Detection of the origin of atrial tachycardia by 3D electro-anatomical mapping and treatment by radiofrequency catheter ablation in horses

Abstract

Background: Atrial tachycardia (AT) can be treated by medical or electrical cardioversion but the recurrence rate is high. Three-dimensional electro-anatomical mapping, recently described in horses, might be used to map AT to identify a focal source or reentry mechanism and to guide treatment by radiofrequency ablation.

Objectives: To describe the feasibility of 3D electro-anatomical mapping and radiofrequency catheter ablation to characterize and treat sustained AT in horses.

Animals: Nine horses with sustained AT.

Methods: Records from horses with sustained AT referred for radiofrequency ablation at Ghent University were reviewed.

Results: The AT was drug resistant in 4 out of 9 horses. In 8 out of 9 horses, AT originated from a localized macro-reentrant circuit (n = 5) or a focal source (n = 3) located at the transition between the right atrium and the caudal vena cava. In these 8 horses, local radiofrequency catheter ablation resulted in the termination of AT. At follow-up, 6 out of 8 horses remained free of recurrence.

Conclusions and clinical importance: Differentiation between focal and macro-reentrant AT in horses is possible using 3D electro-anatomical mapping. In this study, the source of right atrial AT in horses was safely treated by radiofrequency catheter ablation.

Keywords: arrhythmia; atrial flutter; electrophysiology; focal atrial tachycardia; supraventricular tachyarrhythmia.

FIGURE 1

Base‐apex electrocardiogram (ECG) at rest before the procedure, with the negative electrode on the withers and the positive electrode on the left thorax at the height of the elbow. Panel A (ECG of case 3) shows the bifid positive P′ wave as seen in the 3/9 cases. Panel B (ECG of case 5) shows the typical trifid positive P′ wave morphology on the base‐apex lead as seen in 6/9 cases. Paper speed is 50 mm/s

FIGURE 2

Activation map of the right atrium of case 1 showing focal AT with a cycle length of 385 ms. Left lateral view of the right atrium. The color varies following the rainbow spectrum from red (earliest activation) to purple (latest activation). The white arrows indicate the direction of activation, starting at the caudal vena cava (CaVC). The junction between the caudal RA and the caudal vena cava is also indicated. CrVC, cranial vena cava; IVT, intervenous tubercle; TV, tricuspid valve

FIGURE 3

Details of the reentrant AT in cases 2 and 6. (A) Overlay of the 3D electro‐anatomical map of the right atrium of case 2 on a schematic drawing of the right heart, seen from the left as if all other cardiac structures have been removed. The walls of atria and blood vessels are semi‐transparent to show the dark shaded area which represents myocardial tissue from the right atrium and the myocardial sleeves in the cranial and caudal vena cava, and the azygos vein. The 3D electro‐anatomical map of the right atrium and caudal vena cava is shown in its correct anatomical position. Curved white lines represent the clockwise reentry pathway which shows a narrow isthmus ventrally. The double white line shows a line of block. (B) Example of double potentials, recorded at the line of block in case 2. The yellow line indicates the automatically annotated time of activation. The green line indicates the reference point for the mapping system, in this case the tip electrode pair of the coronary sinus catheter. The time in between is 130 ms, the scale is 0.05 mV. (C) On the right, the 3D electro‐anatomical map of case 6 shows a clockwise macro‐reentry circuit with a narrow ventral isthmus. At each number along the entire circuit, the corresponding electrogram is displayed on the left. The complete cycle length of the tachycardia could be found on the macro‐reentry pathway. (D) Surface ECG lead II (upper white trace) and electrograms from the coronary sinus (CS) catheter (yellow traces) of case 6 are shown with CS 1‐2 as the most distal electrodes (deep in the CS). Electrode 10 was outside the coronary sinus. The earliest deflection on the coronary sinus catheter is on electrode pair CS 8‐9, suggesting that the initial depolarization of the atrial tachycardia is originating from the right atrium