Heart Health

Diastology

September 13, 2010

Diastology

In this post I’m going to talk you through a little cardiac physiology.For those of you who have interest in this sort of thing, read on.The remaining 90% of you can simply click the “back” button in your browser and move on to checking your Facebook profile or browsing the latest news about celebrities acting badly.

Every once in a while I feel the urge to write about something that’s actually educational, in contrast to previous posts about drug names, anxiety, and poetry dedicated to toxic flowers.With this in mind I’d like to educate you on the concept of congestive heart failure (CHF) and ejection fraction.

CHF, as most of you already know, is the condition that arises when the heart cannot adequately cycle the needed amount of blood volume to your limbs and organs.The symptoms of CHF arise from an inability to push blood out to the body (fatigue, lightheadedness) or to process the blood that returns from the body (swelling in legs, fluid in lungs, labored breathing).It’s a common condition that can arise from multiple causes.

The term ejection fraction (EF) should not be confused with rejection fraction, a phrase that refers to percentage of girls who turned me down for dates in high school (my RF was somewhere around 93%).No, EF is actually a heart-related thing.It refers to the amount of blood that is squeezed out of the left ventricle (LV) of the heart (the main pumping chamber) with each beat.Intuitively, you would think that a normal EF would be 100% but it turns out that the heart doesn’t ring every drop of blood out of its cavity with every contraction.A normal EF ranges from about 55 to 70 percent (in other words, about two thirds of the volume of blood that has filled the LV between contractions actually gets forced out with each beat; a third stays behind).

A weak heart (or, more precisely, a weak LV) is a common cause of CHF.Instead of having an EF of 60% a patient with CHF symptoms may be found to have an EF of only 20% and is therefore left with a heart that is about a third as strong as it should be.If only 20% of the blood in the ventricle is pushed out to the body with each beat it doesn’t take much imagination to understand how that type of patient may suffer from the symptoms I described above.

In order to demonstrate this concept I’ve created a series of visually stunning and anatomically accurate diagrams representing the highly complex mathematical principles associated with EF (in other words, I made some circles):

You’ll note two words you may not be familiar with: systole (SIS-tuh-lee) and diastole (dye-ASS-tuh-lee).Systole is Greek for “drawing together” and diastole translates to “drawing apart,” and respectively these words refer to ventricular contraction and relaxation.It’s not really important that you know what these words mean in Greek; it just gives me a chance to show off my mastery of ancient languages (and you wonder why I couldn’t get dates in high school).

Now let’s throw in some math.A typical heart fills with about 120 ml of blood in between beats (during diastole) and squeezes out all but about 40 ml during systole.The difference between those two values is called the stroke volume and is the amount of blood that is expelled with each beat (80 ml per beat and 60 beats per minute equals 4.8 liters of blood pumped each minute-a relatively normal resting value).We calculate the EF by dividing the stoke volume by the diastolic volume (80 ml ÷ 120 ml) and in this case come up with an EF of 67%.

Here are diagrams that represent a sick and weak heart.The stroke volume (160 ml minus 120 ml) is only 40 ml, half of what it should be.You’ll note that the size of the LV is somewhat different than in the normal example above: the heart is larger and the volume of blood is greater.This is a normal (albeit unhealthy) compensatory mechanism that allows the heart to continue to produce an acceptable stroke volume despite a lower EF.

To calculate EF we simply divide the stroke volume by the diastolic volume, and in this example we come up with a quotient of 0.25, or 25%.A patient with an EF of 25% could easily develop CHF symptoms and would be a candidate for aggressive medical management.

Now comes the really interesting part.Half of all patients presenting to hospitals in the U.S. with the diagnosis of congestive heart failure actually have a normal EF.How is this possible, you ask?Doesn’t a normal EF imply normal heart function?

The whole concept of EF is a fabricated construct that allows us cardiologists to quantify the strength of the LV contraction but it really has very little physiological bearing.The body doesn’t really care what the EF is-it’s only interested in how much blood gets pumped out with each beat.The stroke volume is the value that determines whether the brain receives enough blood to keep a patient lucid and comfortable.If the LV can squeeze out 80ml with each beat then the kidneys, liver, lungs and legs all stay happy; less than that and the patient develops CHF.

Let’s now introduce the concept of diastolic CHF, but in order to do this properly I need to briefly remind you all about blowing up balloons when you were kids.Do you remember how hard it was to expand a balloon that came straight out of the package?You blow with all your might but the stiffness of the latex resists expansion; only after you pull and stretch on the deflated balloon are you able to push any air into it.Later, after you’ve inflated and deflated the balloon several times, it becomes easy to blow it up to its maximal size.

When you’re young, your heart muscle is pliable and easy to stretch, much like a worn-in latex balloon.It accepts a large volume of blood with nearly no resistance.Furthermore, the young and healthy muscle cells actually participate in the process of relaxation between heart beats by actively stretching to accommodate the incoming blood volume.

As you age, your ventricular walls become gradually stiffer and don’t relax and expand quite as quickly or easily.Persons with poorly controlled high blood pressure compound the problem by developing thickened heart muscle that decreases the effective ventricular cavity during diastole.The heart takes on the characteristics of the stiff new balloon fresh out of the package.

Take a look at the next diagram.This is the heart of an elderly patient who has spent his life ignoring his doctor’s advice to take his blood pressure pills.The heart muscle is thickened and poorly compliant.The overall size of the LV is larger than normal, but due to the thickness of the wall the interior volume is diminished (60 ml versus the normal 120 ml).Ventricular contraction isn’t a problem, and the EF in this patient is robust at 67%.If you were to judge this patient’s heart function on EF alone you’d conclude that it’s quite healthy.

But remember, the really important number to the body is the stroke volume, and in this situation it is a measly 40 ml per heart beat-exactly the same as in our patient with a weak heart, and about half of what it should be.This number worsens anytime the patient develops a rapid heart rate (as with atrial fibrillation) or excessively high blood pressure.When that happens, the stroke volume drops even further, fluid builds up in the lungs and legs, and the patient comes to the emergency room with the exact same symptoms as the patient with an EF of 25%.

There are various ways we can assess the diastolic function of a person’s heart but the most common is with cardiac ultrasound (echocardiography).The science of ventricular relaxation has become quite a hot topic over the last decade and is something of a cottage industry for many academic cardiologists.I attended a conference a few years ago hosted by several self-designated “diastoligists,” experts in the arena of echo-based diagnosis and assessment of diastolic function.That’s right: there are cardiologists who specialize to such a degree that they limit their realm of study to the diastolic portion of the cardiac cycle.Not contraction and relaxation-just relaxation.That’s something like an auto mechanic who specializes in problems of the left front wheel.Of European cars.That are blue.And only during right-hand turns.

With our current epidemic of obesity (which leads to hypertension and diabetes) we’re likely to see a continuing rise in cases of CHF due to diastolic LV dysfunction.The mainstay of treatment is control of blood pressure, following a sensible low-salt diet, and good compliance with prescribed medication-all factors that require active participation on the part of the patient.

So, if you’re a patient with high blood pressure and likes to ignore your doctor’s advice, I’ll give you this warning: Take your meds, watch your salt, do your exercises, and eat your greens.And above all, do not make me call in the diastologist!

Eric Van De Graaff, MD

Eric Van De Graaff, MD is a Heart & Vascular Specialists at CHI Health Clinic.

14 Comments
  1. Jena

    You did a great job explaining such a complex subject. I remember when I taught Dad's anatomy class, one of the hardest subjects for the students to understand was systole and diastole. Aren't you glad you aren't a diastologist? What a boring profession.

  2. Jen

    As one of the 90% of readers who doesn't even really know what cardiac physiology is (apparently they don't teach that in journalism school) and who thoroughly enjoys Facebook and celebrity gossip ... I'd like to thank you for still making this topic understandable! My question - and I apologize if it's a dumb one - is whether or not it's possible to reverse diastolic CHF? Can slowly adding in exercise assist in making your ventricular walls pliable once again? Or are you just forced to live with the symptoms once it's reached that point

  3. karen

    it was really very informative i was able to put each piece together myself and get a more clearer picture of the pieces of an echocardiogram and with the EF and also the twist in the story when it doesn't look like it but really is congestive heart failure on the echo"really cool"

  4. Dr. Van De Graaff

    Jen, This is actually a very good question (even from a journalism major). Diastolic heart failure is actually quite easy to prevent and, to some degree, reverse. What is required is a real effort by the patient. The two keys to correcting the problem are 1) limit triggering factors (such as atrial fibrillation, spikes in BP, dietary salt indiscretion); and 2) decrease the thickening of the ventricular wall. The latter point would help reverse the process and can be accomplished with tight blood pressure control. One study in particular, published in the American Journal of Medicine in 2003, assessed the response of nearly 4 thousand patients with diastolic heart failure who underwent aggressive BP lowering therapy. All improved their ventricular wall thickness, despite which BP med was used (ARBs and ACE-Is worked the best, for those of you who care). Exercise and good dietary habits will also dramatically decrease recurrence of diastolic failure; but since it's a lack of these that start most patients down the road in the first place, you can imagine that we don't have too many patients that avail themselves of this simple therapy. Thanks for your question! Dr. VDG

  5. Jen

    Thanks! I'm sure it's frustrating as a physician to know that there is such a simple solution and yet your patients aren't necessarily willing to take that path. Interesting lesson, nonetheless!

  6. Sharman

    I was finally able to understand what killed my dad. I never could get any kind of detailed explanation of what was going on with my dad's heart. The doctors at UCSD Med Ctr that treated him did not seem to have time.

  7. Dr. Van De Graaff

    Ray, Some types of arrhythmias are simply not preventable. Many forms of supraventricular tachycardia (SVT) involve electrical flow through an electrical connection that has been present since birth and is not the result of unhealthy living. Your particular situation sounds like this. In your situation I'd recommend to find a cardiologist who can discuss a more permanent treatment of SVT. Catheter ablation is a highly successful and relatively low-risk procedure that eliminates the abnormal electrical pathway and permanently eliminates the possibility of having a recurrence of SVT. Check out this link: http://www.webmd.com/heart-disease/tc/supraventricular-tachycardia-treatment-overview Good luck with the physical agility and thanks for the question. Dr. VDG

  8. Pma

    As always, enjoyed the education. The visual of the circles will make it easy to remember and pass on to patients.Thanx!

  9. John Willoz

    I am one of the many patients you and Dr Ramachandran see in the clinic. I am also a volunteer at Midlands and have discovered your blog. It is WONDERFUL! I really enjoy he humor you thow in. Your posts really help me to understand the various aspects of what I may have to worry. Thanks so much.

  10. Michael Aaronson MD

    Professor, Thank you for making this complex information so digestible. I truly enjoy reading your blogs!

  11. Ray

    In april, I decided to start trainging again for Fire Dept physical agility tests. I was doing sprints and am pretty sure I caused myself to go into SVT (my pulse sustained over 200), lasting more than half an hour, finally becoming nauseous and voiding my stomach contents. Sorry, not trying to be too graphic. Of course my pulse went down immediately, and I felt great. I believe I vagaled down. Shortly thereafter had a stress test done, and nothing showed up. I do have hyptertension and use meds. You mentioned keeping yourself out of arrhythmia's such as A-Fib... and my question is how? Along with med compliance and food/exercise regimen. Thanks, Ray - LKS

  12. Mike

    Explained very well. You should conduct a conference for echo techs on how to quantify diastolic function through echocardiography.

  13. Ray

    Hey, thanks a lot. I really appreciate you taking the time to follow with all of our comments. I'm checking out that web site as we speak.

  14. elaine woodwdard

    I am a nurse. Explaining anything medical has the possibility of being dry and leave one to not want to read any further. However, your keen sense of humor makes the reading easy and the explanations , understandable. I found myself smiling at times reading some of your blogs. I wish all physicians could be more down to earth. (You are down to earth aren't you)

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