Pathology of the CVS
Mechanisms of cardiovascular dysfunction :
• Failure of the pump. In the most common circumstance, the cardiac muscle contracts weakly or inadequately, and the chambers cannot empty properly. In some conditions, however, the muscle cannot relax sufficiently to permit ventricular filling.
• An obstruction to flow, owing to a lesion preventing valve opening or otherwise causing increased ventricular chamber pressure (e.g., aortic valvular stenosis, systemic hypertension, or aortic coarctation). The increased pressure overworks the chamber that pumps against the obstruction.
• Regurgitant flow causes some of the output from each contraction to flow backward, adding a volume workload to each of the chambers, which must pump the extra blood (e.g., left ventricle in aortic regurgitation; left atrium and left ventricle in mitral regurgitation).
• Disorders of cardiac conduction. Heart block or arrhythmias owing to uncoordinated generation of impulses (e.g., atrial or ventricular fibrillation) lead to nonuniform and inefficient contractions of the muscular walls.
• Disruption of the continuity of the circulatory system that permits blood to escape (e.g., gunshot wound through the thoracic aorta).
Most clinical cardiovascular diseases result from a complex interaction of genetics and environmental factors that disrupt networks controlling morphogenesis, myocyte survival, biomechanical stress responses, contractility, and electrical conduction.
Heart failure
Left sided heart failure.
Right sided heart failure.
Congenital heart disease.
Left to right shunt. (ASD,VSD,PDA).
Right to left shunt (tetralogy of fallot, transposition of the great arteries).
Obstructive lesions( aortic coarctation)
Heart Failure
Occur when the heart is unable to pump blood at a rate that meets the metabolic requirements of the peripheral tissue; inadequate cardiac output accompanied by increased congestion of the relevant circulation.
Heart failure
Left sided heart failure is most commonly due to :
Ischemic H.dis.
Hypertensive H.dis.
Valvular Hd (mit., tric.)
Cardiomyopathy .
The symptoms are primary related to pulmonary congestion and edema.
Right sided Heart Failure
Right sided heart failure is most commonly due to left-sided heart failure or to primary pulmonary diseases, it is associated with peripheral edema and visceral congestion.
Heart failure (other classification )
Systolic dysfunction (IHD,HHD).
Diastolic dysfunction (HT,DM).
Forward failure (inadequate out put).
Backward failure (increased congestion of the venous circulation).
High out put failure (Wn the heart cannot keep pace with basic peripheral demand).
Cardiac adaptation
Activation of neurohumoral mechanism.
Norepinephrine release.
Renin angiotensin-aldosterone.
Release of atrial natriuretic peptide.
The Frank starling mechanism.
Myocardial structural changes.
Concentric and eccentric hypertrophy.
Morphology of the LHF
Hypertrophy & dilation.
Thrombus formation.
Pulmonary congestion and edema.
Heart failure cells.
The molecular and cellular changes in hypertrophied hearts that initially mediate enhanced function may contribute to the development of heart failure.
Proteins related to contractile elements, excitation-contraction coupling, and energy utilization may be significantly altered through production of different isoforms that either may be less functional than normal or may be reduced or increased in amount. Alterations of intracellular handling of calcium ions may also contribute to impaired contraction and relaxation. Loss of myocytes due to apoptosis may contribute to progressive myocardial dysfunction in cardiac disease with hypertrophy.
Clinical presentation:
1. Due to obstruction to pulmonary vascular out-flow there is pulmonary congestion and edema.
2. Reduction of renal perfusion causes:
(i) Salt and water retention (ii) Ischemic acute tubular necrosis
(iii) Impairment of waste excretion causing azotemia.
3. Reduced perfusion of central nervous system causes hypoxic encephalopathy (irritability to coma).
Morphology of RHF
Liver and portal system (nutmeg liver& centrilobular necrosis with cardiac cirrhosis).
Congestive splenomegaly.
Pleural and pericardial effusion.
Subcutaneous edema and anasarca.
Clinical features:
1. Congestion and edema of portal and dependent peripheral sites (eg: feet, ankle, sacrum) and effusions in pleura and peritoneum (ascites).
2. Hepatomegaly - Centrilobular congestion and atrophy of central hepatocytes (nutmeg liver).
Centrilobular necrosis due to chronic passive venous congestion may cause sinusoidal rupture with central hemorrhagic necrosis followed by hemosiderosis , central fibrosis and cardiac sclerosis.
3. Congestive splenomegaly with sinusoidal dilation, focal hemorrhage followed by hemosiderosis and fibrosis.
4. Renal congestion causes acute hypoxic tubular necrosis.
Congenital heart disease
CHD consist of defects of the cardiac chambers or the great vessels, these either result in shunting of blood between the Rt and Lf circulation or cause out flow obstruction.
Lf to Rt shunts are most common and typically involve ASD, VSD or a PDA.
These lesions result in chronic right-sided pressure and volume overload that eventually cause pulmonary HT with reversal of flow and Rt to Lf shunt with cyanosis (Eisemenger syndrome).
Rt to left shunt are typically caused by tetrallogy of fallot or trasposition of great vessels.
These are cyanotic lesions from the outset and are associated with polycythemia, hypertrophic osteoarthropathy and paradoxical emboli.
Morphology
VSDs are classified according to size and location. Most are about the size of the aortic valve orifice. About 90% involve the region of the membranous septum (membranous VSD).
The remainder lie below the pulmonary valve (infundibular VSD) or within the muscular septum. Although most often single, VSDs in the muscular septum may be multiple (so-called Swiss-cheese septum).
Atrial Septal Defect
An ASD is an abnormal opening in the atrial septum that allows communication of blood between the left and right atria (not to be confused with a patent foramen ovale, present in up to one-third of normal individuals).
ASD & VSD are the most common congenital cardiac anomaly and is usually asymptomatic until adulthood.
Morphology
The three major types of ASDs, classified according to their location in the septum, are secundum, primum, and sinus venosus.
The secundum ASD, accounting for approximately 90% of all ASDs, is a defect located at and resulting from a deficient or fenestrated oval fossa.
ASDs are usually isolated (i.e., not associated with other anomalies).
When associated with another defect, such as tetralogy of Fallot, the other defect is usually hemodynamically dominant. The atrial aperture may be of any size and may be single, multiple, or fenestrated.
Morphology
The three major types of ASDs, classified according to their location in the septum, are secundum, primum, and sinus venosus.
The secundum ASD, accounting for approximately 90% of all ASDs, is a defect located at and resulting from a deficient or fenestrated oval fossa.
ASDs are usually isolated (i.e., not associated with other anomalies).
When associated with another defect, such as tetralogy of Fallot, the other defect is usually hemodynamically dominant. The atrial aperture may be of any size and may be single, multiple, or fenestrated.
Ventricular Septal Defect
Incomplete closure of the ventricular septum, allowing free communication and thus a shunt from left to right ventricles, is the most common congenital cardiac anomaly, frequently, VSD is associated with other structural defects, such as tetralogy of Fallot.
About 30% occur as isolated anomalies. Depending on the size of the defect, it may produce difficulties virtually from birth or, with smaller lesions, may not be recognized until later or may even spontaneously close.
Morphology
VSDs are classified according to size and location. Most are about the size of the aortic valve orifice. About 90% involve the region of the membranous septum (membranous VSD) The remainder lie below the pulmonary valve (infundibular VSD) or within the muscular septum. Although most often single, VSDs in the muscular septum may be multiple (so-called Swiss-cheese septum).
The functional significance of a VSD depends on the size of the defect and the presence of other anomalies.
About 50% of small muscular VSDs close spontaneously, and the remainder are generally well tolerated for years.
Large defects are usually membranous or infundibular, and they generally remain patent and permit a significant left-to-right flow. Right ventricular hypertrophy and pulmonary hypertension are present from birth. Over time, irreversible pulmonary vascular disease develops in virtually all patients with large unoperated VSDs, leading to shunt reversal, cyanosis, and death.
Patent Ductus Arteriosus
Patent (also called persistent) ductus arteriosus (PDA) results when the ductus arteriosus remains open after birth about 90% of PDAs occur as an isolated anomaly. The remainder are most often associated with VSD, coarctation of the aorta, or pulmonary or aortic stenosis. The length and diameter of the ductus vary widely.
Most often PDA does not produce functional difficulties at birth. Indeed, a narrow ductus may have no effect on growth and development during childhood. Its existence, however, can generally be detected by a continuous harsh murmur, described as "machinery-like." Because the shunt is at first left-to-right, there is no cyanosis. Obstructive pulmonary vascular disease eventually ensues, however, with ultimate reversal of flow and its associated consequences.
There is general agreement that an isolated PDA should be closed as early in life as is feasible. Conversely, preservation of ductal patency (by administering prostaglandin E) assumes great importance in the survival of infants with various forms of congenital heart disease with obstructed pulmonary or systemic blood flow, such as aortic valve atresia, therefore, the ductus may be either life-threatening or life-saving.
Obstructive lesion
The clinical severity of the lesion depends on the degree of cyanosis and the patency of the ductus arteriosus these includes:
Coarctation of the Aorta.
Pulmonary Stenosis and Atresia.
Aortic Stenosis and Atresia.
Obstruction can also occur within a chamber, as with subpulmonary stenosis in tetralogy of Fallot.
Coarctation of the Aorta
High in frequency, among the common structural anomalies.
Males are affected twice as often as females.
Two classic forms have been described:
(1) an "infantile" form with tubular hypoplasia of the aortic arch proximal to a PDA that is often symptomatic in early childhood and
(2) an "adult" form in which there is a discrete ridge-like infolding of the aorta, just opposite the closed ductus arteriosus (ligamentum arteriosum) distal to the arch vessels.
Outlook patient with coarctation of the aorta with and without a PDA
leads to manifestations early in life; many infants with this anomaly do not survive the neonatal period without surgical intervention. In such cases, the delivery of unsaturated blood through the ductus arteriosus produces cyanosis localized to the lower half of the body.
Most of the children are asymptomatic, and the disease may go unrecognized until well into adult life. Typically there is hypertension in the upper extremities, but there are weak pulses and a lower blood pressure in the lower extremities, associated with manifestations of arterial insufficiency (i.e., claudication and coldness).
Although surgery may fully correct the hemodynamic abnormalities of congenital heart disease, the heart following repair of a congenital defect may not be fully normal.
Myocardial hypertrophy and other changes of cardiac remodeling brought about by the congenital defect may be irreversible or even necessary for survival and growth. Although adaptive initially, such changes can elicit late-onset arrhythmias, ischemia, and myocardial dysfunction, sometimes after many uneventful years subsequent to the surgery.
Although surgery may fully correct the hemodynamic abnormalities of congenital heart disease, the heart following repair of a congenital defect may not be fully normal.
Myocardial hypertrophy and other changes of cardiac remodeling brought about by the congenital defect may be irreversible or even necessary for survival and growth. Although adaptive initially, such changes can elicit late-onset arrhythmias, ischemia, and myocardial dysfunction, sometimes after many uneventful years subsequent to the surgery.
Associated prosthetic materials and devices, such as substitute valves or myocardial patches, yield an additional risk of complications, most prominently thromboembolism, infection, or dysfunction of the material or device. Moreover, there may be specific difficulties resulting from hyperviscosity of the blood owing to increased hematocrit, and maternal risks associated with childbearing in those with cyanotic congenital disease.