Atrial Ring Research Articles

Proarrhythmic and Antiarrhythmic Effects of Flecainide on Nonsustained Reentry Around the Canine Atrial Tricuspid Ring In Vitro

The effect of flecainide, 0.3 mg/L and 1.0 mg/L, on inducible nonsustained reentry was studied, in vitro, in the canine tricuspid ring. Nonsustained reentry was engineered by cutting the ring and reconnecting it with an adjustable electronic delay. Delays were used that produced reentry lasting 1-3 beats (group A), 4-10 beats (group B), and 11-25 beats (group C). Reentry was initiated multiple times at each selected delay. A proarrhythmic effect, defined as a significant increase in the duration of reentry, was observed in all 14 trials at the low dose and in two of 15 trials at the high dose in seven experiments. In four more trials a transient proarrhythmic response was seen initially during exposure to the high dose. In five of seven experiments, reentry became sustained after at least one dose of flecainide. Proarrhythmic responses resulted when flecainide increased the tachycardia cycle length more than the effective refractory period and there was less cycle length oscillation after initiation. Antiarrhythmic responses resulted either from a marked increase in effective refractory period at the site of block or production of fixed block.

A Multicenter Evaluation of a Single‐Pass Lead VDD Pacing System

Since June 1985 until April 1989, 237 patients (130 males, 107 females, aged 22 to 95 years, mean 71) with symptomatic AV conduction disturbances and competent sinus node, were implanted with a single-pass lead VDD pacing system in 30 centers and followed-up for at least 6 months. The ventricular pacing lead incorporated two atrial ring 3-cm apart electrodes, positioned within the right atrial cavity without contact with the heart wall, in order to detect the atrial activity, which is differentially processed by the pacemaker. At implant, mean atrial electrogram amplitude, derived from a custom pacemaker system analyzer (PSA) with the same input filter of the pacemaker was 1.7 +/- 0.8 mV (n = 93). In all cases, atrial sensitivity at implant was the default value +/- 0.15 mV. The atrial tracking capability of the pacing systems was assessed within the month and every 6 months after implantation by means of clinical evaluation, resting ECG, 24-hour Holter monitoring and the following tests: exercise stress testing, mental stress, isometric exercise, and nifedipine test. These tests evoke an increase of atrial rate in consequence of metabolic needs or as a reflex response. The criterion used to evaluate the correct operation of the system was the percentage of atrial synchronization. This was defined as the ratio between atrial triggered ventricular paced complexes and all ventricular paced complexes. All monitorings showed a ratio higher than or equal to 98% in a percentage of patients not lower than 95%. Mean follow-up was 385 days (range 183-1,370 days).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of LY83583, nordihydroguaiaretic acid, and quinacrine on cyclic GMP elevation and inhibition of tension by muscarinic agonists in rabbit aorta and left atrium.

Elevation of cyclic GMP by muscarinic agonists has been suggested to be responsible for the negative inotropic effects of these agents in cardiac muscle, and for the endothelium-dependent relaxation caused by these agents in vascular smooth muscle. These relationships were studied by monitoring the effects of muscarinic agonists on tension and cyclic GMP levels in rabbit left atrial strips and aortic rings, in the presence and absence of the cyclic GMP lowering agent, LY83583. LY83583 completely blocked both the cyclic GMP increase and the relaxation caused by acetylcholine in rabbit aortic rings with intact endothelial cells. Acetylcholine-induced cyclic GMP elevation and relaxation in these preparations were also blocked by quinacrine and nordihydroguaiaretic acid (NDGA), but neither response was blocked by the 5-lipoxygenase inhibitor U-60257. In the experiments with rabbit left atrium, LY83583 blocked the acetylcholine-induced cyclic GMP elevation but did not block the negative inotropic effects of the drug. Quinacrine, NDGA, and a guanylate cyclase inhibitor, methylene blue, failed to block either the cyclic GMP increase or the decrease in contractile force caused by carbachol in atrial strips. These results support the suggestion that an increase in cyclic GMP may be responsible for the endothelium-dependent relaxation of rabbit aorta by muscarinic agonists, but not for the direct negative inotropic effects of these drugs in rabbit atrium. Muscarinic agents appear to increase cyclic GMP levels in rabbit atrium and aorta by different mechanisms. Although both are blocked by LY83583, they differ not only in their requirements for endothelial cells, but also in their susceptibility to other blocking agents.

Obstruction to left atrial outflow by a supravalvular stenosing ring

Summary The case of a girl who died at 11 years of age, of heart failure, and who was found at post-mortem examination to have a patent ductus arteriosus and a supravalvular left atrial stenosing ring is reported. If the stenosing ring was a congenital malformation its recognition by modern methods of investigation might have permitted surgical relief.