EKG, ECG Interpretation Course | CEUfast Nursing Continuing Education
This ECG Interpretation course will show how to identify normal versus abnormal cardiac anatomy, cardiac cycle and The normal cardiac conduction system occurs in this sequence: . relationship of ecg to cardiac anatomy. The components of the cardiac electrical conduction system transmit the stimulus reflects a relationship between the atria and ventricles and is The recorded strip may be used to evaluate the cardiac rhythm and can be kept for future. Purkinje fibers located here; (electrical conduction system) Your heart's electrical system controls all the events that .. Regular P to P but no relation to QRS.
Certain rhythms are known to have good cardiac output and some are known to have bad cardiac output. Ultimately, an echocardiogram or other anatomical imaging modality is useful in assessing the mechanical function of the heart.
- Understanding the EKG Signal
- EKG, ECG Interpretation
Like all medical tests, what constitutes "normal" is based on population studies. The heartrate range of between 60 and beats per minute bpm is considered normal since data shows this to be the usual resting heart rate. In order to understand the patterns found, it is helpful to understand the theory of what ECGs represent.
The theory is rooted in electromagnetics and boils down to the four following points: For example, depolarizing from right to left would produce a positive deflection in lead I because the two vectors point in the same direction. In contrast, that same depolarization would produce minimal deflection in V1 and V2 because the vectors are perpendicular and this phenomenon is called isoelectric.
Normal rhythm produces four entities — a P wave, a QRS complex, a T wave, and a U wave — that each have a fairly unique pattern. The P wave represents atrial depolarization.
The QRS complex represents ventricular depolarization.
The T wave represents ventricular repolarization. The U wave represents papillary muscle repolarization. However, the U wave is not typically seen and its absence is generally ignored. Changes in the structure of the heart and its surroundings including blood composition change the patterns of these four entities.
Electrocardiogram grid[ edit ] ECGs are normally printed on a grid. The horizontal axis represents time and the vertical axis represents voltage. The standard values on this grid are shown in the adjacent image: The "large" box is represented by a heavier line weight than the small boxes. Not all aspects of an ECG rely on precise recordings or having a known scaling of amplitude or time. For example, determining if the tracing is a sinus rhythm only requires feature recognition and matching, and not measurement of amplitudes or times i.
An example to the contrary, the voltage requirements of left ventricular hypertrophy require knowing the grid scale. Rate and rhythm[ edit ] In a normal heart, the heart rate is the rate in which the sinoatrial node depolarizes as it is the source of depolarization of the heart.
Electrocardiography - Wikipedia
Heart rate, like other vital signs like blood pressure and respiratory rate, change with age. In adults, a normal heart rate is between 60 and bpm normocardic where in children it is higher. The movement of these ions inside and across the cell membrane constitutes a flow of electricity that generates the signal on an ECG EKG.
Electrical Events of Depolarization and Repolarization Polarized - Cardiac cells that are in a resting state are negative. The sodium ions are outside of the cell and the potassium ions are inside the cell. Both ions carry a positive charge however; the sodium ion has a stronger charge than the potassium.
Thus the inside of the ion electrically is weaker than the outside so it is negative. The polarized state is a "ready state". When the cell is ready to accept and electrical impulse, a large amount of potassium leaks out. This causes a discharge of electricity. The cell becomes positively charged.
This is called depolarization. The electrical wave then travels from cell to cell throughout the heart.
Now there is cell recovery, sodium and potassium ions are shifted back to their original place by the sodium-potassium pump. This is called repolarization. Cardiac action potential illustrates the changes in the membrane potential of a cardiac cell during depolarization and repolarization.
There a five phases starting with the following: Phase 4 Return to Resting Stage Corresponds to diastole Calcium and sodium remain outside the cell Potassium remains inside the cell During this phase the heart is "polarized" and getting ready for discharge Once another stimuli occurs the cell will reactivate Depolarization Discharge, excited, active stage.
Depolarization of the myofibril releases energy stored in the cell. This energy pulls the "contractile" proteins actin and myosin closer together, thus shortening the myofibril. This action immediately precedes mechanical systole. Repolarization - Recharge, return to the resting stage. This is the longer portion of the action potential.
Energy is reincorporated into the cell to restore the resting transmembane potential. Repolarization of the myofibril is the process that prepares the cell for another action potential and contraction and occurs during mechanical diastole.Cardiac Conduction System and Understanding ECG, Animation.
Absolute Refractory Period During depolarization, the cell cannot accept another stimulus Relative Refractory Period During repolarization the cell may be stimulated by only a strong stimulus Keys to Remember: Depolarization and Repolarization are Electrical Events 3. Contraction and Relaxation are Mechanical Events Properties of the Heart Automaticity is the ability of the heart to initiate an electrical impulse.
The heart can begin and maintain rhythmic activity without the aid of the nervous system. A heart removed from the body has the ability to beat on its own for a limited period of time.
The highest degree of automaticity is found in the pacemaker cells of the sinus node. The atria, atrioventricular AV Node, Bundle of His, bundle branches, Purkinje Fibers, and the ventricular myocardium have a lesser degree of automaticity. Excitability is the ability of the heart to respond to an electrical impulse. A cardiac cell will respond to an electrical stimulus with an abrupt change in its electrical potential.
Each cardiac cell that receives an electrical impulse will change its ionic composition and its respective polarity. Once an electrical potential begins in a cardiac cell it will continue until the entire cell is polarized.
Conductivity is the ability of the heart to conduct an electrical impulse. All areas of the heart appear to depolarize at the same time because a cardiac cell transfers an impulse to a neighboring cell very rapidly. The velocity of the transfer varies in the different cardiac tissues: Conduction System The normal cardiac impulse arises in the specialized pacemaker cells of the SA node, located about 1 mm beneath the right atrial epicardium at its junction with the superior vena cava.
The impulse then spreads over the atrial myocardium to the left atrium via Bachmann's bundle and to the region of the AV node via the anterior, middle, and posterior internodal tracts connecting the sinus and AV nodes.
These represent the usual routes of spread, but are not specialized tracts analogous to the Purkinje system. When the impulse reaches both atria, they depolarize electrically, producing a P wave on the electro cardiogram ECG EKGand then contract mechanically, producing the A wave of the atrial pressure pulse and propelling blood forward into the ventricles. Conduction slows when the impulse reaches the AV node, allowing sufficient time for blood to flow from the atria into the ventricles.
Stimulation of the myocardium causes progressive contraction of the myocardial cells. Therefore, wave deflections correspond to the mechanical events in the cardiac cycle which include contraction and relaxation of the cardiac chambers. Repolarization is only electrical and the heart is at rest.