Michael S. Lloyd

Hands-On Defibrillation An Analysis of Electrical Current Flow Through Rescuers in Direct Contact With Patients During Biphasic External Defibrillation

Background— Brief interruptions in chest compressions reduce the efficacy of resuscitation from cardiac arrest. Interruptions of this type are inevitable during hands-off periods for shock delivery to treat ventricular tachyarrhythmias. The safety of a rescuer remaining in contact with a patient being shocked with modern defibrillation equipment has not been investigated. Methods and Results— This study measured the leakage voltage and current through mock rescuers while they were compressing the chests of 43 patients receiving external biphasic shocks. During the shock, the rescuers gloved hand was pressed onto the skin of the patients anterior chest. To simulate the worst case of an inadvertent return current pathway, a skin electrode on the rescuers thigh was connected to an electrode on the patients shoulder. In no cases were shocks perceptible to the rescuer. Peak potential differences between the rescuers wrist and thigh ranged from 0.28 to 14 V (mean 5.8±5.8 V). The average leakage current flowing through the rescuers body for each phase of the shock waveform was 283±140 μA (range 18.9 to 907 μA). This was below several recommended safety standards for leakage current. Conclusions— Rescuers performing chest compressions during biphasic external defibrillation are exposed to low levels of leakage current. The present findings support the feasibility of uninterrupted chest compressions during shock delivery, which may enhance the efficacy of defibrillation and cardiocerebral resuscitation.

Early performance of a miniaturized leadless cardiac pacemaker: the Micra Transcatheter Pacing Study

Aims Permanent cardiac pacing is the only effective treatment for symptomatic bradycardia, but complications associated with conventional transvenous pacing systems are commonly related to the pacing lead and pocket. We describe the early performance of a novel self-contained miniaturized pacemaker. Methods and results Patients having Class I or II indication for VVI pacing underwent implantation of a Micra transcatheter pacing system, from the femoral vein and fixated in the right ventricle using four protractible nitinol tines. Prespecified objectives were >85% freedom from unanticipated serious adverse device events (safety) and <2 V 3-month mean pacing capture threshold at 0.24 ms pulse width (efficacy). Patients were implanted (n = 140) from 23 centres in 11 countries (61% male, age 77.0 ± 10.2 years) for atrioventricular block (66%) or sinus node dysfunction (29%) indications. During mean follow-up of 1.9 ± 1.8 months, the safety endpoint was met with no unanticipated serious adverse device events. Thirty adverse events related to the system or procedure occurred, mostly due to transient dysrhythmias or femoral access complications. One pericardial effusion without tamponade occurred after 18 device deployments. In 60 patients followed to 3 months, mean pacing threshold was 0.51 ± 0.22 V, and no threshold was ≥2 V, meeting the efficacy endpoint (P < 0.001). Average R-wave was 16.1 ± 5.2 mV and impedance was 650.7 ± 130 ohms. Conclusion Early assessment shows the transcatheter pacemaker can safely and effectively be applied. Long-term safety and benefit of the pacemaker will further be evaluated in the trial. Clinical Trial Registration ClinicalTrials.gov ID NCT02004873.

Emerging applications for transseptal left heart catheterization old techniques for new procedures.

Transseptal (TS) catheterization was introduced in 1959 as a strategy to directly measure left atrial (LA) pressure. Despite acceptable feasibility and safety, TS catheterization has been replaced by indirect measurements of LA pressure using the Swan-Ganz catheter. Today, TS puncture is rarely performed for diagnostic purposes but continues to be performed for procedures such as balloon mitral valvuloplasty, antegrade balloon aortic valvuloplasty, and ablation of arrhythmias in the LA. Thus, the art of TS puncture has been lost, except in centers that perform these procedures with regularity. Recently, there has been a renewed interest in the TS technique because of emerging therapeutic procedures for structural heart disease and atrial fibrillation ablation. Invasive cardiologists will have to refamiliarize themselves with the TS technique, newer TS devices, and advanced ultrasound imaging for guidance of the procedure.

Pacing Features That Mimic Malfunction: A Review of Current Programmable and Automated Device Functions That Cause Confusion in the Clinical Setting

Modern implantable devices capable of pacing are armed with a multitude of programmable and automated features. While some features represent important advances in device safety and performance, many can also mimic device malfunction. This article discusses these features in terms of the confusion they may cause and highlights important clinical clues that aid in their recognition.

The Relationship of Bipolar Left Ventricular Pacing Stimulus Intensity to Cardiac Depolarization and Repolarization in Humans with Cardiac Resynchronization Devices

Background: Myocardial depolarization can be altered by varying pacing stimulus output. This may have implications on response rates for cardiac resynchronization therapy (CRT). The purpose of our study was to determine the relationship of left ventricular (LV) pacing stimulus intensity to measures of depolarization and repolarization in humans with CRT devices.

Coronary Artery Disease Potentiates Response to Dofetilide for Rhythm Control of Atrial Fibrillation

Background: Dofetilide, a class III antiarrhythmic, is one of the few alternatives to amiodarone in patients with atrial fibrillation (AF) and heart failure or coronary artery disease (CAD). While amiodarone has been extensively studied, little is known about predictors of response to dofetilide. We sought to identify clinical parameters associated with dofetilide success in a large cohort of patients with AF.

Rate adaptive pacing in an intracardiac pacemaker

BACKGROUNDnThe Micra transcatheter pacemaker was designed to have similar functionality to conventional transvenous VVIR pacing systems. It provides rate adaptive pacing using a programmable 3-axis accelerometer designed to detect patient activity in the presence of cardiac motion.nnnOBJECTIVEnThe purpose of this study was to evaluate the systems performance during treadmill tests to maximum exertion in a subset of patients within the Micra Transcatheter Pacing Study.nnnMETHODSnPatients underwent treadmill testing at 3 or 6 months postimplant with algorithm programming at physician discretion. Normalized sensor rate (SenR) relative to the programmed upper sensor rate was modeled as a function of normalized workload in metabolic equivalents (METS) relative to maximum METS achieved during the test. A normalized METS and SenR were determined at the end of each 1-minute treadmill stage. The proportionality of SenR to workload was evaluated by comparing the slope from this relationship to the prospectively defined tolerance margin (0.65-1.35).nnnRESULTSnA total of 69 treadmill tests were attempted by 42 patients at 3 and 6 months postimplant. Thirty tests from 20 patients who completed ≥4 stages with an average slope of 0.86 (90% confidence interval 0.77-0.96) confirmed proportionality to workload. On an individual test basis, 25 of 30 point estimates (83.3%) had a normalized slope within the defined tolerance range (range 0.46-1.08).nnnCONCLUSIONnAccelerometer-based rate adaptive pacing was proportional to workload, thus confirming rate adaptive pacing commensurate to workload is achievable with an entirely intracardiac pacing system.

Cardiac electrophysiology of patients with spinal cord injury

Spinal cord injury is a clinical syndrome encountered frequently in trauma centers and is accompanied by both acute and chronic heart rhythm abnormalities. The injury is characterized by sympathetic nervous system impairment with preservation of parasympathetic output via the vagus nerve. Severe bradycardia in the form of life-threatening sinus arrest or complete heart block may be observed in the acute recovery phase. Therapy for arrhythmias in the acute phase includes atropine, intravenous chronotropes, methylxanthines for the prevention of episodic bradycardia, and pacemaker implantation in severe cases. In the chronic recovery phase, autonomic dysreflexia in the form of paroxysmal hypertension is often induced by visceral organ distension or other stimuli and can be accompanied by bradycardia or tachycardia. The prognosis for survivors of spinal cord injury is expected to improve with further advances in surgical and medical care, and electrophysiologists will likely be called upon more frequently to help manage heart rhythm disorders in this setting.

Recurrences of Atrial Fibrillation after Ablation: When Will This Hydra Meet Its Hercules?

The second labor of Hercules was to kill the hydra, a nine-headed venomous serpent that terrorized the citizens of Lerna. Hercules would destroy one of the serpent’s heads with his club, only to find two more heads growing in its place. With the aid of his nephew, they finally overcame the beast by searing the stump of each head that he clubbed with a torch. Hercules’ struggle against the hydra is likened to a very real problem in ablative therapy for atrial fibrillation (AF). The rate of recurrence after ablation has been reported by a variety of groups and may approach 70%, depending on the ablation strategy used.1 In this issue, Hsieh et al.2 observe that the right atrium (RA) may be a “new head of the hydra” by mediating recurrences more than a year from the initial ablation.2 As longer follow-up data accumulate, recurrence rates may further increase our concern about the durability of successful AF ablation.

Leadless pacemaker implantation and concurrent atrioventricular junction ablation in patients with atrial fibrillation

Atrioventricular junctional (AVJ) ablation and pacemaker implantation are indicated when pharmacotherapy fails to achieve adequate rate control in atrial fibrillation (AF). The purpose of our study is to assess the feasibility and safety of concurrent Micra leadless transcatheter pacemaker implantation and AVJ ablation.