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Instructors' Collection ECG: Isolated Posterior Wall M.I.

This interesting case was provided by Dr. Bojana Uzelac, Emergency Medicine physician.  We are paraphrasing a translation of her comments here.

The patient is a 50-year-old complaining of chest pain.

The ECG shows a rare occurrence – an isolated POSTERIOR WALL MI (PWMI).  Note that leads V1 through V4 show the usual signs of posterior wall MI.  We see ST segment depression, which represents a reciprocal view of the ST elevation present on the posterior wall of the left ventricle.  The relatively tall, wide R waves in V2 and possibly V3 represent pathological Q waves on the posterior wall. (V2 R/S ratio > 1). What is unusual here is that there are no signs of inferior wall MI or lateral wall MI.  Posterior wall MI usually occurs in conjunction with one of these.

 PWMI is most often seen as an extension of inferior wall MI or lateral wall MI, because of shared blood supply.  Usually, it is the right coronary artery that supplies both the posterior and inferior areas of the left ventricle (about 80% - 85% of the population).  In some individuals, the circumflex artery supplies both areas. Posterior M.I. may also be seen in conjunction with lateral wall MI, when the circumflex supplies the posterior and lateral walls.  In the case shown here, only the posterior wall is involved.  Most cases of isolated PWMI involve either the circumflex or one of its marginal (OM) branches.  Only about 3.3% - 5% of all MIs are isolated PWMI.


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Why is this a high-grade AV block? If at least 3 P-waves are not conduced and there is nominal AV conduction before and after, this can be considered a higher-grade AV block. in this Holter strip, P1, P2 and all P-waves from P6 onwards are conduced, albeit with a prolonged PR interval (first-grade AV block). P3, P4, P5 are not conducted. A junctional escape beat is seen before P5. P5 can also not be conducted because the specific conduction system is still refractory at this time due to the junctional escape beat

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Atrial flutter and atrial fibrillation are 2 different cardiac arrhythmias, but occur frequently side by side in the same patient. Here is an example of how atrial flutter degenerataes into atrial fibrillation. The initially ordered atrial activity (left in the picture) with 2 flutter waves/1 QRS complex changes into irregular atrial activity (right in the picture) and the RR intervals become completely irregular.

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Sinus Bradycardia and More

Let's analyze the ECG. It comes from a pacemaker patient whose pacemaker was briefly switched to VVI at 30 bpm due to a stimulation threshold test. The first 3 beats show a sinus rhythm with a frequency of approx. 40 bpm. This is followed by a premature ventricular contraction (PVC). The P wave of the next sinus node beat lands exactly on the T of the PVC. This cannot be conducted to the ventricles, either because the ventricular myocardium is still unexcitable or the PVC has conducted retrogradely into the AV node and this is therefore still refractory.

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Many people are considerably unsettled by ECG recordings from smart watches. However, smartwatch ECGs can be helpful in the diagnosis of paroxysmal atrial fibrillation. Here. you can see an example. It is a 1-channel ECG that corresponds to lead I. Initially there is an irregular fast pulse without P waves, which corresponds to a tachyarrhythmia in atrial fibrillation. At the end of the first line, after a very short pause, there is sinus rhythm. In the third line you see a short SVT over 3 beats, then SR again. The QRS complex is widened to over 120 ms.

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Why is this atypical atrial flutter from the left atrium?

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Ventricular Tachycardia

There are several differential diagnoses in the presence of broad-complex tachycardia. The most common cause of wide-complex tachycardia is ventricular tachycardia. In 2nd place is sinus tachycardia/supraventricular tachycardia with aberrant conduction or preexisting bundle branch block.

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Right Bundle Branch Block

Why is this a right bundle branch block? We see a SR with broad QRS complexes (more than 120 ms). These are positive in the rightward leads III and especially in V1 and V2. In the more leftward leads I, aVL, V4-V6 there are clear S waves. This is a typical RBBB pattern.

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Left Bundle Branch Block

Why is this a left bundle branch block? We see a SR with broad QRS complexes (more than 120 ms). These are positive in the leftward leads I and aVL and in V5 and V6. In the more rightward leads III, aVR, and V1-V3, the QRS complexes are predominantly negative with deep S waves. This is a typical LBBB pattern.

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ECG Basics: Ventricular Fibrillation Seen In Twelve Leads

This is an image of ventricular fibrillation as seen in all twelve standard leads simultaneously.  This is cardioplegic ventricular fibrillation, occurring as the heart is stopped during cardiopulmonary bypass for open heart surgery.  Each channel (horizontal strip) is run during the same ten-second period.  Our thanks to Dr. Andreas Röschl from Germany for contributing this image.

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

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