ECG Guru - Instructor Resources

A gathering place for instructors of ECG and cardiac topics.


Subscribe to me on YouTube

Fusion beats

Sinus Rhythm With Ectopy

Thu, 08/06/2015 - 20:56 -- Dawn

We originally published this ECG in 2012.  It was generously donated to the ECG Guru website by our friend and ECG Guru Extraordinaire, Jason Roediger.  We are re-publishing it today, as it is a great ECG for illustrating how helpful laddergrams can be for showing conduction in dysrhythmias.

This ECG has something for everyone:  The rhythm is sinus, and there is a non-conducted PAC (beat number 3) after the second beat.  Just after the next P wave, there is a ventricular escape beat which prevents that P wave from making a QRS.  The eighth beat is a PVC.  The eleventh is a conducted PAC.  You can use this ECG to illustrate for your students the concepts of "escape" beats, refractory periods, and premature beats.

There are ST changes that suggest coronary artery disease: the ST segments are flat in shape with a tiny amount of elevation in V1 through V4.  The axis is normal, at the border of normal and left axis. It is difficult to see, but there appears to be a tiny r wave in Lead III, so we cannot say for sure if there is or was a pathological Q wave in that lead.

The P waves are wide and "double" in Lead II and biphasic in V1, suggesting LV failure or mitral valve disease.  However, the criteria for LV hypertrophy are not met.

ECG Basics: Paroxysmal Supraventricular Tachycardia Treated With Adenosine

Sun, 12/28/2014 - 17:43 -- Dawn

This series of ECG rhythm strips shows a paroxysmal supraventricular tachycardia successfully treated with adenosine.  The patient was complaining of a rapid heart rate and palpitations, but was hemodynamically stable.  It is not known whether any parasympathetic stimulation, such as a Valsalva maneuver or carotid sinus massage, was used initially.   

The first rhythm strip shows a PSVT, presumably AV nodal reentrant tachycardia, at a rate of about 215 per minute.  (We originally indicated a rate of 240 per minute, but this was a typo). Using the simplist method of determining rate, the six-second method, we see 21, but almost 22, QRS complexes in six seconds. Differential diagnosis would include sinus tachycardia, but this rate is too fast for sinus tach, especially in a resting patient.  Also, sinus tach would slow down as the patient is rested or made more comfortable, and this rate did not vary.  Also, when confronted with a supraventricular tachycardia, one should also consider atrial flutter and atrial fibrillation.  This is somewhat slow for atrial flutter with 1:1 conduction, and that rhythm is much more rare than AVNRT. It is too regular for atrial fibrillation.  So, we are left with the probable diagnosis of paroxysmal supraventricular tachycardia.  The “paroxysmal” part is presumed since AVNRT has an abrupt onset, and the patient’s symptoms started suddenly. 

The second rhythm strip shows what happened after adenosine was administered.  The patient received first a 6 mg dose, rapid IV push.  When that was not effective, he received 12 mg rapid IV push.  The rhythm strip is typical of the first minute or so after adenosine administration.  Adenosine can cause transient AV blocks, escape rhythms, and ectopic irritability.  The half-life of adenosine is only 6 seconds, so the dysrhythmias and uncomfortable symptoms are short-lived.  In this strip, we see frequent PVCs and runs of V tach.  

Wide Complex Tachycardia

Sat, 09/06/2014 - 15:03 -- Dawn

Wide-QRS rhythms can be difficult to diagnose from the ECG alone.  This difficulty is compounded when the rate is fast, as it can be hard to determine if P waves are present before the QRSs, or dissociated, or absent.

This ECG and rhythm strip were donated to the ECG Guru by Ryan Cihowiak.  We don't have clinical information on the patient, unfortunately.  It is a great example, however, of how difficult WCT can be to diagnose.

In the 12-Lead ECG, we see wide QRS complexes that are regular at a rate of 131 / minute. There are no obvious P waves before the QRS complexes, and no obvious distortion of the T waves, which would suggest a "hidden" P wave.  Unfortunately, there is significant artifact, which makes searching for P waves difficult.  The pattern overall suggests left bundle branch block, with the negative QRS in Lead V1 and positive QRS complexes in Leads I and V6.  However, one requirement for the diagnosis of LBBB is a supraventricular rhythm, and P waves are the best indicator of that.  An irregularly-irregular rhythm, indicating atrial fib, would also have made LBBB more likely.  In typical LBBB, the frontal plane axis is usually left-normal or left.  In this ECG, Lead III is taller than Lead I, putting the axis within normal range, but slightly rightward.

The rhythm strip uncovers something else.  Possible P waves are seen in some of the ST segments (arrows).  Are these dissociated?  Do they represent a first-degree AV block?  Are they actually artifact?  If this is a supraventricular rhythm, there is LBBB.   Then, notice beats #7,8,9.  If this rhythm is supraventricular (with LBBB), those must be a salvo of V Tach.  But, one of the possible P waves occurs in front of beat #7.

Another possibility is Right Ventricular Outflow Tract Tachycardia.  RVOT is a type of V Tach that typically has a LBBB pattern, with a slightly rightward axis.  If this is the case, beats #7,8,9 are probably "capture" beats or "fusion" beats.  Capture and fusion beats "prove" that the underlying tachycardia is ventricular, since, by definition, capture and fusion represent a return to supraventricular control of the rhythm.

ECG Basics: Paroxysmal Supraventricular Tachycardia Converted With Adenosine

Mon, 10/28/2013 - 20:15 -- Dawn

Today, you get THREE strips for your basic classes!  The first shows a PSVT - paroxysmal supraventricular tachycardia at a rate of about 220/minute.  The QRS complexes are narrow, and the rhythm is regular.  In the second strip, we see the moment of conversion after a dose of 6 mg. of adenosine was administered by rapid I.V. infusion.  The re-entry cycle is broken, and the patient experiences many PVCs, including groups of two, three, and even four in a row.  Soon, however, the rhythm settles into sinus rhythm with PACs, and later, just sinus rhythm (not shown).  For your more advanced students, the second strip shows the PVCs interacting with the underlying sinus rhythm.  There are several fusion beats with varying degrees of fusion, and one can sometimes see a sinus P wave just before a PVC.  None of this is clinically significant in this patient, because the ventricular ectopy was a side effect of the treatment, and was self-limited.  It is a great strip for teaching, though! 

Sinus Rhythm With Left Bundle Branch Block, PVCs, and Fusion Beats

Sun, 02/03/2013 - 23:19 -- Dawn


This is a great ECG for teaching your students about some of the different causes of wide QRS.  This 89 year old man has a sinus rhythm that is around 100 bpm, and his QRS is widened at 148 ms (.148 sec).  Leads I and V6 are positive, and Lead V1 is negative, meeting the criteria for left bundle branch block. There is a left axis deviation, which is common with LBBB, although it is not always this pronounced, indicating that there is possibly another cause for LAD.  In this ECG, there are also PVCs and probable fusion beats.  The 14th beat is a PVC.  Complexes 1, 6, and 9 are possibly fusion beats. Fusion can be described as an almost simultaneous sinus beat and ventricular beat.  The depolarization waves, one coming from the top of the heart and one coming from the bottom, meet and "fuse" on the ECG.  Fusion beats will have some characteristics of the supraventricular beats and some of the ventricular beats.  They are not significant except that fusion can be said to "prove" the existence of a ventricular pacemaker - either a natural pacemaker or an electronic one.

Do you see anything else interesting in this ECG?  How would YOU describe this rhythm?  Please do not hesitate to add your comments, or ask questions of the experts who contribute to this site.  We will respond quickly to all questions.

Wide-Complex Tachycardia Converted by Adenosine

Mon, 08/13/2012 - 13:58 -- Dawn

This ECG was presented earlier this week as an example of SVT with LBBB aberrancy, which was ultimately converted with one dose of adenosine in the Emergency Department.  It is the most shared and commented on ECG yet to appear on the Guru.  The diagnosis given was the one accepted by the medical staff who cared for the patient, who was a man in his 30's who presented to the Emergency Department complaining of a rapid heart rate.  He was ambulatory with stable vital signs, in spite of the tachycardia. He reported that he has had several episodes of fast heart rate which responded to either Valsalva maneuvers or, in some cases, medication in the ED.  He was told he might benefit from an ablation procedure, but he did not have health insurance and continued to use the ED as his primary source of medical care.  When he was admitted to the ED, the tech initially called for help, thinking the monitor showed ventricular tachycardia.  The ED physician felt that this represented LBBB aberrancy, possibly rate-dependent, and he treated the patient with adenosine.  The rhythm converted to sinus after one dose, and the patient remained stable throughout the process.  He was advised to undergo further observation and testing, but he declined due to financial concerns, and the fact that he usually succeeded in relieving his symptoms with "bearing down".  

Wide-complex tachycardias can be difficult to assess simply from an ECG. The patient's stability depends more upon general health and cardiac output issues than the origin of the tachycardia.  When we presented this ECG, we also presented the diagnosis he had upon discharge from the ED.

Subsequently, ECG Guru Dr. Ken Grauer, a frequent contributer to this site, offered his alternative diagnosis and his explanation of why he believes this to be v tach.  Other well-respected ECG experts have also questioned the original diagnosis.  Please refer to the comments below for this very helpful explanation.  Unfortunately, this patient is lost to followup, as this incident occurred some time ago.

WTCs remain a most fascinating topic, especially for those who enjoy "detective work".  We thank Dr. Grauer, Tom Bouthillet, and others for their contributions to the ECG Guru on this topic.

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.

Subscribe to RSS - Fusion beats