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Instructors' Collection ECG of the WEEK: Subtle ST Elevation And Left Anterior Hemiblock

Mon, 02/01/2016 - 00:11 -- Dawn

We have no clinical information about this patient, except that he was complaining of chest pain, and was initially treated by prehospital paramedics.

ST Changes      The paramedics noted a slight J point elevation in the precordial leads, specifically about one mm of elevation in Leads V2, V3, and V4.  In addition, the ST segments are curved downward like a frown in V1 and straight in the remaining precordial leads. Because of the patient’s symptoms, and the ST abnormalities, they notified the hospital that they believed this was a STEMI.  The patient was transported without complications, and the Emergency Department physician subsequently downgraded the initial assessment of STEMI Alert.  We do not have access to follow up. These ST segments are abnormal, but do not necessarily indicate an acute ST-elevation M.I. (STEMI). A flat or “frowning” ST segment DOES suggest coronary artery disease, and the patient’s symptoms are worrisome.  However, before activating the cath lab emergently, it is sometimes preferable to observe the patient, check cardiac enzymes and other lab results, and repeat ECGs. 


Are These ST Changes Due to Acute M.I.?   There are several accepted guidelines in use for evaluating ST segments for STEMI.  Some are simplified for ease of use, and some are very detailed, taking into consideration the patient’s age and gender. There are ECG features that INCREASE the chances of ST elevation being due to acute M.I.  These features include:

·        ST elevations are in related leads

·        ST segments are flat or convex upward (frowning) 

·        There are reciprocal ST depressions

·        There are associated ECG signs of M.I. such as pathological Q waves and inverted T waves

·        J points are higher than 1 mm (females have less STE requirement for M.I. diagnosis)   Leads V2 and V3 generally require 2 mm of STE for a STEMI diagnosis.

As we evaluate this ECG, we see that the subtle ST elevations are in related leads (V1 - V3).  They are flat (V2 and V3)  or convex (V1).  There is NO reciprocal depression of the ST segments.  There are NO pathological Q waves. T waves are inverted in V1 and flat in Lead III, a non-specific finding.  And the J points are minimally elevated at 1 mm or less. By most standard protocols, this ECG does not meet the criteria for acute STEMI.  This does NOT rule out the possibility of M.I.

Other Considerations    It is worth noting that strictly “normal” R wave progression is not seen in this ECG.  Leads V2 through V6 show normal R wave progression.  That is, the R waves progressively become proportionately larger, while the S waves regress.  V1, however, does not have the morphology expected, a small r wave and a deep S wave. We are not sure if this is a lead placement issue or not.  When V1 has abnormalities not shared by V2, we sometimes see similar changes in Lead III, because V1 and Lead III are both oriented toward the heart’s right side.  In this ECG, Lead III does not resemble Lead V1.  Also, there is a left axis deviation.  If no other cause for left axis deviation is readily apparent, the cause is presumed to be LEFT ANTERIOR HEMIBLOCK, also called left anterior fascicular block.  LAH is sometimes caused by anterior-septal M.I., with an incidence of about 7-15%. 

Ref.: Marriott HJL, Hogan RN. Hemiblock in acute myocardial infarction. Chest.1970; 58: 342–344.

ECG Basics: Atrial Fibrillation With A Rapid Ventricular Response

Sat, 12/19/2015 - 00:11 -- Dawn

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.

Limb Leads

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Hexaxial reference system, Limb leads diagram, Free Illustration

Diagram of the limb leads, or frontal plane leads, on the hexaxial reference system.  This illustration is shown without the degrees marked, for simplicity.


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

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