Endocardial electro-anatomic mapping in healthy horses: Normal sinus impulse propagation in the left and right atrium and the ventricles.
Authors: Van Steenkiste G, L Vera, Decloedt A, Schauvliege S, Boussy T, van Loon G
Journal: Veterinary journal (London, England : 1997)
Summary
Using three-dimensional electro-anatomical mapping in seven anaesthetised horses, researchers established the first detailed reference for normal cardiac electrical conduction patterns across both atrial and ventricular endocardium in sinus rhythm. The technique revealed that atrial depolarisation initiates at the terminal crest with a single interatrial conduction pathway, whilst ventricular activation begins simultaneously at the left ventricular mid-septum and right ventricular apex before propagating rapidly across the free walls in an explosive pattern—findings that challenge previous assumptions about which ventricular regions contribute to the surface ECG. Notably, electrically active tissue was identified throughout the pulmonary veins, and Bundle of His electrograms were successfully recorded in five of the seven horses, providing quantifiable conduction velocities for both chambers. For equine practitioners, this mapping data establishes a critical baseline for diagnosing and understanding complex arrhythmias, since distinguishing pathological conduction disturbances from normal variation requires precise knowledge of healthy impulse propagation; clinicians can now correlate surface ECG findings more accurately with underlying endocardial electrical activity. Future investigations into atrial fibrillation, ventricular ectopy, and conduction blocks in horses will depend heavily on these reference standards to identify abnormal depolarisation patterns.
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Practical Takeaways
- •This study establishes the normal endocardial electrical activation pattern in healthy horses, providing essential reference values for veterinarians diagnosing cardiac arrhythmias
- •Understanding normal conduction pathways and depolarization sequences is critical for distinguishing pathological arrhythmias from normal variants in clinical practice
- •The correlation between endocardial mapping findings and surface ECG helps improve interpretation of equine ECGs and guides further diagnostic investigations
Key Findings
- •First atrial activation occurs at the terminal crest with a single identified interatrial conduction pathway in healthy horses
- •Left ventricular activation originates at the mid septum while right ventricular activation begins apically from the supraventricular crest, followed by explosive depolarization pattern
- •All parts of ventricular depolarization contribute to the surface ECG QRS complex, contrasting with previous study findings
- •Bundle of His electrograms were successfully recorded in 5 of 7 horses, with electrically active tissue found throughout all pulmonary veins