Pacemaker-Detected Atrial Fibrillation in Patients With Pacemakers: Prevalence,Predictors, and Current Use of Oral Anticoagulation

Background

Dual-chamber pacemakers frequently document atrial fibrillation (AF) in patients without symptoms. Pacemaker-detected AF is associated with a 2.5-fold increased risk of stroke, although it is not established whether oral anticoagulation reduces this risk. This study sought to determine the prevalence and predictors of pacemaker-detected AF and to document current oral anticoagulant use.

Methods

A retrospective analysis included all patients from a single academic hospital who had pacemakers capable of documenting AF. Blinded evaluation of all echocardiograms conducted within 6 months of implantation was performed.

Results

Of 445 patients, pacemaker-detected AF was present in 246 (55.3%), who were older (74.3 ± 13.7 years vs 71.7 ± 14.4, P = 0.046), more likely to have a history of clinical AF (29.7% vs 19.1%, P = 0.01), and had a larger left atrial volume index (34.4 ± 11.8 mL/m² vs 30.0 ± 9.9 mL/m², P = 0.019) than the patients without pacemaker-detected AF. Among patients without a clinical history of AF, left atrial volume index was higher among those with pacemaker-detected AF (33.7 ± 11.3 mL/m² vs 29.0 ± 10.1 mL/m², P = 0.034). Anticoagulants were used in 35.3% of patients with pacemaker-detected AF, compared with 21.6% of patients without (P < 0.05). In patients with pacemaker-detected AF, anticoagulants were used more frequently among patients who also had clinical AF (58.9%) compared with those without (23.7%, P < 0.001).

Conclusions

Pacemaker-detected AF occurs in 50% of pacemaker patients and is treated with anticoagulants in less than 25% of patients who do not have a history of clinical AF. Clinical trials are needed to determine the role of anticoagulation in this population.     

De novo design of selective antibiotic peptides by incorporation of unnatural amino acids

The evolution of drug-resistant bacteria is one of the most critical problems facing modern medicine and requires the development of new drugs that exhibit their antibacterial activity via novel mechanisms of action. One potential source of new drugs could be the naturally occurring peptides that exhibit antimicrobial activity via membrane disruption. To develop antimicrobial peptides exhibiting increased potency and selectivity against Gram positive, Gram negative, and Mycobacterium bacteria coupled with reduced hemolytic activity, peptides containing unnatural amino acids have been designed, synthesized, and evaluated. These compounds were designed on the basis of the electrostatic surface potential maps derived from the NMR determined SDS and DPC micelle-bound conformations of (Ala8,13,18)magainin-2 amide. Unnatural amino acids were incorporated into the polypeptide backbone to control the structural and physicochemical properties of the peptides to introduce organism selectivity and potency. The methods and results of this investigation are described below.     

Thermally Cross‐Linkable Poly(p‐xylylene)s for Advanced Low‐Dielectric Applications

A novel series of poly(p‐xylylene) homopolymer and copolymers containing thermally cross‐linkable cyclohexenyl moiety are prepared via base‐catalyzed Gilch route to yield high‐molecular‐weight polymers. The resulting polymers are highly soluble in a wide range of organic solvents and could be solution cast into flexible and transparent films. The polymers are thermally stable up to 350 °C and the glass transition temperature (T_g) is in the range of 136 ? 250 °C. They undergo thermal cross‐linking via the cyclohexenyl moiety. The cross‐linked polymer exhibits a high T_g of 294 °C, a low coefficient of thermal expansion (CTE) of 45 ppm K^?1. A low dielectric constant of 2.5 and a very low dielectric loss tan δ of 0.0004 at 1 GHz are obtained, which are superior to conventional interconnect polymers.     

An unusual mechanism causing inappropriate implantable cardioverter defibrillator shocks: transient reduction in R-wave amplitude

Inappropriate shocks delivered by the implantable cardioverterdefibrillator (ICD) are an increasingly recognized complication.The most frequent cause is related to supraventricular rhythmsassociated with fast conduction to the ventricles that are incorrectlydetected as ventricular tachycardia leading to inappropriateantitachycardia pacing and/or shocks. Oversensing is a frequentcause of inappropriate shocks usually due to increased amplitudeof the T-wave secondary to ischaemia or electrolyte disordersthat lead to T-wave double counting.We describe an unusual caseof T-wave double counting during sinus rhythm caused by transientreduction in R-wave amplitude with no changes in T-wave amplituderesulting in inappropriate shocks.     

Relevance of electrical remodeling in human atrial fibrillation: results of the asymptomatic atrial fibrillation and stroke evaluation in pacemaker patients and the atrial fibrillation reduction atrial pacing trial mechanisms of atrial fibrillation study

Background- In animal models of atrial fibrillation (AF), changes in atrial electrophysiological properties are associated with the development of AF. Their relevance to human AF is unclear. Methods and Results- The Asymptomatic Atrial Fibrillation and Stroke Evaluation in Pacemaker Patients and the Atrial Fibrillation Reduction Atrial Pacing Trial enrolled 2580 patients receiving a dual-chamber pacemaker, who were older than the age of 65 and had a history of hypertension, but no history of AF. Serial noninvasive electrophysiological testing was performed over 2 years in a subgroup of 485 patients. There were no differences in the clinical characteristics between patients with and those without device-detected atrial tachyarrhythmias during the first year. Patients with atrial tachyarrhythmias had longer paced (153±29 versus 145±28 ms; P=0.046) and sensed (128±46 versus 118±25 ms; P=0.06) P-wave durations and were more likely to have AF induced during electrophysiological testing (23.5% versus 13.6%; P=0.03). They had similar corrected sinus node recovery times at 90 bpm (388±554 versus 376 ± 466 ms; P=0.86), atrial effective refractory periods at 90 bpm (250±32 versus 248±36 ms; P=0.70), and rate-adaptive shortening of the atrial effective refractory periods (14±13 versus 12±14 ms; P=0.11). There were no significant differences in the change in electrophysiological properties over 2 years between patients with and those without atrial tachyarrhythmias. Conclusions- Prolonged P-wave duration, but not differences in atrial effective refractory periods, was associated with the development of atrial tachyarrhythmias in pacemaker patients.