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AV dissociation

Complete AV Block

Tue, 09/16/2014 - 14:26 -- Dawn

This ECG is from an 84-year-old man who experienced dizziness and a fall.  He was not injured in the fall.  In this ECG, we can clearly see regular P waves at about 110 per minute.  We also see wide QRS complexes at about 52 per minute.  There is AV  dissociation - there are no regular PR intervals, or even progressively-prolonging PR intervals.  The atrial and the ventricles are beating to separate rhythms.  What is interesting about this rhythm is the origin of the escape rhythm.

ECG Basics: Sinus Rhythm With Complete AV Block and Ventricular Escape Rhythm

Sun, 07/28/2013 - 13:36 -- Dawn

This rhythm strip shows a good example of complete (third-degree) AV block with ventricular escape rhythm.  It will be easy for your basic students to "march out" the P waves.  They are regular at a rate of about 88/min., and they are either visible, or are "hiding" in the QRS complex.  The ventricular rhythm is wide and very slow, and completely dissociated from the sinus rhythm.

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

Sat, 01/12/2013 - 20:49 -- Dawn

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.

Ask The Expert

Tue, 11/06/2012 - 11:03 -- Dawn

 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.

 

jer5150's picture

Jason’s blog: ECG Challenge of the Week for June 24 – July 1, 2012. Pinpoint the primary disturbance.

This patient was seen by his primary care provider (PCP) on an outpatient basis.  The PCP decided to send her patient over to me to perform a routine ECG and establish a baseline, hince the computer's statement below of "No previous ECGs available".  I printed out the above 12-lead ECG and became slightly concerned with the rhythm I was seeing.  Consequently, I also recorded six full pages of continuous rhythm (not shown here).  I don’t ordinarily resort to doing this

Inferior Wall M.I. with Right Ventricular M.I.

Sat, 02/11/2012 - 17:39 -- Dawn

These two ECGs are from a 57 year old man with chest pain. The initial ECG shows ST elevation in Leads II, III, and aVF - inferior wall STEMI. Reciprocal changes are as expected in I and aVL. Reciprocal ST depression also seen in V1 and V2 indicate probable posterior wall involvement. Not surprising since the inferior wall is simply the lower part of the posterior wall. The first ECG also shows the patient in sinus brady with junctional escape: AV dissociation. The sinus node is often affected in IWMI that is caused by right coronary artery occlusion.

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