QT interval measurement and correction in patients with atrial flutter: a pilot study.

BACKGROUND AND PURPOSE: Measurement of QT intervals during atrial flutter (AFL) is relevant to monitor the safety of drug delivery. Our aim is to compare QT and QTc intervals in AFL patients before and after catheter ablation in order to validate QT measurement during AFL. METHODS: 25 patients suffering from AFL underwent catheter ablation; 9 were in sinus rhythm and 16 were in AFL at the time of the procedure. Holter ECGs were continuously recorded before, during and after the procedure. In AFL signals, flutter waves were subtracted using a previously-validated deconvolution-based method. Fridericia's QTc was computed before and after ablation after hysteresis reduction. RESULTS: Comparing QTc values obtained before and after ablation showed that (1) the intervention did not significantly affect QTc, and (2) the QTc during AFL was concordant with the QTc value in sinus rhythm. CONCLUSION: QTc can be reliably measured in patients with AFL using flutter wave subtraction and hysteresis reduction.

Fully automated initiation of simulated episodes of atrial arrhythmias.

AIMS: To develop computational tools for automatically initiating a large number of independent episodes of atrial arrhythmias in electro-anatomical computer models of the atria and therefore facilitating the design of in silico experiments. METHODS AND RESULTS: A biophysical model of the atria was constructed from segmented medical images of the human atria of a patient with atrial fibrillation (AF). A set of 40 initial conditions were generated based on a priori knowledge about wavefront propagation and the number and location of reentries (1-6 randomly distributed over the atrial epicardium). Simulations were run from each of these initial conditions in three substrates representing different forms of AF dynamics (stable rotors; multiple unstable meandering wavelets; and wavelets broken by repolarization heterogeneities). To demonstrate the applicability of the initiation method for testing clinical of therapeutic interventions, the channel I(Kr) was blocked after 2 s of simulation and its effect on the number of functional reentries was documented. The use of pre-computed initial conditions enabled to successfully generate episodes of simulated AF in each substrate. Blockade of I(Kr) channel prolonged action potential duration, resulting in a reduction of the number of functional reentries. In the substrate with unstable spiral waves, the effect was sufficiently large to terminate AF in about two-thirds of the cases. In the two other substrates, the effect was minor. CONCLUSION: These new simulation tools may help investigate in computer models therapeutic interventions in different substrates in order to identify substrate-specific optimal therapy.

Evaluation of ablation patterns using a biophysical model of atrial fibrillation.

Atrial fibrillation (AF) is the most common form of cardiac arrhythmia. Surgical/Radiofrequency (RF) ablation is a therapeutic procedure that consists of creating lines of conduction block to interrupt AF. The present study evaluated 13 different ablation patterns by means of a biophysical model of the human atria. In this model, ablation lines were abruptly applied transmurally during simulated sustained AF, and success rate, time to AF termination and average beat-to-beat interval were documented. The gold standard Cox's Maze III procedure was taken as reference. The effectiveness of twelve less invasive patterns was compared to it. In some of these incomplete lines (entailing a gap) were simulated. Finally, the computer simulations were compared to clinical data. The results show that the model reproduces observations made in vivo: (1) the Maze III is the most efficient ablation procedure; (2) less invasive patterns should include lines in both right and left atrium; (3) incomplete ablation lines between the pulmonary veins and the mitral valve annulus lead to uncommon flutter; (4) computer simulations of incomplete lines are consistent with clinical results of non-transumural RF ablation. Biophysical modeling may therefore be considered as a useful tool for understanding the mechanisms underlying AF therapies.

Study of atrial arrhythmias in a computer model based on magnetic resonance images of human atria.

The maintenance of multiple wavelets appears to be a consistent feature of atrial fibrillation (AF). In this paper, we investigate possible mechanisms of initiation and perpetuation of multiple wavelets in a computer model of AF. We developed a simplified model of human atria that uses an ionic-based membrane model and whose geometry is derived from a segmented magnetic resonance imaging data set. The three-dimensional surface has a realistic size and includes obstacles corresponding to the location of major vessels and valves, but it does not take into account anisotropy. The main advantage of this approach is its ability to simulate long duration arrhythmias (up to 40 s). Clinically relevant initiation protocols, such as single-site burst pacing, were used. The dynamics of simulated AF were investigated in models with different action potential durations and restitution properties, controlled by the conductance of the slow inward current in a modified Luo-Rudy model. The simulation studies show that (1) single-site burst pacing protocol can be used to induce wave breaks even in tissue with uniform membrane properties, (2) the restitution-based wave breaks in an atrial model with realistic size and conduction velocities are transient, and (3) a significant reduction in action potential duration (even with apparently flat restitution) increases the duration of AF. (c) 2002 American Institute of Physics.