The AV Node is just above, but continuous with, a specialized conduction system that distributes depolarization to the ventricles very efficiently.
Atrial contraction forces blood through the sricuspid valve into the right ventricle, which pumps it into the lungs. Tricuspid is right side. The right side of the heart right atrium and right ventricle receives under-oxygenated venous blood from all over the body, and pumps it into the. Remember, both atria contract simultaneously, and also both ventricles contract together. However, the right and left sides of the heart have different responsibilities. The powerful left ventricle, in turn, pumps blood through the aorta to all areas of the body NG?!
Mitral is left side. The left atrium contracts, forcing oxygenated blood through the valve into the left ventricle. That's too easy! Chapter 1: Basie Principles 19 depolarization slows down When the wave of atrial depolarization enters the AV Node, depolarization slows, producing a brief pause, thus allowing time for the blood in the atria to enter the ventricles.
OF course you remember that the AV Node is the only electrical conduction pathway between the atria and the ventricles.
Because depolarization slows within the AV Node, there is a brief delay or before pause depolarization is conducted to the ventricles. At this point, we are correlating electrical activity with mechanical physiology. The atria contract, forcing blood through the AV valves, but it takes a little time for the blood to flow through the valves into the ventricles hence the necessary pause that produces a short piece of flat baseline after each P wave on the EKG.
Please review the illustration again. Bundle Depolarization shoots rapidly through the His Bundle and the Bundle Branches and their subdivisions, so depolarization is quickly distributed to the myocytes of the. The ventricular conduction system originates at the His Bundle, which penetrates the AV valves, then immediately bifurcates in the interventricular septum into the Right and Left Bundle Branches.
Not so! Chapter I: Basic Principles 21 QRS complex terminal filaments of the Purkinje fibers terminal filaments of the Purkinje fibers rapidly distribute depolarization to the sentricular myocytes, Depolarization of the entire ventricular myocardium produces QRS complex on EKG. The ventricular conduction system is composed of bundles of rapidly-conducting Purkinje fibers that carry depolarization away from the AV Node at high speed. The Purkinje fibers terminate in tiny filaments that directly depolarize the ventricular myocytes.
The terminal filaments of the Purkinje fibers spread out just beneath the endocardium that lines both ventricular cavities, therefore ventricular depolarization begins at the lining and proceeds toward the outside surface epicardium of the ventricles. The Purkinje fibers branch and subdivide just beneath the endocardial lining, but they really do not penetrate into the myocardium.
The terminal filaments of the Purkinje fibers depolarize the ventricular myocardium, initiating ventricular contraction while inscribing a QRS complex on EKG. The terminal filaments of the Purkinje fibers rapidly conduct to the myocytes that lie just beneath the depolarization the endocardial lining of both ventricles.
Remember, the entire ventricular conduction system, i. The physical event of ventricular contraction actually lasts longer than the QRS complex, but we will still consider the QRS complex as generally representing the occurrence of ventricular contraction. So the QRS complex is an electrocardiographic recording of ventricular depolarization, which causes ventricular contraction.
Still with me? An upward wave is always called an R wave. Distinguishing between the downward Q and downward S waves really depends on whether the downward wave occurs before or after the R wave. The Qoceurs before the R wave, and the S wave follows the R. Just remember your alphabet. Because there is no upward wave, we cannot determine whether number 4 is a Q wave or an S wave.
The horizontal segment of baseline that follows the QRS complex is known as the segment. ST After the QRS there is a segment of horizontal baseline, followed by a broad hump called the wave. T Noi! The ST segment is horizontal, flat, and most importantly, it is normally level with other areas of the baseline. If the ST segment is elevated or depressed beyond the normal baseline level, this is usually an sign of serious pathology that may indicate imminent problems.
Ventricular repolarization is rather minimal during the ST segment. So ventricular contraction systole spans depolarization and repolarization of the ventricles, This is a convenient physiological marker. The QT interval represents the duration of ventricular and is measured from the beginning of the systole QRS until the end of the T wave.
The QT interval is a good indicator of repolarization, since repolarization comprises most of the QT interval. With rapid heart rates both depolarization and repolarization occur faster for greater efficiency, so the QT interval varies with heart rate. Precise QT interval measurements are corrected for rate, so they are called QTc values. As a simple rule of thumb, the QT interval is considered normal when it is less than half of the R-to-R interval at normal rates.
So, block of one Bundle Branch with intermittent K of the other produces intermittent complete AV block, intermittent Mobitz. The intermittent block may worsen, entuating in a constant complete AV block. All web sites offer free. It has been recommended by cardiologists as they have been using it for reference and teaching for years. The reader's rapid assimilation of medical concepts is the key to the continuing success of this best-selling book. A caption explains the concept illustrated on each page, and a few simple sentences reinforce the concept with interactive programmed learning, which links to the following page.
Dr Dubin's light and entertaining style, known world-wide, makes learning enjoyable. Practice twelve-lead tracings at the end establish self-confidence, and summarised reference sheets with examples designed to be copied provide an excellent review.
ISBN Yale Daily News. Associated Press. Archived from the original on 9 February Retrieved 11 April Cover Publishing Company. Understanding Cardio-pulmonary Resuscitation.
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