Trifascicular block

Trifascicular heart block
Classification and external resources
Specialty	cardiology
ICD-10	I45.3
ICD-9-CM	426.54

Trifascicular block is a problem with the electrical conduction of the heart. It is diagnosed on an electrocardiogram (ECG/EKG) and has three features:^[1]

prolongation of the PR interval (first degree AV block)
right bundle branch block
either left anterior fascicular block or left posterior fascicular block.

Differential diagnosis

Trifascicular block is important to diagnose because it is difficult to tell based on the surface ECG whether the prolonged PR interval is due to disease in the AV node or due to diffuse distal conduction system disease.

In the former case, if the block at the AV node level becomes complete, the escape rhythm will originate from the bundle of His, which typically will generate heart rates in the 40s, allowing the individual to survive and complain of symptoms of fatigue or near-syncope to their physician.
In the latter case, however, because the conduction system disease is diffuse in nature, the escape rhythm may be fascicular or ventricular, which may be at rates that are life-threateningly low.

Diagnosis

The diagnosis of whether the PR prolongation is due to AV nodal disease or diffuse conduction system disease is typically made by an electrophysiology study of the conduction system. In an electrophysiology study, trifascicular block due to AV nodal disease (true trifascicular block does not involve the AV node) block is represented by a prolonged AH interval (denoting prolonged time from impulse generation in the atria and conduction to the bundle of His) with a relatively preserved HV interval (denoting normal conduction from the bundle of His to the ventricles). Trifascicular block due to distal conduction system disease is represented by a normal AH interval and a prolonged HV interval.

Treatment

The treatment for diffuse distal conduction system disease is insertion of a pacemaker. If the PR prolongation is due to AV nodal disease, a case may be made for observation, as it may never progress to complete heart block with life threateningly low heart rates.

Regardless of where in the conduction system the block is, if the block is believed to be the cause of syncope in an individual, a pacemaker is an appropriate treatment.

References

↑ 1161101334 at GPnotebook

External links

Coronary disease	Coronary artery disease (CAD) Coronary artery aneurysm Coronary artery dissection Coronary thrombosis Coronary vasospasm Myocardial bridge

Active ischemia	Angina pectoris Prinzmetal's angina Stable angina Acute coronary syndrome Myocardial infarction Unstable angina

Sequelae	hours Hibernating myocardium Myocardial stunning days Myocardial rupture weeks Aneurysm of heart / Ventricular aneurysm Dressler syndrome

Layers

Pericardium

Myocardium

Endocardium /
valves

Endocarditis	infective endocarditis Subacute bacterial endocarditis non-infective endocarditis Libman–Sacks endocarditis Nonbacterial thrombotic endocarditis

Valves	mitral regurgitation prolapse stenosis aortic stenosis insufficiency tricuspid stenosis insufficiency pulmonary stenosis insufficiency

Conduction /
arrhythmia

Bradycardia

Tachycardia
(paroxysmal and sinus)

Supraventricular	Atrial Multifocal Junctional AV nodal reentrant Junctional ectopic

Ventricular	Accelerated idioventricular rhythm Catecholaminergic polymorphic Torsades de pointes

Premature contraction

Pre-excitation syndrome

Flutter / fibrillation

Other / ungrouped

Other

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