Year three: Pathology: Heart Diseases:
Lecture 1: Heart failure and Congenital Heart Diseases: February 2018. By Dr. Ehsan.
Heart –Normal- Cardiac Structure and Specializations
Weight:
Male - 300-360 gm.
Female – 250-320 gm.
Systole- ventricular contraction
Diastole- ventricular relaxation
Thickness
Thickness (cm)
LV
RV
Normal
1.3- 1.5
0.3- 0.5
Hypertrophy
>2
>0.7
Myocardium: is characterized by:
Circumferentially in spiral orientation.
Coordination of contraction.
Cardiac myocyte has sarcomere, contractile unit, thick filament (myosin), thin filament (actin), regular proteins (troponin and tropomysin).
Striated appearance.
Hypertrophy: greater heart weight or ventricular thickness.
Dilation: enlarged chamber size.
Cadiomegaly: increase in cardiac weight or size or both resulting from hypertrophy and /or dilation.
Specialization: also: valves, conduction system, coronary aretrial circulation.
Mechanisms of cardiovascular dysfunction:
Failure of the pump.
Obstruction to flow.
Regurgitant flow.
Shunted flow.
Disorders of cardiac conduction.
Rupture of the heart or a major vessel.
Heart failure:
Defined as inability of heart to pump blood at a rate sufficient to meet the metabolic demands of the tissues, or can do at an elevated filling pressure.
Causes:
Chronic work overload as valvular disease (pressure and volume overload) or hypertension, result in either hypertrophy or pressure overload.
Ischemic heart disease, with dysfunctional muscle.
Steps:
1- Increase cardiac work:
2- Hypertrophy and /or dilation
3- These result in cardiac dysfunction:
1- Increase cardiac work:
Hypertension causes pressure overload.
Valvular diseases cause pressure and volume overload.
Myocardial infarction causes regional dysfunction with volume overload.
All these factors causes increase in cardiac work. Then increases wall stress. And then causes cell stretch that end with hypertrophy and /or dilation.
2- Hypertrophy and /or dilation are characterized by:
Increase heart size and mass.
Increase protein synthesis.
Induction of immediate early genes.
Induction of fetal gene program.
Abnormal proteins.
Fibrosis.
Inadequate vasculature.
3- These result in cardiac dysfunction: failure and arrhythmias.
Left sided heart failure:
Causes:
Ischemic heart disease.
Systemic hypertension.
Mitral or aortic valve disease.
Primary disease of myocardium.
Morphology:
Findings of underlying disease.
Hypertrophy and dilation.
Enlargement of atrium.
Thrombus formation in atrium.
Pulmonary congestion and edema.
Clinical features:
Dyspnea, Orthopnea and Paroxysmal nocturnal dyspnea.
Cough with frothy sputum.
Tachycardia, and atrial fibrillation.
Right sided heart failure: Causes:
Left ventricular failure with pulmonary congestion and pulmonary arterial hypertension.
Primary pulmonary vascular disease.
Primary lung parenchymal disease.
Primary pulmonary and tricuspid valve disease.
Morphology:
Fluid accumulation in pleural and pericardial spaces.
Generalized edema in subcutaneous tissues.
Liver and portal system: there is venous congestion, Nutmeg liver, Centrilobular necrosis and Cardiac cirrhosis.
Congestive splenomegaly.
Congenital heart diseases:
Definition:
Are abnormalities of the heart or great vessels that are present at birth.
Pathogenesis:
It is of unknown cause in 90% of the cases.
There are environmental factors like congenital rubella infection.
However, genetic factors, are seen in association with trisomy 13, 15, 18, and 21 and Turner’s syndrome.
Also mutation in transcription factors, TBX5 causes ASD and VSD, deletion of chromosome 22q11,2 result in outflow tract abnormalities.
Classification:
Left to right shunt.Right to left shunt with cyanosis.
Malformations cause obstruction.
Left to right shunt:
1- Atrial septal defect.
2- Ventricular septal defect.
3- Patent ductus arteriosus.
ASD results in increased pulmonary blood volume. Others cause both increase volume and pressure and they can be asymptomatic at birth, or severe enough to cause CHF.
1- ASD: Types:
1- Ostium secundum ASD (90%).
2- Ostium primum ASD (5%). And 3- Sinus venosus ASD(5%).
ASD is less likely to close spontaneously, however about 10% results in pulmonary hypertension. As far as it is less likely to close so it is regarded to be more common at adults.
Morphology: Gross:
The primum ASD lies just above the valve leaflet and is oval.
The secundum ASD is more rounded and is more centrally located in the atrial septum. Primum and secundum ASDs are not usually found together in the same heart.
VSD:
It is the most common congenital abnormality.
The basal (membraneous) region is the last part of the septum to develop and is the site of approximately 90% of VSDs.
Physiology of ventricular septal defect:
In utero, the pulmonary circulation is a low-flow, high-resistance circuit.
At birth, the lungs expand, and the lungs and pulmonary arteries become high-flow, low-resistance circuits.
Pulmonary vascular resistance is normally much lower than the resistance of the systemic circulation.
In fluid systems, flow is greatest along the path of least resistance. If a large VSD is present, left ventricular blood will follow the path of least resistance, and a certain percentage will be shunted into the right ventricle and pulmonary arteries.
Clinical features:
The clinical effects and functional significance of a VSD depend on its size. Small VSD is asymptomatic and may close, while large VSD causes left to right shunt, then PH, and CHF. Then right to left shunt.
Infective endocarditis is a common complication in VSD.
Also VSDs can be associated with other structural defects, such as tetralogy of Fallot.
VSDs that are smaller than the aortic orifice have limited left-to-right shunts because the defect itself has some intrinsic resistance. Small ones, especially those less than 0.5 cm, are often very loud and can close spontaneously and these children are generally asymptomatic.
Larger defects offer essentially no resistance to flow. They remain patent and allow a significant left-to-right shunt.
Patients with large undiagnosed or uncorrected VSDs are at risk to develop secondary pulmonary vascular changes, chronic persistent elevations of pulmonary vascular resistance, and, eventually, right ventricular hypertrophy and reversal of shunt (ES) that ends with right heart failure. However, the left ventricle and left atrium are also experience volume overloading and hypertrophy.
Eisenmenger syndrome: is reversal of flow and shunting of unoxygenated blood to the systemic circulation
Patent ductus arteriosus:
During intrauterine life permits blood flow from pulmonary artery to aorta.
After birth close by: 1- increased arterial oxygen, 2- decreased pulmonary vascular resistance, and 3- decreased local prostaglandin E2.
Delayed closure occurs in hypoxia, from respiratory distress or heart problem.
A patent ductus arteriosus (PDA) may also be associated with ventricular septal defects, coarctation, or pulmonary or aortic stenosis.
Large defects can cause ES and CHF.
Also there is increase risk of infective endocarditis.
B- right to left shunt:
1- Tetralogy of Fallot. And 2- Transposition of great vessels.
1- Tetralogy of Fallot (TOF):
Tetralogy of Fallot (TOF) is a constellation of 4 anatomic features:
1- VSD,
2- Overriding aorta,
3- Obstruction to RV outflow,
4- And RV hypertrophy.
TOF is the most common form of cyanotic congenital heart disease.
The degree of RV outflow obstruction and the size of the VSD are the key anatomic features that determine the severity of the clinical symptoms.
When the pulmonic stenosis is mild and the VSD is large, the physiology is similar to that of VSD. The patient may have left-to-right shunt and no cyanosis. Many of these patients live decades with few symptoms.
When the pulmonic stenosis is severe, the resistance in the pulmonary circuit is also more severe and if pulmonary resistance exceeds systemic resistance, a right-to-left shunt occurs, and the patient has cyanosis.
With extreme degrees of pulmonic stenosis/ pulmonic atresia, pulmonary blood flow occurs by retrograde flow through the ductus arteriosus or through bronchial collaterals. In these patients, it is important to keep the ductus open.
Paradoxical embolus:
The lung normally acts as a filter for thromboemboli arising in the peripheral venous circulation, preventing them from reaching the systemic circulation and causing infarcts. In the presence of a VSD with a right-to-left shunt, such emboli may bypass the lung to enter the systemic circulation and produce an infarct (eg, stroke). This is termed a paradoxical embolus, and is an important complication of tetralogy of Fallot, most commonly seen in young children.
Older children may develop cerebral abscesses from a similar mechanism, because bacteria fail to be filtered out by the pulmonary vascular bed.
B-2- Transposition of great vessels:
Transposition is actually a highly diverse group of malformations that have in common abnormal connections between the ventricles and the outflow tracts.
The aorta can be connected to the right ventricle and the pulmonary artery connected to the left ventricle.
Oxygenated blood in the pulmonary circuit mixes with unoxygenated blood in the systemic circuit through the ductus arteriosus, through ventricular septal defects, through atrial septal defects, or through other non-cardiac shunts.
III- malformations causes obstruction:
1- Aortic coarctation.
2- Subpulmonic stenosis in TOF.
2- Pulmonary valve stenosis.
4- Aortic valve stenosis or atresia.
Aortic coarctation:
The aortic arch is markedly narrowed in an area of a coarctation, which markedly obstructs blood flow.
Types: 1- preductal. 2- postductal.
Clinical features:
Clinical manifestations depend on severity of narrowing and patency of ductus arteriosus.
Preductal there is manifestations early in life, infantile. So there is cyanosis in the lower extremities.
Blood reaching the lower extremities in patients with preductal coarctation is poorly oxygenated blood shunted through the ductus arteriosus.
Postductal:
It is of adult presentation, there is upper extremities hypertension, and weak pulses in lower extremities.
Obstruction result in collateral circulation, so the intercostal and internal mammary vessels are enlarged, and result in notching of ribs on X ray.
Microscopy:
There is hyperplasia of smooth muscle and fibrous tissue in an aortic coarctation.
The hyperplasia obstructs blood flow into the descending aorta.
If the coarctation is sev1ere, the infant is dependent on blood flowing through the patent ductus arteriosus to support perfusion to the lower extremities.
Summary:
Heart Failure
CHF occurs when the heart is unable to provide adequate perfusion to meet the metabolic requirements of peripheral tissues; inadequate cardiac output is usually accompanied by increased congestion of the venous circulation.
Left-sided heart failure is most commonly due to ischemic heart disease, systemic hypertension, mitral or aortic valve disease, and primary diseases of the myocardium; symptoms are mainly a consequence of pulmonary congestion and edema, although systemic hypoperfusion can cause secondary renal and cerebral dysfunction.
Right heart failure is most often due to left heart failure, and less commonly to primary pulmonary disorders; symptoms are chiefly related to peripheral edema and visceralcongestion.
Congenital Heart Disease
Congenital heart disease represents defects of cardiac chambers or the great vessels; these either result in shunting of blood between the right and left circulation or cause outflow obstructions. Lesions range from relatively asymptomatic to rapidly fatal. Environmental (toxic or infectious) and genetic causes both contribute, and the manifestations depend on the timing of the environmental insult or which step in cardiac development is affected.
Left-to-right shunts are most common and are typically associated with ASDs, VSDs, or a PDA. These lesions result in chronic right-sided pressure and volume overloads that eventually cause pulmonary hypertension with reversal of flow and right-to-left shunts with cyanosis (Eisenmenger syndrome).
Right-to-left shunts are most commonly caused by TOF or TGA. These are cyanotic lesions from the outset and are associated with polycythemia, hypertrophic osteoarthropathy, and paradoxical emboli.
Obstructive lesions include aortic coarctation; the clinical severity of the lesion depends on the degree of stenosis and the patency of the ductus arteriosus.