The ECG Course. Boone County Fire Protection District EMS Education

Transcription

1 The ECG Course

2 Level I G rated material

3 AV Blocks

4 What Causes AV Block? Long list of bad things that includes ischemia and.. Old age / disease Medications or drugs Electrolyte imbalances

5 Physiologic Blocks Physiologic blocks occur for good reasons, such as when atrial flutter is conducted partially, resulting in a better heart rate. Another example of physiologic block is the nonconducted PAC, when the premature P wave occurs very early after the preceding beat, finding the ventricles refractory and unable to produce a QRS. AV Node attempts to keep the rate <

6 1st Degree AV Block Prolonged PRI (longer than 200 milliseconds) No dropped beats Ratio is 1:1

7 First Degree AVB Medication causes (digitalis is a common one) Associated with Inferior Wall MI (about 13% of the time) May progress don t be fooled by the degree Nodal block

8 1st Degree AV Block

9 2nd Degree Type I Type I (Mobitz I, Wenkebach) Lengthening PRI before dropped beat Only one beat is dropped Ratio is 3:2 or 4:3 or 5:4 etc. 1 run game

10 Mobitz I Medication cause (digitalis) Ischemia cause (Inferior MI common) Usually benign but may progress Nodal block

11 2nd Degree Type I

12 2nd Degree Type II s Infranodal in His Bundle or below Left Coronary Artery lesion Anterior MI Usually symptomatic Frequently progresses to Complete AV Block

13 2nd Degree type II Type II (Mobitz II) Constant length PRI before dropped beat Only one beat is dropped Ratio is 3:2 or 4:3 or 5:4 etc. 1 run game

14 Mobitz II Often, the patient with second degree type II has a pre-existing bundle branch block, usually of the right bundle branch. They sometimes have a hemiblock on the left, as well. (Bi-fascicular block). When the remaining fascicle develops an intermittent block, second degree type II is produced. You could say that second degree AV block type II is an intermittent tri-fascicular block, or an intermittent complete heart block. Second degree AV block, type II usually represents a necrotic, progressive lesion. It is very likely to progress to complete heart block (third-degree). If it does progress to third degree AV block, the escape rhythm, if there is one, will be idioventricular. The bradycardia caused by the AV block may cause syncopal episodes. Patients with second degree AV block, type II usually are treated emergently with a temporary pacemaker until they can receive a permanent, implanted pacemaker. One of the biggest worries with 2:1 conduction, regardless of type, is that the conduction ratio automatically cuts the patient s rate in half. An underlying sinus rate of 70 bpm with 2:1 AV conduction will produce a pulse rate of 35 bpm!

15 2nd Degree Type II

16 2nd Degree AV Block 2:1 Conduction Only one PRI before dropped beat Only one beat is dropped Ratio is 2:1 Can t tell if PRI is constant or lengthening there is only one so nothing to compare.

17 2nd Degree 2:1

18 2nd Degree-High High-Grade AV Block More than one beat is dropped Ratio is 3:1 or 4:1 or 5:1 or more This is NOT a 3rd Degree AV Block

19 2nd Degree-High

20 3rd Degree AV Block AV Dissociation must be present. Atria are firing at a different rate than the ventricles P-waves march out and the QRS s also march out just to different drummers. Technically, there is no PRI but there is a space between P-waves and QRS complexes and that space is changing length randomly. Technically, there are no dropped beats but it may appear that there are.

21 3rd Degree AV Block AV Dissociation must be present. Atria are firing at a different rate than the ventricles P-waves march out and the QRS s also march out just to different drummers.

22 The AV Junction

23 Degree vs Severity Degree of the AV Block is misleading in terms of estimating severity. The location of the block is more predictive.

24 Conduction System Blood Supply AV Node right coronary (about 90%) Bundle Branches left coronary artery

25 Conduction System Innervation SA Node parasympathetic AV Node parasympathetic Bundle Branches no parasympathetic

26 Infranodal AV Blocks Very few parasympathetic fibers innervate below the Node. Infranodal block unlikely caused by excessive parasympathetic tone. (usually ischemia) Atropine will be very unlikely to help.

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29 Location-QRS Width NOT a hard and fast rule but Nodal = QRS is not wide Infranodal = wide QRS

30 Location-Cause Nodal = inferior MI Infra nodal = anterior MI

31 Ratio of P s to QRS s Needed in order to accurately identify the rhythm when there are dropped beats (P-wave does not cause a QRS). First step make sure the P wave that is not conducted is NOT a PAC. Step two if NOT a PAC, then the rhythm is some flavor of 2nd Degree AV Block.

32 Six Foot Strip Print out a long rhythm strip a 12-Lead is only 10 seconds long. Paper is cheap. Print it out, lay it out, march it out (the P- waves). Find out what the P-waves are doing first.

33 AV Blocks

34 Blocks AV Nodal blocks tend to be transient when their cause is relieved, they resolve. Blocks below the AV Node (infranodal) tend to be due to a serious lesion and may progress or become life-threatening.

35 Complete AVB

36 Complete AVB Third degree AV block is diagnosed when no atrial impulses are conducted to the ventricles. This is one form of AV dissociation. Third degree AV block can occur in the AV node, bundle of His, or bundle branches. If the block is in the AV node, it will usually have a reliable junctional escape rhythm. When the condition causing the block is successfully resolved, the block will be, too. Third degree AV block occurring in the His bundle or below will result in an idioventricular escape rhythm. It may occur suddenly, with a block of the His bundle, or the right and left bundle branches simultaneously. Or, third degree AV block may be a result of progressive disease of the fascicles, resulting after a period of second degree AVB, type II. Third degree AV block can also occur without the benefit of an escape rhythm. This results in ventricular standstill. Sometimes there is a warning, with a progressive AV block occurring. At other times, sudden ventricular standstill can occur!

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