Monday, July 30, 2012

High Output Cardiac Failure



Friends, it's Medicine time!




Photo credit to wisdom.blogs.com

Today, let's talk a bit about High Output Cardiac Failure!

By definition, cardiac failure, or simply heart failure, is a pathological condition whereby the heart is unable to pump sufficient blood to meet the demands of the body. In other words, there is reduced cardiac output (CO). Cardiac output is the product of stroke volume and heart rate. Stroke volume is the volume of blood ejected from each ventricle in one cardiac cycle, and the heart rate is the number of the times the heart beats in one minute. So cardiac output is always defined as a certain volume over 1 minute, ie x cm3/min. An average resting cardiac output would be 5.6 L/min for a human male and 4.9 L/min for a female.

Sometimes, people write cardiac output as "Q", so

Q = Stroke Volume × Heart rate

In conclusion, keep this in your head: Heart failure = Low cardiac output = low oxygen supply.

Then there are multiple compensatory mechanisms that aim to increase the oxygen supply, either by eliciting changes in the vascular tone, blood volume or contractility of the heart. But this is beyond our topic.

However, there are a few cases in which there is an increase in cardiac output. But due to certain reasons, it is unable to meet the demands of the body, so it is still considered "heart failure". My lecturer only listed 4 examples of this rare scenario, examples that we can all easily remember with the mnemonic ABAH.


A = Anaemia

B = Beri-beri

A = Arteriovenous fistula

H = Hyperthyroidism / Thyrotoxicosis


So if the 'usual' heart failure is characterize by low CO, what about high-output cardiac failure?

Just like what the name entails, high-output cardiac failure is characterized by an elevated resting cardiac index beyond the normal range of 2.5 to 4.0 L/min per m2.[1]

Wait, wait. What is this "cardiac index"? Don't worry, I've done the googling for you. Cardiac index relates cardiac output with a person's total body surface area (BSA). The formula is:

Cardiac index = CO/BSA = (SV . HR)/BSA

You divide the Cardiac output with the patient's body surface area. So since CO is volume/min, cardiac index is volume/minute/area. The normal value range from about 2.6 - 4.2 L/min. There are small variations between the sources I referred to.


Despite having a high cardiac output, it is still a 'heart failure', so the results is about the same. There are:


1) ineffective blood volume and pressure

2) chronic activation of the sympathetic nervous system and renin-angiotensin-aldosterone axis

3) increased serum vasopressin (antidiuretic hormone) concentrations, which leads to

4) chronic volume overload


all of which gradually cause ventricular enlargement, remodeling, and what we all know as heart failure. [1]


That's all for today folks! My rajinness stops here. Until next time, bye!




Sources (that I bothered to copy the URL):

[1] http://www.uptodate.com/contents/high-output-heart-failure

Wikipedia, of course. Wiki FTW!

2 comments:

  1. No wonder you're a star student. You eat, drink and breathe medicine...even during holidays XD.

    Uptodate.com is new to me, but it's awesome because it lists so many references. Will keep it in mind for future reference insyaAllah.

    Welcome back to the blogging world. =)
    I wish you would get back to writing stories though =P

    ReplyDelete
  2. This just came to my mind, that's all. =P

    The only bummer about uptodate.com is you have to pay to read the full article =(

    Thanks XD.
    I don't know how that can happen. I'm too lazy to read stories/story books la. Why don't you start? And maybe by some telepathic influence, I'll feel like writing too. XD

    ReplyDelete