A denotes 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 (passing out), and
Palpitation s.
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 infrahisian 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 conduct to the ventricles. 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:
Infrahisian block describes block of the distal conduction system. Types of infrahisian block include:
Of these types of infrahisian block, Mobitz II heart block is considered most important because of the possible progression to complete heart block.
1. Fuster V., Alexander R. W., O'Rourke R. A. et al. ''Hurst's The Heart'', 10th Edition. Figure 24-60b.
