Just How Stable Are Escape Rhythms after Atrioventricular Junction Ablation?

Background: Atrioventricular (AV) node ablation with implantation of a permanent pacemaker is an established mode of therapy in the treatment of atrial fibrillation. However, concern exists regarding subsequent dependency on an entirely paced rhythm and the possible sequela of unheralded pacemaker failure. Data regarding escape rhythm lability, an important feature of pacemaker dependency, are limited. Aims and Methods: The purpose of this study was twofold: (1) to determine the characteristics of escape rhythms at predefined serial time intervals following AV node ablation and pacemaker implantation, and (2) to identify risk factors predictive of unstable escape rhythms. Patients undergoing AV node ablation and pacemaker implantation were assessed for the presence or absence of an escape rhythm during pacemaker interrogation at five predetermined serial time points. Baseline demographics and comorbid conditions were evaluated as potential predictors of those with labile escape rhythms. Results : Seventy‐nine percent of the 96 patients studied had an underlying escape rhythm (≥30 beats per minute) immediately postablation. Although the percentage of patients with an escape rhythm increased at each follow‐up interval, the number of patients who consistently demonstrated an escape rhythm declined with each follow‐up, with 28% of patients lacking an escape rhythm at some time point, i.e., labile escape rhythm. There were no significant predictors of a labile escape rhythm. Conclusion: Among patients who have undergone AV node ablation and pacemaker implantation, 72% have a stable escape rhythm over time, but others are at risk for pacemaker dependency, as predicted by an underlying absent or labile escape rhythm. (PACE 2010; 939–944)     

Direct and Telemetered Lead Impedance

Objectives: We undertook this study to determine whether telemetered lead impedance measurements (LIM) can be correlated with direct LIM and to determine the stability of LIM over time when measured directly and via telemetry. Methods: Direct LIM and telemetered LIM were measured in 91 patients; 101 leads during initial implantation and 40 leads during pulse generator replacement. Differences in direct LIM measured during initial implant and pulse generator replacement (direct-direct) were compared in 41 patients (28 atrial leads and 37 ventricular leads). The stability of telemetered LIM obtained immediately postoperatively, at 1 month and 1 year, postimplantation was assessed in 50 patients (23 atrial and 49 ventricular leads). Results: In atrial leads acute direct LIM was 633.9 ± 18.4 Ω versus 575.8 ± 18.5 Ω for telemetered LIM (r = 0.58), and chronic direct LIM was 670.9 ± 49.3 Ω versus 607.0 ± 36.3 Ω for telemetered LIM (r = 0.87). In ventricular leads acute direct LIM was 747.3 ± 16.9 Ω and 684.7 ± 16.4 Ω for telemetered LIM (r = 0.69), and chronic direct LIM was 674.8 ± 29.9 Ω and 625.2 ± 28.5 Ω for telemetered LIM (r = 0.68). The mean direct–direct UM rose 124 Ω (P < 0.001) in atrial leads and 10 Ω (P = NS) in ventricular leads. Telemetered LIM for atrial leads was 581.0 ± 27.6 Ω immediately postimplantation compared to 625.7 ± 34.8 Ω at 1 month and 754.1 ± 43.0 Ω at 1 year. Telemetered LIM for ventricular leads was 661.3 ± 17.5 Ω at implant, 684.6 ± 20.7 Ω at 1 month and 724.7 ± 22.7 Ω at 1 year. Conclusions: There is a good but limited correlation between direct and telemetered LIM. Mean direct LIM obtained at initial implantation is similar to that measured at pulse generator replacement. The telemetered LIM is stable over the first month postimplantation but tends to rise during the first year of follow-up and substantial changes in impedance are not uncommon in individuals with normal function. There is a tendency for LIM to rise with lead maturation. If telemetered LIM is to be followed over time, a baseline telemetered value should be obtained immediately postoperatively.     

The influence of the site of parasite inoculation on the development of Th1 and Th2 type immune responses in (BALB/c × C57BL/6) F1 mice infected with Leishmania major

Although inbred strains of mice are classified as genetically resistant or susceptible to Leishmania major based upon their ability to control infection, other factors such as the strain, dose, and site of parasite inoculation can also affect the outcome of the disease. Here we used the Fl progeny of BALB/c (susceptible) and C57BL/6 (resistant) mice (designated CB6F1) to investigate whether mice or intermediate susceptibility to infection differed from the parental strains in their ability to control infections at different cutaneous sites. CB6F1 mice developed progressive disease when inoculated in the dorsal skin, but healed infections in the footpad. Consistent with these observations, mice inoculated in the footpad ultimately developed Th1 responses, known to be required for healing, while Th2 responses developed in mice inoculated in the dorsal skin. However, IL-4 and IFN-γ production during the first few weeks of infection was similar in CB6F1 mice inoculated at either site, suggesting that factors in addition to the relative levels of these cytokines produced early in infection may influence the nature of the antileishmanial immune response, and the eventual disease outcome. Infection in CB6F1 mice provides a model for the study of immunity to L. major in genetically identical animals, in which a prolonged mixed Thl/Th2 cytokine pattern initially develops, but ultimately diverges into more defined Th1 and Thl type responses.     

Quantification of CMV viraemia in a case of transfusion-related graft-versus-host disease associated with purine analogue treatment

We report a patient who developed transfusion-associated graft-versus-host-disease (GvHD) and concurrent cytomegalovirus (CMV) infection, both complications thought to be related to severe T lymphocyte depletion induced by treatment with a purine analogue drug, fludarabine. CMV viraemia was detected by qualitative PCR and the viral load in positive samples was measured using a fully quantitative PCR assay. This quantitative assay enabled the evaluation of the efficacy of antiviral interventions based on the qualitative PCR result. The case illustrates the risks associated with the use of purine analogue drugs, as well as the value of quantitative CMV PCR assays for monitoring CMV infection in immunocompromised patients.     

Sudden Cardiac Death Despite a Functional Cardioverter‐Defibrillator: The Case for Early and Aggressive Therapy for Ventricular Tachycardia in Selected Patients

We present three cases within 11 months at a single institution of sustained VT that fell below the programmed detection rate of the patients’ implantable cardioverter‐defibrillators (ICDs), two of which continued until converting to an agonal VF that did not meet criteria for detection, and a third case that could not be successfully defibrillated after a prolonged period of VT. These episodes may be under‐recognized due to the dependence of device diagnostic storage on programming and the post‐mortem effort that is often required to review these events. Some patients, likely those with the most advanced heart failure, may not tolerate sustained ventricular tachycardia (VT) and may even die from ventricular arrhythmias without ever having a rhythm that meets detection criteria in a ventricular fibrillation (VF) zone.     

Alcoholism and the Patterning of Outcome: a multivariate analysis

This study takes a particular data set deriving from 10-year follow-up information on 68 male alcoholics as basis for exploring patterns of outcome in multivariate terms. A Principal Components Analysis demonstrates that degree of dependence is intrinsic to the patterning of outcome. The overall relationship between dependence and holistic outcome is a ‘Janus’ effect: high dependence may be related either to good or to bad outcome in different circumstances. When there is good outcome in terms simply of abstinence, dependence then further predicts within abstinent patients the overall quality of outcome which will be achieved. The need for a multivariate model is underlined.     

Initial Experience with Transvenous Implantable Cardioverter Defibrillator Lead Systems: Operative Morbidity and Mortality

Introduction of non-thoracotomy lead systems™ (Medtronic, Inc.) for the implantable cardioverter defibrillator (ICD) has expanded the indications for use of this mode of therapy. Patients previously considered "too ill" to undergo a thoracotomy as well as patients who are at a high risk for developing sudden death but without previous cardiac arrest, are now considered candidates. The initial experience with the non-thoracotomy lead system at our institution was analyzed for morbidity and mortality. Thirty-four patients underwent attempted intravascular lead implantation, with 30 having initial successful implantation (88.2%). There were 23 males; average ejection fraction (EF) was 38.6%. Three patients developed pulmonary edema and low output immediately after the procedure. Three patients developed electromechanical dissociation during defibrillation threshold testing. A prolonged testing time for the non-thoracotomy lead system was noted when compared to the thoracotomy system (57.39 vs 32.30 min; P < 0.0000). There were more intraoperative morbidities with the non-thoracotomy leads than with the thoracotomy system. There were no perioperative deaths. The potential consequences of prolonged anesthesia time and extensive defibrillation threshold testing should be considered when choosing the route of ICD implant, the type of anesthesia, and the intraoperative testing protocol for each patient.     

Orthostatic Responses in Patients with ODD Pacemakers: Signs of Autonomic Dysfunction

Responses to orthostasis may be altered in states associated with autonomic dysfunction. Computerized impedance cardiography, a noninvasive method for continuous assessment of stroke volume and mean blood pressure, was utilized to study the postural hemodynamic changes in eight normal and 27 patients with DDD pacemakers. Twenty patients with complete heart block (five with heart failure) were studied in the VDD mode and seven patients with sick sinus syndrome were assessed in DVI (four] or VDD (three). The results with pacemaker patients are significantly different from those observed in normal. Pacemaker patient responses to standing included: (1) a reduction in systolic, diastolic, and mean blood pressure; (2) an increase in heart rate in patients with intact sinus node function and no change in patients with sick sinus syndrome; and (3) stroke volume was unchanged in patients with sick sinus syndrome or heart failure and only modest reduction occurred in the remaining patients. Conclusions: (1) No reduction in stroke volume during upright posture occurs in DDD patients with sick sinus syndrome and this appears to be a compensatory reaction to an inadequate heart rate response to standing; (2) The hemodynamic response of DDD patients to the assumption of an upright posture is consistent with autonomic dysfunction; and (3) The primary cause for autonomic dysfunction in DDD patients may be the asynchronous ventricular depolarization caused by right ventricular pacing.