ECG of the Month. Atrial fibrillation

ArticleinJournal of the American Veterinary Medical Association 238(10):1258-60 · May 2011with15 Reads
DOI: 10.2460/javma.238.10.1258 · Source: PubMed
  • [Show abstract] [Hide abstract] ABSTRACT: It has recently been recognized that atrial fibrillation can originate from focal sources in the pulmonary veins (PVs). However, the mechanisms of focal atrial fibrillation have not been well characterized. We assessed the electrophysiological characteristics of the PVs using high-resolution optical mapping. Coronary-perfused, isolated whole-atrial preparations from 33 normal dogs were studied. Programmed electrical stimulation was performed, and a 4-cm2 area of the PV underwent optical mapping of transmembrane voltage to obtain 256 simultaneous action potentials. Marked conduction slowing was seen at the proximal PV, compared with the rest of the vein, on both the epicardial (31.3+/-4.47 versus 90.2+/-20.7 cm/s, P=0.001) and endocardial (45.8+/-6.90 versus 67.6+/-10.4 cm/s, P=0.012) aspects. Pronounced repolarization heterogeneity was also noted, with action potential duration at 80% repolarization being longest at the PV endocardium. Nonsustained reentrant beats were induced with single extrastimuli, and the complete reentrant loop was visualized (cycle length, 155+/-30.3 ms); reentrant activity could be sustained with isoproterenol. Sustained focal discharge (cycle length, 330 to 1100 ms) was seen from the endocardial surface in the presence of isoproterenol; each focus was localized near the venous ostium. The normal PV seems to have the necessary substrate to support reentry as well as focal activity. Although reentry occurred more distally in the vein, focal activity seemed to occur more proximally.
    Full-text · Article · May 2003
  • [Show abstract] [Hide abstract] ABSTRACT: There are two approaches to the treatment of atrial fibrillation: one is cardioversion and treatment with antiarrhythmic drugs to maintain sinus rhythm, and the other is the use of rate-controlling drugs, allowing atrial fibrillation to persist. In both approaches, the use of anticoagulant drugs is recommended. We conducted a randomized, multicenter comparison of these two treatment strategies in patients with atrial fibrillation and a high risk of stroke or death. The primary end point was overall mortality. A total of 4060 patients (mean [+/-SD] age, 69.7+/-9.0 years) were enrolled in the study; 70.8 percent had a history of hypertension, and 38.2 percent had coronary artery disease. Of the 3311 patients with echocardiograms, the left atrium was enlarged in 64.7 percent and left ventricular function was depressed in 26.0 percent. There were 356 deaths among the patients assigned to rhythm-control therapy and 310 deaths among those assigned to rate-control therapy (mortality at five years, 23.8 percent and 21.3 percent, respectively; hazard ratio, 1.15 [95 percent confidence interval, 0.99 to 1.34]; P=0.08). More patients in the rhythm-control group than in the rate-control group were hospitalized, and there were more adverse drug effects in the rhythm-control group as well. In both groups, the majority of strokes occurred after warfarin had been stopped or when the international normalized ratio was subtherapeutic. Management of atrial fibrillation with the rhythm-control strategy offers no survival advantage over the rate-control strategy, and there are potential advantages, such as a lower risk of adverse drug effects, with the rate-control strategy. Anticoagulation should be continued in this group of high-risk patients.
    Full-text · Article · Jan 2003
  • [Show abstract] [Hide abstract] ABSTRACT: A mathematical model of impulse propagation in a nonuniform two-dimensional system was prepared as a program for a digital computer. The model exhibited self-sustained turbulent activity having many similarities to atrial fibrillation. The activity was not the result of fixed impulse generators or circuits, but was sustained by irregular drifting eddies which varied in position, number, and size. Increasing the refractory periods while retaining nonuniformity resulted in arrest of activity. Restoration of absolute uniformity resulted in periodic activity characterized by fixed re-entrant circuits without obstacles. Reduction of the area of the model altered the self-sustained activity in the direction of arrest, and the creation of internal obstacles resulted in a periodic circus movement flutter. The behavior of the model suggests the formulation of a “fibrillation” number, similar in concept to the Reynolds number related to turbulence in fluid flow.
    Article · Mar 1964
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