Patients should be placed on a cardiac monitor. prolonged capillary refill time and hypotension) Typical clinical findings in third-degree heart block may include: Shortness of breath (due to heart failure).Typical symptoms of third-degree heart block may include: QRS complex: narrow (0.12 seconds) depending on the site of the escape rhythm (see introduction)įigure 4.PR interval: absent (as there is atrioventricular dissociation).P wave: present but not associated with QRS complexes.Autoimmune conditions: SLE, rheumatoid arthritisĮCG findings in third-degree (complete) heart block include:.Infections: endocarditis, Lyme disease, Chagas disease.Drug-related: digoxin, beta-blockers, calcium channel blockers, amiodarone.Iatrogenic: post-ablative therapies and pacemaker implantation, post-cardiac surgery.Non-ischaemic heart disease: calcific aortic stenosis, idiopathic dilated cardiomyopathy, infiltrative disease (e.g.Ischaemic heart disease: myocardial infarction, ischaemic cardiomyopathy.Idiopathic fibrosis: Lev’s disease (fibrosis of the distal His-Purkinje system in the elderly) and Lenegre’s disease (fibrosis of the proximal His-Purkinje system in younger individuals).Congenital: structural heart disease (e.g transposition of the great vessels), autoimmune (e.g maternal SLE).AetiologyĬauses of third-degree (complete) AV block include: 4 These escape rhythms produce slower, less reliable heart rates and more significant clinical features (e.g. Narrow-complex escape rhythms (QRS complexes of 40bpm.īroad-complex escape rhythms (QRS complexes >0.12 seconds duration) originate from below the bifurcation of the bundle of His. Typical ECG findings include the presence of P waves and QRS complexes that have no association with each other, due to the atria and ventricles functioning independently.Ĭardiac function is maintained by a junctional or ventricular pacemaker. Third-degree (complete) AV block occurs when there is no electrical communication between the atria and ventricles due to a complete failure of conduction. Patients are also at risk of developing asystole. Patients are at risk of progressing to symptomatic complete AV block, in which the escape rhythm is likely to be ventricular and thus too slow to maintain adequate systemic perfusion. Temporary pacing or isoprenaline may be required if the patient is haemodynamically compromised due to bradycardia.Ī permanent pacemaker is usually inserted if there are no reversible causes identified. The underlying cause of the AV block should be investigated. 1 Managementīecause of the risk of progression to complete AV block, patients should be placed on a cardiac monitor as soon as possible. Mobitz type 2 AV block Clinical features HistoryĬlinical examination may detect a ‘regularly irregular’ pulse, where there is a pattern of how many atrial depolarisations (P waves) lead to ventricular depolarisation (QRS waves) such as 3:1 block. The QRS complex will be broad if the conduction failure is located distal to the bundle of His 3įigure 3.QRS complex: normal morphology and duration (0.12 seconds).PR interval: prolonged >0.2 seconds (5 small squares). P wave: every P wave is present and followed by a QRS complex.Drugs: particularly AV blocking drugs such as beta-blockers, rate-limiting calcium-channel blockers, digoxin and magnesium 1ĮCG findings in first-degree AV block include:.Enhanced vagal tone: often seen in athletes (non-pathological).there are no dropped QRS complexes, unlike some other forms of AV block discussed later).įirst-degree AV block is common and can often be an incidental finding. You might also be interested in our medical flashcard collection which contains over 2000 flashcards that cover key medical topics.įirst-degree AV block involves the consistent prolongation of the PR interval (defined as >0.20 seconds) due to delayed conduction via the atrioventricular node.Įvery P wave is followed by a QRS complex (i.e. This article will explore each of the sub-types of AV block including:įor more information on ECG interpretation, see the Geeky Medics guide to how to read an ECG. Some forms of AV block can be managed conservatively, whereas other sub-types require intervention. Echocardiogram: to rule out structural heart disease.FBC, U&Es, TSH, troponin): to rule out underlying causes ECG: to help determine the subtype of AV block.The most common cause of AV block is idiopathic fibrosis and sclerosis of the conduction system.Īny patient presenting with AV block requires investigation to identify underlying causes: This interruption of impulse transmission results in characteristic ECG findings that differ depending on the subtype of AV block. Atrioventricular (AV) block (often referred to as “heart block”) involves the partial or complete interruption of impulse transmission from the atria to the ventricles.
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