Describe the frequency and types of congenital malformation of the heart and great vessels
Congenital heart defects are common with an incidence of 6-8/1000 births.
Most common types are VSDs followed by ASDs.
Other ones include Transposition of the Great Vessels (Conotruncal Septum does not adopt spiral course) and Tetralogy of Fallot.
What all acyanotic defects not result in?
A lower than normal concentration of oxygen in the blood.
Discuss the Aetiology of Congenital Heart Defects
~20% Genetics (e.g. Down's, Turner's, Marfan's syndromes)
Environmental - teratogenicity from drugs such as antidepressants, alcohol etc
Maternal infections (during first trimester) - Rubella, Toxoplasmosis etc
What is an Atrial Septal Defect?
An opening in the septum between the two atria which persists following birth.
Failure of the foramen ovale to close or an abnormal communication allows blood to continue to flow between the two atria postnatally.
Incidence of ~67 in 100,000 live births
What are the possible consequences of an Atrial Septal Defect?
Because left atrial pressure is normally higher than right atrial pressure, flow will mainly be from left to right and there is no mixing of deoxygenated blood with the oxygenated blood being pumped around the systemic circulation.
Therefore this is an ACYANOTIC LESION
What are the different types of Atrial Septal Defects?
Such defects can occur almost anywhere along the atrial septum but the most common site is at the foramen ovale (Ostium Secundum ASD). This defect arises from inadequate formation of the septum secundum, excessive resorption of the septum primum or a combination.
An Ostium Primum ASD occurs in the inferior portion of the septum, adjacent to the AV valves and is less common. This results from the failure of the septum primum to fuse with the endocardial cushions.
Describe a Sinus Venosus Defect
Closely related to ASDs but morphologically distinct.
This condition represents an "unroofing" defect with abscence of normal tissue between the right pulmonary vein (a) and the right atrium but is technically not a deficiency of the anatomic atrial septum (which is fully intact).
As sinus venosus defects are often large and result in flow from the right pulmonary veins and left atrium into the right atrium, the pathophysiology is similar to that of a true ASD.
Is a Patent Foramen Ovale a true ASD?
No. The one-way valve, though not sealed, remains functionally closed.
PFOs may be present in ~20% of the population and are generally clinically silent since the higher LA pressure causes functional closure of the flap valve.
When may a PFO be clinically important/significant?
If RA pressure becomes elevated (e.g. In states of pulmonary hypertension or right heart failure) resulting in pathological right - to - left intra cardiac shunting. In that case deoxygenated blood passes directly into the arterial circulation
Also a PFO may be the route by which a venous embolism reaches the systemic circulation if pressure on the right side of the heart increases even transiently (paradoxical embolism). This occurs when thrombus in a systemic vein breaks loose, travels to the RA, passes across the PFO to the LA and then into the systemic arterial circulation.
Describe a Ventricular Septal Defect
Abnormal opening in the interventricular septum. M
ost commonly occurs in the membranous portion of the septum (70%) but can occur at any point (Muscular 20%). Rare VSDs occur just below the aortic valve or adjacent to the AV valves.
Most common congenital Heart defect
What are the consequences of a Ventricular Septal Defect?
Since left ventricular pressure is much higher than right, blood will flow from left to right.
The amount of flow depends on the size of the lesion.
Describe a Patent Ductus Arteriosus
The DA exists in the fetus to shunt blood from the pulmonary artery to the aorta (bypassing the lungs).
This vessel should close shortly after birth as pressure in the pulmonary artery drops following perfusion of the lungs.
Failure to close leads to a PDA. Blood flow through a PDA will be from aorta to pulmonary artery after birth (high to low pressure)
A mechanical murmur is heard constantly throughout systole/diastole as pressure in the sorts is always greater than in the pulmonary artery. ACYANOTIC
Why may a Patent Ductus Arteriosus be clinically significant?
Although L to R shunting does not cause cyanosis, it can be problematic later on if untreated, with the extent of the problems depending on the degree of the shunting.
Chronic L to R shunting can lead to vascular remodelling of the pulmonary circulation and an increase in pulmonary resistance.
If the resistance of the pulmonary circulation increases beyond that of the systemic circulation, the shunt will reverse direction as pressures on the right side of the heart increase. (Eisenmerger syndrome)
What is Eisenmerger Syndrome?
The condition of severe pulmonary vascular obstruction that results from chronic left to right shunting through a congenital cardiac defect.
The elevated pulmonary vascular resistance causes reversal of the original shunt (to the right-to-left direction) and systemic cyanosis.
What is Coarction of the Aorta?
Narrowing of the aortic lumen in the region of the ligamentum arteriosum.
Narrowing of the aorta increases the afterload on the LV and can lead to LV hypertrophy.
Because the vessels in the head and upper limbs usually emerge proximal to the coarctation, the blood supply to these regions is not compromised. However blood flow to the rest of the body is reduced.
What does the extent of the symptoms of Coarctation of the Aorta depend on?
Depends on the severity of the coarctation. If very severe, an infant may present with symptoms of heart failure shortly after death.
In mild cases, the defect may be detected in adult life. Femoral pulses will be weak and delayed, with upper body tension.
What is Congenital Aortic Stenosis?
Most often caused by abnormal structural development of the valve leaflets.
Occurs in 5/10,000 bits.
The aortic valve usually has a bicuspid leaflet structure in congenital AS instead of the normal three-leaflet configuration, causing an eccentric stenotic opening through which blood is ejected. Most bicuspid aortic valves are non-obstructive at birth and therefore only rarely react in congenital AS.
What happens to the bicuspid aortic valves over many years?
Become progressively stenotic as the leaflets progressively fibrose and calcify.
Congenital AS represent a common cause of aortic stenosis (narrowing) in adults
What are the consequences of congenital aortic stenosis?
Because the valvular orifice is significantly narrowed, LV systolic pressure must increase to pump blood across the valve into the aorta.
In response to this increased pressure load, the LV hypertrophies.
The high-velocity jet of blood that passes through the stenotic valve may impact the proximal aortic wall and contribute to dilation of that vessel.
Describe Pulmonary Stenosis
Obstruction to right ventricular outflow may occur at the level of the pulmonic valve or in the pulmonary artery.
Valvular pulmonic stenosis is the most frequent form.
Consequence of pulmonic stenosis is impairment of right ventricular outflow which leads to increased RV pressure and hypertrophy.
Although mild pulmonic stenosis rarely progresses and is unlikely to affect RV function, untreated pulmonic stenosis typically results in findings of right sided heart failure.
What are the haemodynamic effects of a Left to Right Shunt?
Blood from the left side of the 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.
What is Tetralogy of Fallot?
Group of 4 lesions occurring together as a result of a single developmental defect which places the outflow portion of the interventricular septum too far in the anterior and cephalad directions
Four lesions: VSD, overriding aorta, a variable degree of pulmonary stenosis and right ventricular hypertrophy.
Most common form of cyanotic congenital heart disease after infancy, occurring in 5 of 10,000 live births and is often associated with other cardiac defects.
What are the consequences of Tetralogy of Fallot?
Pulmonary Stenosis causes persistence of the fetal RV hypertrophy as the RV must operate at a higher pressure to pump blood through the pulmonary artery.
The increased pressure on the right side of the heart along with VSD and the overriding aorta (receives blood from both ventricles) allow R to L shunting and mixing of deoxygenated blood with the oxygenated blood going to the systemic circulation, resulting in cyanosis.
What is the Natural History of Tetralogy of Fallot?
Present in infancy or early childhood with cyanosis or spells of cyanosis. Mild cases compatible with adulthood.
The magnitude of the shunt and level of severity depends on the severity of the pulmonary stenosis.
Explain about Tricuspid Atresia
Lack of development of the tricuspid valve leaves no inlet to the right ventricle.
There must be a complete right to left shunt of all the blood returning to the right atrium (via ASD or PFO) and a VSD or PDA to allow blood flow to the lungs
What is Transposition of the Great Arteries?
This results in two unconnected parallel circulations instead of two circulations in series.
In this defect, the RV is connected to the aorta and the LV is connected to the pulmonary trunk.
Is Transposition of the Great Arteries compatible with life?
Not viable unless a shunt exists to allow the two circulations to communicate. A shunt must be maintained or created immediately following birth to sustain life until surgical correction can be made.
The ductus Arteriosus can be maintained patent and/or an atrial septal defect formed.
Describe a Hypoplastic Left Heart
The left ventricle and ascending aorta fail to develop properly,
A PFO or ASD are also present and blood supply to the systemic circulation is via patent ductus Arteriosus.
Without surgical correction, this condition would be lethal.
Describe the Natural History of ASDs and VSDs
ASD: usually asymptomatic late into adulthood. Late onset arrhythmia and right heart failure.
VSD: unless very small, present in infancy with left heart failure. Untreated, can lead to inoperable pulmonary hypertension
Describe the Natural History of Coarctation
Neonatal variety: associated with PDA, R to L shunt
Adult variety: complicated by Renal hypertension, left ventricular hypertrophy, often associated with aortic valve stenosis
Describe the Natursl History of Transposition/Hypoplastic left heart/Pre-ductal Coarctation/Pulmonary Atresia
Present as neonatal emergencies, often due to reduced pulmonary blood flow.
Describe Pulmonary Atresia
No RV outlet
R to L atrial shunt of entire venous return
Blood flow to lungs via PDA.
Describe the internal structure of the Right Atrium
Deep surface of the anterior wall is rough due go the comb-like ridges of cardiac muscle fibres (pectinate muscles).
Posterior wall is smooth
Anterior and Posterior walls are separated by a prominent vertical ridge of cardiac muscle (crista terminalis). Fossa ovalis is a thumb-like impression on the posterior wall (I.e. The interatrial septum)
What does the RA lie in relation to the LA?
Lies anterior and to the right of the LA such that the posterior wall of the RA lies between the two atria hence the posterior wall is also called the interatrial septum
Describe blood flow into and out of the RA
Blood flows in via the Superior and Inferior Vena Cavae and the Coronary Sinus.
The coronary sinus enters the RA through an opening on its lower posterior wall.
The right atrioventricular orifice, which leads out of the RA and into the RV, lies to the far left of the chamber.
The tricuspid valve is located in the floor of the RA and opens into the RV.
Describe the Right Ventricle
Rough triangular in shape
The funnel-shaped upper region is called the infundibulum and it has a smooth surface. It is the outflow tract leading to the pulmonary trunk.
The lower region of the chamber, the inflow tract, is wider than the infundibulum and its surface is characterised by irregular bundles of cardiac muscle called trabeculae carnae, Posterior wall is also called the interventricular septum because the LV lies behind it.
What are Chordae Tendineae?
Narrow cords of dense connective tissue that attach at one end to the free edges of the cusps of the valve and on the other end attach to elevations of cardiac muscle called papillary muscles.
What are the Papillary Muscles?
Vary a lot in size and may be absent (particularly in the septal region) in which case the chordae Tendineae attach directly to the inner wall of the chamber.
The RV contains 3 papillary muscles which in turn attach to the edges of the tricuspid valve leaflets (via chordae Tendineae).
What happens when the papillary muscles contract?
Contraction of the papillary muscles prior to other regions of the ventricle tightens the chordae Tendineae, helping to align and restrain the leaflets of the valve as they are forced closed.
This action prevents blood from regurgitation into the RA during ventricular contraction.
What is the role of the Tricuspid Atrioventricular Valve?
Guards the right atrioventricular orifice between the RA and the RV, preventing a regurgitation of blood into the RA during systole.
The leaflets of the tricuspid valve are attached to the fibrous ring that supports the valve between the RA and the RV
What happens during relaxation of the RV?
Elastic recoil of the pulmonary arteries forces blood back toward the heart, distending the valve cusps towards one another.
This action closes the pulmonic valve and prevents regurgitation of blood back into the RV.
Describe the structure of the left atrium
Slightly thicker wall than RA.
Valveless pairs of right and left pulmonary veins enter the smooth posterior wall.
The tubular, muscular left auricle, its wall trabeculated with pectinate muscles forms the superior part of the left border of the heart and overlaps the root of the pulmonary trunk. The left auricle represents the remains of the left part of the primordial atrium.
A mitral valve orifice is also present allowing oxygenated blood into the LV.
Describe the structure of the Left Ventricle
Cavity of the LV is approximately cone-shaped and longer than that of the RV.
Wall is ~3x thicker than of RV
The aortic vestibule is - smooth-walled part of the left ventricular cavity located just inferior to the aortic valve.
Inferior to this most of the ventricle is covered by trabeculae carneae which are finer and more numerous than those in the RV
The anterior wall of the LV is called the interventricular septum because the RV lies in front of it.
Compare the papillary muscles and chordae Tendineae present in the LV to those present in the RV
LV contains two large papillary muscles, larger than their counterparts in the RV and their chordae Tendineae are thicker but less numerous.
The chordae Tendineae of each papillary muscle distribute to both leaflets of the mitral valve. Similarly as in RV, contraction of the papillary muscles leading to tensing of the chordae Tendineae during LV contraction, helps restrain and align the mitral leaflets, enabling them to close properly and prevent the backflow of blood.
Describe the aortic valve
Separates the LV from the aorta.
Surrounding the aortic valve opening is a fibrous ring to which is attached the three cusps of the valve.
Just above the right and left aortic valve cusps in the aortic wall are the origins of the right and left coronary arteries (right and left aortic sinuses).