4. Congenital Disorders Of The Heart Flashcards
Congenital heart defects - definition
• Congenital heart defects = born with them, present from birth
○ These must be very closely monitered but don’t mean that patients die sooner
○ Detection has been possible for ~25 years – prenatal ultrasound
○ Patients may have to see their cardiologists from when they are born until they die
Prenatal detection
Via ultrasound
—> By week 8 post-conception cardiogenesis is complete
- Congenital abnormalities in cardiac structure are typically screened for a 20 weeks gestation
- Most defects which permit 6 months of intrauterine life = live offspring at full term (compatible with life)
Foetal echocardiogram
Ultrasound of baby heart
4-chamber view
–Symmetry in size of all four chambers
– Left vs right morphology
– Valve morphology and function
– Intracardiac shunts (ASD’s difficult to detect)
– Pulmonary venous return
– Pericardial effusion = accumulation of pericardial fluid
• Outflow tracts
– Origins of PA and aorta from RV and LV, respectively
• LAV
– Aortic and ductal arches
• 3-vessel view
– Entry of SVC and IVC into RA
4 causes of congenital heart defects
• Genes
○ Turners syndrome, marfan’s syndrome = caused by one gene
○ Other defects are caused by multiple genes
• Environment
• Drugs
○ Not just recreational drugs but also alcohol
• Maternal infections
○ Rubella – deafness and intercardiac problems
Congenital heart defects arise from many diverse aetiologies
• Can also occur before patient even realises they are pregnant
2 types of congenital heart defects
- Acyanotic
* Cyanotic
Acyanotic - definition
○ No cyanosis of mucous membranes
• Cyanotic - definition
○ Patient is cyanotic – blue purple discolouration of mucous membranes in mouth, lips toes etc
Acyanotic defect examples
Left to right shunts
- atrial septal defects
- Ventricular septal defects
- patent ductus arteriosus
Obstructions
- congenital aortic stenosis
- pulmonic stenosis
- coarctation of aorta
Cyanotic defects-examples
Tetralogy of fallot
Transposition of the great arteries
Eisenmenger syndrome
Anatomy of foetal heart
Foramen ovale (fetal shunt)
• Move blood from RA to LA
• Oxygenated blood bypasses lungs and goes to systemic circulation
• Occurs due to fact that pressure on right side > left side pressure
• So blood moves down pressure gradient from high pressure RA to low pressure left side
When a baby takes its first breathe when born
• Pressure gradient reverses so left pressure> right pressure
• Closes septum primum against septum secundum to seal foramen ovale
Atrial septal defect - definition
Acycanotic
→ persistent opening of atrial septum wall
Classes
Primum ASD (15%) − Superior sinus venosus defect (5%) − Inferior sinus venosus defect (<1%) − Unroofed coronary sinus (<1%)
Atrial septal defect - pathophysiology
Acycanotic
• = defect where blood flows from LA to RA and out of the right outflow tract
1. Blood moves into LA but instead of all the blood going to LV like normal, some of it it goes to RA 2. Blood passes across atrial septal defect from LA to RA 3. Blood goes from RA to RV and out of pulmonary artery
• Simple shunt – left-to-right because of higher compliance of RV
− Causes RV volume overload and pulmonary hypertension (9-35% of patients with Secumdum ASD).
• Shunt volume depends on RV/LV compliance, defect size and LA/RA pressure.
Atrial septal defect - symptoms
Acycanotic
• Often undiagnosed until adulthood – 25% clinically silent in childhood
– Reduced functional capacity
– Shortness of breath upon exertion
– Palpitations
– Repeated respiratory infections
Atrial septal defect - physical examination
Acycanotic
- Parasternal heave – RV enlargement
- As increased blood volume moves into RV it is stretched and enlarged overtime
- Can be palpated over sternal angle – lifting effect due to large RV lifitn sternum as heart beats
• Murmur at upper-left sternal border – due to increased blood flow across PV (pulmonary valve)
• Murmur at lower-left sternal border – increased flow across TV (tricuspid valve)
○ More blood than normal passes from RA to RV
Atrial septal defect - treatment
Acyanotic
- only surgical repair if volume is significantly large
Patent foramen ovale
—> opening in foramen ovale
• This is not a true atrial septal defect, as no septal tissue is missing, it is just a persistence of foetal anatomy
• Clinically silent when LA pressure is greater than RA pressure - generally can overcome patency so no blood volumes pass over
• Clinically relevant in states of increase RA pressure when RA pressure > LA pressure
– Pathological right-to-left shunt
Acyanotic – ventricular septal defects
Definition
—-> abnormal openings in inter ventricular septum – wall between LV and RV
—> blood will still move normally through the heart in these defects but some volumes of blood will follow the defect
• Can occur anywhere in intraventricular septum
Membranous (70%)
– Muscular (20%)
– Aortic or adjacent to AV valves (rare)
– Singular defects most common but multiple defects do occur
Acyanotic – ventricular septal defects
Pathophysiology
- Blood enter LA
- Blood moves to LV
- Some blood passes through the venticular septal defect to RV
○ on size of defect in ventricular septal defects
○ Compliance of receiving chamber (right ventricle
○ Pressure difference
− Small VSD’s = defect offers more resistance that pulmonic and systemic circulations therefore small left-to-right shunt
− Large VSD’s = low resistance relative to low-ish pulmonary and high-ish systemic resistances, therefore, RV, pulmonary circ., LA and LV have volume overload.
Acyanotic – ventricular septal defects
Symptoms
Most common CHD
– Small VSD’s are symptom-free
– Large VSD’s develop symptoms of heart failure
– Repeated respiratory infections
Acyanotic – ventricular septal defects
Physical examination
• Harsh holosystolic murmur (mumur throughout all of systoel)– left sternal border
○ As systole is contraction – causes blood to move across VSD = murmur
• Systolic thrill palpated over same area
○ Blood volumes squeezed through VSD
• Apical mid-diastolic rumble murmur – increased mitral valve flow
○ increased flow across this valve
Acyanotic – ventricular septal defects
Treatment
- Most undergo spontaneous closure overtime
- Larger ones need surgical treatment
Acyanotic – patent ductus arteriosus
Definition
• Persistant communcication between proximal left pulmonary artery and descending aorta
○ Sometimes this doesn't close sufficiently – patent ductus arteriosus ○ So some blood can move from aorta across patent ductus arteriosus into pulmoary artery and pulmoary circulation
Acyanotic – patent ductus arteriosus
Presentation
Small duct
– no LV left ventricular vol. overload and normal PAP (pulmonary arteriole pressure)
• Moderate PDA
– Predominant LV vol. overload
• Moderate PDA
– Predominant PAH
• Large PDA
– Eisenmenger physiology
Anatomy - normal ductus arteriosus
- Ductus arteriosus in utero = moves blood from pulmonary artery up into aorta - so blood is pumped to systemic circulation
- Moves venous blood from IVC and SVC to systemic ciruclation and placenta for gas exchange
Acyanotic – patent ductus arteriosus
Pathophysiology
—> Normally closes due to constriction due to sudden rise in O2 tension after birth.
• If it doesn’t close sufficiently = Left-to-right shunt with LV volume overload. In moderate and large PDA’s, pulmonary pressure is increased.
− Flow depends on haemodynamics of ductus (length/radius/resistance)
− LA, LV and pulmonary circ. vol. overload
• Large PDA’s may develop Eisenmenger’s physiology
Acyanotic – patent ductus arteriosus
Symptoms
• Small PDA are asymptomatic
• Large PDA
○ Heart failure with tachycardia, poor feeding, slow growth and respiratory infections
• Moderate PDA – Fatigue, dypsnea and palpitations
• AF due to LA dilatation
• If Eisenmenger syndrome develops
○ Cyanosis of feet and lower extremities but normal colouration upper extremities – as upper extremities receive oxygenated blood from aorta (proximal to PDA) but the lower extremities are supplied by descending aorta (distal to PDA)
Acyanotic – patent ductus arteriosus
Physical examination
- Continuous machine-like murmur – left subclavicular region
- Constant flow through PDA
- Cyanosis of lower extremities if Eisenmenger syndrome develops
Acyanotic – patent ductus arteriosus
Treatment
—> if it is problematic
• Constriction of ductus with prostaglandin synthesis inhibitors
• Surgical division or ligation
Acyanotic – aortic stenosis
Definition
Formation of Bicuspid leaflet structure
• Aortic valve normally is tricuspid
Obstruction of blood flow from left ventricle
Acyanotic – aortic stenosis
Presentation
• values can become stenotic and fibrotic due to Progressive stenosis due to calcification and fibrosis • Classes – Valvular – Subvalvular – Supravalvular
Acyanotic – aortic stenosis
Pathophysiology
- Thickening of aortic valve leaflets/ cusps
- More difficult for LV to move blood out across stenotic aortic valve into aorta
- Significant narrowing of valve opening between LV and aorta
- Less flow through that valve
- LV hypertrophy to meet increase ‘afterload
- Build up of pressure in LV
Acyanotic – aortic stenosis
Symptoms
• Depends on lesion severity
• In few children (10%)
– Tachycardia, tachypnea and poor feeding
• Older children
– Asymptomatic
• Adults
– Fatigue, exertional dypsnea, angina and syncope (fainting)
Acyanotic – aortic stenosis
Physical examination
• Cresendo-decrescendo murmur – loudest at base
○ Turbulent flow through stenotic aortic valve
Acyanotic – aortic stenosis
Treatment
• In milder forms no intervention needed
• Severe obstruction might require repair
– Balloon valvuloplasty = catheter passed through IVC into aortic valve, stretched out – in aoritc stenosis stretch out valve leaflets in mitral valve
Acyanotic-Pulmonic stenosis
Definition and presentation
- Stensosis of pulmonary value
• Valvular pulmonic stenosis most common form
Acyanotic-Pulmonic stenosis
Pathophysiology
- Impairment of RV outflow which increases RV pressures and leads to dilation and chamber hypertrophy
- Progression characterised by severity
- Can lead to heart faliure and pedal oedema – good indication of pulmoinc stenosis
Acyanotic-Pulmonic stenosis
Symptoms
• Children with mild and moderate stenosis are asymptomatic
• Severe stenosis
○ Dypsnea on exertion, exercise intolerance, pedal oedema
Acyanotic-Pulmonic stenosis
Physical examination
• Depend on severity
• Severe
– Prominent a wave on JVP = jugular venous pulse
– Parasternal heave over sternum = hypertrophy of RV due to increased pressure
– EARLY systolic ejection murmur – on upper left sternal border with palpable thrill
– Splitting of S2 heart sound – due to delayed closure of PV
• Moderate
– Click following S1 heart sound
Acyanotic-Pulmonic stenosis
Treatment
• Doesn’t really progress or need treatment
– If required transcatheter balloon valvuloplasty
Acyanotic – coarctation of aorta
Definition t presentation
- narrowing of lumen of aorta
Turbulent flow of that narrowing – due to the greater resistance to flow (due to change in radius) - Often present in patient’s with Turner Syndrome
- Narrowing near the ductus
- More common in men
Acyanotic – coarctation of aorta
Pathophysiology
- Increased afterload in LV
- Dilation and hypertrophy
- Rib notching due to collateral formation – seen on ribs x ray
Acyanotic – coarctation of aorta
Symptoms
Symptoms of HF shortly after birth = hf is heart failure
• Differential cyanosis – As in patent ductus arteriosus
○ Cyanosis of lower limbs but normal colouration of upper limbs
• In less severe coarctation – Often asymptomatic and only symptomatic upon exertion – claudication (ischaemia of lower limbs)
• Lower extremities more poorly supplied
Acyanotic – coarctation of aorta
Physical examination
- Increased blood pressure in upper body (systolic 15-20mmHg greater in arm than leg)
- Weak femoral pulse
- Mid-systolic ejection murmur – turbulent flow through narrowing
Acyanotic – coarctation of aorta
Treatment
- Prostaglandins in neonates maintains patency of ductus until surgery
- Surgical repair or balloon dilation with or without stent
Cyanotic – tetralogy of fallot
Definition
- Ventricular septal defect
- Obstruction to RV outflow tract
- An overriding aorta – blood from both ventricles
- RV hypertrophy
PROVe it • Pulmonary obstruction • Right ventricular hypertrophy • Overriding aorta • Ventricular septal defect
Cyanotic – tetralogy of fallot
Pathophysiology
- Dypsnea on exertion
- Increased vasodilation promotes the rightto-left shunt
- May concomitantly present with ASD and VSD
Cyanotic – tetralogy of fallot
Symptoms
- Identified in prenatal ultrasound
- Dypsnea on exertion
- Progressive cyanosis
- Hyperventilation to meet oxygen requirements
- Syncope
Cyanotic – tetralogy of fallot
Physical examination
- Cyanosis of digits, mucous membranes and lips ‘
- Deoxy blood goes across VSD into aorta and systemic circualtion
- Pulmonary stenosis
- Parasternal heave – RV hypertrophy, presses against sternal angle, lifts hand on plapation
Cyanotic – tetralogy of fallot
Treatment
- Surgical closure of the VSD and expansion of the subpulmonary infundibulum
- Decrease outflow tract obstruction
- Limit movement of deoxy blood into systemic circulation
Cyanotic - pulmonary atresia
Definition
- Pulmonary atresia (with Tetralogy of Fallot)
* Incomplete or compleyte absence of pulmonary artery
Cyanotic - pulmonary atresia
Pathophysiology
- Same internal cardiac anatomy present in ToF (tetraology of falot)
- – But with NO communication between RV and PA’s
Cyanotic - pulmonary atresia
Symptoms
- Dypsnea
- Failure to thrive
- Heart Failure
- Cyanosis (Progressive in severity if duct closes)
- Arrhythmias – scarring and/or haemodynamic changes
- RV dilation and dysfunction – PR and RVOT obstruction
Cyanotic - pulmonary atresia
Physical examination
• Split S2 heart sound
– Pulmonic valve dysfunction
– Pulmonary regurgitation
– VSD murmur
Cyanotic - pulmonary atresia
Treatment
• Surgical repair similar to that of ToF with patch
Put patch over right ventricular outflow tract to allow blood movement from RV to pulmonary arteries
Cyanotic - transposition
Definition
• Transpotisiton = incorrect origin or great arteries from vessels
○ Aorta leaves RV
○ Pulmonary artery leaves LV
Incompatible with life
Cyanotic - transposition
Pathophysiology
Thought due to incomplete spiralling of great arteries in embryogenesis
• Circuits become parallel instead of series
• Deoxygenated blood from systemic circulation returns to RV but is pumped out again to systemic circulation via aorta
Cyanotic - transposition
Symptoms
- Cyanosis
- – Dependent on degree of intermixing between the parallel circuits
- – Apparent often from post-natal day 1
Cyanotic - transposition
Physical excimination
• RV impulse at sternal border
– RV accepting systemic blood vol.
• Accentuated S2 heart sound from more anteriorly placed aortic valve due to abnormal arrangeemnt
Cyanotic - transposition
Treatment
- Medial emergency – incompatible with life
- Immediate prostaglandin infusion (in utero)– Maintain ductus patency
- Interatrial communication created – Rashkind procedure
- Jatene procedure – switch vessels
Eisenmenger syndrome
—> alot of acyanotic defects can develop into cyanotic
• Severe pulmonary vascular obstruction
– Reverses a left-to-right shunt
– Leads to systemic cyanosis
• Patients appear cyanotic with digital clubbing
• Prominent a wave on JVP – jugular venous pulse examination
– Increased RA pressure (right side volume overload)
Deoxy blood moves into left side to be pumped to systemic circualation.
Cardiomyocytes
Structure
→ cardiac muscle cells
- Elongated, cylindrical, striated cells
- Have single nucleus
- Contain high numbers of mitochondria = for constant contraction and relaxation
Speciality of cardiomyocytes
- Gap junctions between 2 cardiomyocytes: Allow the depolarizing current to flow through the cardiac muscle cells from one to another
- Desmosomes: Serve to anchor ends of cardiac muscle fibers together, so cells are tightly packed together
- Gap junctions and desmosomes present in the same area collectively form intercalated discs
Automaticity of heart
—> • Intrinsic ability to generate action potentials spontaneously and depolarize contractile myocardial cells causing them to contract
2 classification of myocardium
- Nodal
* Contractile
Nodal cells
• Non-contractile cells • Can generate spontaneous action potentials • Spread to contractile cells o SA node o AV node o AV bundle (Bundle of His) o Bundle branches (Left & Right) o Purkinje fibers
Contractile cells
- Can contract
- Have actin, myosin, troponin, tropomyosin - in order to contract
- Have sarcoplasmic reticulum – for calcium reservoir
• SA node:
– Located just beneath superior vena cava
– Pacemaker of the heart
– Can generate action potentials = all by itself
– Sinus rhythm (beats generated by SA node) : 60-80 beats per minute
– Without any extrinsic innervation!
• Bachmanns’s bundle:
– Pass signals from SA node to left atrium
Signals from SA node goes from RA and also to LA - both atria receive action potential and contract
AV nodes
– Located just beneath pulmonary trunk
– Act as connection between atria and ventricles
– 0.1s delay in conduction in AV node = delay is needed to allow atria to contract first before ventricles
• Purpose of 0.1s: Gives adequate time for atria to contract before ventricles, so all blood has been moved down to ventricles
How does 0.1s delay occur:
– How: AV node has fewer gap junctions
– How: Fibers are smaller in diameter
How does the action potential travel
- From SA node then to AV node via internnodal pathway
- Bachmannn’s bundle carries potential from SA node to left atrium
- From AV node signal goes to bundles of his
- Then down to different branches of bundle of his
• AV bundle (Bundle of His):
– Carries action potentials from AV node to bundle branches
• Right bundle branch (RBB):
– Carries action potentials to right myocardium
• Left bundle branch (LBB):
– Carries action potentials to left myocardium
• Purkinje Fibers:
– Carries action potentials to ventricular muscle
Depolarisation – nodal cells
-60mv to +40 mu
At -60mV
• Funny Na+ channels open: -60mV→ -55mV = positive ions move into nodal cells so potential rises to –55
At -55mV
• T-type Ca++ channels open: -55mV→ -40mV = a lot more positive ions move into nodal cells, so potential rises to –40mV
At –40mV threshold potential of nodal cells
• Threshold potential reached (-40mV)
• L-type Ca++ channels open: -40mV→ +40mV = a lottt of positive ions move into the cell, increasing membrane potential to +40
Ions move to neighbouring cells via gap junctions, move from cell to cell until reaching contractile cell
—> Resting membrane potential (RMP) - no net ion movement of nodal cells
= - 60mV
threshold potential of nodal cells
• Threshold potential reached (-40mV)
Depolarisation - contractile cell
- Positive ions move in to contractile cells via gap junction
- In-flow of positive ions: -90mV→ -70mV = membrane potential increases slightly to –70
At –70mv (threshold potential of contractile cells)
• Voltage-gated Na+ channels open: -70mV→ +10mV = lots of positive ions move into cell, so potential rises to +10mV
• When +10mV is reached, Na+ channels close
• K+ channels open and K+ moves out of the cell and brings the membrane potential down to 0mV
• Some Ca++ moves in as well – at the same time = bring in calcium ions
○ Positive ions move in and out at the saame time so membrane potential is constant – plateau
—> RMP of contractile cell
-90mV
Contraction of contractile cells
• Ca++ ions that have moved into cell during depolarisation activate ryanodine receptors (RYRs) in sarcoplasmic reticulum of contractile cells
Induced calcium release
• RYR opens up channels and more Ca++ ions move out into the cytoplasm = calcium pumped out into contractile cells cytoplasm
Released calcium helps in contraction
• Ca++ ions bind to troponin (troponin C)→ changes the shape of tropomyosin→ moves tropomyosin away→ allowing myosin head to interact with actin→ more cross-bridges→ more contraction→ more pumping
• Multiple cardiomyocytes receive signals at same time, synchronise their action, they contract together as a unit→ functional syncytium
Repolarisation – nodal cells
- L-type Ca++ channels close at +40mV
- K+ channels opens and K+ starts exiting the cell
- Cell begin to repolarize
- At -60mV K+ channels close and funny Na+ channels open = process then repeats
Repolarisation – contractile cells
At 0mV – few miliseconds after phase 2 plateau
• L-Type Ca++ channels close
- Ca++ is taken back to sarcoplasmic reticulum via Sodium Calcium exchanger and calcium proton ATPase pumps
- Ca++ is taken back to ECF via Sodium-Calcium exchanger and calcium proton ATPase pumps
- K+ channels opens and K+ starts exiting the cell
- Decrease membrane potential down to resting membrane potential
- Phase 3
Phase 4
• Recovery phase, cells are not contracting, slight delay before next current
5 steps in heart contraction
Depolarisation – nodal cells Depoalrisation - contractile cell Contraction of contractile cells Repolarisation – nodal cells Repolarisation – contractile cells
Phase 0
= when voltage gated sodium channels are open and in flow of positive ions
Rapid depolarisation
Phase 1
= potassium channels open, positive ions move out fastly – drop in membrane potential to 0
Early repolarisation
Phase 2
= plateau constant potential, equal number of potassium and calcium moving in and out
Plateau
Phase 3
- K+ channels opens and K+ starts exiting the cell
- Decrease membrane potential down to resting membrane potential
Rapid repolarisation
Phase 4
• Recovery phase, cells are not contracting, slight delay before next current
At -90mv ?
Diastolic current
