Session 4 - Lecture 1 - Congenital Heart Defects Flashcards
1 - Understanding Congenital Heart Disease
Understanding Congenital Heart Disease
“Had a lecture on the pericardium, used a blackboard rubber (block with foam on it) and duster how it folded around it, did one of those courses - pericardial taps, central lines and things, not allowed to do that anymore, but if you’re interested people will do that with you, although it was a v long time ago Prof knew everything there was about CHD (not much), nice talking to children and their parents, had a kid with Type II storage disease – v v rare, only about 3 ppl in the country – diss on overall principles with managing rare diseases, did a research reg job, did some adult med, paed med, neonates, and all the way through that I learnt to scan, went along to post-mortem room, played with dead babies hearts to appreciate 3D anatomy – 99% of us have a relatively normal heart, and most of cardiology is about acquired heart disease things go wrong if you don’t look after heart. Other 1% is much more interesting. [Transposition.] So it’s a womb-to-tomb specialty, look after pts when they’re born right till the end of their lives – a lot of people can get sick v quickly so you really need to sort things out, and there’s a lot of innovation, as every case is kinda unique. 1st heart operation done in 1900s, most of them just clipping things or whatever, this chap was Peter Gabriel – first person to have aorta-pulmonary chap, had Tetralogy of Fallot – came over to UK in early 1940s, see here Sep 27th, and I met him, he became my pt 10 years ago, hadn’t had any surgery since – repaired his ToF, good QoL, but sadly died since then. So it’s been going on a long time, and started closing heart defect, one of the first atrial-septal defects was done in Leics – q a lot of our pts are normal, but q a lot of them are not, and most of these people need help to get the best out of their lives as well, remember there are often other things going on, so I q like that. Come to us v sick, used to only be able to do things like ECGs and CXRs then they die and we dissect them, now we start to look at them in other ways, angiograms, MRIs, reconstruct them in 3D, and this has all happened since I’ve been in specialty – just started to do USS when I started – able to diagnose things before birth now – quality of images are completely diff to anything we ever used to be able to see – get 3D pics of baby’s faces, treat them medically. Any treatment we do tends to be palliative, this is a heart with endocarditis, full of vegetations, can give Abs, don’t really cure anything, give drugs for heart rhythm disturbances, anything we do has side effects. We gave this person adenosine; and that heart never restarted. So it is q dangerous, and we’re always balancing risks, and we discuss that endlessly. We can do keyhole treatments, blow balloons up. We can stent things, we can blow a balloon up with a stent on it, so we can do lots of things but they all carry a risk, sometimes things bleed out, have to have contingencies in place – surgeons, v specialised area, they’re doing the exact same thing, they’re buying time, no one’s curing anything, surgeons put tubes in heart to support the circulation”
2 - Contents
- Aetiology
- Pathophysiology
- Simple and complex conditions
- Natural history of common conditions
- Surgical and non surgical treatment
“You need to know about CHD, bc although it’s rare it’s not that rare. And also, if you can understand CHD you can understand anything else about the heart bc it’s all interlinked and related, this is the more interesting bit. You also need to know what causes it, how it happens and bit about it, already given you a bit of a flavour for that but we’ll go through it in a bit more detail.”
3 - Aetiology of Congenital HD
• Genetic – Down’s, Turner’s, Marfan’s syndromes • Environmental – Teratogenicity from drugs, alcohol etc • Maternal infections – Rubella, Toxoplasmosis, etc
“Syndromes – maybe tested you on pics but you’ve all heard of Down’s syndrome – underlying genetic defect here, trisomy 21. Turner’s syndrome – sorry, no Turner’s syndrome is a single X chromosome. Marfan’s syndrome, that’s a single gene defect – that’s a defect in the fibrillin gene – so there’s lots of syndromes like that with true gene associations but probs polygenic, may have a gene abnormality bc you have a gene, myosin genes for cardiomyopathy can also cause ventricular septal defects, it depends on what other genes you inherited from your parents; often it is what goes on in making the egg and the sperm. Environmental issues, probably are, certainly more from some areas of the world than others – Eastern European babies from Eastern European migration, undoubtedly an element of prior environmental exposures here. Drugs, lots of drugs, not just sort of recreational ones but phenytoin, sodium valproate, lithium (bipolar disorder – causes rare anemology of tricuspid valve), alcohol - foetal alcohol syndrome – relatively minor CHD. Internal infections, rubella is classic one, associated with deafness, patent ductus; toxoplasmosis tends to cause functional problems. Lots of environmental things can cause it, often it’s random, can occur really early in development, before most people even know they’re pregnant, the heart is forming, so it’s important that we try and remove any blame from parents who have a child with a congenital heart problem.”
4 - Patho-physiology
Basics
• Know and understand the NORMAL anatomy and physiology
• Pathologic findings logical
• READ about the details
[heart picture]
“The reason I like cardiology as I said is bc it’s easy to understand. If you know and understand the normal physiology then you can work everything else out, and if there are fancy details you can look them up.”
5 - Pathophysiology of Congenital Heart Disease
Pathophysiology of Congenital Heart Disease
Basic considerations
- Right Ventricle pumps deoxygenated blood to lungs
- Pulmonary circulation has low resistance
- Left ventricle pumps oxygenated blood at systemic blood pressure to Aorta
- Each ventricle is morphologically adapted for its task
“So erm, this is really fundamental, this is rly v basic. The right ventricle pumps deoxygenated blood to the lungs. Circulation in the lungs has low resistance – you’ve got all those sort of football fields of alveoli with capillaries in it and blood whooses through it. Left ventricle pumps oxygenated blood around body, two ventricles different, cylinder, right ventricle doesn’t look anything like the left ventricle, it’s more like a banana, wraps around the left ventricle, and they’re intrinsically different, not just bc on the left or right, and that’s something that causes a problem when they’re on back to front or upside down or missing.
(4) Right, so this is our normal heart, yeah, looks vaguely recognisable? I want you to do some work. I want you to tell me about pressure and oxygen levels on this side of the heart here – so let’s, I think we’re starting with the oxygen levels – what are the O2 levels, how do we measure oxygen levels in the body, or blood, do you know how we do that? Finger probe on finger - measures % O2 saturation in blood, it’s a good way of thinking about it bc haemoglobin is very avid for oxygen, so it’ll suck it up, if it’s there it’ll have it, if given away, won’t have. Venous circulation average oxygen saturation – what do you think it is in the aorta, in your hand, your arteries? 98-100%. What’s it going to be when it gets back to the heart? Give me a number, come on. 20? No, bit higher than that. It’s around Right atria - 67% - differs from top and bottom half of your head - oxygen saturation coming back from head probably about 20% but from different places can be like 80% and from liver’s about 20% so it averages out in RA in sort of high 60s low 70s – estimate of systemic O2 sat in body. So same in the right ventricle is 67%. So will be the same in the pulmonary arteries 67%. Okay so it’s not v difficult is it, it’s actually going to be very slightly lower than that, bc you have the venous return from the heart muscle itself coming in from the coronary sinus. The lungs on the left side is 99%, it’s high, the lungs are really really efficient – same in left ventricle and aorta. So that’s the point, so the point is you know all that. Pressures is a bit more difficulty, measured in mm Hg, approx. = 1cm of blood. So what’s the venous pressure in the right atria? Averages about 4 mm Hg (goes up and down, but average). So really quite low pressure, goes through into the right ventricle - right ventricle ejects it into the lungs – so we need 2 numbers diastolic (resting) and systolic pressure. What’s the diastolic pressure going to be? 10? How’s that going to work? It has to be less than 4 on average, so it will be about 3. And what’s the systolic pressure going to be? Abouttt 20-25, not v hard to pump blood over the lungs. In the right ventricle the pressure is about 25/3 (systolic, diastolic) (random numbers, doesn’t rly matter, point is relatively low). Systolic pressure in the lungs, bearing in mind that’s peak systolic pressure, pulmonary valves open perfectly, creates no barrier to flow, so peak pressure going to be 25, diastolic pressure is going to be less than 25 and more than 3 bc pulmonary valve closes and stops blood falling back in. So there you go, it’s easy, you can work it out. So it goesthrough lungs and goes into left atrium – 25/10 to push out through lungs into LA - in the pulmonary artery pressure is about 25/10. Left atria pressure, 8 is a bit high – get pulmonary oedema, but lower than 10 – gotta get through resistance so it’s about 5, only slightly higher than right atrial pressure because left side is thicker and more muscly, so bit more resistance going in. Obvs it contracts to shove blood through in mitral valve. LV diastolic pressure – what’s that going to be, ish? What’s it going to be? LV pressure there, we know atrial pressure a lil bit higher, so it’s going to be 4 – going to be slightly higher than in right and slightly lower in LA, and what’s systolic pressure going to be? 120. This is a child so it’s In a child - 80/4, although whatever your systolic pressure is e.g. 120, but doesn’t really matter. In the aorta, it’s going to be your blood pressure - in a child 80/40, for example, if an adult, 120/80 – but basically diastolic pressure reflects the peripheral vascular resistance, systolic pressure represents ejection pressure from LV – point is if you can work that out doesn’t matter exact numbers but just ratios. Now we know if you have an atrial septal defect, which way’s the blood going to go? Go from left atrium to right atrium bc pressure’s high. Ventricular septal defect L to R bc pressure higher. Patent ductus, blood will flow L to R bc of pressure. Under normal circumstances can work out. Big hole – pressure equalises quickly, small hole, squirt out, so can understand the genesis and work it out.”
6 - Haemodynamic effects of shunts
• Left to right shunt :
– Requires a hole !
– Blood from the left heart is returned to the lungs instead of going to the body
– Increased lung blood flow by itself is not damaging, but increased pulmonary artery or pulmonary venous pressure is.
• Right to left shunt :
– Requires a hole and distal obstruction !
– De-oxgenated blood bypasses the lungs
“So L to R shunts, need a hole, and the blood from left heart goes back round the lungs. That blood flow causes certain haemodynamic effects, means blood has to work harder to get around the body, but also can also increase blood flow through the lungs, so alveolar capillaries leak, get breathless, a lot of it, going on at high pressure, cause hypertrophy of pulmonary vasculature and get vascular disease. Just said, think about that diagram, if you make a hole, blood will go from left to right. But we know because people can be siolosed, people can have low arterial concentration, can go the other way, so we can get right to left shunt. How can that happen? You’ve got to have a hole, but what else have you got to have? But need something to increase the right side pressure of your heart, most common thing for that is obstruction distal to that heart e.g. ASD, no tricuspid valve, blood from R to L; VSD and pulmonary stenosis then blood R to L - so it requires a hole and obstruction distal to that hole. So that’s CHD from you. Can have things back to front - deoxygenated blood bypasses the lungs - cardiac cyanosis. Not to do with the lungs not oxygenating flood (respiratory cyanosis) - cardiac cyanosis- blue blood in arterial circulation because it’s bypassed the lungs.”
7 - Classification of Congenital HD
Classification of Congenital HD
• Acyanotic
– Left to right shunts: ASD,VSD,PDA
– Obstructive lesions: Aortic stenosis (Hypoplasia)
Pulmonary stenosis (Valve, outflow, branch)
Coarctation of the Aorta, Mitral stenosis
• Cyanotic (Complex, Right to Left shunts)
– Tetralogy of Fallot (VSD/Pulm stenosis …)
– Transposition of the Great Arteries
– Total Anomalous Pulmonary Venous Drainage
– Univentricular Heart
“That’s how we classify CHD, so you have L to R shunts, you can have obstruction, there’s that aortic stenosis in itself which doesn’t make you blue, pulmonary stenosis itself doesn’t make you blue – blue is if you have hole as well. Can have narrowing or coarctation of aorta – so either have hole with distal obstruction, arteries back to front, or veins coming back to wrong place. Or we can just have a complete mismatch.”
8 - Shunts
Shunts • ATRIAL • VENTRICULAR • ATRIO-VENTRICULAR • AORTO-PULMONARY (DUCTAL)
“These are the common shunts, okay, we’ve talked about those before and you see where those go L to R.”
9 - Atrial Septal Defects
Atrial Septal Defects
Haemodynamic effects
- Increased pulmonary blood flow
- RV Volume overload
- Pulmonary hypertension is rare
- Eventual Right Heart Failure
- SVC
- Sinus venous defect
- Pulmonary vein
- Secundum atrial defect
- Fossa ovalis
- IVC
- Primum atrial defect
- Aorta
- Pulmonary artery
- Crista supraventricularis
“ASD can occur anywhere in atrial septum, they’ve all got diff names, the common one’s in the middle – the secundum defect, you can get them under the SVC, can get them right down at valve – primum defect, so low pressure shunt. So you get increased pulmonary blood flow due to low resistance, so causes R heart to stretch up, can fail, but doesn’t usually kill you but can make you q tired and a bit old, so we can fix them.”
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