Conduction blocks

Conduction blocks…the only way we can see a block is through an ECG

SA block (sinus block/arrest/SSS) where SA node doesn’t fire

During the time when there is no SA signal is called asystole, after this the AV node will stimulate a beat, this is called a nodal escape beat or junctional escape beat (nodal = junctional)

AV Blocks

Left vagus goes to AV node & Right goes to SA node. Time b/t between P-wave & QRS is the AV delay. When this time is increased, it is due to increased vegal tone. (Dr. Christy thinks this can be due to excessive upper cervical adjusting.)

The purpose of the AV node is to hold the signal for a brief signal (.2 seconds), if it holds is too long there is a block

1° - presence of an excessive AV delay, All P-waves conducted,

lesion is in AV node, think UC problem

By itself is not life threatening, pts don’t know they have it

50% of people w/1° will develop 2°

2° - presence of some non-conducting p-wave

Problem can be in common bundle or in

It’s more serious when with common bundle

This can be fatal, will end up with asystole (p-waves will still be present)

A 1° block is not required to have a 2° (60% of pts with 1° will develop 2° blocks)

2 Types of 2° Blocks

- Mobitz I (Wenckebach), it is predictable, there is a pattern. = lesion is in AV node

The PQ interval (AV delay) is ever increasing, then there will be a non-conducting signal

4:3 block (4 p-waves for every 3 QRS); there must be a minimum of a 3:2 block to tell if it’s a Wenckebach

The common bundle will take over when needed

- Mobitz II (Non-Wenckebach) = lesion is in common bundle

Block site is infranodal,

there is no pattern as to which p-wave will not conduct

PVCs can happen in the middle of these

These are deadly; many believe this is what happens to young athletes who die on the field

If this is detected b/f an outpatient procedure they won’t do the procedure until further tests & care by a cardiologist

If you can’t see if it’s a Mobitz I or II, then assume it is II = non-Wenckebach

We determine if it Mobitz I or II to determine where the lesion is

3° - No P-wave is conducted, total heart block, in this case all signals for beats are from below AV node, but the heart is still beating

AV junction is the same as AV node

Ventricular Asystole

W/ a Type II Block (lesion is in Common Bundle), and it doesn’t let a signal get down, the next place is the bundle branch, but if they are blocked also, the only thing left is a spot in ventricular wall.

Ventricular asystole is not always so sinister. If it develops as a result of vagal storm such as with vomiting, the level of block is in the AV node and the disturbance may be relatively mild and transient (cam also happen with UC adjusting)

3° Block – Complete Block – Total heart block

None of the P-waves never get down to the ventricles; therefore every beat of the heart is an escape beat.

There will be a nice rhythmic p-waves, and a QRS that have a nice rhythm, but the two don’t correlate with each other

There is both atrial & ventricular depolarization, but they are not working together

Category: Cardiology Notes