congenital left to right shunts
•atrial septal defect (ASD) •ventricular septal defect (VSD) •atrioventricular septal defect (AVSD) •patent (persistent) ductus arteriosus (PSD) •aycanotic
congenital right to left shunts
•tetralogy of Fallot •transposition of the great arteries (TGA) •truncus arteriosus -above are conotruncal defects •tricuspid atresia •total anomalous pulmonary venous connection (TAPVC) •cyanotic
•pulmonary stenosis •aortic stenosis •coarctation of aorta •acyanotic
•Ebstein's Anomaly •cyanotic
•reversal of left to right shunt to a right to left shunt, occurring as a result of the interval development of significant pulmonary hypertension and increased vascular resistance •acyantotic to cyanotic
most common cardiovascular anomaly
•bicuspid aortic valve
most common cardiac anomaly
•ventricular septal defect
•increased blood pressure in the lungs •congenital heart disease can cause pulmonary hypertension over time if shunts are present •results in hypertrophy of pulmonary arteries and formation of "plexiform lesions (twisted balls of proliferating capillary channels), a severe form of pulmonary hypertension called "plexiform pulmonary hypertension" -irreversible once they form -most common with VSD, less common with PDA, much less common with ASD •when severe, causes Eisenmenger syndrome
atrial septal defect (ASD)
1) Abnormal opening between the two atria (other than a patent foramen ovale [PFO]). 2) Three types of ASDs: a. Secundum-type: At fossa ovalis - most common type of ASD (90% of cases) b. Primum-type: Low on septum, adjacent to AV valves (uncommon). c) Sinus venosus-type: High on septum, near superior vena cava (rare). 3) May be asymptomatic until adulthood. 4) Secondary cardiac effects: RV hypertrophy and dilatation, RA and LA dilatation 5) Pulmonary hypertension is infrequent (<10% of cases) and, if it does occur, it’s a late complication.
ventricular septal defect (VSD)
1) Abnormal opening between right and left ventricles. 2) Two types: a. Membranous VSD: Involves membranous septum – most common type of VSD (90% of cases), and often large. b. Muscular VSD: Involves muscular septum; may be multiple; usually small. 3) If large (and unoperated), VSD will eventually cause pulmonary hypertension in 100% of cases, with reversal of the shunt (conversion to a right-to-left shunt) and conversion to cyanotic heart disease (Eisenmenger syndrome). 4) If small, VSD usually spontaneously closes, no surgery is needed, and no pulmonary hypertension ever develops; spontaneous closure occurs in the 1st year of life in >60% of cases
pathophysiology of ASD
•VOLUME LOAD •An ASD allows left to right shunting at the atrial level (LA pressure is higher than RA pressure after birth). Given the low pressure in the atria, there is insufficient velocity of blood flow across the atrial septum to cause a murmur. However, over time (years), the excessive flow will lead to volume overload in the RA and RV. As the heart tries to cram extra blood across tricuspid and pulmonary valves that are only designed to take one ‘unit’ of blood per cardiac cycle, the blood will speed up to accommodate this. This mild increased flow velocity can cause soft diastolic (tricuspid valve) and/or systolic ejection (pulmonary valve) murmurs. Over years, the excess flow leads to right heart enlargement. This can lead to: 1) Atrial dysrhythmias 2) Pulmonary vascular occlusive disease 3) RV dysfunction These do not typically occur until the 3rd or 4th decade of life, and pediatric CHF almost never occurs. It is extremely uncommon for a child to have symptoms from an ASD before the age of 10 years. ASD are volume lesions, not pressure, so it takes much longer for symptoms and irreversible changes to occur.
interventions for ASD
•Given the long time course until irreversible damage, ASDs are typically repaired electively, usually before kindergarten, if diagnosed early enough. If the child, or young adult, is older at diagnosis, they can be closed at that time. However, it will be important to confirm that the pulmonary arterial resistance is normal before closing a defect, and this can only be done by cardiac catheterization. The first line treatment of secundum ASDs is now catheter-based, device closure. However, larger or more complex defects still require surgical closure with a median sternotomy and cardiopulmonary bypass.
pathophysiology of VSD
•PRESSURE LOAD •A VSD causes left to right shunting at the ventricular level. However, the blood spends almost no time within the right heart, and is almost immediately ejected to the pulmonary artery. Blood through the VSD joins systemic venous blood, leading to excessive flow to the pulmonary arteries and increased blood return to the left heart. The pathophysiology is very similar to that of a PDA (CHF, PVOD/Eisenmenger, left heart dilation). The LV pressure is higher than the RV pressure for the entirety of systole, so VSDs cause holosystolic murmurs.
intervention for VSD
•Symptomatic infants with VSDs can be trialed on medication (diuretics, ACE-inhibitors) to help reduce pulmonary overcirculation and encourage growth, but typically if a baby needs medication, they really need a ‘cold steel cure’ (surgery). VSDs are typically closed between 4 and 6 months of age via a median sternotomy and cardiopulmonary bypass. There are occasions when a VSD may be appropriate for catheter-based device closure, but this is the exception not the rule with current technology.
atrioventricular septal defect (AVSD)
•1) Deficient AV septum, associated with mitral and tricuspid valve anomalies; also called an “endocardial cushion defect”, due to failure for the embryologic endocardial cushions to fuse in the center of the heart; also called “atrioventricular canal defect”, because a canal-like hole is present in the center of the heart. 2) Two types: a. Partial AVSD: Primum ASD with cleft mitral anterior leaflet (and mitral regurgitation). b. Complete AVSD: Primum ASD and membranous VSD, producing a single large hole in the center of the heart and a common AV valve (instead of separate mitral and tricuspid valves). 3) Strongly associated with Down syndrome (20% of Down syndrome patients have an AVSD, especially a complete AVSD). •The VSD component is often quite large and the two ventricles act as a single chamber, so there is not typically a VSD murmur. The most common murmur is a systolic ejection murmur at the pulmonary valve due to the excessive flow across it.
pathophysiology of AVSD
•PRESSURE and VOLUME LOAD •An AVSD causes left to right shunting at both the atrial and ventricular level. This leads to excessive flow to the pulmonary arteries and increased blood return to the left heart. The pathophysiology is very similar to that of a VSD (CHF, PVOD/Eisenmenger, left heart dilation), however given the large shunt volume, symptoms of CHF are more likely and at a younger age.
intervention for AVSD
•Symptomatic infants with AVSDs can be trialed on medication (diuretics, ACE-inhibitors) to help reduce pulmonary overcirculation and encourage growth, but typically if a baby needs medication, they really need a ‘cold steel cure’ (surgery). AVSDs are typically closed between 4 and 6 months of age via a median sternotomy and cardiopulmonary bypass. These defects are never appropriate for catheter-based device closure.
patent ductus arteriosus
1) Persistence of normal fetal structure (ductus normally undergoes functional closure within 12 hrs of birth, and structural [permanent] closure by 3 months of age). 2) Isolated defect in most cases. 3) Approximately 80% of patients will develop pulmonary hypertension (if unoperated), usually after age 5 yrs. 4) May be required for survival in some complex cyanotic (“ductus-dependent”) congenital heart diseases, such as aortic valve atresia or pulmonary valve atresia (if the ductus is allowed to undergo normal physiologic closure after birth in these conditions, the baby will die) •Since the aortic pressure is always significantly higher than the pulmonary artery pressure in systole and diastole, PDAs cause continuous, machine-like murmurs.
pathophysiology of PDA
•PRESSURE LOAD •If a PDA is large, it is basically an open communication between the systemic and pulmonary vasculature and can lead to increased flow and pressure in the pulmonary arteries (normally should be 25 – 30% of systemic pressure). Excessive flow to the pulmonary arteries can lead to several problems: 1) Pediatric congestive heart failure (CHF), or pulmonary overcirculation. In this situation, the excess flow leads to pulmonary edema, which decreases the efficiency of gas exchange and causes tachypnea to compensate. In addition, the total cardiac output (volume ejected by both ventricles) increases, so the heart is working harder too. Now, there is increased oxygen demand and a decreased efficiency in getting oxygen into the body. Add to this that feeding is exercise for a baby (like running up a flight of stairs), and you have a tachypneic baby with a revved up metabolism and an inability to eat well – this leads to poor weight gain in infants. 2) Pulmonary vascular occlusive disease. The pulmonary arterioles respond to the increased pressure and flow by constricting. If the infant is able to survive their CHF and remain with high pressure and flow to the lungs for a prolonged period (years), the arterioles muscularize and lose the ability to relax, leading to fixed elevated pulmonary arterial resistance and eventually right to left shunting through the PDA (this is Eisenmenger syndrome and is bad!). 3) Excessive blood return to the left heart. This leads to LV dilation and increased end-diastolic pressure and wall stress. 4) Endarteritis risk. There is approximately 1%/year risk of infection of a PDA (endarteritis) likely from the turbulent flow in the area being a potential site of bacteria setting up infection.
intervention for PDA
Symptomatic infants, typically very premature, may need their PDA closed early in life. This is first attempted with indomethacin or ibuprofen, prostaglandin inhibitors, which can stimulate ‘natural’ PDA closure. Those that fail medical therapy and are still symptomatic may require surgical ligation via a lateral thoracotomy and without cardiopulmonary bypass. Those who do not have significant neonatal symptoms, and if the PDA is still present after a year of life, can undergo elective catheter-based closure of the PDA.
pulmonary valve stenosis
1) Pulmonary valve obstruction, due to hypoplasia, dysplasia, atresia, or abnormal number of cusps. 2) Two types, based on severity of obstruction: a) Isolated PV Stenosis: Causes RV hypertrophy, tricuspid regurgitation, dilatation of RA, and dilatation of pulmonary artery; may be asymptomatic until adulthood. b) PV Atresia with Intact Ventricular Septum: PDA required for survival; RV and tricuspid valve are hypoplastic. •When the pulmonary valve is being formed, sometimes the leaflet separation is halted, leading to a valve that does not open completely. Some patients also have thickening (dysplasia) of the leaflets which can lead to additional obstruction to flow out of the RV. Pulmonary stenosis is associated with a harsh systolic ejection murmur, typically at the left upper sternal border with radiation to the periphery and back.
pathophysiology for PS
•PRESSURE LOAD •Chronic obstruction of flow out of the RV produces a pressure load on the ventricle. The heart responds to pressure loads in two ways: 1) Hyperplasia (neonates only) – the heart grows more myocytes to deal with the increased work 2) Hypertrophy (neonates and older children) – the existing myocytes enlarge to deal with the increased work Hyperplasia produces more efficient work, and therefore, neonates can handle the pressure load better than older children and adults. It is not uncommon for a neonate with pulmonary valve stenosis to have RV pressure that is double the LV pressure and be completely asymptomatic. Eventually, the RV may dilate as it loses the ability to generate forceful contractions. Through ventriculo-ventricular interactions (two pumps, limited pericardial space to work in), the dilated RV can limit LV filling and subsequently, limit cardiac output.
intervention for PS
Intervention timing varies with age. Neonates with critical PS (require the PDA to have adequate pulmonary flow) need intervention regardless of the degree of obstruction as estimated by echo. For older infants and children, typically a peak echo gradient of at least 40 mmHg is the criteria for intervention. Historically, PS was treated with a surgical valvotomy. This has almost completely been replaced by catheter-based balloon valvuloplasty which works by completing the separation of the valve leaflets (like tearing the perforation on coupons). Thick, dysplastic valves do not always respond well to balloon valvuloplasty because there is still thick tissue obstructing flow. Balloon valvuloplasty can lead to new pulmonary regurgitation, but this is often tolerated well for many years before any (surgical) intervention is needed.
1) Aortic valve obstruction, due to hypoplasia, dysplasia, atresia, or abnormal number of cusps. 2) Two types, based on severity of obstruction: a) Isolated AV Stenosis: Causes LV hypertrophy, mitral regurgitation, dilatation of LA. b) AV Atresia with Intact Ventricular Septum (“Hypoplastic Left Heart Syndrome” [HLHS]): PDA required for survival; LV is hypoplastic; mitral valve is hypoplastic; ascending aorta is hypoplastic. HLHS represents about 1% of cases of congenital heart disease. •When the aortic valve is being formed, sometimes the leaflet separation is halted, leading to a valve that does not open completely. Some patients also have thickening (dysplasia) of the leaflets which can lead to additional obstruction to flow out of the LV. Many patients with AS will have a bicuspid, or even unicuspid, valve that does not function properly. These valves may also have associated regurgitation if they cannot close completely. Aortic stenosis is associated with a harsh systolic ejection murmur, typically at the right upper sternal border with radiation to the neck and back.
pathophysiology of AS - neonates
•PRESSURE LOAD •Chronic obstruction of flow out of the LV produces a pressure load on the ventricle. •Presentation and pathophysiology vary based on the age of presentation. Neonates (critical AS) In utero, the LV typically deals with a low afterload (placenta), as opposed to the RV which also pumps against the higher resistance pulmonary vasculature, so the LV does not have to work as hard. In addition, the RV can help support systemic flow via the ductus arteriosus in utero. However, once the baby is born and the umbilical cord is clamped, there is a sudden increase in systemic afterload on top of the aortic valve obstruction, and the LV may not be able to handle the increased work. In addition, if the LV has been working hard for a while in utero, there may already be diastolic dysfunction, particularly if the ventricle has not grown as well. This diastolic dysfunction can lead to increased LV end-diastolic pressure, increased LA pressure, increased pulmonary venous pressure and eventually increased PA and RV pressure. The RV can dilate in response to this and limit LV filling further, creating a vicious cycle and a very sick neonate.
pathophysiology of AS - older children
•PRESSURE LOAD •Chronic obstruction of flow out of the LV produces a pressure load on the ventricle. Presentation and pathophysiology vary based on the age of presentation. •Older children are rarely symptomatic from their AS, and are often diagnosed after being evaluated for a murmur. Since the onset of worsening obstruction is slower, they are able to maintain LV systolic performance through hypertrophy. While there can eventually be diastolic dysfunction secondary to the hypertrophy, this is usually a late finding. It is possible for older children to present with a syncopal episode due to an inability to increase cardiac output during exercise because of fixed obstruction to LV outflow.
intervention for AS
•Intervention timing varies with age. Neonates with critical AS (require the PDA to have adequate pulmonary flow) need intervention regardless of the degree of obstruction estimated by echo. They typically have poor ventricular function and cannot generate a significant gradient. For older infants and children, typically a peak cath gradient of at least 50 mmHg is the criteria for intervention (40 mmHg if symptomatic or want to be active or get pregnant). Historically, AS was treated with a surgical valvotomy. This has almost completely been replaced by catheter-based balloon valvuloplasty which works by completing the separation of the valve leaflets (like tearing the perforation on coupons). Thick, dysplastic valves do not always respond well to balloon valvuloplasty because there is still thick tissue obstructing flow. For critical AS, there is a 10% procedural mortality – these are sick neonates! A sometimes catastrophic results can be the development of acute aortic regurgitation after valvuloplasty, which is not often tolerated well and may require urgent surgical intervention.
coarctation of aorta (CoA)
1) Ridge-like indentation or narrowing of distal aortic arch, across from ductus arteriosus. 2) Two types: a. With PDA (presents in infants). b. Without PDA (presents in adults). 3) 50% of patients also have a congenitally bicuspid aortic valve. 4) 3 - 4 times more common in males, but also associated with Turner Syndrome. 5) Hypertension in arms, hypotension in legs, and shunting around narrowing through enlarged collateral arteries.
pathophysiology of CoA - neonates
•The pathophysiology and presentation of CoA can vary with age. •Neonates (critical CoA) Neonates with severe coarctation are usually completely asymptomatic. They often present around 1 week of life (80% within the first 2 weeks of life) with poor perfusion, CHF (pump failure), acidosis and shock. WHY? A better way to diagnose critical coarctation is with a thorough physical exam in the Newborn Nursery and noting that there are no palpable femoral pulses, indicating inadequate lower body perfusion distal to the coarctation. They may have a systolic ejection murmur if there are associated aortic valve abnormalities.
pathpphysiology of CoA - older children
•The pathophysiology and presentation of CoA can vary with age. •Older children have a slower onset of obstruction. This allows the LV time to compensate with hypertrophy. They are also able to generate collateral arteries that bypass the coarctation to provide (abnormal) flow to the lower body. As the high velocity, turbulent flow continues in the region of the coarctation, the fibrosis can progress and in extreme cases patients can develop acquire aortic atresia. Chronic LV hypertrophy can lead to diastolic dysfunction. These patients may have systolic ejection murmurs if there are associated aortic valve abnormalities and bruits over the back from collateral arteries. Other associated findings include upper extremity hypertension, headaches, leg pain/claudication and decreased femoral pulses.