Today’s expert is Dr. Jerry W. Jones, MD, FACEP, FAAEM

Jerry W. Jones, MD FACEP FAAEM is a diplomate of the American Board of Emergency Medicine who has practiced internal medicine and emergency medicine for 35 years. Dr. Jones has been on the teaching faculties of the University of Oklahoma and The University of Texas Medical Branch in Galveston. He is a published author who has also been featured in the New York Times and the Annals of Emergency Medicine for his work in the developing field of telemedicine. He is also a Fellow of the American College of Emergency Physicians and a Fellow of the American Academy of Emergency Medicine and, in addition, a member of the European Society of Emergency Medicine. 

 Dr. Jones is the CEO of Medicus of Houston and the principal instructor for the Advanced ECG Interpretation Boot Camp and the Advanced Dysrhythmia Boot Camp. 

QUESTION:  How can I explain to students that injury from an M.I. “localizes” on the ECG, but subendocardial ischemia/injury does not?

ANSWER:                 Allegory of Subendocardial Ischemia

Question:

Dr. Jones,

I am confused about the repolarization abnormalities that occur in conditions other than acute M.I. (Bundle branch block and hypertrophy, for example). I have been taught that the repolarization abnormalities should point opposite the MAIN part of the QRS, but also I have been told that they should point opposite the TERMINAL deflection of the QRS.  Which is right?

Today’s expert is Dr. Jerry W. Jones, MD, FACEP, FAAEM

Jerry W. Jones, MD FACEP FAAEM is a diplomate of the American Board of Emergency Medicine who has practiced internal medicine and emergency medicine for 35 years. Dr. Jones has been on the teaching faculties of the University of Oklahoma and The University of Texas Medical Branch in Galveston. He is a published author who has also been featured in the New York Times and the Annals of Emergency Medicine for his work in the developing field of telemedicine. He is also a Fellow of the American College of Emergency Physicians and a Fellow of the American Academy of Emergency Medicine and, in addition, a member of the European Society of Emergency Medicine. Dr. Jones is the CEO of Medicus of Houston and the principal instructor for the Advanced ECG Interpretation Boot Camp and the Advanced Dysrhythmia Boot Camp. 

Answer:

Which Direction Should the Repolarization Abnormality Point?

OK. You've got an abnormal QRS complex followed by a repolarization abnormality (RA). Which direction should the repolarization abnormality point? As a young resident, I was taught that the RA should point in the direction opposite the terminal deflection of the QRS complex. But years later, I see other physicians stating that the repolarization abnormality should point opposite the main deflection of the QRS complex. Which is correct?

The answer is both are correct. Why? How?

The reason is that the repolarization abnormality is connected to the ventricle in which the problem is located - not the QRS complex itself. To better understand this, let's look at some of the major causes of repolarization abnormalities (you can find examples in the illustration at the top of this page):

Right Bundle Branch Block (RBBB) - When you look at the QRS complex in V1, you see an R and an R'. The R represents left ventricular activation while the R' represents right ventricular activation. So, the problem lies in the right ventricle represented by the R'. The repolarization abnormality reflects the problem in the RV so it should be opposite the R' which is always the last deflection in V1 in the presence of RBBB. Therefore, in cases of RBBB, the repolarization abnormality is always opposite the terminal deflection of the QRS.

Left Bundle Branch Block (LBBB) - When you look at the QRS complex from V6 which has a LBBB, we see a relatively tall, upright monophasic QRS complex. Part of that QRS represents right ventricular depolarization and part represents left ventricular depolarization. But how much of which? We don't know, but all we need to know is that this is a monophasic complex and it is upright. Therefore, since the repolarization abnormality reflects the problem in the left ventricle, and the LV is represented somewhere in that monophasic R, the repolarization abnormality should be opposite the main deflection. Therefore, in cases of LBBB, the repolarization abnormality is always opposite the main deflection of the QRS.

Left Ventricular Hypertrophy (LVH) - When you look at the QRS complexes from V5 and V6, we see a relatively tall, upright monophasic QRS complex. Part of that QRS represents right ventricular depolarization and part represents left ventricular depolarization. But how much of which? Again, we don't know, but all we need to know is that this is a monophasic complex and it is upright. Therefore, since the repolarization abnormality reflects the problem in the left ventricle, and the LV is represented somewhere in that monophasic R, the repolarization abnormality should be opposite the main deflection. Therefore, in cases of LVH, the repolarization abnormality is always opposite the main deflection of the QRS.

Right Ventricular Hypertrophy (RVH) - The same concept discussed regarding LVH applies in cases of RVH. Therefore, in cases of RVH, the repolarization abnormality is always opposite the main deflection of the QRS.

Ventricular Pre-excitation - Most people reading ECGs don't realize that ventricular pre-excitation can also produce a repolarization abnormality. Just as repolarization abnormalities are not always present in cases of LVH and RVH, they are not always present in cases of ventricular pre-excitation, either. However, the repolarization abnormality IS present in some cases. The RA is connected to the ventricle containing the accessory pathway, but don't worry: you don't have to determine which ventricle that is. If a repolarization abnormality is present in a lead, it should be negative if the delta wave is positive and vice versa. Therefore, the repolarization abnormality points opposite to the direction of the delta wave.

So, the question really isn't whether the repolarization abnormality should be opposite the terminal or the main deflection of the QRS. It should be opposite the deflection that represents the involved ventricle.

Question:

Dr. Jones, do you have any tips to help me teach axis determination to my students?

Today’s expert is Dr. Jerry W. Jones, MD, FACEP, FAAEM

Jerry W. Jones, MD FACEP FAAEM is a diplomate of the American Board of Emergency Medicine who has practiced internal medicine and emergency medicine for 35 years. Dr. Jones has been on the teaching faculties of the University of Oklahoma and The University of Texas Medical Branch in Galveston. He is a published author who has also been featured in the New York Times and the Annals of Emergency Medicine for his work in the developing field of telemedicine. He is also a Fellow of the American College of Emergency Physicians and a Fellow of the American Academy of Emergency Medicine and, in addition, a member of the European Society of Emergency Medicine. 

Dr. Jones is the CEO of Medicus of Houston and the principal instructor for the Advanced ECG Interpretation Boot Camp and the Advanced Dysrhythmia Boot Camp. 

Answer:

Frontal Plane Axis Shortcuts

 When we speak of axes and vectors, we are usually referring to the mean QRS axis in the frontal plane – much more so than in the horizontal plane (where it’s more properly called “rotation” rather than “axis”). We are also concerned with the P axis and the T axis in the frontal plane. And, at times, we are even concerned with the ST (segment) axis!

That can be a lot of drawing of lines and angles and expenditure of brain power – especially after being awake and on duty most of the night. Well… relax! It doesn’t have to be difficult at all. And you don’t have to draw any diagrams!

Before we start, let’s be certain that we are speaking the same language: in electrocardiography, when we say “left” we mean the PATIENT’S “left;” when we say “right” we mean the PATIENT’s “right.” We are not referring to the right side of the diagram or ECG tracing in front of you. The positive pole of Lead I may be on the right side of the drawing of Einthoven’s triangle, but it is on the PATIENT’S left! OK, let’s proceed…

First of all there are three generalizations about axes that you should know:

FIRST, forget about axes of +23 degrees, -14 degrees or +61 degrees. You never – let me repeat – NEVER have to be so exact in electrocardiography unless you are calculating the QRS-T angle (and most healthcare providers don’t need to do that). 99 % of the time if you are within 15° to 30° of the correct mean axis you are doing JUST FINE! The reason is because 99 % of the time we just want to know if the axis is normal or not, or if it is located closer to one of the extremes of axis (the “extremes” being left axis deviation or right axis deviation). Besides, the mean QRS axis is very labile – just taking a deep breath can change it considerably!

SECOND, knowing that an axis is “normal” really doesn’t tell you a whole lot since both normal and abnormal hearts can have perfectly normal mean QRS axes in the frontal plane. However, very, very few normal hearts will have an abnormal axis. So, although knowing that the mean QRS axis in the frontal plane is normal really doesn’t help much, knowing that the axis falls outside the normal range is an extremely good indication of cardiovascular pathology.

The first axis we are concerned about is the mean QRS axis in the frontal plane. There are four leads that we use to tell us what we need to know.

First of all, to decide whether the axis is normal or not, we look at leads I and II. If the QRS is negative in I (but positive in II), then there is a right axis deviation. If the QRS is negative in II (but positive in I), then there is left axis deviation. If it is upright in both, then the mean QRS axis in the frontal plane is perfectly normal. But again – “normal” really doesn’t tell us a lot. Forget about aVF! We no longer use it in determining the mean QRS axis in the frontal plane other than to diagnose an axis in the northwest quadrant (“no man’s land”), which is very rare.

Second, we often want to know if the “normal” mean axis is tending rightward or leftward. We do that by looking at leads aVL and III. If the QRS complex is predominantly negative in aVL, then it has to be more positive than +60° (rightward). If the QRS is predominantly negative in III, then it has to be more negative than +30° (leftward). If the QRS complexes in leads aVL and III are both positive, then the mean QRS axis in the frontal plane will lie between +60° and +30° and could not be more “NORMAL!”

Tall, thin people usually have long, elongated hearts that seem to just “hang” in their chest (and some actually do!). We would expect these individuals to have hearts that are nearly vertical, so we would also expect to see a QRS complex in aVL that is predominantly negative or maybe equiphasic. If the QRS in aVL were very positive, we would wonder about the presence of a conduction disturbance that sends the terminal depolarization upwards. (FYI, in electrocardiography, when we say an impulse is traveling “upwards,” we really mean “to the left.” If we say it’s traveling “downwards, we really mean “to the right.”)

Short, stocky people tend to have hearts that lie a bit more horizontally on the diaphragm, so we would expect their mean QRS axis in the frontal plane to be more horizontal. Therefore, we shouldn’t be surprised to see that lead III is predominantly negative or equiphasic.

So if we look at a 12-lead ECG and quickly see that the QRS complexes in both leads I and II are positive but the QRS complex in lead III is negative, we would say that although the mean QRS axis (or vector) in the frontal plane is normal, it is also somewhat leftward or horizontal. If the QRS in aVL were negative instead, then we would report the mean QRS axis as somewhat rightward or vertical.

Rightward means downward and leftward means upward (and vice versa, respectively).

Years ago, we were taught that any axis more negative than 0° was left axis deviation. Then, it was decided that the axis could be up to -30° and still be normal. This presented a lot of confusion regarding how to refer to a normal axis. Basically, if the mean QRS axis in the frontal plane falls between -30° and +90° call it NORMAL. If it falls between -30° and -90° call it LEFT AXIS DEVIATION. Some people still want to refer to the area from 0° to -30° as left axis deviation but with a normal axis and they do make a good argument. The issue of how to refer to that section between 0° and -30° still isn’t completely resolved.

Let’s talk about P waves. Anytime I mention “P wave axis” or “P wave vector” I usually see eyes rolling up to the ceiling. But the P wave axis is determined exactly the same way as the QRS axis!

A good pearl to remember is that any P wave axis, QRS axis or T wave axis that is located between 0° and +90° is NORMAL! Of course, a QRS axis located between 0° and -30° is also NORMAL. The vast majority of P wave axes and T wave axes are going to be found within a more narrow range within that 90° spread between 0° and +90°, but they are still NORMAL as long as they are between 0° and +90°.

That being said, we usually want to know the general direction of the P wave axis (I’m going to stop repeating “mean axis” and “in the frontal plane”). Abnormal P wave axes tend to be vertically oriented.

Normally, the P wave axis is almost parallel to the lead II axis and so it tends to cluster around +60°. A P wave in the frontal plane that is moving rightward – i.e., more inferiorly or vertically – is very characteristic of chronic lung disease such as COPD or an acute strain on the right side of the heart such as a pulmonary embolus.

If the P wave vector becomes more vertically oriented, what happens to the P wave in lead I? Lead I is perfectly horizontal on the Einthoven triangle, so if the P axis is vertical, then it must be perpendicular to lead I. When a vector is perpendicular to a lead it can be either isoelectric or equiphasic. In the case of the P wave, it is usually isoelectric – or nearly so. In any case, a P wave with a vertical axis will be very small or totally isoelectric in lead I. Obviously, we normally do see P waves in lead I so equally obviously the P wave axis is usually not particularly vertical.

The T wave axis can be handled exactly the same way as the QRS and P wave axes. However, we really don’t look at the T wave axis that much. When we do, it’s usually in reference to the angle formed between the T wave axis and the QRS axis (on the hexaxial reference grid) called the QRS-T angle. In calculating the QRS-T angle, we really do want to use axes that are as accurate as possible. However, determining those axes to the nearest degree isn’t really as difficult as you might imagine. Here’s my method:

I use the R and T axes printed on the ECG printout. Seriously… this is how 98% of all physicians calculate the QRS-T angle (and the other 2% are liars!).

Joking aside, advanced electrocardiographers do sometimes use the T wave axis to interpret 12-lead ECGs, but most healthcare providers need only note that the T wave is inverted in certain leads under certain conditions.

I said there were three generalizations about axes, so here’s the third…

THREE, most healthcare providers reading ECGs at a beginners’ or low-intermediate level tend to focus on positive deflections and really don’t pay that much attention to negative deflections (except for Q waves and deeply inverted T waves). But there’s a lot of information to be gathered from negative deflections.

Let’s focus on S waves. Let’s say we are dealing with a heart that has a nearly vertical QRS axis with predominantly negative QRS complexes in leads II, III and aVF. That means that the ventricular depolarization is heading straight up. But what if the deepest S wave is in lead III? That would tell us that the preponderance of the electrical force is pointing up and to the left (around -60° and parallel to the lead III axis) which would point to the basal-lateral area of the left ventricle. Therefore, we likely have a heart with a problem in the left ventricle – perhaps in the area served by the LAD, LCx or ramus intermedius. One would also like to see what’s happening in lead aVL because it’s up in that area also. Usually the problem will be LVH or LAFB (anterior hemiblock). And what if lead II has the deepest S wave? That would indicate that the QRS axis is likely parallel (or nearly so) to lead II and traveling away from its positive pole which would be up and to the right (around -120°) – likely a problem in the right ventricle or the RCA circulation. If that were the case, one would want to look at lead aVR because it’s up there in that vicinity, too.

Just remember that when we speak of positivity or negativity of a deflection in any of the frontal leads, we are talking about vertical or horizontal axis. Positivity or negativity in lead I is considered the “gold standard” for determining “rightwardness” or “leftwardness,” but it often really isn’t that useful for the simple reason that it is rather unusual to see predominantly negative complexes in lead I. That’s because axes in the frontal plane are typically normal. So we have to look at other leads that indicate a rightward tendency or leftward tendency within the context of a normal axis and those leads are lead III (negativity indicates “leftwardness”) and lead aVL (negativity indicates “rightwardness”). The inferior leads – II, III and aVF – indicate verticality (downward or rightward if positive, upward or leftward if negative).

So, in the final analysis, you usually just want to know if you have a vertical axis or a horizontal axis, if the axis is outside the limits of normality and occasionally, when the axis is normal, you may want to know if it is trending leftward or rightward. Now you know how to determine this information without doing any diagraming or calculating.

QUESTION: 

Can you provide some guidelines on how to convey the large body of information associated with clinical evaluation and management of cardiac arrhythmias from a primary care perspective? 

Today’s Expert is the ECG Guru’s Contributing Expert, Dr. Ken Grauer. 

KEN GRAUER, MD is Professor Emeritus (Dept. Community Health/Family Medicine, College of Medicine, University of Florida in Gainesville).

Dr. Grauer has been a leading family physician educator for over 30 years. During that time he has published (as principal author) more than 10 books and numerous study aids on the topics of ECG interpretation, cardiac arrhythmias, and ACLS (including an ongoing Educational ECG Blog) . Dr. Grauer is the Contributing Expert for the ECG Guru. 

ANSWER: 

The topic of evaluating the patient with a cardiac arrhythmia – and then formulating an optimal approach to management is HUGE. It encompasses assessing both symptomatic and asymptomatic patients – determining if an arrhythmia is truly present, and if so, whether the arrhythmia is worrisome or benign – and then deciding on whether drugs, lifestyle changes, or referral for specialized EP (electrophysiologic) evaluation is in order. 

I have developed a 3-part (less than 90-minute) video series that addresses this tremendously important clinical topic from start to finish. Included in these videos are assessment of the patient, arrhythmia monitoring methods, when to refer, and targeted discussion of the most commonly encountered arrhythmias in primary care. These include ectopic beats (PACs; PJCs; PVCs) – ventricular arrhythmias (nonsustained vs sustained VT occurring in different clinical settings) – bradycardias (diagnosis of Sick Sinus Syndrome plus indications for pacing) – MAT – PSVT/AVNRT – Atrial Flutter – and Atrial Fibrillation. 

Links to these 3 Videos – plus LOTS of additional relevant information (including pdf excerpts available for free download from my ECG and ACLS ePubs on specifics of arrhythmia diagnosis) – is now all available for use on my new clinical arrhythmia webpage, www.fafpecg.com. I hope this material is helpful to you in your teaching! The beauty of these videos is that content is appropriate and understandable for primary care providers of virtually any level or degree of training – and that by assignment, learning can be entirely self-instructional OR under your direct guidance and instruction.  

P.S. I am still finishing a Power Point Show (without audio) that you can use if you choose to teach this subject yourself using my slides. This should be completed soon. The rest of this web page is finished and READY for use. Your comments and feedback is WELCOME!

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