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Heart block
Classification & external resources

ICD-10	I44.-I45.
ICD-9	426.9
DiseasesDB	10477
MeSH	D006327

A heart block is a disease in the electrical system of the heart. This is opposed to coronary artery disease, which is disease of the blood vessels of the heart. While coronary artery disease can cause angina (chest pain) or myocardial infarction (heart attack), heart block can cause lightheadedness, syncope (fainting), and palpitations.

Contents 1 Types of heart block 1.1 Types of SA nodal blocks 1.2 Types of AV nodal blocks 1.3 Types of infra-Hisian block 2 See also 3 References

A heart block can be a blockage at any level of the electrical conduction system of the heart.

• Blocks that occur within the sinoatrial node (SA node) are described as SA nodal blocks.
• Blocks that occur within the atrioventricular node (AV node) are described as AV nodal blocks.
• Blocks that occur below the AV node are known as infra-Hisian blocks (named after the bundle of His).

Clinically speaking, most of the important heart blocks are AV nodal blocks and infra-Hisian blocks.

The SA nodal blocks rarely give symptoms. This is because if an individual had complete block at this level of the conduction system (which is uncommon), the secondary pacemaker of the heart would be at the AV node, which would fire at 40 to 60 beats a minute, which is enough to retain consciousness in the resting state.

Types of SA nodal blocks include:

• SA node Wenckebach (Mobitz I)^[1]
• SA node Mobitz II
• SA node exit block

In addition to the above blocks, the SA node can be suppressed by any other arrhythmia that reaches it. This includes retrograde conduction from the ventricles, ectopic atrial beats, atrial fibrillation, and atrial flutter.

The difference between SA node block and SA node suppression is that in SA node block an electrical impulse is generated by the SA node that doesn't make the atria contract. In SA node suppression, on the other hand, the SA node doesn't generate an electrical impulse because it is reset by the electrical impulse that enters the SA node.

There are four basic types of AV nodal block:

• First degree AV block
• Second degree AV block
  • Type 1 second degree AV block (Mobitz I) (also known as Wenckebach phenomenon)
• Third degree AV block (Complete heart block)

Infrahisian block describes block of the distal conduction system. Types of infrahisian block include:

• Type 2 second degree heart block (Mobitz II)
• Left bundle branch block
  • Left anterior fascicular block
  • Left posterior fascicular block
• Right bundle branch block

Of these types of infrahisian block, Mobitz II heart block is considered most important because of the possible progression to complete heart block.

• Electrical conduction system of the heart
  • Sinoatrial node (SA node)
  • Atrioventricular node (AV node)

• Trifascicular heart block

• Lev's disease

1. ^ (November, 2000) Hurst's The Heart, 10th Edition. McGraw-Hill Professional Publishing, Figure 24-60b. ISBN 0071356959. 

v • d • e Circulatory system pathology (I, 390-459)
Hypertension	Hypertensive heart disease - Hypertensive nephropathy - Secondary hypertension (Renovascular hypertension)
Ischaemic heart disease	Angina pectoris (Prinzmetal's angina) - Myocardial infarction - Dressler's syndrome
Pulmonary circulation	Pulmonary embolism - Cor pulmonale
Pericardium	Pericarditis - Pericardial effusion - Cardiac tamponade
Endocardium/heart valves	Endocarditis - mitral valves (regurgitation, prolapse, stenosis) - aortic valves (stenosis, insufficiency) - pulmonary valves (stenosis, insufficiency) - tricuspid valves (stenosis, insufficiency)
Myocardium	Myocarditis - Cardiomyopathy (Dilated cardiomyopathy, Hypertrophic cardiomyopathy, Loeffler endocarditis, Restrictive cardiomyopathy) - Arrhythmogenic right ventricular dysplasia
Electrical conduction system of the heart	Heart block: AV block (First degree, Second degree, Third degree) - Bundle branch block (Left, Right) - Bifascicular block - Trifascicular block Pre-excitation syndrome (Wolff-Parkinson-White, Lown-Ganong-Levine) - Long QT syndrome - Adams-Stokes syndrome - Cardiac arrest - Sudden cardiac death Arrhythmia: Paroxysmal tachycardia (Supraventricular, AV nodal reentrant, Ventricular) - Atrial flutter - Atrial fibrillation - Ventricular fibrillation - Premature contraction (Atrial, Ventricular) - Ectopic pacemaker - Sick sinus syndrome
Other heart conditions	Heart failure - Cardiovascular disease - Cardiomegaly - Ventricular hypertrophy (Left, Right)
Cerebrovascular diseases	Intracranial hemorrhage/cerebral hemorrhage: Extra-axial hemorrhage (Epidural hemorrhage, Subdural hemorrhage, Subarachnoid hemorrhage) Intra-axial hematoma (Intraventricular hemorrhages, Intraparenchymal hemorrhage) - Anterior spinal artery syndrome - Binswanger's disease - Moyamoya disease
Arteries, arterioles and capillaries	Atherosclerosis (Renal artery stenosis) - Aortic dissection/Aortic aneurysm (Abdominal aortic aneurysm) - Aneurysm - Raynaud's phenomenon/Raynaud's disease - Buerger's disease - Vasculitis/Arteritis (Aortitis) - Intermittent claudication - Arteriovenous fistula - Hereditary hemorrhagic telangiectasia - Spider angioma
Veins, lymphatic vessels and lymph nodes	Thrombosis/Phlebitis/Thrombophlebitis (Deep vein thrombosis, May-Thurner syndrome, Portal vein thrombosis, Venous thrombosis, Budd-Chiari syndrome, Renal vein thrombosis, Paget-Schroetter disease) - Varicose veins / Portacaval anastomosis (Hemorrhoid, Esophageal varices, Varicocele, Gastric varices, Caput medusae) - Superior vena cava syndrome - Lymph (Lymphadenitis, Lymphedema, Lymphangitis)
Other	Hypotension (Orthostatic hypotension)
See also congenital (Q20-Q28, 745-747)