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Monday, March 1, 2010

Ejection fraction vs. cardiac index

Occasionally I will hear someone with amyloidosis comment on their Ejection Fraction with the idea that it correlates with the degree of heart involvement from their disease. It seems prudent to discuss ejection fraction versus cardiac index. Primary amyloidosis (or familial), when it involves the heart, tends to cause restrictive cardiomyopathy. As the name indicates, restrictive refers to the stiffness of the heart and the subsequent difficulty in achieving muscle relaxation. However, contractility may still be preserved. In other words, the heart can pump, it just can't fill. Ejection Fraction or E.F. measures the percentage of blood volume expelled by the left ventricle with each beat. As a percentage it does not tell you the actual volume pumped per heartbeat. Therefore, if you start with with a cup of blood and push out 1/2 cup per beat, the ejection fraction is 50%. If you start with a 1/2 cup in the left ventricle and push out a 1/4 cup with contraction, the E.F. is still 50%. But your volume output is 1/2 of what it should be.
Cardiac index measures the actual volume of blood pumped per minute (adjusted for body size) This is a much more accurate measure of whether your heart is working up to the capacity your body needs.
The ejection fraction can be measured non-invasively with an echocardiogram, however measurement of the cardiac index generally requires cardiac catheterization. A heart stiffened by amyloid deposits does not relax well and the right ventricle has very little time between beats to adequately fill. A fast heart rate further diminishes filling time and cardiac output drops (so do we). A slower heart rate cannot provide enough blood per minute to meet demand. The restricted heart therefore finds an optimum rate and stays there. For me it was 85 beats/min. If I took a beta-blocker, and it slowed my heart rate, I felt horrible. If I ran, I fell down. When my cardiac index was finally measured it was 1.7 L/min/meter-squared. I copied the normal range from Wikipedia:

The normal range of cardiac index is 2.6 - 4.2 L/min per square meter.

If the CI falls below 1.8 L/min, the patient may be in cardiogenic shock.


Now I know why my doctor told me to stop operating, (eventually).

Bottom line: Just because your ejection fraction is normal doesn't mean your heart is.

Food for thought.

Kevin

1 comment:

Aunt Renie said...

It is amazing that you can do so much with so little.
You are a blessing in ways only God knows.