Heart disease question

See if you can solve this before scrolling down to see the answer and explanation!

A 20-year-old male died suddenly and unexpectedly while playing basketball. (more…)

Which direction does blood flow through the ductus arteriosus?

Q. I just had a quick question for you. Our notes say that a ductus arteriosus allows flow from the pulmonary artery to the aorta, which I knew.
However, they also say that it’s a left to right shunt, and that it can become right to left. This confuses me, since from what I know, flow would be going from right (pulmonary artery) to left (aorta).

A. When we talk about the ductus allowing flow from the pulmonary artery (right) to aorta (left), we’re talking about intrauterine flow through the ductus. Before birth, the pressure on the right side of the heart is greater than the pressure on the left – so blood flows from pulmonary artery to aorta (through the ductus).

After birth, though, the pressure on the left becomes greater than the pressure on the right. In most babies, the ductus closes (probably in response to the new levels of oxygen in the blood). In some babies it remains patent, in which case flow would now be from the aorta (left; higher pressure) to the pulmonary artery (right; lower pressure).

If the ductus is widely patent, then after a while, that left to right shunt can put enough pressure on the lungs that they react by closing down vessels, effectively making it more difficult to push blood through. Now the right heart has to work really hard to push blood through the lungs – and it can get to the point where the right heart is actually bigger and stronger than the left, making the shunt reverse and go from pulmonary artery (right; higher pressure) to aorta (left; lower pressure).

Student questions about congenital heart defects

why

I received a bunch of great questions from a student in my pathology course, and thought I’d share them with you. I think reading about things in in question/answer format helps the material stick in your head. These particular questions are about congenital heart defects.

Q. Can VSD and PDA also lead to the same pulmonary problems as ASD since they are all left to right shunts?
A. Yes! Any left-to-right shunt, if it is big enough, can eventually put enough pressure on the right side of the circulation that the lungs respond by constricting vessels and laying down fibrotic tissue, leading to pulmonary hypertension. Eventually, if pressures on the right side exceed those on the left, the shunt reverses, becoming a right-to-left shunt.

Q. What is the effect/outcome of the overriding aorta in Tetralogy of Fallot?
A. The main problem in Tetralogy of Fallot is the pulmonary outflow obstruction – that really determines the extent and severity of the clinical picture. The overriding aorta doesn’t contribute much. It does allow unoxygenated blood to flow directly into the aorta, which doesn’t help matters. There already is a ventricular septal defect, which allows mixing of blood, so the overriding aorta would just exacerbate that mixing, making it even easier for blood to bypass the lungs and go straight to the peripheral circulation. Which manifests as cyanosis.

Q. Can you surgically repair transposition of the great arteries?
A. Yes. Patients with TGA usually have some sort of shunt as well (like a VSD) – and depending on the degree of shunting, they may be fairly stable for a little while. However, most of the time, the transposition is repaired surgically within weeks of birth.

Q. Is mitral valve prolapse an insufficiency since it cannot close properly?
A. Yes – that’s exactly right. Insufficiency means the valve can’t close properly; stenosis means it can’t open properly. In mitral valve prolapse, the leaflets are floppy, and they don’t come together like they should, so during diastole, blood regurgitates into the left atrium.

Congenital heart defects

blended heart

Congenital heart diseases are abnormalities of the heart and/or great vessels present at birth. They are not all that uncommon: 1% of live births in this country has a congenital heart defect! The clinical spectrum is broad. Some congenital heart diseases cause death in the perinatal period; others are so mild that there are only minimal symptoms, even in adulthood.

Something happens in embryogenesis at the time of heart development (weeks 3-8) – but the actual cause can be traced only 10% of the time. Of the known causes, infections (like rubella) and genetic disorders (like trisomy 13) are the most common.

You can divide congenital heart defects into two broad groups: those that cause shunts (abnormal communication between chambers or vessels) and those that cause obstructions (narrowed chambers, valves, or major vessels). Shunts are more common than obstructions; the more common of these are atrial septal defects, ventricular septal defects, patent ductus arteriosus, and tetralogy of Fallot. The most common obstruction is aortic coarctation. Let’s take a really quick look at these defects.

Atrial septal defects
In this type of congenital heart disease, there is a hole between the two atria. Initially, this causes a left-to-right shunt. Left to right shunts, in general, are pretty well tolerated, and that’s the case for ASD too. However, over time, especially if the defect is large, pulmonary vessels can become annoyed by all that extra blood volume they are exposed to – and the pressure in the lungs goes up (due to vessel constriction and fibrous tissue deposition). So the pressure on the right side goes up, and eventually it can even exceed the pressure on the left, leading to a reversal of the shunt. This is called Eisenmenger Syndrome. This is not a good thing, because it can lead to heart failure, irreversible pulmonary vascular disease, and paradoxical embolism (where blood clots from the heart go to the systemic, rather than pulmonary, circulation).

Ventricular septal defect
This is the most common congenital cardiac anomaly, and it’s just what the name says: a hole between the two ventricles. Small VSDs are generally asymptomatic; large VSD cause big left-to-right shunt, which may become right-to-left (as described above). Most close spontaneously in childhood.

Patent ductus arteriosus
The ductus arteriosus is a normal connection between the pulmonary artery and the aorta that exists in fetal life to allow most of the blood to bypass the unoxygenated lungs (this helps the left ventricle get stronger). The ductus normally closes spontaneously by day 1 or 2 of life; if it remains open, then you can get a left to right shunt. Most of the time PDAs are asymptomatic, but if they big enough, they can eventually lead to Eisenmenger syndrome.

Tetralogy of Fallot
This defect is an example (the most common example) of a right-to-left shunt. Right-to-left shunts in general present with cyanosis at birth, because poorly-oxygenated blood from the right heart gets mixed into the arterial circulation. Patients can get clubbing of the fingertips and erythrocytosis as a result. Tetralogy of Fallot has four features: VSD, obstruction to the right ventricular outflow tract, an aorta that overrides the VSD, and right ventricular hypertrophy. Even untreated, though, many patients survive into adult life. It all depends on the severity of the pulmonary outflow obstruction.

Aortic coarctation
“Coarctation” means “narrowing” – so aortic coarctation means narrowing of the aorta. There are two forms: infantile (in which the narrowing occurs proximal to the ductus arteriosus) and adult (in which the narrowing occurs distal to the ligamentum arteriosum). In the infantile form, there is delivery of poorly-oxygenated blood through the ductus, which leads to cyanosis in the lower half of body. The femoral pulses are generally weaker than those of the upper extremities. This is a severe abnormality; these babies need intervention or they may not survive the neonatal period. The adult form is usually asymptomatic, and the disease may go unrecognized into adult life. When there are symptoms, they consist of upper extremity hypertension (due to poor perfusion of kidneys) but weak pulses and lower blood pressure in lower extremities.

Image credit: qthomasbower (http://www.flickr.com/photos/qthomasbower/3470650293/), under cc license.

Risk factors for atherosclerosis

smoker

Atherosclerosis is responsible for half the deaths in the US today! If you get it in your coronary arteries, you’re at risk for myocardial infarction; if it’s in your carotid arteries, you’re at risk for stroke. And lest you think this is something you don’t need to worry about until you’re old, you should know that this process starts very, very early in life – somewhere during childhood – and you just can’t tell you have it until you suddenly start getting nasty symptoms (doctors call this the “clinical horizon,” which sounds strangely picturesque). Scary.

There are lots of risk factors for getting atherosclerosis. They are divided into two groups: major risk factors (which are known for sure to cause atherosclerosis) and lesser or uncertain risk factors (which have less of an effect, or are as yet unproven). Let’s take a look at both groups.

Major risk factors

Some of the major risk factors for atherosclerosis you are simply stuck with, and there is not a thing you can do about them. These include:

  • increasing age (atherosclerosis is more common as people get older)
  • gender (At younger ages, males are more at risk. Premenopausal women are relatively protected; after menopause the risk in women increases and eventually exceeds the risk in males.)
  • family history
  • genetic abnormalities (lots of these probably exist; many aren’t fully understood).

The good news is that there are several major risk factors that you can potentially do something about. These include:

  • Hyperlipidemia (best thing to do is have a high level of HDL cholesterol, which actually scavenges lipids and removes them from atherosclerotic plaques, and a low level of LDL, which is the “bad” cholesterol that makes up part of the plaques.
  • Hypertension (there’s no one right number, but it should be at least below 140 systolic and 90 diastolic)
  • Cigarette smoking (smoking potentiates the other risk factors)
  • Diabetes (patients with diabetes mellitus have an increased amount of atherosclerosis at a younger age)
  • C-reactive protein level (this is a serum marker of inflammation; the higher the level, the greater the risk for atherosclerosis)

Lesser or uncertain risk factors

Then there are a bunch of other things that may be related to an increased risk, but the data is not yet conclusive. These include:

  • Obesity
  • Physical inactivity
  • Stress
  • Postmenopausal estrogen deficiency
  • High carbohydrate intake
  • Lipoprotein (a) (an altered form of LDL that seems to be independently associated with increased risk of atherosclerosis)
  • Trans-fat intake
  • Chlamydia pneumoniae infection (Chlamydia pneumoniae and other bugs have been detected in plaques but not in normal arteries, and there are increased antibody titers to C. pneumoniae in patients with more severe atherosclerosis. But a causal link hasn’t been established.)

So: don’t smoke; eat well (not too many carbs, no trans fats), exercise, and maintain a healthy weight; keep your blood pressure and lipids within the normal range; if you have diabetes, work to keep it as controlled as possible; don’t get Chlamydia pneumoniae. Oh, and don’t get all worried about it – stress is another potential risk factor!

Image credit: Hamed Masoumi (http://www.flickr.com/photos/hamedmasoumi/2266654041/), under cc license.

Hemolytic disease of the newborn

Phototherapy

Hemolytic disease of the newborn (HDN) is a disease in which there is hemolysis in a newborn or fetus caused by blood-group incompatibility between mother and child. (more…)