Peer-reviewed veterinary case report
Ventriculophasic response in a horse with atrioventricular block.
- Journal:
- Journal of veterinary cardiology : the official journal of the European Society of Veterinary Cardiology
- Year:
- 2025
- Authors:
- Liu, J et al.
- Affiliation:
- Department of Veterinary Clinical Sciences · United States
- Species:
- horse
Plain-English summary
This study looked at a horse with a specific heart condition called second-degree atrioventricular nodal (AVN) block, which means there were issues with how electrical signals were passing through the heart. The horse showed some unusual heart activity at rest and after light exercise, suggesting a phenomenon known as ventriculophasic response (VR), which is when the heart's rhythm changes in a specific way. The researchers proposed a few reasons why this might happen, including changes in blood flow and pressure in the heart. It's important for veterinarians to be aware of these kinds of heart responses when they check a horse's heart activity. The horse's condition was noted, but the study did not specify the outcome of any treatments.
Abstract
Ventriculophasic response (VR) in atrioventricular nodal (AVN) block is characterized by a shortening of the sinoatrial cycle length when a QRS complex is interposed between two P waves. This has been well documented in humans and dogs with AVN blocks but not in horses. Herein, we describe a horse with second-degree AVN blocks and constant PR intervals that exhibited 5:3 conduction and suspected VR at rest but less consistently after submaximal exercise. Proposed VR mechanisms include (1) inhibition of the Bezold-Jarisch reflex from reduced end-systolic volume during ventricular contraction; (2) vagal inhibition from increased intra-atrial pressure (Bainbridge reflex); and (3) accelerated sinus node discharge from changes in sinus nodal blood supply during ventricular contraction. This case exhibited some electrocardiogram characteristics of the first two mechanisms to explain the PP interval alteration and suspected VR. Horses often exhibit physiologic AVN blocks, and clinicians should consider VR when interpreting equine electrocardiograms.
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Search related cases →Original publication: https://pubmed.ncbi.nlm.nih.gov/40489904/