AssessmentsHeart failure: Pathology review
USMLE® Step 1 style questions USMLE
A 74-year-old woman presents to her primary care physician for evaluation of shortness of breath. Over the past several weeks, the patient has been using three to four pillows to prop herself up to sleep at night. Past medical history includes hypertension, diabetes, hyperlipidemia, and myocardial infarction with stent placement. Temperature is 37.0°C (98.6°F), pulse is 78/min, respirations are 18/min, blood pressure is 148/82 mmHg, and O2 saturation is 97% on room air. Physical examination demonstrates an additional low frequency heart sound heard just after S2. Which of the following best describes the underlying pathophysiology of this cardiac finding?
On the cardiology ward, there were two people who had been admitted to the hospital repeatedly.
The first one is 70 year old Lidia, who had a myocardial infarction about 3 years ago.
She presents with fatigue, and dyspnea.
She says that she usually wakes up at night because of shortness of breath, but using more pillows when sleeping helps relieve it somewhat.
On examination, she has pitting edema in her legs and on auscultation, an S3 sound is heard.
The other person is 81 year old Richard who has been a smoker for the past 50 years.
He is also experiencing fatigue, and has pitting edema, but on further examination, there’s also jugular venous distention and hepatomegaly.
Okay, so, both these individuals suffer from heart failure.
Heart failure is a clinical syndrome used to describe the inability of the heart to pump enough blood or a point at which the heart can’t supply enough blood to meet the body’s demands.
This can happen in two ways, either the heart’s ventricles can’t pump blood hard enough during systole, called systolic heart failure, or not enough blood fills into the ventricles during diastole, called diastolic heart failure.
In both cases, blood backs up into the lungs, causing congestion or fluid buildup, which is why it’s also often known as congestive heart failure, or just CHF.
Alright, first up is systolic heart failure.
One way to think about this is that the heart needs to squeeze out a certain volume of blood each minute, called cardiac output, which can be calculated as the heart rate multiplied by the stroke volume.
The heart rate is pretty intuitive, but the stroke volume is a little tricky.
For example, an adult heart might beat 70 times per minute and the left ventricle might squeeze out 70ml per beat, so 70 x 70 equals a cardiac output of 4900 ml per minute, which is almost 5 liters per minute.
Now, the stroke volume is only a fraction of the total volume.
The total volume might be closer to 110 ml, and 70ml is the fraction that got ejected out with each beat, the other 40ml kind of lingers in the left ventricle until the next beat.
In this example, the ejection fraction would be 70ml divided by 110 ml or about 64%, a normal ejection fraction is around 50-70%.
Now, in systolic heart failure, there’s decreased contractility of the left ventricle, which causes a decreased cardiac output because the stroke volume is low.
This means there’s also a decreased ejection fraction.
During diastole blood returns to the ventricles and combines with the leftover blood that didn’t get pumped out during systole, and this is called the EDV or end diastolic pressure volume.
With systolic heart failure, don’t forget that EDV is high, because there’s more blood leftover after each heartbeat.
Regarding the end diastolic pressure or EDP, which is the pressure that’s found in the ventricle at the end of diastole, this will also be high, because the volume at the end of diastole is high as well.
Systolic heart failure is mainly caused by low contractility which can happen with ischemia caused by myocardial infarction, where a part of the cardiac tissue is damaged so it won’t contract properly anymore.
Another cause is dilated cardiomyopathy, where the ventricle is dilated and weakened.
Now in addition to systolic heart failure, you’ve also got diastolic heart failure, which is where the cardiac contractility is sufficient but not enough blood is returning to the ventricles.
In this case, again, the stroke volume is low, but the ejection fraction is normal.
So for example, the total volume might be lower than normal, say about 69 mL, and we pump out 44 mL, so if we divided 44 by 69, we get 64%, which is in the normal range.
With diastolic heart failure, we need to look at the end diastolic pressure, or the EDP, as well.
The problem is that the left ventricle isn’t compliant enough, so when the ventricle is filling during diastole, the pressure within will rise, so keep in mind that EDP is elevated during diastolic heart failure.
Also remember that with diastolic heart failure, EDV is normal, at least in the beginning, because the atria are capable of squeezing more blood into the ventricle.
One cause of diastolic heart failure is ventricular hypertrophy, where the ventricular myocardium gets thicker, and this decreases the ability of the chamber to stretch when filling.
Alright, so heart failure can be systolic or diastolic a