From the Guidelines
In complete heart block, auscultation typically reveals bradycardia with a regular, slow ventricular rate usually between 20-40 beats per minute, with characteristic findings including "cannon" A waves in the jugular venous pulse and varying intensity of the first heart sound (S1) due to the changing relationship between atrial and ventricular contractions, as described in the 2018 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay 1.
Key Auscultation Findings
- Bradycardia with a regular, slow ventricular rate usually between 20-40 beats per minute
- "Cannon" A waves in the jugular venous pulse, which occur when the atria contract against closed AV valves
- Varying intensity of the first heart sound (S1) due to the changing relationship between atrial and ventricular contractions
- Intermittent loud S1 sounds when atrial and ventricular contractions happen to coincide
- The second heart sound (S2) remains normal in splitting pattern but occurs at a slow rate
- Independent atrial sounds or "atrial gallops" that bear no consistent relationship to ventricular sounds, creating an irregular rhythm when listening to both atrial and ventricular components together
Clinical Context
These findings reflect the complete electrical dissociation between atria and ventricles, where the atria follow the sinoatrial node at a normal rate (60-100 bpm) while the ventricles are controlled by a slower escape rhythm from the AV node or ventricular tissue, as noted in the guideline 1.
Diagnostic Considerations
Careful evaluation of the ECG is required for the diagnosis of atrioventricular block, and the presence of complete heart block may be imputed in the setting of AF when the ventricular response is slow (<50 bpm) and regular, although junctional rhythm in the setting of atrioventricular conduction abnormalities may be associated with this electrocardiographic finding, as discussed in the guideline 1 and further defined in the 2018 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay 1.
From the Research
Expected Auscultation Findings in Complete Heart Block
- The heart rate is dependent on the location of the block and a functioning secondary pacemaker within the conduction system 2
- For escape rhythms originating at the AV node or high in the His-Purkinje system, the QRS complex will typically be narrow, and the ventricular rate typically in the 40-60 bpm range 2
- For blocks with ventricular escape rhythms, the QRS will appear wide, with rates of 20-40 bpm 2
- Patients presenting with 3rd-degree AVB with ventricular escape rhythms can destabilize, and if no escape rhythm generates, patients develop asystole and cardiac arrest 2
Clinical Presentation
- Complete heart block is a cardiovascular emergency that requires prompt recognition 2
- Symptoms may include hypotension, syncope, and bradycardia 2
- The most common etiology of AV block is ischemic heart disease, with up to 1 in 5 patients developing some type of conduction disturbance after an MI 2
Management
- Effective management includes accurate interpretation of a 12-lead EKG, assessment of hemodynamic stability and systemic perfusion, and time-sensitive pharmacologic or procedural intervention 2
- Treatment options may include administration of IV atropine, attempt at transcutaneous pacing, placement of a transvenous pacemaker, and emergent consultation with interventional cardiology 2
- In selected patients with inferior MI and advanced atrioventricular block, percutaneous coronary intervention (PCI) should be considered as a treatment option before recommending permanent pacemaker implantation 3