A three-dimensional human atrial model with fiber orientation. Electrograms and arrhythmic activation patterns relationship

Abstract

The most common sustained cardiac arrhythmias in humans are atrial tachyarrhythmias, mainly atrial fibrillation. Areas of complex fractionated atrial electrograms and high dominant frequency have been proposed as critical regions for maintaining atrial fibrillation; however, there is a paucity of data on the relationship between the characteristics of electrograms and the propagation pattern underlying them. In this study, a realistic 3D computer model of the human atria has been developed to investigate this relationship. The model includes a realistic geometry with fiber orientation, anisotropic conductivity and electrophysiological heterogeneity. We simulated different tachyarrhythmic episodes applying both transient and continuous ectopic activity. Electrograms and their dominant frequency and organization index values were calculated over the entire atrial surface. Our simulations show electrograms with simple potentials, with little or no cycle length variations, narrow frequency peaks and high organization index values during stable and regular activity as the observed in atrial flutter, atrial tachycardia (except in areas of conduction block) and in areas closer to ectopic activity during focal atrial fibrillation. By contrast, cycle length variations and polymorphic electrograms with single, double and fragmented potentials were observed in areas of irregular and unstable activity during atrial fibrillation episodes. Our results also show: (1) electrograms with potentials without negative deflection related to spiral or curved wavefronts that pass over the recording point and move away, (2) potentials with a much greater proportion of positive deflection than negative in areas of wave collisions, (3) double potentials related with wave fragmentations or blocking lines and (4) fragmented electrograms associated with pivot points. Our model is the first human atrial model with realistic fiber orientation used to investigate the relationship between different atrial arrhythmic propagation patterns and the electrograms observed at more than 43000 points on the atrial surface.

Figure 1. 3D model of human atria.

Frontal (A) and dorsal (B) views of the 3D model of human atria. Colored areas show regions with different conductivity and/or electrophysiological heterogeneity.

Figure 2. Fiber orientation in the model.

Frontal (A) and dorsal (B) views of the model. The model was divided into 42 areas (represented with different colors) according to the orientation of the muscle bundles (left) and fiber orientation (see black arrows) assigned to the main areas (right).

Figure 3. AP for different atrial areas and APD₉₀ restitution curve for AWM under physiological and remodeling conditions.

AP time courses for the considered atrial cellular models (CT, PM, APG, AVR and AWM) under physiological (A) and remodeling conditions (B). APD₉₀ restitution curve for AWM under physiological (control) and remodeling conditions (C).

Figure 4. Sinus rhythm propagation under physiological and remodeling conditions.

Propagation of the last sinus beat applied for both physiological (A) and remodeling (B) conditions. The color scale represents the range of AP values (mV). The depolarizing fronts can be identified by the red color.

Figure 5. Flutter and reentrant tachycardia episodes. Snapshots, APs, EGM and spectral analysis in selected points.

(A) Atrial flutter and (B) reentrant tachycardia episodes. In the snapshots, the color scale represents the range of values of the AP in mV. The depolarizing front is identified by the red color. The black arrow indicates the wavefront direction and the dash line a blocking line. AP time-courses of selected sites (indicated in the snapshots) are showed at the left, the dotted arrows indicate the activation sequence. EGM and their spectral analysis showing DF and OI values are shown (See text for more details).

Figure 6. AF episodes. Snapshots, APs, EGM and spectral analysis in selected spoints.

(A) AF triggered by a transient ectopic focus and (B) AF triggered by a continuous ectopic focus, both in the ostium of the RPV. The color scale represents the range of values of the AP in mV. The depolarizing front is identified by the red color. The black arrows indicate the direction of the wavefronts and the dash line shows a blocking line. AP time-courses of selected sites (indicated in the snapshots) are showed at left, down to the snapshots. The corresponding EGM and their spectral analysis showing DF and OI values are shown at the right. In (A): + indicates AP and single potential with only a long-lasting negative deflection (snapshot at 2160 ms), • indicates AP and single potential with positive deflection greater than negative (snapshot at 2355 ms), ▪ indicates AP and potential with a small additional positive deflection (snapshot at 3220 ms) and * indicates AP and CFAE (snapshot at 8675 ms). In (B): x indicates AP and potential with deviations from the baseline, CFAE, at site 1 (snapshots at 4545 ms and 4650 ms), □ indicates AP and potentials with only negative deflections at site 2 (snapshot at 7625 ms), and ○ indicates AP and double potentials at site 3 (snapshots at 7625 ms and 7670 ms).