Kathy L. Lee

Effects of Biatrial Pacing in Prevention of Postoperative Atrial Fibrillation After Coronary Artery Bypass Surgery

BACKGROUNDnAtrial fibrillation (AF) is common after coronary artery bypass surgery (CABG) and results in prolonged hospitalization. The purpose of this study was to evaluate the efficacy of biatrial pacing in preventing post-CABG AF compared with single-site atrial pacing.nnnMETHODS AND RESULTSnA total of 132 patients who had no history of AF and who underwent CABG were randomized to 1 of the following 4 groups: biatrial pacing (BiA), left atrial pacing (LA), right atrial pacing (RA), or no pacing (control) in postoperative period. Overdrive atrial pacing was performed for 5 days. The incidence of AF was significantly reduced in the BiA group (12.5%) compared with the other 3 groups (LA, 36.4%; RA, 33.3%; control, 41. 9%; P<0.05). The mean length of hospital stay was significantly reduced in the BiA group. At baseline, the mean P-wave duration (P(dur)) and dispersion (P(dis)) were not prolonged. BiA pacing resulted in the most significant percentage of reduction in P(dis) when compared with the LA or RA groups (BiA, 42+/-8%; LA, 13+/-6%; RA, 10+/-9%; P<0.05 for BiA versus LA or RA). No significant differences existed in mean P(dur) and P(dis) between patients who developed AF and those who remained in sinus rhythm at baseline. However, only those patients who remained in sinus rhythm had a significant reduction in mean P(dur) and P(dis) after pacing therapy.nnnCONCLUSIONSnBiatrial overdrive pacing is more effective in preventing post-CABG AF than single-site atrial pacing; this therapy also results in a shortened hospital stay. The overall reduction in atrial activation time with BiA pacing was reflected in the reduction in P(dis).

QT prolongation and Torsades de Pointes associated with clarithromycin.

Clarithromycin is a macrolide antibiotic that possesses an improved antimicrobial spectrum and side-effect profile compared with erythromycin. Torsades de pointes is known to be related to erythromycin(1–5), but its association with clarithromycin has not been reported. In this article, we describe 2 patients who developed QT prolongation and torsades de pointes after receiving clarithromycin.

Avoidance of Right Ventricular Pacing in Cardiac Resynchronization Therapy Improves Right Ventricular Hemodynamics in Heart Failure Patients

Background: Cardiac resynchronization therapy (CRT) applied by pacing the left and right ventricles (BiV) has been shown to provide synchronous left ventricular (LV) contraction in heart failure patients. CRT may also be accomplished through synchronization of a properly timed LV pacing impulse with intrinsically conducted activation wave fronts. Elimination of right ventricular (RV) pacing may provide a more physiological RV contraction pattern and reduce device current drain. We evaluated the effects of LV and BiV pacing over a range of atrioventricular intervals on the performance of both ventricles.

Automatic Optimization of Resting and Exercise Atrioventricular Interval Using a Peak Endocardial Acceleration Sensor: Validation with Doppler Echocardiography and Direct Cardiac Output Measurements

Peak endocardial acceleration (PEA) measured by an implantable acceleration sensor inside the tip of a pacing lead reflects ventricular filling and myocardial contractility. The contribution of the plateau phase of PEA as an indicator of optimal ventricular filling, hence of the appropriate atrioventricular interval (AVI) at rest and during exercise, was studied in 12 patients (age 69 ± 6 years) with complete AV block and a PEA sensing DDDR pacemakers (Living 1 Plus, Sorin Biomedica). At a mean resting heart rate of 79 ± 15 beats/min, the mean AVI optimized by PEA versus Doppler echocardiography (echo) were identical (142 ± 37 vs 146 ± 26 ms, P = 0.59). During submaximal exercise at a mean heart rate of 134 ± 6 beats/min, AVI optimized by PEA was 135 ± 37 ms. Cardiac output at rest, measured by the CO2 rebreathing method, was comparable with AVI determined by echo versus PEA (4.3 ± 2.9 and 3.7 ± 2.4 L/min, respectively), and increased to the same extent (8.0 ± 3.9 vs 8.3 ± 5.2 L/min) during sub‐maximal exercise. In patients with AV block, AVI automatically set by PEA was comparable with AVI manually optimized by Doppler echocardiography and was associated with comparable exercise induced hemodynamic changes.

Internal Cardioversion of Chronic Atrial Fibrillation During Percutaneous Mitral Commissurotomy Insight Into Reversal of Chronic Stretch-Induced Atrial Remodeling

Background—Mechanoelectrical feedback caused by atrial dilatation plays an important role in atrial fibrillation (AF). To test the hypothesis that remodeling is reversible by reducing atrial stretch, we investigated electrophysiological changes after a reduction of left atrial (LA) pressure in patients undergoing percutaneous balloon mitral commissurotomy (PBMC). Methods and Results—In 22 patients with chronic AF who were undergoing PBMC for mitral stenosis, internal cardioversion was successful in 19 patients (86%). Twelve patients with sinus rhythm acted as controls. Mean LA pressure was significantly reduced after PBMC (18.5±5.9 mm Hg versus 10.2±4.1 mm Hg;P <0.001). The effective refractory period (ERP), conduction delay (CD), and the index of heterogeneity (CoV) of the ERP and CD were compared. Changes in LA pressure were only significantly correlated with AF vulnerability (r =0.7;P =0.02) and CoV of CD (r =0.3;P =0.03). There were no significant changes in ERP and CD immediately after PBMC in the AF group. However, the overall CoV of ERP was reduced in the AF group after PBMC. There were homogenous, although not significant, increases in regional ERP in the control group immediately after PBMC. Atrial CD and CoV of CD were significantly reduced after PBMC in the control group; this was most prominent within the regions of the LA. Conclusions—AF vulnerability and CoV of CD correlated significantly with LA pressure. A homogenous increase in regional ERPs could be demonstrated in the control group after an immediate reduction of atrial stretch, whereas the recovery course of electrical remodeling was prolonged and heterogenous in the AF group. Regional conductions were irreversible in patients with preexisting AF.

Prevention of Ventricular Fibrillation by Pacing in a Man with Brugada Syndrome

Pacing Prevents VF in Brugada Syndrome. The unique ECG appearance of Brugada syndrome is caused by failure of the dome of the action potential to develop. It occurs when the outward currents (mainly Ito) overwhelm the inward currents (mainly Ica) at the end of phase 1 of the action potential. Because Ito becomes less prominent at a faster rate, increased heart rate is associated with decreased ST segment elevation on ECG and probably decreased incidence of ventricular arrhythmia. We present the first report on prevention of ventricular fibrillation in a man with Brugada syndrome by overdrive pacing from his dual chamber implantable cardioverter defibrillator.

STATT: a titrate-to-goal study of simvastatin in asian patients with coronary heart disease

BACKGROUNDnMost published studies on the use of lipid-lowering agents to treat hypercholesterolemia have focused on Western populations, with few data on Asian populations.nnnOBJECTIVEnThe Simvastatin Treats Asians to Target (STATT) study used a titrate-to-goal protocol to evaluate the efficacy and tolerability of simvastatin 20 to 80 mg/d in the treatment of Asian patients with coronary heart disease.nnnMETHODSnThis was a multicenter, open-label, uncontrolled, 14-week study in patients with coronary heart disease and serum low-density lipoprotein cholesterol (LDL-C) levels of 115-180 mg/dL and triglyceride levels of < or = 400 mg/dL. The dose of simvastatin was titrated from 20 to 80 mg/d to achieve the National Cholesterol Education Program (NCEP) LDL-C target of < or = 100 mg/dL. The primary efficacy measure was the percentage of patients achieving the NCEP target. Among secondary measures were the percentage of patients achieving European Society of Cardiology/European Atherosclerosis Society/European Society of Hypertension target LDL-C levels of < or = 115 mg/dL and the percentage change from baseline in lipid parameters. Tolerability was assessed in terms of the overall incidence of adverse experiences and the incidences of the most commonly reported adverse experiences.nnnRESULTSnThe intent-to-treat analysis included 133 Asian patients (93 men, 40 women; mean age, 59.5 years), of whom 125 completed 14 weeks of therapy. Their mean blood pressure was 130.2/79.4 mm Hg. Overall, 104 (78.2%) patients treated with simvastatin achieved LDL-C levels < or = 100 mg/dL at week 14, and 125 (94.0%) achieved this target at some point during the study. Similarly, 122 (91.7%) patients achieved an LDL-C level < or = 115 mg/dL at week 14, and 130 (97.7%) achieved this target at some point during the study. Treatment with simvastatin had favorable effects on the lipid profile, producing significant percentage changes from baseline in all parameters (P < 0.001). Simvastatin was well tolerated across the dose range. Overall, 40 patients (30.1%) had > or = 1 clinical adverse experience. Only 14 (10.5%) had adverse experiences that were possibly, probably, or definitely related to study drug; none of these experiences were considered serious. The most common adverse experiences (> or = 3% incidence) were abdominal pain (6%); chest pain (5%); dizziness (4%); and asthenia/fatigue, fibromyalgia, headache, insomnia, and upper respiratory tract infection (3% each). No new or unexpected adverse experiences were seen at the higher doses.nnnCONCLUSIONSnSimvastatin was effective and well tolerated at doses of 20, 40, and 80 mg/d in Asian patients with coronary heart disease. Titration enabled the majority to achieve target LDL-C levels of < or = 100 mg/dL.

Effect of Adenosine and Verapamil in Catecholamine‐Induced Accelerated Atrioventricular Junctional Rhythm: Insights into the Underlying Mechanism

Accelerated AV junctional rhythm is postulated to he due to enhanced automaticity of a high AV junctional focus. The adenosine response of this rhythm was tested in 17 patients (7 males, 12‐83 years). The indications of electrophysiology study were nonspecific palpitation (n = 5), unexplained syncope (n = 6), postablation of accessory pathways (n = 4), and postmodification of AV nodal reentry tachycardia (n = 2). The sinus node and AV nodal functions were normal. Pacing and programmed electrical stimulation failed to induce anv arrhythmia at baseline. The accelerated junctional rhythm (cycle length = 553 ± 134 ms) was initiated spontaneously in all patients after isoproterenol infusion (1‐2 μg/min). It was not suppressible bv overdrive pacing. Cessation of isoproterenol infusion terminated the rhythm in all patients. Adenosine (6 mg) reproducibly terminated the accelerated functional rhythm in all patients. In six patients, adenosine suppressed the junctional rhythm without producing AV nodal block. In the other 11 patients, the junctional rhythm was terminated prior to the occurrence of AV nodal block. Verapamil was tested in ten patients and 5 mg of intravenous verapamil terminated the junctional rhythm in all patients. In conclusion, the mechanism of catecholamine‐induced accelerated AV junctional rhythm is most likely enhanced automaticity, and catecholamine‐induced accelerated AV functional automaticity is sensitive to adenosine and verapamil. Adenosine appears to have differential effects on catecholamine‐enhanced AV junctional automaticity and AV nodal conduction. This suggests that, under catecholamine stimulation, adenosine may have different mechanisms of action on AV nodal conduction and automaticity.

In the wireless era: leadless pacing

Cardiac pacemakers have been the standard therapy for patients with bradyarrhythmias for several decades. The pacing lead is an integral part of the system that serves as a conduit for the delivery of energy pulses to stimulate the myocardium. However, it is also an Achilles tendon that directly causes most device complications both acutely during implant and chronically years afterwards. Both durability and optimization of the stimulation site are important areas of improvement for manufacturers and implanters. Elimination of the pacing lead and the utilization of other means for energy transfer is the only way to avoid lead complications and allow a better choice of stimulation site. Leadless pacing with ultrasound-mediated energy has been demonstrated in animals and humans in acute studies. This has aroused intense interest in the field of cardiac pacing. With concerted effort from the profession and the industry, leadless pacing may indeed become a realizable concept.

Interatrial Mechanical Dyssynchrony Worsened Atrial Mechanical Function in Sinus Node Disease With or Without Paroxysmal Atrial Fibrillation

Introduction: Atrial electromechanical dysfunction might contribute to the development of atrial fibrillation (AF) in patients with sinus node disease (SND). The aim of this study was to investigate the prevalence and impact of atrial mechanical dyssynchrony on atrial function in SND patients with or without paroxysmal AF.