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ECG Basics

ECG Basics: Second-degree AV Block With Characteristics of Type I and Type II

Thu, 09/01/2016 - 11:51 -- Dawn

This strip shows a second-degree AV block.  During most of the strip, 2:1 conduction is present.  At the beginning, however, two consecutive p waves are conducted, revealing progressive prolongation of the PR interval.  This usually represents a Type I , or nodal, block:  progressive refractoriness of the AV node.   However, the wide QRS ( possibly left bundle branch block), and the fact that the non-conducted p waves are "out in the open" where they should have conducted, points to Type II - an intermittant tri-fascicular block. Wenckebach periods in patients with LBBB can be caused by progressive conduction delay in the right bundle branch.

ECG Basics: Sinus Bradycardia

Sat, 08/13/2016 - 23:56 -- Dawn

Sinus bradycardia.  This strip meets the criteria of:  regular rhythm, rate less than 60 bpm (40 bpm in this case), regular P waves before every QRS.  Sinus bradycardia can have many causes from a completely normal variation to a malfunction of the sinus node.  In some cases, enhanced parasympathetic tone causes sinus bradycardia.  Well-conditioned athletes typically have sinus bradycardia. Treatment depends upon the cause and the patient's response to the rate.  If the rate does not cause hemodynamic impairment, treatment may not be necessary.

ECG Basics: Sinus Tachycardia, Peaked T Waves, and Baseline Artifact

Sun, 03/13/2016 - 21:45 -- Dawn

This strip offers several good teaching opportunities.  If it were a 12-lead ECG, no doubt it would be a bonanza!  First, there is sinus tachycardia at a rate of about 138 per minute.  The P waves are all alike and regular.  The T waves are tall and narrow, with a sharp peak.  This is often a transient sign of hyperkalemia, and should be investigated with serum electrolyte tests and with a 12-lead ECG.  In addition, the baseline shows a wandering type of artifact.  This is due to the patient's deep breathing, and the fact that the arm electrodes were placed on the chest.  This patient was a diabetic in ketoacidosis with hyperkalemia. 

ECG Basics: Retrograde P Waves

Wed, 03/02/2016 - 23:04 -- Dawn

This Lead II rhythm strip is from a nine-year-old girl being monitored for an outpatient surgical procedure.  She has no known heart disease.  Her heart rate is 110 per minute.  The PR interval is .12 seconds (120 ms), the QRS is upright and narrow at .06 seconds (60 ms), and the rhythm is regular.

The most noticeable abnormality here is the RETROGRADE P WAVES.  In Lead II, normal P waves are upright.  In this case, the rhythm is being initiated in the lower atria, or possibly in the AV junction.  The impulse is traveling backward, or in a retrograde fashion, toward the SA node.  The electrical impulse travels forward, or in an antegrade direction, to produce a NORMAL QRS complex.  Retrograde P waves that are very close to the QRS, or within it, are presumed to occur from a junctional rhythm, as the impulse leaves the ectopic pacemaker and travels forward and backward at the same time.  When a normal PR interval is present, it is probably more likely that the impulse originated in the lower atrial tissue, and is delayed as it travels through the AV node.

This ECG abnormality is probably of no clinical significance in a healthy child, but should be worked up in a child with cardiac symptoms or complaints.  This strip is a very good one for illustrating retrograde and antegrade conduction to beginning students.

ECG Basics: Atrial Fibrillation With A Rapid Ventricular Response

Fri, 12/18/2015 - 23:11 -- Dawn

This ECG rhythm strip has all the hallmarks of atrial fibrillation:  the rhythm is irregularly irregular and there are no P waves.  The rate is about 150 beats per minute. There is no P wave because the atria are being irregularly depolarized by many ectopic pacemakers at once, causing the atria to "quiver".  This patient has new-onset atrial fib, and has been medicated with a calcium channel blocker.  The rate shows signs of slowing, but has not reached the target rate for this patient of less than 80 bpm.

At the onset of atrial fib, the rate is usually fast, because the AV node is being bombarded by numerous impulses from the atria.  The impulses arrive irregularly, and with different "strengths".  The AV node conducts as many impulses as it is able to, usually resulting in a rate over 110-120 bpm.  Medications can affect the rate, of course, and we use medications to slow AV conduction and allow a more normal heart rate.  

There are many methods of correcting atrial fib, not always with permanent success. Some patients tolerate this rhythm well as long as the rate is kept in check.  But others suffer a loss of cardiac output due to the loss of "atrial kick", which is the forceful filling of the ventricles by the contracting atria.  This loss of cardiac output can severely impair some people, making it necessary to try to convert the atrial fibrillation.  In addition, people living with atrial fib must be anticoagulated, as the loss of forceful emptying of the atria can cause collections of blood clots which can break free and embolize.

ECG Basics: Atrial Flutter With 2:1 Conduction And An Aberrantly-conducted Beat

Sun, 08/23/2015 - 12:20 -- Dawn

This strip was taken from a patient at rest.  It shows a regular tachycardia with a slightly-widened QRS complex at about .10 seconds duration.  It is somewhat difficult to evaluate the baseline for P waves or flutter waves.  We ALWAYS recommend multi-lead assessment for such evaluation.  The P waves (or flutter waves) here have a sharp point, and can be easily "marched out", with a rate of about 300 per minute.

Whenever the ventricular rate is near 150/min., we should always consider the possibility of atrial flutter with 2:1 conduction.  Since atrial flutter results in atrial depolarization at around 250 - 350 per minute, conducting every other P wave results in a rate of about 150.  It can masquerade as sinus tach, but a patient with sinus tach at such a fast rate would probably have an obvious cause for a rapid heart rate, such as hypovolemia, drug overdose, or exertion.  This rhythm could also be mistaken for atrial tachycardia or other forms of supraventricular tachycardia (SVT, PSVT, AVNRT, etc.).   Multiple leads can more easily uncover the flutter waves running continuously "behind" and "through" the QRS complexes.

There is one beat that is obviously different from the others.  This beat is about the same width as the other QRS complexes, but is opposite in direction.  This probably represents aberrant conduction, possibly a hemiblock that occurs only in this beat.  Careful measurement will show that this QRS is very slightly early, while the others are all very regular. The slight width of all the QRS complexes suggests that there is a conduction delay, which cannot be diagnosed on one strip with no patient history available.

There are other differential diagnoses, such as ventricular tachycardia with a captured sinus beat.  We welcome discussion of this interesting strip. 

ECG Basics: Atrial Fibrillation With a Rapid Ventricular Response

Sun, 07/26/2015 - 13:54 -- Dawn

This rhythm strip is recorded in two simultaneous leads, which is always preferable to one single lead.  It is a good example of atrial fibrillation with a rapid ventricular response.  Atrial fib that has not been treated will usually have a rapid ventricular rate.  This reflects the ability of the AV node to conduct a tachycardia, within limits.  The natural slow conduction of the AV node allows it to act as a "filter", preventing the huge numbers of impulses generated by the atrial fibrillation from reaching the ventricles.  In this case, about 140 beats per minute are able to make it through the AV node into the ventricles.   In some patients, preexisting cardiac conditions such as valve insufficiency or CHF may make this rate dangerous for the patient.  The rate may lower cardiac output in some people, and this must be considered in light of the fact that the loss of P waves in atrial fib also lowers cardiac output significantly.

ECG Basics: Sinus Rhythm With Ventricular Bigeminy

Tue, 07/07/2015 - 15:03 -- Dawn

This rhythm strip offers two leads taken at the same time, Lead II and Lead V1.  The Lead II strip may not look "typical" to a beginning student, because the sinus beats are very small and biphasic.  This is due to an axis shift, which cannot be evaluated without more leads.

One of the best teaching opportunities in this strip is the concept of "underlying rhythm" with ectopy.  The underlying rhythm here is sinus.  But there are sinus P waves which are hidden, making the sinus rate twice what it appears to be.  The P waves are invisible in the Lead II strip, with baseline artifact making them even harder to see.  But in V1, we are able to find them at the end of the PVCs' T waves.  The sinus rhythm is a bit irregular toward the end of the strip.  There are probably many things a more advanced practitioner could say about this strip, but it usually requires more than one or two leads to do a complete evaluation.  For your basic student, it is a good example of sinus rhythm with ventricular bigeminy.

ECG Basics: Sinus Tachycardia

Wed, 06/10/2015 - 20:53 -- Dawn

This is a good teaching strip on many levels.  At the BASIC level, we see a strip that clearly meets all the criteria for sinus tachycardia:  a regular rhythm over 100/min. with P waves that look normal and all look alike.  The rate is 110 per minute.  The PR interval is just at the upper limits of normal at .20 second, or 200 ms.  The QRS complex is within normal limits, but slightly wide at .10 seconds.

This strip is good for teaching rate determination by several different methods.  It is helpful that QRS complexes 1, 5, and 10 fall on the dark lines of the paper.

This is a Lead II rhythm strip, and it is helpful to show students that not ALL Lead II strips produce an upright QRS complex.  Of course, correct lead placement should be confirmed.  In this particular case, the patient had suffered an anterior - septal wall M.I., and has a left anterior hemiblock, also called left anterior fascicular block.  This shifts the frontal plane axis to the left, causing Lead II to have a negative QRS.  Axis can't be accurately determined from one lead, but axis shift explains the negative QRS in this strip.

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