Treatment
A slow ventricular rate usually does not need to be treated.
Multifocal ventricular tachycardia should be treated.
Treatment should be initiated if the HR is >100 beats/min.
Treatment is similar to that for PVCs.
Diagnose and treat underlying cause.
Suggested Reading
1 Durando, M. (2019). Cardiovascular causes of poor performance and exercise intolerance and assessment of safety in the equine athlete. Vet. Clin. North Am. Equine Pract. 35: 175–190.
2 Hubbell, J. and Muir, W. (2015). Oxygenation, oxygen delivery and anaesthesia in the horse. Equine Vet. J. 47: 15–25.
3 van Loon, G. (2019). Cardiac arrhythmias in horses. Vet. Clin. North Am. Equine Pract. 35: 85–102.
4 McGuirk, S.M. and Muir, W.W. (1985). Diagnosis and treatment of cardiac arrhythmias. Vet. Clin. North Am. Equine Pract. 1: 353–370.
5 McGurrin, M. (2015). The diagnosis and management of atrial fibrillation in the horse. Vet. Med. (Aukl) 26: 83–90.
6 Muir, W.W. (1998). Anesthesia for dogs and cats with cardiovascular disease ‐ Part II. Compend. Contin. Educ. Vet. 20: 473–484.
7 Reef, V.B. (1985). Evaluation of the equine cardiovascular system. Vet. Clin. North Am. Equine Pract. 1: 275–288.
8 Sage, A., Keating, S., Lascola, K. et al. (2018). Cardiopulmonary effects and recovery characteristics of horses anesthetized with xylazine‐ketamine with midazolam or propofol. Vet. Anaesth. Analg. 45: 772–781.
9 Shih, A. (2019). Cardiac monitoring in horses. Vet. Clin. North Am. Equine Pract. 35: 205–215.
4 The Respiratory System: Anatomy of the Equine Respiratory System
Robert Reed
I Organization of respiratory system
The respiratory system is primarily a collection of tubular organs designed for the conduction of air and gas exchange.
The respiratory system can be divided into:Conducting components.Gas exchange components.
A Conducting components
Consist of the nasal cavity, paranasal sinuses, pharynx, larynx, trachea, bronchi, and bronchioles.
B Gas exchange components
The gas exchange components include the respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli.
II Tubular organs
The tubular organs that comprise the respiratory system are made up of four layers.
A Tunica mucosa
Contains the epithelial layer that lines the internal surface of the organ.
The function of the organ determines the type of epithelial cells present in this layer.
B Tunica submucosa
The tunica submucosa is a layer of collagenous connective tissue that supports glands, blood vessels, and nervous structures.
The glands are responsible for secretions, which moisten the epithelial surface or assist with movement of materials.
The submucosa acts as a flexible surface on which the tunica mucosa can attach.
C Tunica muscularis
Is the thickest layer of the tubular organ.
It acts to regulate lumen size and tone.
D Tunica adventitia
A loose collagenous connective tissue layer that anchors organs to surrounding tissues.
III Nasal cavity
Each half of the nasal cavity is divided into four regions or meatuses by the mucous membrane covered dorsal and ventral conchae.Conchae serve to warm and humidify inspired air.Conchae also clean the inspired air by trapping particulate matter in mucus secretions.
IV Paranasal sinuses
Paranasal sinuses of the equine are found within the frontal, maxillary, palatine and sphenoid bones as well as the dorsal and ventral conchae.
Paranasal sinuses are mucous‐membrane lined, air‐filled cavities within bones, which serve to decrease the weight of the skull. Connections exist between the middle nasal meatuses and the paranasal sinuses that allow for increased exposure of air to mucous membrane.
V Pharynx
The wall of the pharynx contains cartilage and skeletal muscle and is lined with a mucous membrane.
The pharynx is sub‐divided into three regions (nasopharynx, oropharynx, and laryngopharynx).
The opening of the auditory tubes is located in the lateral walls of the nasopharynx.
Guttural pouch
In the equine, each auditory tube has an expanded caudoventral diverticulum called the guttural pouch.
The internal carotid arteries are closely associated with the medial compartments of the guttural pouches.
It is believed that the air inside the pouches cools the blood within the internal carotid arteries before the blood reaches the brain.
VI Larynx (see Figure 4.1)
The larynx is, in part, composed of skeletal muscle and five individual, mucous membrane‐lined cartilages.
The opening into the larynx is called the rima glottis.
The muscles which attach to the larynx are used for swallowing and phonation.
A Cartilages
Epiglottic cartilage functions to occlude the rima glottis during swallowing.
Thyroid cartilage is a trough‐shaped cartilage, which forms the majority of the lateral and ventral extremities of the larynx.
Arytenoid cartilages (paired) are associated with the actions of the vocal ligaments and phonation.
Cricoid cartilage is the caudal‐most cartilage of the larynx and forms a complete ring. It is responsible for maintaining patency of the larynx.
B Innervation of the larynx
Nervous supply to