Chronic Bifascicular Or Trifascicular Block

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Patients with chronic bifascicular block (right bundle branch block and left anterior hemiblock, right bundle branch block and left posterior hemiblock, or complete left bundle branch block) and patients with trifascicular block (any of the above and first-degree AV block) are at an increased risk of progression to complete AV block.

In the 1980s, the results of several prospective studies of the role of His bundle recordings in asymptomatic patients with chronic bifascicular block were published.2-7 In these studies, more than 750 patients were observed for 3 to 5 years. The incidence of progression from bifascicular to complete heart block varied from 2% to 5%. Most important, the total cardiovascular mortality was 19% to 25%, and the mortality from sudden cardiac death was 10% to 20%. In these patients, the presence of bifascicular block on the ECG should be taken as a sign of coexisting organic heart disease. These studies concluded that patients

Box 1.1. Causes of Acquired High-Grade AV Block

Ischemic

Acute myocardial infarction Chronic ischemic heart disease Nonischemic cardiomyopathy Hypertensive Idiopathic dilated Fibrodegenerative Lev's disease Lenegre's disease After cardiac surgery

Coronary artery bypass grafting Aortic valve replacement Ventricular septal defect repair Septal myomectomy (for IHSS surgery) Other iatrogenic

After His bundle (AV junction) ablation

After ablation of septal accessory pathways, AV nodal reentry After radiation therapy (e.g., lung cancer, Hodgkin's lymphoma) Infectious

Bacterial endocarditis Chagas' disease Lyme disease

Other (viral, rickettsial, fungal, etc.) Neuromuscular disease Myotonic dystrophy

Muscular dystrophies (fascioscapulohumeral) Kearns-Sayre syndrome Friedreich's ataxia Infiltrative disease Amyloid Sarcoid

Hemochromatosis Carcinoid Malignant Connective tissue disease Rheumatoid arthritis Systemic lupus erythematosus Systemic scleroderma Ankylosing spondylitis with chronic asymptomatic bifascicular block and a prolonged HV interval (HV interval represents the shortest conduction time from the His bundle to the endocardium over the specialized conduction system) have more extensive organic heart disease and an increased risk of sudden cardiac death. The risk of spontaneous progression to complete heart block is small, although it is probably slightly greater in patients who have a prolonged HV interval. Permanent pacing appears to prevent recurrent syncope in these patients but does not reduce the frequency of sudden death, which is often due to heart failure or ventricular arrhythmias.2 Routine His bundle recordings are therefore of little value in evaluating patients with chronic bifascicular block and no associated symptoms (e.g., syncope or presyncope) (Fig. 1.7).

In patients with bifascicular or trifascicular block and associated symptoms of syncope or presyncope, electrophysiologic testing is useful.8 A high incidence of sudden cardiac death and inducible ventricular arrhythmias is noted in this group of patients. Electrophysiologic testing is useful for identifying the disorder responsible for syncope, and potentially avoiding implantation of a pacemaker (Fig. 1.8). In patients who have a markedly prolonged HV interval (>100 milliseconds) and syncope not attributable to other causes, there is a high incidence of subsequent development of complete heart block, and permanent pacing is warranted. However, these patients comprise a relatively small percentage of patients undergoing electrophysiologic testing with cardiac symptoms and bifascicular block. In the majority of patients, the HV interval is normal (HV: 35 to 55 milliseconds) or only mildly prolonged, and His bundle recording does not effectively separate out high-risk and low-risk subpopulations with bifascicular block who are likely to progress to complete heart block. Electro-physiologic testing will often provoke sustained ventricular arrhythmias, which are the cause of syncope in many of these patients. In patients with left ven-

Chronische Polyarthritis

Figure 1.7. An intracardiac recording in a patient with left bundle branch block. The prolonged HV interval (80 milliseconds) is indicative of infranodal conduction disease, but in the absence of transient neurologic symptoms (syncope, dizzy spells, etc.), no specific therapy is indicated. From top to bottom: I, F, and V1 are standard ECG leads; HBE is the intracardiac recording of the His bundle electrogram. Abbreviations: A = atrial depolarization, H = His bundle depolarization, V = ventricular electrogram. Paper speed is 100 mm/sec.

Figure 1.7. An intracardiac recording in a patient with left bundle branch block. The prolonged HV interval (80 milliseconds) is indicative of infranodal conduction disease, but in the absence of transient neurologic symptoms (syncope, dizzy spells, etc.), no specific therapy is indicated. From top to bottom: I, F, and V1 are standard ECG leads; HBE is the intracardiac recording of the His bundle electrogram. Abbreviations: A = atrial depolarization, H = His bundle depolarization, V = ventricular electrogram. Paper speed is 100 mm/sec.

Branch Interval

Figure 1.8. A 68-year-old man was admitted complaining of recurrent dizziness and syncope. His baseline 12-lead ECG showed a PR interval of 0.20 seconds and a right bundle block QRS morphology. During the electrophysiologic study, the patient's baseline HV interval was 90 milliseconds. Top: During atrial pacing at a cycle length of 600 milliseconds (100 ppm), there is block in the AV node. Bottom: During pacing at 500 milliseconds (120 ppm), there is block below the His bundle. These findings are indicative of severe diffuse conduction system disease. A permanent dual-chamber pacemaker was implanted, and the patient's symptoms resolved. From top to bottom: I, II, III, and V1 are standard ECG leads; intracardiac recording from the right atrial appendage (RA) and His bundle (HBE1 for the proximal His bundle and HBE2 for the distal His bundle). Abbreviations: A = atrial depolarization, H = His bundle depolarization, V = ventricular depolarization.

Figure 1.8. A 68-year-old man was admitted complaining of recurrent dizziness and syncope. His baseline 12-lead ECG showed a PR interval of 0.20 seconds and a right bundle block QRS morphology. During the electrophysiologic study, the patient's baseline HV interval was 90 milliseconds. Top: During atrial pacing at a cycle length of 600 milliseconds (100 ppm), there is block in the AV node. Bottom: During pacing at 500 milliseconds (120 ppm), there is block below the His bundle. These findings are indicative of severe diffuse conduction system disease. A permanent dual-chamber pacemaker was implanted, and the patient's symptoms resolved. From top to bottom: I, II, III, and V1 are standard ECG leads; intracardiac recording from the right atrial appendage (RA) and His bundle (HBE1 for the proximal His bundle and HBE2 for the distal His bundle). Abbreviations: A = atrial depolarization, H = His bundle depolarization, V = ventricular depolarization.

tricular systolic dysfunction, advanced heart failure, and bundle branch block, especially left bundle branch block and QRS interval greater than 120 milliseconds, defibrillators with biventricular pacing have been shown to improve symptoms from heart failure and reduce mortality.9

Barold has pointed out that the standard definition of trifascicular block is often too loosely applied.10 Thus, in patients with right bundle branch block and either left anterior or left posterior fascicular block or in patients with left bundle branch block and first-degree AV block, the site of block could be located either in the His-Purkinje system or in the AV node. The term "trifascicular block" should be reserved for alternating right and left bundle branch block or for block of either bundle in the setting of a prolonged HV interval.

The indications for pacing in the setting of chronic bifascicular/ trifascicular block are listed subsequently.

Class I

1. Intermittent third-degree AV block. (Level of evidence: B.)

2. Type II second-degree AV block. (Level of evidence: B.)

3. Alternating bundle-branch block. (Level of evidence: C.)

Class IIa

1. Syncope not demonstrated to be due to AV block when other likely causes have been excluded, specifically ventricular tachycardia. (Level of evidence: B.)

2. Incidental finding at electrophysiology study of markedly prolonged HV interval (greater than or equal to 100 milliseconds) in asymptomatic patients. (Level of evidence: B.)

3. Incidental finding at electrophysiology study of pacing induced infra-His block that is not physiologic. (Level of evidence: B.)

Class lib

1. Neuromuscular diseases such as myotonic muscular dystrophy, Kearn-Sayre syndrome, Erb's dystrophy, and peroneal muscular atrophy with any degree of fascicular block with or without symptoms, because there may be unpredictable progression of AV conduction disease. (Level of evidence: C.)

Class III

1. Fascicular block without AV block or symptoms. (Level of evidence: B.)

2. Fascicular block with first-degree AV block without symptoms.

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Responses

  • GOYTIOM
    Why does bacterial endocarditis cause high grade av block?
    8 years ago
  • suoma
    What Is Atrial Depolarization?
    8 years ago
  • tamara
    What is bifascicular block?
    3 years ago
  • uta burger
    How a bifasicular block progresses?
    9 months ago

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