ECGElectrocardiogram; also called an EKG; a representation of electrical voltage measured across the chest over a period of time. 1. Six Second ECG Guidebook (2012), T Barill, p. 196 interpretation relies heavily on the QRS complexThe electrical representation of ventricular depolarization; the atrial repolarization is also a part of the QRS. ECG interpretation relies heavily on the QRS complex. The QRS complex represents the depolarization of the ventricles. The repolarization of the atria is also.... The QRS complexA collection of waveforms (i.e. QRS complex and the ECG complex). 1. Six Second ECG Guidebook (2012), T Barill, p. 194 represents the depolarizationThe rapid influx of positive ions (sodium and/or calcium) into a cell – depolarization is necessary for contraction to occur. A depolarizing wave moves through the myocardium on average along a trajectory or vector. A vector is a force moving... of the ventriclesThe larger chambers of the heart (3 times the volume and muscle thickness than the atria), responsible for the pumping of blood to the lungs and the rest of the body.. The repolarizationFollows depolarization, involving the return to a pre-depolarization state; the myocardial cell’s electrical potential returns from +30 mV to its polarized state of –90 mV; the ions potassium, calcium and sodium are largely involved; note that contraction of the myocardial... of the atriaRight and left atria (1/3 volume and muscle mass of the ventricles) pump blood to the ventricles. Chambers and Layers of the Heart 1. Six Second ECG Guidebook (2012), T Barill, p. 190 is also buried in the QRS complex.
While the direction of the QRS complex is generally not important with basic ECG interpretation, the width of the QRS complex is key. The width of the QRS complex often indicates the location of the originating electrical impulse. This is a rather important point since the first and foremost word of an ECG interpretation is the location of impulse initiation.
A QRS complex is produced from an electrical wave of depolarization across the ventricular myocardiumThe muscle layer of the heart; the middle layer that is responsible for contraction of the heart. The muscular myocardium is the thickest layer and the workhorse of the heart. It is composed of specialized muscle and electrical cells that.... The time taken for the QRS offers insight to the location of the originating impulse.
A normal QRS is .10 seconds or less (2.5 mm or less in width).
The narrower a QRS, the quicker the wave of depolarization crosses the ventricles. This rapid wave is accomplished with the help of 4 rapid waves travelling from the bundle branchesThe bundle of His terminates in the right and left bundle branches, insulated rapidly conducting electrical pathways that connect with the Purkinje network and thus begin depolarizing waves across the ventricles; the left bundle branch splits into three smaller branches... (right bundle branch, left bundle branch – splitting into the septal fascicleNormal ventricular depolarization begins with the septal fascicle of the left bundle branch (causing a Q wave) followed by a simultaneous depolarization of the remaining ventricular walls via the right and left bundle branches. The left bundle branch splits into..., anterior fascicleThe left bundle branch splits into the septal, anterior and posterior fascicles. Normal ventricular depolarization begins with the septal fascicle of the left bundle branch (causing a Q wave) followed by a simultaneous depolarization of the remaining ventricular walls via... and posterior fascicleNormal ventricular depolarization begins with the septal fascicle of the left bundle branch (causing a Q wave) followed by a simultaneous depolarization of the remaining ventricular walls via the right and left bundle branches. The left bundle branch splits into...). The waves move into the myocardium via the Purkinje networkA matrix of fibres located throughout the myocardium that connects the impulse from the bundle branches to the myocardial tissue. The bundle branches and the Purkinje network facilitate rapid depolarization throughout the ventricles. The Purkinje network also creates a typical....
When one or more of the waves from the bundle branches are not utilized, the time taken to cross the ventricles is longer – less waves, more distance for each remaining wave to travel. For example, with a right bundle branch blockA bundle branch block must satisfy two criteria - a wide QRS complex and a notch in the QRS complex. To distinguish between a RBBB and a LBBB, first make certain that the rhythm is indeed supraventricular (P waves before..., the remaining 3 waves would also need to extend their reach to captureEffective depolarization of the atria and/or the ventricles by an artificial pacemaker. An electronic pacemaker, or just pacemaker, delivers electrical current to the heart to stimulate depolarization. Pacemaker leads may connect with ventricular tissue and/or atrial tissue (permanent or transvenous... the right ventricleThe right ventricle ejects blood through the main branches of the left and right pulmonary arteries to the lungs. The chambers of the heart are the main drivers within an intricate pathway, delivering blood to the lungs for gas exchange..., which is normally depolarized with the help of the right bundle branch. With more distance per wave, the time of depolarization is extended to yield a wider QRS than normal (when all 4 waves are in use). A QRS of .12 seconds or longer is a wide QRS.
Consider impulses that begin in the myocardium (i.e PVCA wide QRS complex that arrives early is called a premature ventricular complex (PVC). A PVC has a width of 0.12 seconds or longer. The elongated period of ventricular depolarization is caused by an abnormal, less efficient pathway of ventricular...). Without the advantage of the 4 possible waves attributed to the bundle branches, the single wave would need to fully cross the ventricles. The distance taken would be significantly more than 4 waves sharing the distance. A wide QRS results.
A narrow QRS makes use of all 4 waves for a rapid depolarization. To engage all 4 waves, the impulse would need to begin at above the ventricles (sinus node, atria, AV nodeIs located in the inferior aspect of the right atria; functions to slow the conduction speed to allow for atrial conduction prior to ventricular conduction (atrial kick); also serves as a pacemaker if the SA node fails to fire. The..., or bundle of HisPart of the AV junction, the bundle of His conducts the impulse through the fibrous plate that separates the atria and the ventricle; the bundle of His is also a pacemaker, firing at 40-60/minute. The bundle of His serves as... – supraventricularLocated above the ventricle – includes the bundle of His, AV node, atria and the SA node. 1. Six Second ECG Guidebook (2012), T Barill, p. 206).
A wide QRS can be produced by impulses that originate in the ventricles (most common with a wide QRS) or that originate supraventricular with a bundle branch blockSince the bundle branches are insulated – they are encapsulated with a fibrous sheath – an obstacle to conduction in any bundle (i.e. ischemia or infarct) results in the impulse not carried through to the ventricle; as a result, the... (less common cause of a wide QRS – about 15%).
Since a wide QRS can result from either a ventricular originated impulse or a supraventricular impulse with a bundle branch block (other causes too i.e. ventricular hypertrophyVentricular hypertrophy is reflected in QRS axis deviation towards the hypertrophied ventricle, increased amplitude in the QRS complex, altered R wave progression, and possibly signs of ventricular strain - ST depression and T wave inversion. Note that ST changes can...), you can differentiate between them with the tell tale sign of most supraventricular rhythms – P wavesA wave generated from the depolarization of the atria; the P wave is upright when originating from the SA node. The P wave represents the depolarization of the right and left atria. The P wave begins with the first deviation... present before each QRS (step 3).
Figure 4.13 depicts the component parts of the QRS complex. The QRS complex consists of a series of waves, the ‘Q’, ‘R’, and ‘S’ waves. The ‘Q’ wave is the first negative deflection from baselineThe baseline or isoelectric line is a reference point for the waves, intervals and segments. While the PR segment is often used as the baseline, the TP segment - between the end of the T wave and the beginning of.... The ‘R’ wave is the first positive deflection above baseline. The ‘S’ wave follows the ‘R’ wave with a negative deflection. A QRS complex may or may not have all three waveforms. The ST segmentSegment (line) between the end of the QRS complex and the beginning of the T wave; the end of the QRS is marked by the J point. Between the QRS complex and the T wave, lies the ST segment. The... begins at the J pointA small notch in the QRS where the ST segment begins. The point where the S Wave ends and begins to flatten out. Figure 4.13 The QRS Complex, ST Segment and the T Wave Figure 4.13 depicts the component parts... and continues to the beginning of the T waveThe wave that arrives after the QRS; is a graphical presentation of ventricular repolarization. Expect a T wave to follow every QRS complex. The T wave is a graphic representation of the repolarization of the ventricle. The T wave is....
1. Six Second ECG GuidebookA Practice Guide to Basic and 12 Lead ECG Interpretation, written by Tracy Barill, 2012 Introduction The ability to correctly interpret an electrocardiogram (ECG), be it a simple six second strip or a 12 lead ECG, is a vital skill... (2012), T Barill, p. 83