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Inferior Wall M.I. With Right Ventricular M.I.

Submitted by Dawn on Sat, 01/12/2013 - 20:49

This week's ECG of the Week is from an elderly woman who suffered an acute occlusion of the right coronary artery. The ECG clearly shows ST elevation in leads II, III, and aVF, indicating inferior wall injury. In this case, this ECG was obtained in the field by paramedics, and was the second ECG done on this patient. For this tracing, the paramedics obtained V3 and V4 on the right side to better view the right ventricle. V3 and V4 right clearly show ST elevation as well, indicating RVMI. The slight coving and elevation observable in V1 is also an indication of RV involvement, and the ST depression in V2 indicates posterior wall injury. All of this results from a proximal lesion of the RCA in this patient. Such a lesion carries a high morbidity and mortality.

Taking the time to obtain a right ventricular lead is controversial in some settings. Some believe the patient's hemodynamic condition should be treated, regardless of the presence or absence of ST elevation in right chest leads. Others find it very helpful to know that the right ventricle is affected. In this case, paramedics in this community have a protocol to avoid the use of nitroglycerine in RVMI patients, even when the BP is adequate. So, for them, it is important to have the information gathered from V Right leads.

The rhythm here is interesting, as well, and not at all uncommon for IWMI patients. The baseline artifact makes it a bit difficult to march out all the P waves, but it appears they are sinus P waves that are slightly irregular at a rate of 52 to 54. The PR intervals appear to be progressively prolonging, but there is no "grouped beating" observable on this short strip. A lack of a concurrent Lead II rhythm strip also makes it difficult to determine the rhythm, as Lead II does have very visible P waves, and would be helpful. The regularity of the narrow complex bradycardia points to a junctional escape rhythm, which would make this a third-degree AVB at the AV node level, which is very common with IWMI. What do you think?

This month's strip from Jason Roediger's ECG Challenge blogpost is a nice complement to the strip presented here. His is much clearer, and has a Lead II rhythm strip. Do you think these ECGs show the same rhythm, or two different rhythms?

For an excellent discussion of "AV Dissociation" vs. "AV Block", go to Christopher Watford's Ask the Expert post. Thanks very much to ECG Guru Sebastian Garay for this interesting ECG.

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Inferior Wall M.I. With Third-degree AV Block

Submitted by Dawn on Thu, 11/15/2012 - 23:15

This ECG was obtained from an elderly woman who suffered a complete right coronary artery occlusion and inferior wall M.I. In her case, the AV node was also affected, and she developed a third-degree AV block with a junctional escape rhythm. A good ECG for ACLS classes as well as for ECG classes. A lively discussion can be had regarding "types" of complete heart block and the nature of the escape rhythm - when to treat and when to leave the rhythm alone. In this case the rate of the junctional escape rhythm was adequate for perfusion, and the patient's blood pressure was stable. Priority for treatment in this situation is restore blood flow through the coronary artery, if the patient is a candidate for PCI. You might want to review Christopher Watford's contribution to the Ask the Expert page on AVB vs. AV Dissociation.

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Ask The Expert

Submitted by Dawn on Tue, 11/06/2012 - 11:03

QUESTION: How do you explain the difference between "AV block" and "AV dissociation" to your students?

Our Expert today is Christopher Watford, BSc, NREMT-P

Christopher began in EMS as an EMT on a volunteer industrial fire brigade at GE's Global Nuclear Fuels facility in Wilmington, North Carolina. He has worked there as a Lead Software Engineer since 2001 and currently is a Captain on the fire brigade. Outside of his day job, he volunteers as a Paramedic and Field Training Officer for Leland Volunteer Fire/Rescue where he also serves on the board of directors.Through Cape Fear and Brunswick Community Colleges heteaches continuing educat ation for all levels of providers. He also is an associate editor for the EMS 12-Lead Blog and Podcast, presenting electrocardiography case studies for pre-hospital personnel.

Christopher's excellent blog can be found at My Variables Have Only Six Letters. His contributions to EMS 12-Lead can be found at this link.

Answer:

I think the first step in understanding the difference between an atrioventricular block and atrioventricular dissociation is to have a firm understanding of physiological and pathological conduction. The most common example of this is a non-conducted premature atrial contraction (PAC). If an atrial stimulus arrives early enough at the atrioventricular node (AVN), while it is still refractory, forward conduction will be blocked. Likewise in atrial flutter, you typically see one ventricular activation for every two F-waves, due to the physiological rate limiting by the AVN. However, as this is due to the physiological function of the AVN we would not consider this a block!

In higher degree AV blocks, we encounter a pathological decrease in conduction and so we label non-conducted stimuli as "blocked". Type I and Type II AV blocks provide visual confirmation of pathological conduction as you have examples of both conducted and non-conducted stimuli. However, in the case of a presumed complete AV block, it is important that you look at whether the atrial impulses were blocked or simply not conducted. With monomorphic ventricular tachycardia you may see uncoordinated atrial and ventricular impulses on the ECG. In this case the ventricular rhythm and the atrial rhythm "compete" for access to the AV nodal tissue. There is no "AV block" present, instead we say they are "dissociated" from the ventricular rhythm. More specifically, we say that the atrial rhythm is dissociated from the ventricular rhythm due to usurpation. Best illustrating the competitive nature of two rhythms during dissociation are capture or fusion beats.

Therefore when classifying dyssynchrony between the atria and ventricles, students should look to see whether conduction blocked due to pathological processes or because the AV node is appropriately refractory.

Sinus Tachycardia With High-grade AV Block

Submitted by Dawn on Wed, 05/02/2012 - 14:34

This ECG has always caused a lively conversation in ECG classes, both beginner classes and advanced. There is an obvious underlying sinus tachycardia, with clear P waves.

Some propose that the ECG shows a second-degree AVB, Type II, in that the PR intervals are constant, or nearly so. There is a slight discrepency if you compare the first PRI with the others. The QRS complexes, while very slow, have a pattern of right bundle branch block with left anterior fascicular block - not an unlikely finding in second-degree AV block, Type II, since that is a block in the fascicles of the interventricular conduction system. Type II blocks usually are accompanied by signs of bundle branch dysfunction.

Others strongly believe this is a third-degree, or complete, heart block. They argue that the PR intervals are not identical, and propose that a longer strip would uncover the discrepency. The wide QRS complexes have a strong left axis deviation, which could support the argument for idioventricular escape rhythm.

What do you think? Please comment below.