From the Guidelines
In junctional bradycardia, P waves may be absent, inverted, or occur after the QRS complex, as the electrical impulse originates from the atrioventricular (AV) junction rather than the sinoatrial (SA) node. This is because the impulse can travel retrograde (backward) to the atria, causing inverted P waves in leads II, III, and aVF, as described in the 2018 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay 1. When the impulse starts in the junction, it can travel retrograde to the atria, causing inverted P waves, which may appear before, during (buried in the QRS), or after the QRS complex, depending on the exact location of the junctional pacemaker.
Key Characteristics of Junctional Bradycardia
- A regular but slow heart rate (typically 40-60 beats per minute) with narrow QRS complexes
- Inverted P waves in leads II, III, and aVF, which may be subtle
- Absence of normal upright P waves in these leads with a regular bradycardic rhythm, strongly suggesting a junctional origin If the retrograde conduction to the atria is blocked, P waves will be completely absent. The 2018 ACC/AHA/HRS guideline 1 provides a comprehensive overview of the definitions and descriptions of various types of bradycardia and cardiac conduction delays, including junctional bradycardia.
Clinical Implications
- Carefully examine leads II, III, and aVF for inverted P waves when interpreting an ECG with suspected junctional bradycardia
- Consider the clinical context and other ECG findings to determine the underlying cause of the bradycardia and guide management decisions, as outlined in the guideline 1.
From the Research
Junctional Bradycardia and P Waves
- Junctional bradycardia is a type of bradycardia that originates from the atrioventricular (AV) junction, which includes the AV node and the bundle of His 2.
- In junctional bradycardia, the P waves are typically absent or retrograde, meaning they are inverted in leads II, III, and aVF 3.
- The absence or retrograde nature of P waves in junctional bradycardia is due to the abnormal origin of the cardiac impulse in the AV junction, rather than the sinoatrial node 4.
- However, it is possible to see P waves in junctional bradycardia, but they are usually retrograde and may be difficult to detect on an electrocardiogram (ECG) 3.
Diagnosis and Management
- The diagnosis of junctional bradycardia is based on the presence of a slow heart rate, typically less than 60 beats per minute, and the characteristic ECG findings, including the absence or retrograde nature of P waves 2.
- The management of junctional bradycardia depends on the underlying cause and the presence of symptoms, such as syncope, dizziness, or fatigue 5.
- Treatment options for junctional bradycardia may include atropine, pacing, or the placement of a permanent pacemaker, depending on the severity of the condition and the presence of underlying heart disease 4.