History and exam
Key diagnostic factors
common
presence of risk factors
Strong risk factors for AV block include increased vagal tone; use of AV nodal blocking agents; underlying cardiovascular disease (e.g., CAD or an acute coronary syndrome; HTN, CHF; LVH or cardiomyopathy); acid-base disturbance; neuromuscular disorders; or recent cardiac surgery.
age >50-60 years
syncope
Syncope potentially implies a profound decrease in the ventricular rate, such as with the sudden development of complete heart block with a slow or absent ventricular escape rhythm. More urgent timing of pacemaker placement may be indicated. For example, syncope in a patient with high-degree AV block (Stokes-Adams attack) is usually an indication for prompt pacemaker placement unless a reversible cause, such as an inferior infarction or severe electrolyte or pH disturbances, is identified. Thus, supportive care may avert the need for permanent pacing.
heart rate <40 bpm
The overall ventricular rate helps determine appropriate timing and level of therapy. With very slow ventricular rates (<40 bpm), hospital admission and either urgent permanent pacemaker implantation or temporary transvenous pacing should be considered.
uncommon
pre-syncope
Pre-syncope potentially implies a significant decrease in the ventricular rate and would prompt more urgent timing of pacemaker placement, if indicated.
Other diagnostic factors
common
male sex
In one study of His-Purkinje disease, men were twice as likely as women to have a widened QRS interval, a precursor to advanced degrees of heart block.[8]
fatigue
Fatigue, especially related to exertion, may be a function of a relatively slow ventricular rate. Because fatigue is such a non-specific symptom, its onset and duration should be correlated to that of the heart block as much as possible. Exercise testing to evaluate the dynamic heart rate response may also be helpful in establishing the contribution of bradycardia to fatigue or dyspnoea.
dyspnoea
Dyspnoea, especially related to exertion, may be a function of a relatively slow ventricular rate. Similarly to fatigue, because dyspnoea is such a non-specific symptom, its onset and duration should be correlated to that of the heart block as much as possible.
This symptom is of concern for an acute coronary syndrome in those with new-onset heart block. The acute coronary syndrome can be a proximate and reversible cause of heart block.
chest pain, palpitations, and nausea or vomiting
Of concern for an acute coronary syndrome in those with new-onset heart block. Chest pain, palpitations, nausea, and vomiting are often encountered in patients with AV block in the acute setting. Acute coronary syndrome can be a proximate and reversible cause of acute heart block.
high (less commonly, low) blood pressure
Slow ventricular rates with significant heart block are usually associated with elevated systolic blood pressures and relatively wide pulse pressures, rather than with hypotension. Low blood pressures in patients with heart block usually reflect significantly decreased ventricular rates (<40 bpm).
cannon A waves
The presence of structural heart disease is associated with His-Purkinje disease and may imply an irreversible cause for heart block.[8] Examination of the jugular venous pressure may reveal cannon A waves that may indicate the presence of AV dissociation due to complete heart block. The intermittently prominent (cannon) A waves reflect the contraction of the right atrium against a closed tricuspid valve.
uncommon
hypoxaemia
Profound hypoxaemia may be a reversible cause of heart block.
family history of AV block
Some causes of heart block have been shown to be hereditary.[14] Fetal third-degree AV block is known to occur in the setting of maternal SLE.
features of Lyme disease
Lyme disease is an uncommon cause of AV block, although there are regions where the disease is endemic and should be considered more readily.[33] As a potentially reversible cause, its presence should be considered, especially in younger patients presenting with exposure in these endemic areas. The diagnosis is a clinical one, with presenting symptoms including headache, stiff neck, fever, muscle and joint aches, fatigue, and erythema migrans. Even in patients diagnosed with Lyme disease, the incidence of heart block is low (<2%).
Risk factors
strong
age-related degenerative changes in the conduction system
Usually take the form of either Lenegre's disease (progressive fibrosis and sclerodegenerative changes) or Lev's disease (fibrosis or calcification of the conduction system extending from adjacent fibrous structures of, usually, the aortic and/or mitral valves).[14][18][19] These degenerative changes may account for up to half of the cases of complete heart block.[20]
increased vagal tone
Increased vagal tone may be due to either a tonic high level of vagal tone or transient vagotonia. High tonic vagal tone is found in younger, athletic patients or in patients with autonomic dysfunction.
Transient vagotonia occurs in vasodepressor syncope; during sleep; during episodes of nausea, vomiting, or gagging (i.e., endotracheal suctioning); during pain (including postoperatively), micturition, or bowel movements; during paroxysmal coughing or other instances of Valsalva (such as extreme straining to sit up); and during carotid sinus stimulation or cardiac ischaemia. Excessive vagotonia can also occur in patients with carotid sinus hypersensitivity, particularly common in older patients or in patients who have undergone head and neck surgery or radiation. Carotid sinus hypersensitivity usually manifests as severe high-degree AV block precipitated by changes in head position or in response to neck pressure.
AV-nodal blocking agents
Most commonly implicated agents are AV-nodal blocking medications such as beta-blockers, calcium-channel blockers, digitalis, and adenosine. Anti-arrhythmic medications, including some sodium-channel blocker and some class III agents (sotalol and amiodarone), may also cause AV block.[10]
chronic stable coronary artery disease
The presence of cardiovascular comorbidities has been shown to be associated with His-Purkinje disease, a precursor to advanced degrees of heart block.[8] Presumably, this is due to an acceleration of the process of degenerative fibrosis and calcification of the conduction system.
AV block can be seen in the setting of chronic ischaemic heart disease or as a complication of acute MI.
acute coronary syndrome
In this setting, AV block can be as a result of imbalance in autonomic tone, ischaemia, or necrosis of the conduction system. It can complicate both anterior and inferior wall MI, typically being an adverse prognostic factor when seen with the former and more often reversible with the latter. Primary percutaneous coronary intervention for the treatment of acute MI has decreased the incidence of AV block in the acute setting.[21]
In one older study of 134 acute MI patients, first-degree AV block was seen in 11.8% of patients, second-degree AV block in 4.8%, and complete heart block in 5.9%.[22] These percentages are probably lower in the modern era of early reperfusion therapy for acute MI. One more recent study of 14,096 acute coronary syndrome patients identified high-degree AV block in only 1% of patients.[23] Still, AV block remains a real and potentially serious complication of acute MI.
The incidence of complete heart block in non-ST-elevation myocardial infarction is 1.0% to 3.7% based on anterior or posterior/inferior location, respectively.[24] High-grade AV block after inferior NSTEMI is usually transient, with a narrow QRS complex and a junctional escape rhythm.[25] High-degree AV block in anterior NSTEMI is more ominous because of a greater extent of myocardial injury and involvement of the conduction system.
recent cardiac surgery, intervention, or ablation
May present a reversible cause for heart block.
In one study of patients in Denmark aged <50 years with AV block, complications of cardiac surgery was found to be the most common cause of AV block, accounting for 15.3% of all cases. Other causes included complications of radio-frequency ablations, planned His ablations and alcohol septal ablations.[16]
congestive heart failure (CHF)
The presence of cardiovascular comorbidities has been shown to be associated with His-Purkinje disease, a precursor to advanced degrees of heart block.[8] Presumably, this is due to an acceleration of the process of degenerative fibrosis and calcification of the conduction system.
Progression of left ventricular systolic dysfunction to CHF is associated with gradual prolongation of the PR interval and intraventricular conduction disturbances, usually left bundle-branch block, in up to about one third of patients.
hypertension
The presence of cardiovascular comorbidities has been shown to be associated with His-Purkinje disease, a precursor to advanced degrees of heart block.[8] Presumably, this is due to an acceleration of the process of degenerative fibrosis and calcification of the conduction system. In one cohort study, every 10 mmHg increase in systolic blood pressure was associated with a 22% higher risk of developing AV block.[6]
cardiomyopathy
The presence of cardiovascular comorbidities has been shown to be associated with His-Purkinje disease, a precursor to advanced degrees of heart block.[8] Presumably, this is due to an acceleration of the process of degenerative fibrosis and calcification of the conduction system.
left ventricular hypertrophy
The presence of cardiovascular comorbidities has been shown to be associated with His-Purkinje disease, a precursor to advanced degrees of heart block.[8] Presumably, this is due to an acceleration of the process of degenerative fibrosis and calcification of the conduction system.
acid-base or electrolyte disturbance
Severe electrolyte disturbance or acidosis may result in AV block.
neuromuscular disorders
For example, myotonic dystrophy, Kearns-Sayre syndrome, Erb dystrophy, or peroneal muscular atrophy.
sarcoidosis
The true prevalence of cardiac sarcoidosis remains unknown and is potentially underestimated since many individuals with cardiac sarcoidosis may have non-specific symptoms or sub-clinical disease.[26] AV block can occur as a result of granulomatous involvement of the interventricular septum or the conduction system. Such patients usually present with syncope at an earlier age than AV block due to other aetiologies. AV block requiring permanent pacemaker is the most common initial manifestation of cardiac sarcoidosis. One-fourth of unexplained AV block in adults aged <55 years are caused by cardiac sarcoidosis.[26][27] The risk of sudden cardiac death is significant in cardiac sarcoidosis presenting with high-grade AV block with or without ventricular tachycardia or LV dysfunction.[28] Data from the National Inpatient Sample (NIS) database 2012-2014 found that sarcoidosis was associated with increased risk of complete heart block.[29]
weak
giant cell myocarditis
Giant cell myocarditis may present as AV block.[30]
cardiac tuberculosis
lyme disease
Rarely, Lyme disease is linked to AV block; as a potentially reversible cause, it is important to identify.[33]
infective endocarditis
AV block can be associated infrequently with infective endocarditis affecting the aortic valve (e.g., aortic valve abscess).
hypoxemia
Myocardial hypoxia, due to any cause, can result in depression of conduction in the AV node and, hence, AV block.
blunt cardiac injury
Complete heart block may occur secondary to blunt cardiac injury.[12]
some indigenous medicines
Some indigenous medicines, for example mad honey, have been associated with AV block.[13]
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