Matters Of The Heart-Hemibock

Sometimes a heart attack's worst damage is not to the myocardial damage itself, but to the nerve bundles that help distribute the depolarization to the ventricals. An occlusion in arteries supplying oxygent to particular bundle brances can cause a type of heart block called a hemiblock.

Cardiac Circulation

Even though the heart is filled with blood, this is not the same blood that supplies the heart with nutrients. After the blood leaves the heart for the aortia, two main arteries break off almost immediately and lead back towards the heart from the outside.These are called coronary arteries and they are the ones that supply the heart with nutrients. The most importiant for supplying the nerve fibers with nutrients are the two following:

Anterior Decending section of the Left Coronary Artery

Right Coronary Artery

Stupid Memory Thingy:

Yesterday I was trying to memorize which artery goes to which nerve bundle (because they kinda twist around and branch out like fingers to supply different areas) So wrote an outline that would help me remember:

I took a pin and wrote 'Right Coronary Artery' on the thumb and pinkie of my dominant hand.

The three middle fingers of my dominant hand I wrote 'Anterior Decending Left Coronary Artery' (or I would have, but it was too long so I wrote 'ADLCA')

On my non-dominant hand I wrote out the sections of the nerve fibers below the atria:

The AV node is my wrist

The Bundle of His is my hand

My thumb is the Right Bundle Branch

My index finger is the anterior segment of the left bundle branch

My ring finger is the Posterior Segment of the Left Bundle branch.

Now when I hold my hands together and fold my fingers over like I'm going to say a prayer (with my dominant hand's thumb on top) an outline forms that tells me which arteries suppy which sections of the AV conduction system:
The right coronary artery (on my thumb) is supplying blood to the AV Node and the His Bundle (on my wrist and the top part of my hand). (On my Pinkie) It is also supplying the posterior divistion of the Left Bundle Branch.

The Anterior Division of the Left Coronary Artery on my three middle fingers suppies the right bundle branch, the anterior segment of the left bundle branch, as well as also supplying the Postertior division of thet left bundle branch.

It helped me visualize the bundle branch fasicles and the arteries that serve them. I think it would have been more convenient to reverse the hands, because I normally rest the thumb of my non-dominant hand on top when I fold my hands, but it still worked.

Types of Hemiblock-

Hemiblocks are catergorized by the section of the bundle branches in which they disrupt electrical energy.

Anterior Hemiblock blocks the anterior division of the left bundle branch.

(The Anterior Division of the Left Coronary Artery supplies this area with blood)

On an EKG, this block will be revealed by a slightly widened QRS and an altered Q wave in lead I, as well as an altered S wave in lead III (abreviated S1Q3). (Left Axis Deviation)

Posterior Hemiblock Blocks the posterior divistion of the left bundle branch

(This area is supplied by both the Anterior Division of the Left Coronary Artery and the right coronary artery)

On an EKG, this block will be revealed by a normal or slightly widened QRS complex and an altered S wave in lead I, as well as an altered Q wave in lead III. (Abrevieated S1Q3). (Right Axis Deviation)

Right Hemiblock (or Right Bundle Branch Block) blocks the right bundle branch.

(This area is supplied by the Anterior Decending Left Coronary Artery)

On an EKG, this block shows minimal Right Axis Deviation, because the net electrical activity of the heart is moving away from this area anyway. However, this type of block often occurs with an anterior hemiblock (because they are supplied by the same artery!).

Complete Heart Block (involving the AV node/Bundle of His)

(Supplied by the right coronary artery)

The atria and ventricles will beat indepenedently of each other at an inherent rate.

Intermittent Mobitz

This happens when two of the three bundle branch pathways to ventricular depolarization are blocked, but the third still works intermittently.

This will appear as a bundle branch block of the perminently disabled fasicles, with an occasional missing QRS complex that is blocked by the remaining semi-functional bundle branch.

Because the atria are conductiong electricity normally, the P wave will always be present (and not premature), even when it is not conducted to the ventricles. (The problem is below the atria, so there are no premature atrial beats.)