If the QRS is narrow, the rhythmOften refers to a discernible pattern in time or distance between QRS complexes and/or P waves. originates from a 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 site. Otherwise, if the QRS is wide, chances are, the rhythm is a ventricular rhythmA cardiac rhythm with the impulse originating in the ventricles and an absence of atrial activity (no P waves); heart rate is 20-40/minute; cardiac output is often poor with this slow rate and no atrial kick | cardiac rhythm that....
Remember that the 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 is a two dimensional plotting of voltage (height or amplitudeThe height or depth of waves and complexes of an ECG in millimetres; represents millivolts where 10 mm is 1 millivolt with a properly calibrated monitor. 1. Six Second ECG Guidebook (2012), T Barill, p. 190) over time (width or length). 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... is a representation of ventricular depolarizationThe depolarization of the myocardium is represented on an ECG by a series of waveforms, one for atrial depolarization and soon after a larger waveform for ventricular depolarization. Normal ventricular depolarization begins with the septal fascicle of the left bundle... and to a much lesser extent atrial 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....
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. are rapid when the impulse follows first 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... and then 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.... The bundle branches take the one initiating supraventricular impulse and multiplies it into at least three simultaneous impulses. These impulses follow the right bundle branch (1 or 2 routes to 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...) and the left bundle branch (2 or 3 routes called fascicles to the left ventricleThe left ventricle ejects blood into the aortic arch to the body. Within the arch, the coronary arteries branch off first followed by three main arteries that branch to the brain (carotids) and the upper thorax (subclavian artery). The chambers...). As a result, the one impulse wave across 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 becomes several waves across the ventricle. As a result, both the distance the waves need to travel and the time taken is dramatically decreased.
Supraventricular impulses ride the AutobahnAn electrical wave envelops the ventricles very quickly IF the Bundle Branches and the Purkinje Network are utilized. This is comparable to getting off the back country roads and racing down the freeway. The rapidly conducting bundle branches could be... (the bundle branches) causing rapid ventricular depolarization and a narrow QRS complexA collection of waveforms (i.e. QRS complex and the ECG complex). 1. Six Second ECG Guidebook (2012), T Barill, p. 194. But what of the wide QRS? What causes a QRS to be 3 mm or more in width? In other words, what slows down the depolarization of the ventricles?
IschemiaInsufficient supply of oxygen to meet the oxygen demands of tissue. Anaerobic metabolism becomes increasingly important during periods of ischemia. Ischemia results from an inadequate blood flow that fails to meet the oxygen demands (energy demands) of tissues. If tissues... and sympathetic stimulationIschemia and sympathetic stimulation can enhance a ventricle’s automaticity, stimulating the ventricle to initiate an impulse before a sinus initiated wave reaches the ventricles. This solitary wave doesn’t ride the Autobahn. Rather, this one wave must traverse both ventricles. The... can enhance a ventricle’s automaticityA cardiac cell’s (usually pacemaker cells such as the SA node, AV node or His-Purkinje network) ability to self-initiate an impulse; note that abundant catecholamines and/or ischemia enhances automaticity – non-pacemaker cells may become pacemaker cells. The SA node, usually..., stimulating the ventricle to initiate an impulse before a sinus initiated wave reaches the ventricles. This solitary wave doesn’t ride the Autobahn. Rather, this one wave must traverse both ventricles. The efficient autobahn is not utilized; instead, slower routes cross 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.... As a result, the distance and time taken to depolarize the ventricles are longer. A wide QRS of 3mm or more is produced.
Rhythms that are initiated in the ventricles have wide QRS complexes. A second characteristic of these ventricular rhythms is that 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... is usually (though not always) facing the opposite polarity as the R waveFollowing the depolarization of the interventricular septum, ventricular depolarization then progresses from the endocardium through to the epicardium across both ventricles producing an R wave and an S wave. An R wave is the first positive deflection of the QRS....
A wide QRS complex is produced most often from an impulse that originates from within the ventricles. In fact, a wide QRS has a ventricular origin about 85% of the time in the general population. With those with known coronary arteryMain vessels carrying blood from the heart; the arteries have minimal elasticity and contain approximately 20% of the blood supply. Major Vessels 1. Six Second ECG Guidebook (2012), T Barill, p. 15, 190 disease, tachycardias with wide QRS complexes are indeed ventricular tachycardiaIs a cardiac rhythm characterized by rapidly occurring wide QRS complexes with absent or infrequent P waves evident; the absence of atrial kick, the lack of filling time, and the tendency for ventricular tachycardia to change to ventricular fibrillation makes... almost 95% of the time. As a general rule, if it looks like ventricular tachycardiaA cardiac rhythm with a rate above 100/minute; for example, if the impulse originates from the atria with a rate of 160/minute, the rhythm is called an atrial tachycardia. A cardiac rhythm is usually named first by the location of..., treat it like ventricular tachycardia.
Again, exceptions exist. For about 15% of rhythms with wide QRS complexes, impaired bundle branch conductivityThe ability of a cell to receive and transmit an electrical impulse. 1. Six Second ECG Guidebook (2012), T Barill, p. 194 prolongs ventricular depolarization. Ischemia, infarctionThe necrosis of tissue; acute myocardial infarction involves the acute death of myocardial cells. 1. Six Second ECG Guidebook (2012), T Barill, p. 198, and antiarrythmics can slow or block transmission of an impulse along these bundle branches. The resulting widening of the QRS complex is called aberrant conductionFor about 15% of rhythms with wide QRS complexes, impaired bundle branch conductivity prolongs ventricular depolarization. Ischemia, infarction, and antiarrythmics can slow or block transmission of an impulse along these bundle branches. The resulting widening of the QRS complex is....
Slowed and aberrant ventricular conduction can also occur due to Ashman phenomenonWith premature beats, the His-Purkinje fibers may not completely repolarize before the next wave arrives. The ion channels may not yet be fully operational. The resulting depolarization is slower, as is the conducting impulse resulting in aberrant conduction and a.... With premature beats, the His-Purkinje fibers may not completely repolarize before the next wave arrives. The ion channels may not yet be fully operational. The resulting depolarization is slower as is the conducting impulse resulting in aberrant conduction and a wider QRS. This phenomenon of an aberrantly conducted QRS occurring with premature or early beats is known as Ashman phenomenon.
Supraventricular rhythms with aberrant conduction can be recognized to be supraventricular in origin by the presence of a 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... before each QRS. In other words, a consistent PR intervalThe time and interval measured from the beginning of the P wave to the beginning of the QRS; should be called the PQ interval; normal PR interval is 0.12-0.20 seconds. The PR interval is measured from the start of the... implies a connection or relationship between the ventricles and supraventricular structures. A consistent PR intervalA period measured on rhythm strip paper that measures a wave and a segment; the distance measured is equal to time taken as an ECG is voltage over time; a PR interval for example is measured from the beginning of... is a diagnostic criterion of a supraventricular rhythm.
For faster rhythms, the T wave often overshadows the P wave making P wave detection difficult. Occasionally a P wave notches the T wave. A notched T wave strongly suggests the presence of a P wave.
Bottom line: the impulse for a narrow QRS originates above the ventricles. A wide QRS requires a little more investigative work. A wide QRS is almost always caused by an impulse originating in the ventricles. The presence of a P wave before each wide QRS, though, strongly suggests a supraventricular rhythm with aberrant conduction.
The QRS complex is narrow, meaning that the rhythm originates above the ventricles = supraventricular
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. 110