In cattle, atrial fibrillation (irregular arrhythmia) can appear as a consequence of abomasal displacement. What is the mechanism behind it that explains atrial fibrillation caused by abomasal displacement?
Atrial fibrillation (AF)is the commonest dysrhythmia in adult cattle and can occur associated with various diseases including abomasal disorders. The presentation is generally paroxysmal (eg it reverts spontaneously to sinusal rythm within a week when adressing the primary presentation problem). The exact pathophysiology is not precisely known in cattle but the large atria size may increase the risk of ectopic foci of depolarisation especially when homeostasia is perturbed (eg electrolic imbalance observed in abomasal diseases but also with inflammatory diseases). Interaction with sympathetic/parasympathetic tone has also been mentioned. From my experience, I would not say it is commonly associated with abomasal displacement (I would say max 5-10% from my best guess so not "often" as mentioned in your post). Japanese researchers also reported that up to 2.5% dairy cows have AF (285 dairy cows followed 18months, Machida et al., 1993) which was more idiopathic (ie no specific disease associated with it but only hypothesizing that increased sympathetic tone could be associated with this form of AF). A small proportion of cattle also display persistent AF and in this case it has been associated with the presence of small fibrotic lesions within the atrial wall which may perturb the normal eletric conduction and increased the risk of ectopic depolarization foci (Machida et al., 2001).
A good overview of AF pathophysiology is available from general cardiology textbooks and it has to be remembered that this is generally considered as a relatively benign condition in cattle vs small animals where AF generally occurs associated with enlarged atrial size due to advanced stage of cardiac disease.
Machida N, Nakamura T, Kiryu K, Kagota K. Electrocardiographic features and incidence of atrial fibrillation in apparently healthy dairy cows. Zentralbl Veterinarmed A. 1993 Apr;40(3):233-9. doi: 10.1111/j.1439-0442.1993.tb00622.x. PMID: 8328231.
Machida N, Kiryu K. Cardiac lesions in dairy cows with idiopathic atrial fibrillation. J Vet Med Sci. 2001 Aug;63(8):873-8. doi: 10.1292/jvms.63.873. PMID: 11558542.
Thank you very much dear Sébastien Buczinski for this exhaustive and full answer! So basically, there are two hypothetical potential etiologies: electrolytic disbalance and/or interaction with the sympathetic/parasympathetic tone. As you mentioned, unfortunately, the exact pathophysiology is not yet known. I hope future research elucidates this interesting phenomenon.
This is difficult to answer since we don't fully understand the pathophysiology of atrial fibrillation in humans. All tachyarrhythmias require a trigger to induce the tachyarrhythmia in addition to a particular substrate, enabling its perpetuation. This abomasal condition sounds abysmal, but it sounds as though the AF is vagally induced by the significant distention of the abdominal viscus. Attempting to fault the size of the atria or suggest there is underlying heart disease may be a wrong turn, unless, of course, there is evidence for either. I looked at a couple of articles on the topic and found no cardiac disease associations. Vagally induced AF is not at all uncommon in humans.
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