From the Guidelines
In complete heart block, extra heart sounds such as a "cannon a wave" or S4 heart sound, variable intensity of S1, and potentially an S3 gallop sound may be heard due to the dissociation between atrial and ventricular contractions. The presence of these extra sounds can be attributed to the independent beating of the atria and ventricles, as described in the 2018 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay 1. This guideline provides a comprehensive overview of the definitions and descriptions of various cardiac conduction abnormalities, including complete heart block, which is characterized by the absence of atrioventricular conduction.
When examining a patient with suspected complete heart block, it is essential to listen carefully at the apex and left lower sternal border, using the bell of the stethoscope for low-frequency sounds like S3 and S4. The diagnosis should be confirmed with an ECG, which will show independent P waves and QRS complexes with no relationship between them, as defined in the guideline 1. Key points to consider in the diagnosis and management of complete heart block include:
- The presence of extra heart sounds, such as a "cannon a wave" or S4 heart sound, which can indicate the dissociation between atrial and ventricular contractions
- The importance of ECG confirmation, which will show independent P waves and QRS complexes with no relationship between them
- The potential development of heart failure, which may be indicated by the presence of an S3 gallop sound
- The need for definitive management, typically involving pacemaker implantation, to prevent symptoms like syncope, heart failure, or sudden cardiac death.
The guideline emphasizes the importance of prompt recognition and treatment of complete heart block to prevent morbidity and mortality, and to improve quality of life 1. By prioritizing the diagnosis and management of complete heart block, healthcare providers can help reduce the risk of complications and improve patient outcomes.
From the Research
Extra Heart Sounds in Complete Heart Block
- Complete heart block (CHB) is a condition where atrial impulses are not conducted to the ventricles 2.
- The presence of extra heart sounds, such as third heart sounds, can be an indicator of heart failure or other cardiac conditions 3.
- In patients with valvular heart disease, the presence of third heart sounds can depend on the type of valvular disease, with higher prevalence in patients with mitral regurgitation or aortic regurgitation 3.
- In the context of complete heart block, extra heart sounds may be related to the underlying mechanisms of the condition, such as impaired left ventricular compliance and diastolic mitral regurgitation volume 4.
- Studies have shown that patients with high-degree atrioventricular block (AVB) may present with heart failure, and that the causes of heart failure in these patients are poorly understood 4.
- The diagnosis of heart failure in patients with AVB is based on the Framingham criteria, and correlates with decreased cardiac output, impaired left ventricular compliance, and increased diastolic mitral regurgitation volume 4.
Clinical Features of Complete Heart Block
- Complete heart block can occur in association with many conditions, including acute myocardial infarction 2.
- The clinical manifestation of CHB can occur within 72 hours of injury, and 1:1 AV conduction may be restored within 7-10 days in some patients 5.
- Permanent pacemaker implantation may be indicated in patients with recurrent or permanent CHB 5.
- Cardiac troponins may be elevated in patients with CHB, and electrocardiographic features of aberrancy may be present in some cases 5.
Echocardiography in Heart Failure
- Echocardiography is an essential investigation in patients with suspected heart failure, providing assessment of cardiac chamber size and structure, ventricular function, valvular function, and key haemodynamic parameters 6.
- Echocardiography can provide diagnostic information about the cause of heart failure, and may indicate what further investigations are required and what therapy is indicated 6.
- Echocardiography can also be used for noninvasive quantitative monitoring, and identification of impaired systolic function is important as there is evidence-based therapy that can improve prognosis in this condition 6.