Figure 4: The electrical conduction through the heart (Martini et. al, 2006).
The main function of the heart is to circulate blood throughout the body. Blood is essential for the human body because it provides perfusion and nutrients to the individual cells so they will function at their optimum level. As I previously mentioned blood flow in the heart in the anatomy section, I would like to now discuss the electrophysiological aspects of the heart. The cardiac myocytes that make up the heart are a Functional Syncytium, which means that they are able to act essentially as a single cell in terms of physiology. They are able to do so because they are connected through Intercalated Disks, which allow the sharing of the cytoplasm so that the action potential generated by the SA Node can propagate to the AV Node, and then move towards the Bundle of His, and finally to the Purkinje Fibers, allowing the electrical conduction to occur. Here are some examples of when the heart does not function as a syncytium, which has very serious consequences.
Figure 5: The top image shows the location of the Purkinje cells. The bottom image shows the dark stained Purkinje cells, located in periphery position of the myocytes.
Tachycardia
- An extremely fast heart beat that can cause a myocardial infarction if persistent for long periods.
- Under sympathetic nervous system control, can occur during ‘fight or flight’ response due to stimulants such as ephedrine’s, adrenaline, or hyperthyroidism.
- Can occur in the atria or ventricles of the heart. They are characterized by rapid irregular heart beat.
- Atrial Fibrillation's need to be treated with anticoagulants such as Heparin, because the heart’s electrical impulses are not strong enough to cause a forceful contraction to push the blood to the ventricle.
- Ventricular Fibrillation's are very serious as they are a cessation of electrical signals and require the heart to be “jump started” by a defibrillator.
- This occurs when all cardiac activity has completely stopped in every part of the heart.
- Often characterized as the “flat line” of the ECG, more than likely a patient will die if their heart is not started ASAP because all cells in your body are not receiving any perfusion or nutrients.
