% of patients showed intrinsic fluctuations hiding any therapy-induced burden reduction lower than 30%. Demonstrating therapeutic breakthrough through a 6 month study would require 290 patients with crossover design and 5800 patients with parallel design. Doubling the study period requires 400 and 3000 patients, respectively.

CONCLUSION

Patients with AT and paced for SND showed high intra-patient burden variability, which could possibly hide an AT burden reduction induced by a therapy. Previous studies involving non-pharmacological therapies utilizing AT burden endpoints could lack the power to reach statistical significance.

The Circadian Variation of Atrial Defibrillation Thresholds

BACKGROUND

A circadian variation exists for ventricular defibrillation thresholds (DFTs) with a morning peak and a corresponding decrease in therapy success rates from implantable cardioverter defibrillators. Such a variation in atrial DFTs may have implications for the timing of internal cardioversion of atrial arrhythmias. The aim of this study was therefore to determine the circadian variation of atrial DFTs in patents with recurrent atrial fibrillation (AF).

METHODS AND RESULTS

Data were collected as part of the worldwide Jewel AF-only study. Patients had recurrent persistent AF and no history of ventricular arrhythmias. The atrial DFT was assessed at device implantation using a step-up protocol and was recorded for 100 patients (age 63.0 +/- 11.7, 74% male, ejection fraction 49.6 +/- 17.8%, left atrial diameter 46 +/- 9 mm). The mean atrial DFT was 6.3 +/- 4.3 J. For the most commonly tested lead configuration (right atrium to coronary sinus in 56 patients), the atrial DFT for patients implanted in the morning (3.3 +/- 1.5 J) was significantly lower than for both the DFT measured in the afternoon (5.8 +/- 3.4 J, p < 0.01) and the DFT measured in the evening (7.4 +/- 5.9 J, p < 0.01).

CONCLUSION

There may be a significant variation in measured atrial DFT for the right atrium to coronary sinus configuration, with a nadir in the morning. This is the converse to measurements of ventricular DFTs suggesting different regulatory electrophysiological mechanisms. Further investigation of this possible variation is warranted.

Comparison of the effects on drug concentrations, electrophysiologic parameters, and termination of atrial fibrillation in dogs when procainamide and ibutilide are delivered into the right atrium versus intravenously

INTRODUCTION

We tested the hypothesis that right intra-atrial (i.a.) administration of antiarrhythmic drugs resulted in higher peak serum drug concentrations, greater electrophysiologic effects, and greater efficacy for termination of atrial fibrillation (AF) than intravenous (i.v.) drug delivery.

METHODS AND RESULTS

Eight dogs were treated with 9.7 mg/kg procainamide infusion and eight dogs with 0.02 mg/kg ibutilide infusion, injected over 5 minutes. Each dog had both an electrophysiologic (EP) and an AF termination study during i.a. and i.v. drug administration at > or = 2-day intervals (total four studies each). Right atrial pacing capture threshold, right atrial effective refractory period (ERP), right atrial and right ventricular monophasic action potential (MAP) durations at 70% and 90% of repolarization (MAPD70, MAPD90), AH, HV, and QT intervals, QRS width, intra-arterial systolic and diastolic blood pressures, and cardiac output were measured at different time-points. Blood samples were drawn from the coronary sinus and femoral vein for drug level determination. The right atrium was paced at 400-msec cycle length throughout the study. AF was induced by rapid right atrial pacing and maintained by methacholine infusion at 1.5 to 3 microg/kg/min. The sustained AF was allowed to persist for 10 minutes before starting the antiarrhythmic drug infusion. We found no significant difference between the procainamide concentrations in the coronary sinus and femoral vein during i.a. and i.v. drug delivery. The time course and extent of increase in right atrial ERP, MAPD70, MAPD90, and all the other measured EP parameters did not differ between the two routes of drug administration. No significant difference was found in termination of AF between i.v. (5/7 procainamide; 4/8 ibutilide) or i.a. (3/8 procainamide; 3/8 ibutilide) drug delivery or between drugs (8/15 procainamide; 7/16 ibutilide).

CONCLUSION

Our data do not support any beneficial effect of i.a. versus i.v. procainamide or ibutilide delivery.

Wave front-obstacle interactions in cardiac tissue: a computational study

An understanding of wave front-obstacle interactions will greatly enhance our knowledge of the mechanisms involved in cardiac arrhythmias and their therapy. The goal of this computational study is to examine the interactions between wave fronts and various obstacles in a two-dimensional sheet of myocardium. The myocardium is modeled as an isotropic sheet with Luo-Rudy I membrane kinetics. An examination is conducted of wave front interactions with nonconductive and passive-tissue obstacles. Simulations were performed either in environments of reduced myocardial excitability, or with rapid stimulation via a line electrode. The shape of the obstacles and their ability to withdraw current from the active tissue greatly influence wave front-obstacle interactions in each of these environments. The likelihood of wave front detachment from an obstacle corner increases as the curvature of the obstacle corner is increased. A passive-tissue obstacle promotes wave front-obstacle separation in regions of depressed excitability. Under rapid pacing, the presence of the passive obstacle results in wave fragmentation, while the insulator obstacle promotes wave front detachment. The results of this study reveal the importance of obstacle composition and geometry in wave front interactions with cardiac obstacles.

Oral herpetic lesions in an edentulous patient

This article reports a case of oral herpetic lesions that recurred several times over 1 1/2 years in an edentulous 65-year-old woman. The patient was under treatment for complete dentures at the New Jersey Dental School. A differential diagnosis of mucosal ulcerative lesions is described, along with the laboratory methodology for confirmation of herpes simplex virus type 1 (HSV-1) infection.

Manipulating the intracellular environment of hippocampal slices: pH and high-energy phosphates

The intracellular energetic environment of rat hippocampal slices was manipulated by bolstering ATP levels following the addition of adenosine to the incubation medium, or by manipulating intracellular pH. Addition of 8 mM adenosine to the incubation medium increased total tissue adenylate and ATP content, but did not prolong electrical function during anoxia. Further, it resulted in long-lasting alterations in normoxic evoked responses. Intracellular pH (pHi) was changed by manipulating the bicarbonate/CO2 ratio of the incubation medium, or by adding amiloride, a hydrogen/sodium antiport blocker. Estimates of intracellular pH using the creatine kinase equilibrium agree with those obtained by Neutral red scanning spectrophotometry in control conditions. However, only Neutral red indicated an acidification with amiloride treatment, while the creatine kinase equilibrium was preferentially affected by hypercapnia, suggesting the presence of at least two pH compartments in hippocampal brain slices. These manipulations cannot be carried out easily in vivo, and provide a means of determining the importance of metabolic changes on neural function during anoxia.