From the Guidelines
Complete heart block (third-degree AV block) on ECG is characterized by no relationship between P waves and QRS complexes, with the atria and ventricles beating independently, and a variable PR interval as P waves "march through" the QRS complexes. The P waves occur at a regular rate, typically between 60-100 beats per minute, while the QRS complexes appear at a slower, regular escape rhythm, typically between 30-40 beats per minute if junctional, or slower if ventricular 1. The QRS complexes are typically wide, greater than 0.12 seconds, if the escape rhythm originates from the ventricles, but may be narrow if from a junctional pacemaker.
Key Features of Complete Heart Block on ECG
- No consistent relationship between P waves and QRS complexes
- Atrial rate typically between 60-100 beats per minute
- Ventricular rate typically between 30-40 beats per minute if junctional, or slower if ventricular
- Variable PR interval as P waves "march through" the QRS complexes
- QRS complexes are typically wide if ventricular in origin, but may be narrow if junctional
This arrhythmia results from complete failure of electrical impulse conduction from atria to ventricles, often due to fibrosis of the conduction system, ischemia, medication effects, or infiltrative diseases, as outlined in the 2018 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay 1. Complete heart block is a medical emergency that usually requires temporary or permanent pacemaker implantation to prevent symptoms like syncope, fatigue, or sudden cardiac death from profound bradycardia.
Clinical Implications
- Complete heart block is a medical emergency
- Requires temporary or permanent pacemaker implantation
- Prevention of symptoms like syncope, fatigue, or sudden cardiac death from profound bradycardia is crucial
- Careful evaluation of the ECG is required for diagnosis, considering conditions like isorhythmic dissociation, atrial bigeminy, and sinus bradycardia coupled with an accelerated junctional rhythm without consistent retrograde ventriculoatrial conduction 1.
From the Research
ECG Findings for Complete Heart Block
The electrocardiogram (ECG) findings for complete heart block (Third-degree atrioventricular (AV) block) are characterized by:
- No atrial impulses reaching the ventricular conduction system 2
- The heart rate is dependent on the location of the block and a functioning secondary pacemaker within the conduction system 2
- Analysis of the EKG will determine the location of this escape rhythm 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
Specific ECG Findings
- A case report described a 64-year-old female patient with complete atrioventricular block and escape junctional rhythm with a heart rate of 17 bpm 3
- Another study reported a case of a 59-year-old male patient with intermittent complete atrioventricular block, with the longest RR interval lasting for 4.36 s 4
- A study of 62 patients with complete heart block found that the mean age was 67 years in the ischemic group and 75 years in the non-ischemic group, with a lower mean ejection fraction in the ischemic group 5
Clinical Implications
- Complete heart block is a medical emergency that requires prompt recognition and treatment 2
- The ECG findings are critical in determining the location of the block and the appropriate treatment 2
- Permanent pacemaker placement is usually required for complete heart block 5
- The clinical characteristics and outcomes of patients with ischemic and non-ischemic complete heart block can vary, with ischemic patients being younger and having a lower ejection fraction 5