The same mechanism has been suspected in dogs, with unknown prevalence, as it has been documented that 13% of dogs presented with transient AV conduction disturbances. The pathogenesis of transient AVB secondary to acute myocarditis implies the presence of myocardial interstitial edema, and a correlation between increased thickness of the edematous cardiac walls and severity of AVB has been described. In human beings, the most common cause of transient AVB is acute myocarditis. More rarely, congenital forms or functional disorders (hyperkalemia, toxicity, antiarrhythmic drugs, high vagal tone, and hyperthyroidism) have also been described, ,, ,, ,, ,. Any primary or secondary cardiac disease that affects the AV conduction system (congenital, acquired, or secondary to traumatic, neoplastic, infiltrative, inflammatory, and systemic disorders) may result in complete AVB. Similar degenerative changes have been reported in veterinary medicine in dogs with chronic mitral valve disease. In human medicine, two degenerative diseases (Lev and Lenegre diseases) have been described as idiopathic degeneration with fibrosis replacement of the intraventricular conduction system, with or without changes in the cardiac skeleton. Atrioventricular disturbances can occur as a result of a primary disorder or secondary to acute or chronic myocardial abnormalities. ![]() Atrial impulses can be conducted with delay or be completely blocked depending on anatomical or functional impairment along the conduction system. This review describes the indications for pacing and evaluates the available evidence with the aim of assisting veterinarians in selecting the best management strategy for individual patients, taking into account the impact on outcome and the risk–benefit ratio of particular diagnostic or therapeutic methods.ĪVB is a disturbance of impulse conduction through the atrioventricular (AV) node and/or the His–Purkinje system that can be permanent or transient. Artificial pacing rate, voltage, current, pulse width, and sensitivity can be programmed by a telemetry system, allowing intraoperative and postoperative adjusting. ![]() Modern PMs consist of a sealed pulse generator with a lithium–iodine battery that generates electrical impulses and senses intrinsic cardiac rhythm via a unipolar or a bipolar lead attached to the endocardial or epicardial surface of the heart. In dogs, most PMs are implanted transvenously using endocardial leads, whereas, in cats and in particular circumstances also in dogs, the use of epicardial leads via thoracotomy or laparotomy may be necessary. In human medicine, the first reported PM implantation dates from 1952, whereas, in veterinary medicine, the first case was reported in 1967. In recent years, implantation of artificial cardiac pacemakers (PMs) has become a standard procedure for dogs with symptomatic bradycardia, such as advanced second-degree and third-degree atrioventricular block (AVB), sinus node disease, persistent atrial standstill (PAS), and vasovagal syncope (VVS), ,, ,, ,, ,, ,, ,. It is expected that this review will assist veterinarians in recognizing arrhythmias that may require permanent pacing and the risk-benefit of each pacing modality and its impact on outcome. We described the etiology of bradyarrhythmias, clinical signs and electrocardiographic abnormalities, and the choice of pacing modality, taking into account how different choices may have different physiological consequences to selected patients. The goal of this review was, therefore, to describe the indications for pacing by evaluating the available evidence in both human and veterinary medicine. ![]() To decide whether a patient is a candidate for pacing, as well as which pacing modality should be used, the clinician must have a clear understanding of the etiology, the pathophysiology, and the natural history of the most common bradyarrhythmias, as well as what result can be achieved by pacing patients with different rhythm disturbances. Most pacemakers are implanted transvenously, using endocardial leads, but rarely epicardial leads may be necessary. Advanced second-degree and third-degree atrioventricular blocks, sick sinus syndrome, persistent atrial standstill, and vasovagal syncope are the most common rhythm disturbances that require pacing to either alleviate clinical signs or prolong survival. Pacemaker implantation is considered as a standard procedure for treatment of symptomatic bradycardia in both dogs and cats.
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