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Left axis deviation

Syncope and tachycardia

Sun, 01/13/2019 - 22:32 -- Dawn

The patient:  This ECG is taken from a 55-year-old man whose wife called 911 because he had a syncopal episode.  When the paramedics arrived, he was conscious and alert, and denied any symptoms.  He gave a history of "cardiac", diabetes, and opiate abuse.  We do not know the nature of his cardiac history or his medications.  

It is difficult to pinpoint a definite diagnosis with this lack of information and a clearly abnormal ECG.  We will limit our discussion to listing the abnormalities seen:

The ECG rhythm:  There is a fast, regular rhythm that is supraventricular in origin (there are P waves).  When a supraventricular rhythm has a rate of about 150 per minute, we should ALWAYS consider ATRIAL FLUTTER WITH 2:1 CONDUCTION.  Atrial flutter produces P waves (flutter waves) at approximately 250-350 per minute.  The normal AV node is able to conduct half of these, at a rate of about 150 per minute. Atrial flutter with 2:1 conduction is the most common presentation of new-onset atrial flutter.  It is often missed by people who expect to see several flutter waves in a row, producing the "sawtooth pattern".  That being said, atrial flutter is usually discernable in at least a few leads if it is present.  We do not see any signs of flutter waves in this ECG.

That leaves us with a differential diagnosis of sinus tachycardia vs. one of the regular supraventricular tachycardias like reentrant tachycardias or atrial tachycardia.  Sinus tachycardia can be recognized by several features. If we are fortunate enough to witness the onset or offset of the fast rhythm, will will recognize sinus tachycardia by a "warm up" or gradual speeding up of the rate, and a "cool down", or gradual slowing.  On the other hand, SVTs often have abrupt onset and offset.  Sinus tachycardia often has a very obvious cause, such as hypovolemia, fever, pain, anxiety, vigorous exercise, or hypoxia.  Sinus tachycardia usually has a distinct, upright P wave in Lead II, and a clearly-seen, often negative, P wave in Lead V1.  This ECG does not show the onset of the tachycardia, and is not long enough to evaluate for rate changes. Lead II appears to have upright P waves on the downslope of the previous T waves. V1 has deeply negative P waves, and V4 has the most clearly-seen P waves.  Without being positive, this looks more like sinus tachycardia than a reentrant tachycardia.  It would help to know more about the patient's condition.

Bifascicular Block

Fri, 11/16/2018 - 14:35 -- Dawn

This ECG is from a 77 year old woman who was brought to the Emergency Department by EMS. She was found to be suffering from sepsis.

ECG Interpretation      The ECG shows the expected sinus tachycardia at 123 beats per minute.  There is significant baseline artifact, of the type usually seen with muscle tension.  The artifact makes it difficult to assess P waves and PR intervals.

 

What we do see is RIGHT BUNDLE BRANCH BLOCK and LEFT ANTERIOR HEMIBLOCK, also called LEFT ANTERIOR FASCICULAR BLOCK.  Together, these are called BIFASCICULAR BLOCK.  Most people have three main fascicles in the interventricular conduction system:  the right bundle branch and the two branches of the left bundle branch, the anterior-superior fascicle and the posterior-inferior fascicle.  In bifascicular block, two of the three are blocked.

The ECG criteria for right bundle branch block are:

     *     wide QRS (> .12 seconds)

 

     *     rSR’ pattern in V1 .  (the initial R wave may be hard to see, but the QRS will be predominantly upright.

Left Bundle Branch Block

Tue, 01/17/2017 - 18:36 -- Dawn

This ECG was taken from an unknown patient.  It shows sinus tachycardia with left bundle branch block. The ECG criteria for left bundle branch block are: 

* Wide QRS (.12 seconds or greater)

* Negative QRS deflection in V1

* Positive QRS in Leads I and V6 

* Supraventricular rhythm

In addition to these criteria, left bundle branch block will cause repolarization abnormalities.  This is because depolarization is altered through the left ventricle, which causes repolarization to also be altered.  Instead of the electrical impulse traveling down the left bundle branch to depolarize the left ventricle, it depolarizes the right ventricle first, then spreads cell-to-cell across the larger left ventricle. The ST and T wave changes caused by left bundle branch block are normally “discordant”.  That is, the ST segment will be elevated in leads with negative QRS complexes, and depressed in leads with positive QRS complexes.  This elevation and depression of the ST segment may “imitate” the changes caused by acute myocardial infarction.  They may also work to conceal M.I. changes, as we may not recognize  STEMI as we attribute the ST changes to the left bundle branch block itself. 

For more on determining the presence of acute M.I. when the patient has left bundle branch block, check out these links:  ECG Guru, LBBB with AMI; Life in the Fast Lane, Sgarbossa CriteriaEMS 12-Lead, Sgarbossa Criteria;  Dr. Smith's Modified Sgarbossa Criteria. 

Previous Inferior Wall M.I. and Left Axis Deviaton

Fri, 01/17/2014 - 21:39 -- Dawn

If you are teaching frontal plane axis to your students, you will need to teach them HOW to determine the axis - usually beginning with the QRS axis and then adding the P and T waves.  But, you also need to teach them WHY we measure axis, to provide relevance to something that may seem challenging to beginners.  There are many ECG interpretations that rely heavily or are dependent upon the determination of the axis.  

This ECG is a great example of left axis deviation.  The cause is readily discernible, if your students know the ECG signs of myocardial infarction. This patient had an inferior wall M.I. in the distant past, and now has pathological Q waves in Leads II, III, and aVF.  Pathological Q waves in related leads in a patient with history of M.I. are a sign of necrosis, or permanent damage, in that part of the heart.  The inferior wall has lost an extensive amount of tissue, which is now electrically inactive as well as mechanically inactive.  (You may also find it helpful to show students videos of ventriculograms showing normal LV function and hypokinesis of the LV due to M.I.)  Because of the loss of electrical activity in the inferior wall, the "mean" electrical direction (or axis) is AWAY from the inferior wall.  That is, the electricity travels AWAY from II, III, and aVF and TOWARD I and aVL.

Many of the blogs and webpages listed in our "Favorites" address the subject of axis determination.  Here is one from Cardio Rhythms Online if you would like a review.

 

 

 

jer5150's picture

Jason's Blog: ECG Challenge of the Week for July 8-15. Which lead do both of these ECGs share a “common-thread”?

 

Two more ECGs classified under the general heading:  “Tracing suggestive of   ____ ”.  I  like ECGs that strongly favor a very specific clinical disorder.

jer5150's picture

Jason's Blog: ECG Challenge of the Week for June 10-17. Why did the ventricular rate abruptly decrease?

 

From June 10, 2012:   As is the case with all practical blogs, I’m encouraging ECG Guru members to engage in active group participation.  Share your thoughts, observations, impressions, findings, and interpretations.  Feel free to compare notes with one another and pick each other’s brains.

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