ECG Guru - Instructor Resources

A gathering place for instructors of ECG and cardiac topics.


Subscribe to me on YouTube

Welcome to the ECG GURU

Serving ECG instructors and their students since 2011.
Download ECGs, Illustrations, and other Resources for your classes!


Featured App

Instructors' Collection ECG of the WEEK: Anterior Wall M.I. With Bifascicular Block

Sat, 03/25/2017 - 15:13 -- Dawn

This ECG is taken from an 82-year-old man who called 911 because of chest pain.  He has an unspecified “cardiac” history, but we do not know the specifics. 

WHAT IS THE RHYTHM?  The heart rate is 69 bpm, and there are P waves before every QRS complex. The underlying rhythm is regular, with one premature beat that is wide without a P wave.  The PR interval is slightly prolonged at .25 seconds.  The rhythm is normal sinus rhythm with first-degree AV block and one PVC. 

WHY THE WIDE QRS?   The QRS complex is wide at .14 seconds. The QRS in V 1 has a wide R wave after a small Q wave.  This in consistent with right bundle branch block pattern, with loss of the normal initial small r wave (pathological Q waves).  The diagnosis of RBBB is further corroborated by the wide little S waves in Leads I and V6.  The QRS frontal plane axis is -66 degrees per the machine, and clearly “abnormal left” because the QRS in Lead II is negative, while the QRS in Leads I and aVL are positive.  This is left anterior fascicular block, also called left anterior hemiblock.  The combination of RBBB and LAFB is a common one, as the two branches have the same blood supply.  It is also called bi-fascicular block. 

WHAT ABOUT THE ST SEGMENTS?  The ST segments in leads V2 through V6 are elevated, and their shape is very straight, as opposed to the normal shape of coved upward (smile). Even though the amount of ST elevation at the J points appears subtle, the shape of the segments, the fact that they appear in related leads, and the fact that the patient is an elderly male with chest pain all point to the diagnosis of ANTERIOR WALL ST elevation M.I. (STEMI).  Additional ST changes include a straight shape in Leads I and aVL and ST depression in V1 and aVR.  

PATIENT OUTCOME  The patient was transported to a cardiac center, where he received angioplasty in the cath lab.  The left coronary artery was found to be occluded, and was repaired and stented.  He recovered without complications and was sent home in a few days.

ECG Challenge: Wide-complex Rhythm

Wed, 02/15/2017 - 22:20 -- Dawn

This ECG Challenge is taken from a 95-year-old man.  We do not know his clinical information, except that he called 911 for assistance.  We also do not have information on his past medical history.  The QRS complexes are wide, and there are P waves present.  What do you think the etiology of this rhythm is?

Feb. 22, 2017 UPDATE:  The wide complexes in this ECG indicate an intraventricular conduction defect.  The most likely IVCD at this man's age is left bundle branch block.  However, the morphology of the QRS complexes in V5 and V6 are NOT typical of LBBB.  Usually, there is very little or no S wave in those leads.  We cannot confirm that lead placement is correct, and failing to place the left sided electrodes (V4 through V6) correctly can affect the transition of the R waves in the precordial leads.  It would be SO helpful to know more about this patient, of course, but a lot is possible by age 95.

For a more in-depth look at this ECG, please refer to the Comments below.

ECG Basics: Onset of Atrial Fibrillation

Fri, 12/16/2016 - 19:44 -- Dawn

This strip shows the onset of atrial fibrillation.  A fib can be "paroxysmal," meaning that it has a sudden onset, but then stops spontaneously, usually within 24 hours to a week.  A fib can also be classified as "persistent", meaninging that the a fib lasts more than a week.  It can stop spontaneously, or be halted with medical treatment.  "Permanent" a fib is a fib that is resistent to treatment.  

The first three beats in this strip represent sinus rhythm at 75 beats per minute.  At the onset of atrial fibrillation with beat number four, the rhythm becomes irregularly irregular, and the rate is around 140-150 bpm. We can expect new-onset a fib to have a fast ventricular rate, as the atria are sending hundreds of impulses to the AV node every minute. The AV node will conduct as many of those impulses as it can to the ventricles.  Most AV nodes can easily transmit 130-160 bpm.  In a fib, the atria are quivering, not contracting. Because of this fibrillation of the atrial muscle, a fib has no P waves, and therefore, no "atrial kick".  The contribution of the atria to cardiac output (25-30%) is lost. An extremely fast rate can also lower output and overwork the heart, so one treatment goal for a fib is to lower the rate.  This can be done independently of attempts to convert the rhythm.

During a fib, blood clots can form in parts of the atria, especially the left atrial appendage.  If sinus rhythm is restored after these thrombi form, they can embolize and travel to the brain, causing stroke.  Before electively converting atrial fib to a sinus rhythm, the patient may need to be anticoagulated.


Instructors' Collection ECG of the WEEK: Incorrect Machine Interpretation

Wed, 03/01/2017 - 23:07 -- Dawn

This ECG is presented as an example of INCORRECT MACHINE INTERPRETATION.  While there are many abnormalities in this ECG, it does not represent a paced rhythm. While there are exceptions, most paced rhythms represent either AV sequential pacing, right ventricular pacing, or bi-ventricular pacing.


Recognizing a paced rhythm can be difficult in some cases. Because pacemakers now have so many programmable features, there is a wide variety of ECG changes associated with them.  Pacer “spikes” can be difficult to see in all leads.  Finding evidence of the device on the patient’s chest or via patient history is a big help in reminding us to scrutinize the ECG for paced rhythm.

An AV sequential pacemaker or a right ventricular pacemaker will pace the ventricles via the right ventricle.  This produces a WIDE QRS and a leftward axis, often causing Leads II, III, and aVF to be negative and aVL and aVR to be positive.  Along with the wide QRS, we will see DISCORDANT ST CHANGES.  That is, there will be ST depression and T wave inversion in leads with positive QRS complexes and ST elevation and upright T waves in leads with negative QRS complexes.

Bi-ventricular pacing can be a little more complicated to recognize, as the QRS can be narrow, with signs of fusion between the wave produced by the LV electrode and the RV electrode.

The frontal plane axis is usually far right – aVR will be positive.  Lead I will be negative.

The machine is wrong:  there is no indication of a pacemaker, and P waves are present, even though they are not noted in the "PR Interval" or "P Axis".


There are many abnormalities in this ECG, and they can be due to many different conditions. All ECGs should be evaluated in a clinical setting, with the patient’s symptoms, signs, and medical history all considered.  That being said, I will point out what I see to be abnormal, and await our readers’ and experts’ opinions.

The rhythm is sinus, at a rate of 62 bpm.  The PR interval is not given by the machine, but P waves are very obvious, and the PR interval is about .24 seconds, a first-degree AV block.  The QRS complex is measured by the machine as 114 ms wide (.11 seconds).  This is barely under the 120 ms usually required for diagnosis of wide-complex rhythm, and many would consider it adequate for a wide QRS.  If we accept that this is a wide-complex QRS, then we should look for the ECG criteria for RIGHT BUNDLE BRANCH BLOCK and  LEFT BUNDLE BRANCH BLOCK. In RBBB, there will be an rSR’ pattern in V1 and a small s wave in Leads I and V6.   In LBBB, Leads I, V5 and V6 should have a broad, monomorphic, upright QRS.  In this ECG, V5 and V6 have small s waves that contribute to the total width of the QRS, while the R waves are narrow in appearance. The term for a wide-complex, supraventricular rhythm that does not meet the criteria for either right or left BBB is INTRAVENTRICULAR CONDUCTION DELAY. (IVCD)

The frontal plane axis is -17 degrees, which is normal, but slightly to the left.  That would be typical of left bundle branch block.  However, the pronounced S wave in Lead II and the deep S wave in Lead III are not typical.  In a study of S waves in these two leads, they have been found to be very rare in healthy hearts, and often associated with M.I. and cardiomyopathy.  The abnormal S waves studied were deeper than the R wave was tall, however. S waves can be seen in Leads II and III in ventricular conduction defects that cause wide QRS – like LBBB and IVCD .

The ST segments and T waves in this ECG are clearly abnormal. T waves are inverted in Leads II, III, aVF; Lead I; Leads V4, V5, and V6; and they are biphasic in V3 as they transition from V2 (positive) to V4 (negative).  The inverted T waves are very shallow in most leads, so it is hard to determine if they are symmetrical (indicating ischemia) or asymmetrical (with many causes).   In cases of wide QRS, we expect to see DISCORDANT ST AND T WAVE CHANGES.  That is, the ST and T waves will go opposite the main direction of the QRS.  Right chest leads like V1 and V2, which have negative QRSs will have some ST elevation and upright T waves.  The opposite is true over the left side, where we expect upright QRS complexes (I, aVL, V5, V6) and, in the case of wide QRS, depressed ST segments with inverted T waves.  This is seen for the most part in this ECG, but Leads III and aVF seem to have CONCORDANT STs.  It would be very helpful to know this patient’s current symptoms and recent medical history.

There are also Q waves in V1 and V2 that meet the criteria for "pathological Q waves", a sign of necrosis.  However, large Q waves (or more accurately, loss of initial R waves) are common in V1 and V2, and may not be related to acute M.I.  This is where knowing the patient's presentation and history would be very helpful. 

As stated, the MAIN REASON for posting this ECG is to show students, beginners and advanced alike, that the machine’s interpretation should be taken with a “grain of salt”, and the interpreter should never rely solely on that interpretation.  But we must also make the point that every ECG should be interpreted, when possible, in the setting of the patient’s presentation.




Bi-ventricular Pacemaker Illustration

Click to open: 
Bi-ventricular pacemaker illustration

This is an original illustration by Dawn Altman.  For non-commercial use, this work is protected by Creative Commons, and is free and free of copyright for such use.  For commercial use, please contact Dawn Altman at [email protected]

ECG Guru Ads - Products and Services of Interest to our Members

 If you would like to place ads for products or services of interest to our readers, please contact us at


1924:  Willem Einthoven wins the Nobel prize for inventing the electrocardiograph.

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 ECG Guru - Instructor Resources RSS