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Archives of cardiovascular diseases
Volume 103, n° 11-12
pages 585-594 (novembre 2010)
Doi : 10.1016/j.acvd.2010.10.008
Received : 20 December 2009 ;  accepted : 22 October 2010
Variations in duration and composition of the excitable gap around the tricuspid annulus during typical atrial flutter
Variations dans la durée et la composition de la fenêtre d’excitabilité du flutter atrial typique autour de l’anneau tricuspidien

Figure 1

Figure 1 : 

Schematic representation of the tricuspid annulus in left anterior oblique view: the quadripolar catheter allows pacing from the high right atrium (HRA; 10 o’clock) and the low right atrium (LRA; 8 o’clock), while the radiofrequency catheter is successively placed at different locations along the tricuspid annulus: at the cavotricuspid isthmus (CTI; 6 o’clock), at the coronary sinus ostium (CSO; 4 o’clock), at the right atrial septum (Sept; 2 o’clock) and at the atrial roof (AR; 12 o’clock). IVC: inferior vena cava; SVC: superior vena cava.

Figure 2

Figure 2 : 

V1 lead and intracardiac recording (high right atrium [HRA]) depicting the technique used for determining the duration and composition of the excitable gap (EG). Atrial flutter cycle length (AFLCL) is 310ms. A: late extrastimulus (coupling interval 290ms) fails to advance the following atrial event (i.e. the interval encompassing the stimulus is exactly twice the AFLCL=620ms), implying that no resetting has occurred. B: resetting first occurs with a coupling interval of 240ms (resetting coupling interval [RCI]), advancing the next atrial depolarization, with a post-pacing interval (PPI)=360ms.C: the same happens with a shorter coupling interval of 200ms and PPI is 360ms again. D: when the coupling interval is shortened to 190ms, atrial flutter (AFL) is still resetted but PPI lengthens to 380ms. E: for an early coupling interval of 160ms, AFL is still resetted with a much longer PPI of 410ms. F: resetting no longer happens with an earlier coupling interval of 150ms because the effective atrial refractory period (EARP) is reached (spontaneous atrial event after the spike) and the encompassing interval is again twice the AFLCL. Duration of the whole EG is therefore RCI (240ms)EARP (150ms)=90ms. Duration of the partially EG (PEG) can be calculated as the difference between the longer coupling interval leading to increased PPI and EARP=190150ms=40ms. Duration of the fully EG can be calculated as the difference between the durations of the PEG and the whole EG=9040ms=50ms. The slope of the resetting response curve is evaluated as 50ms/40ms=1.25ms/ms. See text for explanation.

Figure 3

Figure 3 : 

Example of excitable gap (EG) with an increasing-type response at the low right atrium (LRA). A: the latest coupling interval has already reset atrial flutter (as the interval encompassing the stimulus is slightly less than twice the atrial flutter cycle length). B: following the next coupling interval, the post-pacing interval (PPI) already increases, indicating an increasing-type response. C: earliest coupling interval leading to atrial capture followed by very long PPI. D: a still earlier coupling interval reaches atrial refractoriness as there is no capture and there is no more resetting. The whole EG duration is therefore 100ms in this example, without the FEG. The slope of the resetting response curve is evaluated as 85ms/100ms=0.85ms/ms. See text for explanation. Of note, the remaining intracardiac lead allows clear determination of atrial capture (arrows in C and D). Correct location of the catheter along the tricuspid annulus is attested by the recording of ventricular far-fields potentials (V). HRA: high right atrium.

Figure 4

Figure 4 : 

Respective parts of the refractory period, of the whole excitable gap (EG) and of the difference between atrial flutter cycle length (AFLCL) and resetting coupling interval (RCI), relative to AFLCL, at the different pacing sites. EARP: effective atrial refractory period.

Figure 5

Figure 5 : 

Examples of the three types of resetting response curve constructed by plotting the duration of the post-pacing interval (ms) against the coupling interval (ms): A: mixed. B: flat. C: increasing (see text for explanation).

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