Lethal Diseases of Heart

Topics: Heart block, Sinoatrial node, Heart Pages: 8 (2150 words) Published: August 28, 2013
Heart Blocks7/ 2005

Hi all. Yet another one, which occurred to me that I should do about two weeks ago, when a patient was doing some pretty strange things on the monitor. As usual, please remember that this is not meant to be an official reference, but is supposed to represent the information that a preceptor would pass on to a new orientee in the unit. Please get back to me if things aren’t clear, have been left out, or are just plain wrong, and I’ll fix them up right away. Thanks!

1- What is a heart block?
2- What exactly is being “blocked” in heart block?
2-1- The key idea: all of the time, some of the time, none of the time…
2-2- It can not be that simple…
3- Why do heart blocks happen?
4- What are the three types, or degrees of heart block? What is a “dropped beat”?
4-1- A normal rhythm for reference.
4-2- First degree heart block.
4-3- Second degree heart block.
4-3-1- Second degree, type 1: Wenckebach/ Mobitz 1
4-3-2- Second degree, type 2: Mobitz 2
4-4- How I tell them apart?
4-5- Third degree (complete) heart block.
5- A puzzler…
6- What is the treatment for heart block?
7- Where can I learn more about pacemakers?

1- What is a heart block?

Heart block is a kind of arrhythmia, usually caused by ischemia or an MI. There are three kinds, or degrees of heart block, and although sometimes people get confused about them, actually they’re pretty simple to understand.

2- What exactly is being “blocked” in heart block?

The signal from the SA node is trying to get to the AV node, and it’s being slowed down, or blocked altogether – it’s having a hard time getting through. The result is that the SA signal going through the atria makes a normal P wave, but if that signal doesn’t trigger a response from the AV node, no QRS gets produced – so you’ll see a P wave that isn’t followed by a QRS. The QRS represents ventricular depolarization – so what? So what is: no depolarization, no contraction, no blood pressure!

The signal is trying to get from here…

To here…

www.arrhythmia.org/ general/whatis/

2-1- Here’s the key idea - the signal is either getting through:

1- All the time (but taking a little longer than usual). 2- Some of the time.
3- None of the time.

Got that? All, some, or none of the time. And see, those are the three kinds, or degrees of heart block: first, second, and third degree. All, some, or none.

2-2- It can not be that simple…

Sure it can. This is one of those things that people get scared of, and they build it up in their heads as if it were this enormous mysterious thing, like running a nuclear reactor. (When she learns about something new, Jayne always says: “Well, is it easier or harder than a ventilator?”)

3- Why do heart blocks happen?

Heart blocks usually happen when the patient is having ischemia, or an MI. The blood supply to the nodes is interrupted, or reduced, and they become unhappy – but at least in this regard, they do it in recognizable ways.

CCU nurses – what kind of MI or ischemia commonly produces heart blocks?

4- What are the three types, or degrees of heart block? What is a “dropped beat”?

4-1- First of all, here’s a normal strip for reference:

[pic]

Right – a quick bit of review. See the P wave? Now, see where it meets the QRS? Actually, that first upright part of the QRS is the R wave - there’s no Q-wave here. (There’s more about Q waves and what they mean in the faq on “Reading 12-lead EKGs” – basically you don’t want to see them, because they mean the patient has gotten into the tissue necrosis stage of an MI.)

So – no Q waves here. Ok… so the first, upright move of the QRS complex is the R wave, right? So the measurement from the beginning of the P wave, until it hits the R wave, is called (surprise) the P-R interval. A...
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