The left bundle splits further into the left anterior fascicle and left posterior fascicle. The left bundle branch activates the left ventricle, whilst the right bundle activates the right ventricle. The distal part of the AV node is called the Bundle of His which splits into two bundle branches in the inter ventricular septum (left and right). The AV node introduces a critical delay (the PR interval) into the conduction system allowing blood to flow from the atria into the ventricles. The impulse is propagated from the right atrium to the left atrium via Bachmann’s bundle.Ĭonduction to the AV node occurs in specialised tissue called intermodal tracts. Normally, electrical activity is spontaneously generated by the SA node (the ‘physiological pacemaker’) Signals arising from the SA node stimulate the atria to contract and are conducted to the AV node (the P wave on the ECG). The conduction pathways of the heart consist of: A final section describes drug therapy and pacing in more detail.įigure 1: The conduction pathways of the heart. The causes, clinical presentations and management for each type of bradycardia are discussed in more detail in the sections below. May be asymptomatic worsening of angina pectoris or heart failure. Other symptoms may relate to the underlying cause. Organophosphates (including nerve agents)īradycardia may present as an incidental finding or with symptoms related to hypotension: Various drugs can also affect the electrophysiology of the heart myocytes and their nerve supply (Table 1). Electrolyte disturbance: Hyperkalaemia and hypokalaemia.Normal physiological variants as seen, for example, in athletes.The causes of bradycardia can be broadly categorised as: Our analysis received exemption from the Colorado Multiple Institutional Review Board (Protocol 19-0547).Bradycardia is defined as a heart rate of less than 60 beats per minute. Given this background, we present AN patients transferred to our medical stabilization unit with marked bradycardia, all of whom had manifestations typical of “symptomatic bradycardia.” Two were initially referred by outside facilities for PPM, and had recent pacemaker implants, which we ultimately extracted. Despite this natural history, profound bradycardia is often distressing to caregivers and may lead to unnecessary PPM placement and attendant iatrogenic morbidity, including exacerbation of existing distorted body self-image. Weight restoration, therefore, is the mainstay of treatment, with normalization of heart rate upon achieving 85%–90% of ideal body weight (IBW). ![]() Several mechanisms have been postulated to explain bradycardia: increased parasympathetic tone, decreased intracardiac glycogen stores, and myocardial atrophy with resultant structural changes, including fibrosis, on gadolinium-enhanced magnetic resonance imaging.ĭespite functional and structural myocardial changes, bradycardia may principally reflect reduced metabolic demand and cardiac output as a compensatory response to starvation. In a prior inpatient case series the mean heart rate was 44 bpm, with 69% of patients less than 50 bpm. The degree of bradycardia can be extreme, with junctional escape rhythms as low as 20 beats per minute (bpm) and may be an indication for hospitalization. Guidelines on the evaluation and management of patients with bradycardia enumerate many potentially reversible causes of sinus node dysfunction, but do not mention severe AN, nor do they proscribe PPM among eating disorder populations. ![]() However, symptoms may not reflect bradycardia per se, but rather extreme malnutrition, deconditioning, and hypovolemia associated with restricted caloric intake and purging. While most patients are asymptomatic, a significant minority present with presyncope, lightheadedness, fatigue, and exercise intolerance that could be construed as concordant with current guidelines for permanent pacemaker (PPM) implantation. Though generally reversible, marked bradycardia may be worrisome to clinicians with limited experience treating eating disorders. Bradycardia is common among patients with severe anorexia nervosa (AN).
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