Displaying 21 - 30 of 69
Dawn's picture

ECG Basics: Sinus Tachycardia vs. PSVT

Submitted by Dawn on Thu, 04/21/2016 - 00:13

Narrow-complex tachycardias can be very confusing to students of basic-level ECG.  There are very many rhythms that fall into the broad category of narrow-complex tachycardia.  We usually further divide them into sinus tachycardia and other "supraventricular tachycardias".  The basic student will want to make this distinction, as well as be able to differentiate atrial fib and atrial flutter from the other SVTs.  The more advanced student will want to go into more detail about which mechanism for supraventricular tachycardia is present.

Just the basics, please.   When the tachycardia is regular, it is most important to determine whether it is a SINUS TACHYCARDIA or a SUPRAVENTRICULAR TACHYCARDIA.  (Yes, we are aware that sinus rhythms are supraventricular, but the term "supraventricular tachycardia" or "SVT" is usually reserved for the fast, regular rhythms that are not sinus.)  So, what clues will be most helpful to our beginner students?

Rate    SVTs tend to be faster than sinus tachycardia.  More importantly, they are fast regardless of the patient's situation.  Sinus tachycardia almost always is reacting to the patient's situation.  For instance, a 22-year-old woman resting in a chair with a heart rate of 150 is likely to have an SVT.  A 22-year-old woman who is running in a 10 k marathon race and has a heart rate of 160 is responding appropriately to an increased need for oxygen and nutrients to her cells. Sinus tachycardia will ususally be 160 or less, and have an obvious reason for being, such as fever, pain, anxiety, exercise, hypovolemia, hypoxia, or drugs.  Unfortunately, many beginning students are told that any narrow-complex tachycardia with a rate of 150 or less is sinus, and over 150 is SVT. While they may be right most of the time, or on the written test they are about to take, this rule should not be applied in "real life".  Sinus rhythms can go over 150, and SVTs can be slower than 150.  So, what other clues should we be teaching beginners?

Consider the clinical situation    Look for an obvious cause for sinus tachycardia.  If none is found, strongly consider SVT.  Remember that pediatric patients have faster heart rates, especially infants.  If the strip is on a test, with no clinical information, consider these:

Dawn's picture

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

Submitted by Dawn on Sun, 03/13/2016 - 21:45

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. 

Dawn's picture

ECG Basics: Atrial Fibrillation With A Rapid Ventricular Response

Submitted by Dawn on Fri, 12/18/2015 - 23:11

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.

Dawn's picture

ECG Basics: Third-degree AV Block, Complete Heart Block

Submitted by Dawn on Wed, 11/18/2015 - 12:31

This rhythm strip shows third-degree AV block, also called complete heart block or complete AV block.  The P waves are from the sinus node, and are regular at a rate of about 120/min. (Sinus tachycardia). This is a good strip for showing your students how to "march out" the P waves to find the ones that are hidden behind QRS complexes or T waves. Knowing that the P waves are regular, it is easy to find the hidden ones.

The QRS complexes are wide at 0.14 seconds, and regular, with a rate of about 28/min.  On first glance, it APPEARS that there are PR intervals.  That is, it appears that some of the P waves are conducting. If you measure the PR intervals carefully, you will note that they are NOT equal.  There is no connection between the P waves and the QRS complexes - this strip has just caught them near each other.  If we ran the strip longer, we would see the PR intervals "come apart", proving they are not real.  The QRS complexes are coming from an IDIOVENTRICULAR ESCAPE RHYTHM.  They are regular, wide, have no P waves associated with them, and the rate is below 40 bpm.

Patients with CHB that results in a very slow heart rate sometimes need emergency treatment aimed at increasing the rate.  When the escape rhythm is idioventricular, it is assumed that the AV block is located below the AV node, and emergency temporary pacing is often the method of choice.  In fact, a permanent implanted pacemaker is almost always needed.  When the AV block is located in the AV node, the escape rhythm will be junctional (narrow QRS complexes, rate about 40-60 bpm).     

 

Dawn's picture

ECG Basics: Retrograde P Waves

Submitted by Dawn on Tue, 10/20/2015 - 22:28

This Lead II rhythm strip shows a regular rhythm with narrow QRS complexes and retrograde P waves.  The strip was taken from a nine-year-old girl.  The rate is about 110 per minute and the PR interval is .12 seconds (120 ms).

When retrograde conduction is seen in the atria, it is often assumed that the rhythm is originating in the junction.  When a junctional pacemaker is initiating the rhythm, the atria and ventricles are depolarized almost simultaneously.  This can produce a P wave in front of the QRS with a short PR interval, during the QRS, or after the QRS.  Sometimes, in junctional rhythm, a block prevents the impulse from entering the atria, producing NO P wave.  Junctional rhythms are usually slow "escape" rhythms, but can be accelerated or tachycardic.

The fact that this rate is 110 / minute and the PR interval is normal at .12 seconds, we should consider that this rhythm could also be from an ectopic pacemaker low in the atria.  From this low starting point, the impulse will travel backward, in a "retrograde" fashion, through the atria, producing a negatively-deflected P wave in Lead II.

We do not have clinical data on this patient, and so do not know what possible causes of arrhythmia might be present, and what the expected rate should be in this situation.  

Dawn's picture

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

Submitted by Dawn on Sun, 08/23/2015 - 12:20

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. 

Dawn's picture

ECG Basics: Atrial Fibrillation With a Rapid Ventricular Response

Submitted by Dawn on Sun, 07/26/2015 - 13:54

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.

Dawn's picture

ECG Basics: Sinus Rhythm With Ventricular Bigeminy

Submitted by Dawn on Tue, 07/07/2015 - 15:03

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.

Dawn's picture

ECG Basics: Sinus Tachycardia

Submitted by Dawn on Wed, 06/10/2015 - 20:53

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.

Dawn's picture

ECG Basics: Atrial Fibrillation With Complete AV Block

Submitted by Dawn on Tue, 05/19/2015 - 11:41

This patient has an underlying atrial fibrillation with complete heart block and an idioventricular escape rhythm.  She was treated successfully with a permanent implanted pacemaker.

Pages

All our content is FREE & COPYRIGHT FREE for non-commercial use

Please be courteous and leave any watermark or author attribution on content you reproduce.