Electrical conduction system of the heart - Wikipedia
11 ECG InterpretationFree Access their skills and knowledge in relation to this problem if patients are to obtain the best possible . The heart's electrical cells are arranged in a conduction system that carries the electrical. Learn the principles of cardiac physiology, electrocardiography and ECG interpretation. The action potential and conduction system are also. Abnormalities within this conduction system will compromise cardiac output and are . Most basic courses in ECG interpretation emphasize the precise recognition of at . Adopted by the House of Delegates, American Dental Association.
This electrical current can be detected on the surface of the body i. Pathway of the electrical impulse: From the sinus node, the electrical impulse starts by spreading throughout the atria from right to left.
When this happens, the cells lose their internal negativity, a process known as depolarization. The depolarization of the atria causes them to contract. The electrical current then spreads to the atrioventricular node AV nodefrom where it is further transmitted to the intraventricular Septum separates the left and right ventricles.
In order to depolarize the ventricles, the electrical impulse travels through the bundle of His, along the right and left bundle branches from left to rightand ends at the Purkinje fibers.
This process causes depolarization of the ventricles, causing them to contract. While the ventricles are being depolarized, the atria are regaining their internal electrical negativity, a process known as repolarization.
This allows them to relax. Once the ventricles have fully depolarized, they too become repolarized, and which point they relax as well. The heart's conduction system Update your cardiac diagnostics You can record a clinical lead ECG using just 4 electrodes and an app on your iPad or iPhone. However, there are fewer conduction cells than contractile cells, which implies that conduction cells only communicate with a portion of the contractile myocardium.
Recall that all cells in the heart are connected, both mechanically and electrically and this enables the electrical impulse to spread from one cell to the next.
Electrical conduction system of the heart
Atrial impulse transmission The conduction system is vaguely defined in the atria, as compared with the ventricles which boasts with distinct conduction structures such as the bundle of His and the bundle branches. There are, however, three rather distinct fiber bundles which appear to serve as the conduction system of the atria.
Refer to Figure 1 above. The atrioventricular conduction system The atrioventricular node AV node The atrioventricular AV node is the bridge between the atria and the ventricles. It is located in the atrial septum and normally the only connection between the atria and ventricles Figure 1. The delay is due to the slow conduction through the atrioventricular node. The purpose of the slow conduction is to give the atria adequate time to fill the ventricles with blood, before ventricular contraction commences.
Clinical electrocardiography and ECG interpretation – ECG learning
The bundle of His The atrioventricular node continues in the bundle of His which splits up in the left bundle branch and the right bundle branch.
These bundles successively branch into finer bundles and ultimately Purkinje fibers which sprout into the myocardium. Note that the left bundle branch splits into an anterior and a posterior fascicle. This means that activation of the ventricles except from the septum starts in the endocardium and spreads towards the epicardium Figure 5.
The rapid impulse transmission in the Purkinje network allows virtually all ventricular myocardium to be activated simultaneously. As noted above, when the impulse is delivered to the contractile myocardial cells, the subsequent impulse transmission takes place from one contractile cell to the next, which is much slower 0. Schematic figure of the ventricular wall. Note that the term myocardium is often used to refer to all layers.
Influences of the autonomic nervous system The vagus nerve provides the heart with parasympathetic fibers. These fibers primarily innervate the sinoatrial node and the atrioventricular node.
Increased vagal tone leads to slowed automaticity in the sinoatrial node and slowed conduction through the atrioventricular node. This leads to lower heart rate and a negligble increase in the delay in the atrioventricular node. Sympathetic fibers innervate the entire heart, both the conduction system and contractile myocardium.
The fibers run along the blood vessels and are particularly dense in ventricular myocardium. Sympathetic stimulation leads to increased excitability in all cells. Definition of heart rhythm A rhythm is defined as three consecutive heart beats displaying more or less identical waveforms on the ECG.
The similarity of the waveforms indicates that their origin is the same.
Clinical electrocardiography and ECG interpretation
Although it is not possible to discern the electrical potentials of the sinoatrial node itself, there are indirect evidence from the ECG that confirm the origin of the rhythm discussed later. If an ectopic rhythm is a replacement for the normal sinus rhythm, it is referred to as escape rhythm. These topics will be discussed in detail later on. The action potential spreads in the form of an electrical impulse, by cell-to-cell transmission of the depolarization.
It is then delayed briefly in the atrioventricular node before it is rapidly disseminated — via the His-Purkinje network — through the ventricular myocardium. The action potential consists of a depolarization activation and a repolarization recovery. This process includes rapid changes in the membrane potential, which is a consequence of ions flowing across the cell membrane. Flow of ions is equal to an electrical current and the electrical activity of atrial and ventricular myocardium is recorded and analysed by electrodes placed on the skin.
An electrocardiogram is a recording of the electrical activity of the heart. P wave[ edit ] Under normal conditions, electrical activity is spontaneously generated by the SA nodethe cardiac pacemaker. This electrical impulse is propagated throughout the right atriumand through Bachmann's bundle to the left atriumstimulating the myocardium of the atria to contract. The conduction of the electrical impulses throughout the atria is seen on the ECG as the P wave.
AV node and bundles: PR interval[ edit ] The AV node functions as a critical delay in the conduction system. Without this delay, the atria and ventricles would contract at the same time, and blood wouldn't flow effectively from the atria to the ventricles.
The distal portion of the AV node is known as the bundle of His.
The left bundle branch activates the left ventriclewhile the right bundle branch activates the right ventricle.