Abstract
Simple SummaryVentricular arrhythmias occur commonly in horses. Knowledge on the origin of ventricular arrhythmias is essential for proper treatment. Former studies in horses showed contradictory results regarding the diagnostic value of 12-lead electrocardiography and vectorcardiography due to the anatomical differences in horses compared to humans and small animals. As a consequence, no standardized approach is available for electrocardiography electrode configurations in horses. The current study investigated whether the anatomical origin of experimentally induced ventricular premature depolarizations in horses could be differentiated based upon spherical statistics of the vectorcardiography characteristics. Vectorcardiography shows the magnitude and direction of the cardiac electrical forces in three dimensions. The vectorcardiogram was recorded in seven horses under general anesthesia while right and left ventricular pacing was performed from inside the heart. Using spherical statistics, it could be shown that pacing induces significantly different initial and maximum electrical axes between different locations and between pacing and normal sinus rhythm. The current approach could be used in clinical patients to identify the origin of ventricular arrhythmias without the need for invasive studies. The technique could also be used in other species for which a standardized electrocardiogram electrode configuration is not available.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.
Highlights
The use of a 12-lead ECG has proven to be a very effective method for identification and differentiation of the underlying mechanisms of ventricular arrhythmias as well as for preparticipation screening for cardiovascular diseases in human athletes in order to reduce the casualties of sudden cardiac death [1]
The vector cardiogram (VCG) can be used to increase the power of statistical analyses by decreasing the number of independent variables because calculating the VCG from the 12-lead ECG offers a reduction in the number of independent leads from eight to three, with only minimal information loss [16]
The directions of the maximum electrical axis (MEA) were significantly different (p < 0.001) when comparing the combined paced locations against sinus rhythm (SR). No such significant difference could be found for the initial electrical axis (IEA) (p = 0.393)
Summary
The use of a 12-lead ECG has proven to be a very effective method for identification and differentiation of the underlying mechanisms of ventricular arrhythmias as well as for preparticipation screening for cardiovascular diseases in human athletes in order to reduce the casualties of sudden cardiac death [1]. Because knowledge from human cardiology cannot be directly extrapolated to horses due to their different ventricular conduction system [2], preparticipation screening of equine athletes with their high prevalence of ventricular arrhythmias is cumbersome [3]. Former studies in horses had contradictory results regarding the diagnostic value of the 12-lead ECG for localization of premature depolarizations or prediction of the associated risk of ventricular arrhythmias [4,5,6,7], possibly partly due to suboptimal electrode positioning [8,9,10]. The VCG can be used to increase the power of statistical analyses by decreasing the number of independent variables because calculating the VCG from the 12-lead ECG offers a reduction in the number of independent leads from eight to three, with only minimal information loss [16]
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