An Exploratory Study on Vectorcardiographic Identification of the Site of Origin of Focally Induced Premature Depolarizations in Horses, Part II: The Ventricles

Abstract

In human cardiology, the anatomical origin of ventricular premature depolarizations (VPDs) is determined by the characteristics of a 12-lead electrocardiogram (ECG). Former studies in horses had contradictory results regarding the diagnostic value of the 12-lead ECG and vectorcardiography (VCG), which results were attributed to the different cardiac conduction system in this species. The objective of this study was to determine if the anatomical origin of pacing-induced VPDs could be differentiated in horses based upon VCG characteristics. A 12-lead ECG was recorded in seven horses under general anesthesia while right and left ventricular endomyocardial pacing was performed (800–1000 ms cycle length) at the apex, mid and high septum and mid and high free wall, and at the right ventricular outflow tract. Catheter positioning was guided by 3D electro-anatomical mapping and echocardiography. A median complex, obtained from four consecutive complexes, was calculated for each pacing location and sinus rhythm. The VCG was calculated from the 12-lead ECG-derived median complexes using custom-made algorithms and was used to determine the initial and maximum electrical axes of the QRS complex. An ANOVA for spherical data was used to test if VCGs between each paced location and between pacing and sinus rhythm were significantly (p < 0.05) different. The model included the radius, azimuth and elevation of each electrical axis. Pacing induced significantly different initial and maximum electrical axes between different locations and between pacing and sinus rhythm. The current results suggest that VCG is a useful technique to identify the anatomical origin of ventricular ectopy in horses.

Electrocardiographic characteristics of trained and untrained standardbred racehorses

“…28 This study included a thorough description of endocardial electroanatomical mapping in horses, unfortunately not specifying the duration of the obtained His intervals, preventing comparison with our findings. 28 However, a review from 2004 exploring allometric scaling among different animal species in regard to AV nodal conduction reported on P-A, A-H, and H-V intervals obtained from horses. 29 In this study, the average H-V duration in horses was reported to be 84 ms, which is shorter than the H-V intervals measured in our study.…”

“…24 Recently, His recordings were obtained from the LV in 5 horses and from the right ventricle in 1 horse during general anesthesia. 28 In humans, His signals can be recorded from both the right and left side of the heart, 57 which also has been shown to be possible in horses. 28 This study included a thorough description of endocardial electroanatomical mapping in horses, unfortunately not specifying the duration of the obtained His intervals, preventing comparison with our findings.…”

“…In humans, recordings of the specialized conduction system of the heart including SNRT, AV, and His bundle recordings commonly are used to assess conduction abnormalities 24‐26 . In horses, SNRT and His bundle recordings are described infrequently 27‐29 . However, with the emerging possibility of invasive electrophysiological studies and mapping procedures, these types of recordings have great potential to identify the mechanisms of SAN and AV conduction and possibly the effect of training in horses.…”

“…[24][25][26] In horses, SNRT and His bundle recordings are described infrequently. [27][28][29] However, with the emerging possibility of invasive electrophysiological studies and mapping procedures, these types of recordings have great potential to identify the mechanisms of SAN and AV conduction and possibly the effect of training in horses.…”

Three‐dimensional electro‐anatomical mapping and radiofrequency ablation as a novel treatment for atrioventricular accessory pathway in a horse: A case report

“…In order to attempt localization of the AP, a 12‐lead ECG was recorded during pre‐excitation and vectorcardiograms (VCG) in different planes were calculated 2,3 . The VCG identified a left, caudoventral direction of the ventricular wavefront, suggesting an AP localized at the craniodorsal region of the right ventricular free wall.…”