Heart Anatomy Flashcards
Answer B
A venous catheter traveling from the femoral vein to the heart passes through the iliac vein and inferior vena cava to reach the right atrium. Once in the right atrium, structures within the right side of the heart and the pulmonary arteries are readily accessible.
However, because the pulmonary capillaries are far too small to pass through, the left side of the heart must be accessed by traversing the interatrial septum. The interatrial septum is traversed at the site of the foramen ovale, which in adults is typically covered by a thin membrane of fibrous tissue that can be easily punctured.
Entry into the left atrium allows for direct measurement of left atrial pressure (rather than an estimate via pulmonary capillary wedge pressure) and for access to arrhythmogenic foci that may be located on the left atrial myocardium or the pulmonary veins. Following the procedure, the small atrial septal defect created by the catheter typically closes spontaneously.
(Choice A) Arterial catheterization of the left side of the heart typically starts in the femoral or radial artery and proceeds to the ascending aorta where pressure can be measured or dye can be placed into the coronary arteries to visualize atherosclerotic obstruction (ie, coronary angiography). In addition, the aortic valve may be crossed to measure left ventricular pressure. However, retrograde crossing of the structurally complex mitral valve is highly difficult, and the left atrium is not accessed via this route.
(Choice C) The interventricular septum is not traversed during heart catheterization because the myocardium is thick and difficult to puncture, and high left ventricular pressure would likely prevent spontaneous closure of the ventricular septal defect that is created.
(Choices D and E) The tricuspid valve is crossed during venous catherization to access the right ventricle, and the pulmonic valve is subsequently crossed to access the pulmonary arteries. However, because the catheter cannot pass through the pulmonary capillaries, the left atrium cannot be accessed via this route.
Educational objective:
To access the left side of the heart, cardiac venous catheters must cross the interatrial septum at the site of the foramen ovale. Entry into the left atrium allows for direct measurement of left atrial pressure and for access to arrhythmogenic foci on the left atrial myocardium or pulmonary veins.
Answer E
The coronary circulation is composed of 3 major epicardial vessels.
* The left anterior descending artery (LAD) arises from the left main artery and courses down the anterior heart, supplying the anterior left ventricular (LV) wall and septum.
* The left circumflex artery (LCx) arises from the left main artery and courses around the left side of the heart to supply the lateral LV wall. Occasionally, the LCx extends all the way around the heart to supply the inferior LV wall (left-dominance).
* The** right coronary artery (RCA)** comes directly off the aorta and courses around the right side of the heart to supply the right ventricle (RV). In most patients, the RCA extends past the RV to also supply the inferior LV wall (right-dominance).
Blood supply to the inferior LV wall depends on coronary artery dominance. Right coronary dominance is present in approximately 85% of patients and involves the RCA coursing past the RV to give off the posterior descending artery (PDA) and supply the inferior LV wall. Left coronary dominance is present in approximately 10% of patients and involves the LCx extending around the left side of the heart to give off the PDA and supply the inferior LV wall. Approximately 5% of patients have codominant circulation.
In virtually all patients, the RV is fully supplied by the RCA, and in patients with left-dominant circulation, none of the inferior LV wall is supplied by the RCA. Therefore,** isolated RV myocardial infarction (MI)** can occur due to RCA occlusion in a patient with left-dominant circulation. Given the low prevalence of left-dominant circulation, isolated RV MI is an uncommon event (approximately 3% of Mis).
(Choices A, B, C, and D) The LAD and LCx do not supply the RV and are not involved in RV MI.
(Choice F) With right-dominant circulation, the RCA supplies the inferior LV wall. Therefore, RCA occlusion would cause MI involving the RV and the inferior LV wall, or the inferior LV wall alone if the occlusion is distal to the RV.
Educational objective:
Blood supply to the inferior left ventricular (LV) wall is determined by coronary dominance. Most patients have right-dominant circulation, in which the inferior LV wall is supplied by the right coronary artery. Approximately 10% of patients have left-dominant circulation, in which the inferior LV wall is supplied by the left circumflex artery. The right ventricle is fully supplied by the right coronary artery in virtually all patients.
Answer B
Coronary dominance is determined by the coronary artery that supplies blood to the posterior descending artery (PDA [or posterior interventricular artery]). The PDA originates from one of the following:
* Right coronary artery in approximately 70%-80% of the population (right dominant)
* Left circumflex artery in approximately 5%-10% of the population (left dominant)
* Both right coronary and left circumflex artery in 10%-20% of the population (codominant)
The atrioventricular (AV) nodal artery most often arises from the dominant coronary artery. This patient has left-dominant coronary circulation; therefore, his atherosclerotic lesion is most likely in the left circumflex artery. Involvement of the AV nodal artery during myocardial infarction can cause varying degrees of AV block.
(Choice A) The left anterior descending artery travels in the anterior interventricular groove and supplies the anterior part of the septum and the anterior wall of the left ventricle. It does not supply the AV node.
(Choice C) The diagonal arteries arise from the left anterior descending artery and supply the anterolateral wall of the left ventricle.
(Choice D) The right coronary artery gives rise to the AV nodal artery in patients with right-dominant or codominant circulation. This patient has left-dominant circulation, so the AV node is most likely supplied by the left circumflex artery.
(Choice E) The right marginal arteries arise from the right coronary artery and supply blood to the free wall of the right ventricle.
Educational objective:
Coronary dominance is determined by the coronary artery supplying the posterior descending artery. The posterior descending artery originates from the right coronary artery in approximately 70%-80% of patients (right dominant), both the right coronary and left circumflex artery in 10%-20% (codominant), and the left circumflex artery in 5%-10% (left dominant). The dominant coronary artery supplies blood to the atrioventricular (AV) node via the AV nodal artery.
Answer B
This patient with ST elevations in leads I and aVL most likely has an acute lateral myocardial infarction (MI) due to occlusion of the left circumflex artery. ECGs are useful in the diagnosis of MI and may help localize the area of infarction. ST elevations typically represent acute MI, whereas prominent Q waves are suggestive of old MI.
**Leads I and aVL **correspond to the lateral limb leads on ECG; therefore, ST elevation or Q waves in these leads are indicative of infarction involving the lateral aspect of the left ventricle. Because the chest leads V5-V6 are also laterally placed, they may also show ST elevation during a lateral infarction. The lateral aspect of the left ventricle is supplied by the left circumflex artery, which originates from the left main coronary artery.
(Choices A and D) The left anterior descending artery (LAD) primarily supplies the anterior aspect of the left ventricle and interventricular septum (septal branches), which corresponds to the anterior chest leads (V1-V4). Proximal occlusion of the LAD may involve all of these leads; however, distal LAD occlusion typically spares the septal leads (V1-V2).
(Choice C) The left main coronary artery gives rise to the LAD and left circumflex arteries. Therefore, left main coronary artery occlusion typically results in anterolateral infarction, which corresponds to ST elevation in the anterior (eg, V1-V4) and lateral (V5-V6,
1, and aVL) leads.
(Choice E) The right coronary artery typically supplies the right ventricle and inferior aspect of the left ventricle. Occlusion of this vessel therefore results in inferior Mi, which corresponds to ST elevation in the inferior leads (II, Ill, and aVF).
Educational objective:
Leads I and aVL correspond to the lateral limb leads on ECG. Therefore, ST elevation or Q waves in these leads are indicative of infarction involving the lateral aspect of the left ventricle, which is supplied by the left circumflex artery.
Answer A
This patient’s presentation suggests acute endocarditis, with confirmation pending the results of the blood cultures and cardiac imaging. Transesophageal echocardiography (TEE) uses ultrasound waves generated from within the esophagus to produce clear images of the neighboring cardiac structures. The left atrium makes up the majority of the heart’s posterior surface, with the** esophagus** passing immediately posterior to the heart. Therefore, the esophagus lies within closest proximity to the left atrium. This allows the left atrium, atrial septum, and mitral valve to be particularly well visualized on TEE.
Due to its proximity, conditions that result in left atrial enlargement (eg, mitral stenosis or regurgitation) can cause dysphagia through external compression of the esophagus.
(Choice B) The left ventricle forms the majority of the inferior (diaphragmatic) surface of the heart and the left border of the heart on frontal chest x-ray.
(Choice C) The right atrium, along with the superior vena cava, forms the right lateral cardiac border on frontal chest x-ray.
(Choice D) The right ventricle forms the anterior (sternal) surface of the heart and the majority of its inferior border on frontal chest x-ray.
Educational objective:
The left atrium forms the majority of the posterior surface of the heart and resides adjacent to the esophagus. Enlargement of the left atrium can compress the esophagus and cause dysphagia.
Answer A
The aorta has 4 major divisions: the ascending aorta, the aortic arch, the descending thoracic aorta, and the abdominal aorta. The ascending aorta lies posterior and to the right of the main pulmonary artery. The aortic arch travels above the right pulmonary artery and the left bronchus. The brachiocephalic, left common carotid, and left subclavian arteries (in that order) originate from its superior aspect.
The descending thoracic aorta travels down the anterior surface of the vertebral column, becoming the abdominal aorta as it crosses the diaphragm. As it descends, the aorta moves from the left side of the vertebral column toward the midline; at the level of the cardiac chambers, the descending aorta lies posterior to the esophagus and the left atrium. This permits clear visualization of the descending aorta during transesophageal echocardiography (TEE), allowing for the detection of abnormalities such as dissection or
aneurysm.
The other answer choices describe structures located anterior to the esophagus.
(Choice B) The main pulmonary artery ascends anteriorly and to the left of the ascending aorta and is directed toward the left shoulder. After the pulmonary artery bifurcates, the right pulmonary artery travels horizontally under the aortic arch posterior to the superior vena cava, and the left pulmonary artery courses superiorly over the left main bronchus.
(Choice C) The superior and inferior pulmonary veins arise bilaterally from each lung and enter the left atrium. The proximal 2-3 cm of the pulmonary veins contain cardiac muscle within the media and function like sphincters during atrial systole.
(Choice D) The superior vena cava (SVC) is formed behind the right first costal cartilage by the merger of the right and left brachiocephalic veins. It returns blood from the head, neck, and upper extremities to the right atrium of the heart. Mediastinal neoplasms can compress the SVC and result in SVC syndrome.
(Choice E) The tricuspid valve is located between the right atrium and right ventricle and is composed of 3 valve leaflets, the annulus, supporting chordae tendinee, and the papillary muscles. It is commonly infected (endocarditis) in intravenous drug users.
Educational objective:
The descending thoracic aorta lies posterior to the esophagus and the left atrium. This position permits clear visualization of the descending aorta by transesophageal echocardiography, allowing for the detection of abnormalities such as dissection or aneurysm.
Answer A
This patient with a recent history of upper respiratory infection has likely developed viral pericarditis complicated by pericardial effusion. Viral infection is the most common cause of acute pericarditis, with coxsackievirus (types A and B) and echovirus being the most common organisms. Patients with pericarditis typically experience chest pain, which may be intermittent (as in this patient) but is often pleuritic and/or positional (eg, relieved by leaning forward).
As in this patient, viral pericarditis can be complicated by pericardial effusion due to fibrinous or serofibrinous pericardial inflammation. Symptoms of pericardial effusion may include a sensation of chest tightness or fullness and dyspnea on exertion (due to decreased diastolic ventricular filling that leads to decreased stroke volume). In addition, pericardial effusion often causes the following clinical findings:
* Tachycardia to compensate for decreased ventricular filling
* Low voltage QRS on ECG and diminished heart sounds to auscultation due to pericardial fluid accumulation increasing the distance between the heart and the ECG leads or stethoscope
* Electrical alternans on ECG due to the swinging motion of the heart in the fluid-filled pericardial cavity, causing a beat-to-beat variation in the QRS axis
Patients with pericardial effusion classically have an enlarged, globular cardiac silhouette on chest x-ray, which occurs when progressive pericardial stretching over days to weeks (ie, subacute course) allows large volumes (eg, up to 1-2 L) of pericardial fluid to accumulate.** Clear lung fields** are typically seen because the increase in pericardial pressure (due to pericardial fluid accumulation) affects the lower pressure, right-sided heart chambers more than the left-sided heart chambers. When right-sided obstruction to blood flow is greater than left-sided obstruction, pulmonary edema is unlikely to develop.
(Choice B) Hyperinflated lungs with increased bronchial markings are commonly seen in patients with chronic obstructive pulmonary disease.
(Choice C) Bilateral patchy infiltrates (perihilar › peripheral) are concerning for pulmonary edema. A normal cardiac silhouette may be present (as in this x-ray) due to an acute cardiac process (eg, MI) that causes acute systolic dysfunction and pulmonary congestion. In contrast, pulmonary edema in the setting of cardiomegaly is often due to chronic heart failure.
(Choice D) Absence of right-sided, peripheral lung markings surrounding a small, collapsed lung is consistent with a large right-sided pneumothorax.
(Choice E) Blunting of the right costophrenic angle and loss of diaphragmatic contour are characteristic of a pleural effusion.
Educational objective:
Acute viral pericarditis is commonly complicated by pericardial effusion. Classic features of pericardial effusion include tachycardia and ECG findings of low voltage QRS and electrical alternans. Chest x-ray classically reveals an enlarged cardiac silhouette with clear lungs.
Answer E
The right renal vein is a relatively short structure and runs anterior to the right renal artery before joining the inferior vena cava
(IVC). The right gonadal vein also drains directly to the IVC. In contrast, the left renal vein is significantly longer and runs posterior to the splenic vein before crossing the aorta beneath the superior mesenteric artery. The left gonadal vein joins the left renal vein upstream of where it crosses the aorta and does not enter the IVC directly.
The pressure within the left renal vein is often higher than on the right due to compression between the aorta and the superior mesenteric artery (“nutcracker effect”). Pressure in the left renal vein can also be elevated due to compression from a left-sided abdominal or retroperitoneal mass. Persistently elevated pressure in the left renal vein can cause flank or abdominal pain, along with gross or microscopic hematuria (left renal vein entrapment syndrome). Increased pressure in the left gonadal vein results in valve leaflet failure and varices of the testicular pampiniform plexus (varicocele).
(Choices A, C, and D) Esophageal varices, rectal varices, and periumbilical venous distension are signs of portal venous hypertension. The renal veins are not part of the portal system.
(Choice B) Unilateral left-sided ankle swelling can result from many causes, including obstruction of the left common iliac vein, left external iliac vein, left femoral vein, or any of the other major veins of the left leg.
Educational objective:
Pressure in the left renal vein may become elevated due to compression where the vein crosses the aorta beneath the superior mesenteric artery. This “nutcracker effect” can cause hematuria and flank pain. Pressure can also be elevated in the left gonadal vein, leading to formation of a varicocele.
Answer B
This patient with deep venous thrombosis (DVT) has had recurrent episodes of gastrointestinal hemorrhage, including a recent one requiring prolonged hospitalization. Given the risk of bleeding associated with anticoagulation therapy in this patient, inferior vena cava (IVC) filter placement is planned. IVC filters are designed to prevent the embolization of DVT from the legs to the lung vasculature (ie, pulmonary embolism), and are used in patients who have contraindications to anticoagulation.
CT images are always visualized as though standing at the patient’s feet and looking through the patient’s body toward the head; therefore, the left side of the image corresponds to the patient’s right side. Both kidneys are viewed in this section, and the inferior pole of the right lobe of the liver is noted anterior to the right kidney and posterolateral to the large bowel. The filter will be placed in the IVC, which lies medial to the descending part of the duodenum and anterior to the right side of the vertebral body. The common iliac veins merge to become the IVC inferior to this plane of section at the L5 level.
(Choice A) With its dark center, representing an air-filled lumen, and mucosal folds, this structure is likely the second (descending) part of the duodenum, which typically lies at the level of L2.
(Choice C) This structure represents the abdominal aorta, which bifurcates at the level of L4. The structure is on the patient’s left, so it is unlikely to be the IVC.
(Choice D) This structure likely represents the fourth (ascending) part of the duodenum. This CT section likely captures only the wall of the fourth part of the duodenum as it briefly courses transversely across the abdomen (before descending as the jejunum), so the lumen is not visible.
(Choice E) This structure is likely the left renal vein. The left renal vein receives drainage from the left gonadal vein and courses anterior to the aorta, but posterior to the superior mesenteric artery, before draining into the IVC.
Educational objective:
The inferior vena cava (IVC) courses through the abdomen and inferior thorax in a location anterior to the right half of the vertebral bodies. The renal veins join the IVC at the level of L1/L2, and the common iliac veins merge to become the IVC at the level of L5.
VC filters are placed in patients with deep venous thrombosis who have contraindications to anticoagulation therapy.
Answer E
The mitral valve apparatus consists of the mitral valve annulus, anterior and posterior mitral leaflets, and chordae tendineae, which are tethered to the left ventricular wall via the anterolateral and posteromedial papillary muscles. Pathologic processes that disrupt any of these structures can lead to improper alignment of the mitral leaflets, resulting in mitral regurgitation and pulmonary edema.
The patient’s mitral regurgitation is the result of papillary muscle rupture, a life-threatening mechanical complication typically occurring 3-5 days following acute myocardial infarction. The anterolateral papillary muscle has a dual blood supply from the left anterior descending (LAD) and left circumflex arteries. In contrast, the posteromedial papillary muscle is supplied solely by the posterlor descending artery, a branch of the right coronary artery (right dominant circulation) or left circumflex artery (left dominant circulation). Because blood flow to the posteromedial papillary muscle depends on a single artery, it is more likely to become schemic and rupture following myocardial infarction.
(Choice A) The conus artery is an early branch of the proximal right coronary artery; it supplies the anterior area of the interventricular septum and conus of the pulmonary artery.
(Choice B) Diagonal arteries branch from the LAD artery and supply blood to the anterolateral walls of the left ventricle.
(Choice C) The LAD artery supplies the anterior two thirds of the interventricular septum, anterior wall of the left ventricle, and anterolateral papillary muscle. Abrupt occlusion of the LAD rarely results in ischemic rupture of the anterolateral papillary muscle as this muscle also receives blood supply from the left circumflex artery.
(Choice D) The obtuse (left) marginal artery is a branch of the left circumflex artery and supplies the lateral wall of the left ventricle.
Educational objective:
Papillary muscle rupture is a life-threatening complication that typically occurs 3-5 days after myocardial infarction and presents with acute mitral regurgitation and pulmonary edema. The posteromedial papillary muscle is supplied solely by the posterior descending artery, making it susceptible to ischemic rupture.
Answer B
This patient has symptoms consistent with an obstructed right brachiocephalic (innominate) vein. This may be the result of external compression by an apical lung tumor or thrombotic occlusion as can occur when a central catheter has been in place for an extended period. The right brachiocephalic vein is formed by the union of the right subclavian vein and the right internal jugular vein. The right external jugular vein drains into the right subclavian vein, so obstruction of the right brachiocephalic vein will also cause venous congestion of structures drained by the external jugular vein. It is important to note that the right brachiocephalic vein also drains the right lymphatic duct, which drains lymph from the right upper extremity, the right face and neck, the right hemithorax, and the right upper quadrant of the abdomen.
(Choices A and E) The subclavian vein is the continuation of the axillary vein. Both drain blood from the upper extremity.
Blockage at any of these 2 sites would cause unilateral arm swelling without associated facial swelling.
(Choices C and D) The external jugular vein drains the scalp and portions of the lateral face. The internal jugular vein drains the brain and superficial face and neck. Obstruction of the internal jugular veins would not cause arm swelling.
(Choice F) Superior vena cava (SVC) syndrome results when the superior vena cava is obstructed. The signs and symptoms of SVC syndrome are similar to those of obstructed right brachiocephalic (innominate) vein, except that both sides of the face, neck, and chest and both arms would be involved.
Educational objective:
The brachiocephalic vein drains the ipsilateral jugular and subclavian veins. The bilateral brachiocephalic veins combine to form the superior vena cava (SVC). Brachiocephalic vein obstruction causes symptoms similar to those seen in SVC syndrome, but only on one side of the body.
Answer D
A penetrating, laterally directed stab wound (possibly from a left-handed assaulter) that involves the fifth intercostal space (ICS) at the left anterior midclavicular line (MCL) would most likely injure the left lung. The lungs occupy most of the volume of the thoracic cavity. The apex of each lung extends into the neck (3-4 cm above the first rib). The lung bases are in direct contact with the diaphragm, which separates the right lung from the right lobe of the liver and the left lung from the stomach, spleen, and (occasionally) left lobe of the liver. The mediastinal surface of each lung has a cardiac impression that accommodates the heart.
A deeper (and more medially directed) wound could have injured the left (not the right) ventricle. The heart is located behind the sternum, and its anterior surface is partially** covered** by the lungs. The cardiac apex is formed by the left ventricle. Depending on heart size, the point of maximal apical impulse can be felt at the fifth left ICS (between the fifth and sixth ribs) at the left MCL. All other heart chambers, including the right ventricle, lie medial to the left MCL and are unlikely to have been affected by the injury.
The right ventricle forms the sternocostal (anterior) surface of the heart (Choice E). The diaphragmatic (inferior) surface is formed by the left and right ventricles and is in contact with the central tendon of the diaphragm. The posterior surface of the heart is formed mainly by the left atrium (Choice C).
(Choice A) The azygos vein lies in the posterior mediastinum immediately to the right of the midline. It drains blood from the posterior intercostal veins into the superior vena cava.
(Choice B) The inferior vena cava is located in the mediastinum, lies to the right of midline, and drains into the right atrium.
Educational objective:
The left ventricle forms the apex of the heart and can reach as far as the fifth intercostal space at the left midclavicular line (MCL).
All other chambers of the heart lie medial to the left MCL. The lungs overlap much of the anterior surface of the heart.
Answer B
Femoral vein catheter placement is usually done in patients with unavailable preferred access sites (eg, subclavian, jugular vein) or those at increased risk of complications (eg, emergency access, uncooperative patient). The femoral vein is the major deep vein of the lower extremity and passes through the femoral triangle beneath the inguinal ligament before entering the pelvis as the external iliac vein. The femoral triangle is a subfascial space in the upper thigh that is bordered by the inguinal ligament (superiorly), adductor longus muscle (medially), and sartorius muscle (laterally).
Within the femoral triangle lies (lateral to medial) the femoral nerve, femoral artery, femoral vein, and deep inguinal nodes/lymphatic vessels. The femoral artery is located at the midinguinal point (midway between the pubic symphysis and anterior superior iliac spine), and the femoral vein lies immediately medial to the artery. Cannulation of the femoral vein should occur approximately 1 cm below the inguinal ligament and 0.5-1.0 cm medial to the femoral artery pulsation (Choices C, D, and
티.
(Choice A) The femoral nerve is approximately 1 cm lateral to the femoral artery pulsation and could be damaged by needle
insertion at this site.
Educational objective:
The femoral triangle (lateral to medial) consists of the femoral nerve, femoral artery, femoral vein, and deep inguinal nodes/lymphatic vessels. Cannulation of the femoral vein should occur approximately 1 cm below the inguinal ligament and just medial to the femoral artery pulsation.
Answer D
This axial CT image reveals the abdomen near the L1 vertebral level. At this level, the Inferior vena cava (IVC) lies just anterior to the right renal artery and to the right of the aorta. The IVC is formed by the union of the right and left common iliac veins at the level of L4-L5 and drains into the right atrium just above the level of the diaphragm at T8. The IVC returns venous blood to the right atrium from the lower extremities, portal system, and abdominal and pelvic viscera.
(Choice A) The thoracic duct drains lymph from the entire left side of the body and all regions inferior to the umbilicus (including the entire gastrointestinal tract). It enters the thorax through the aortic hiatus and empties into the left subclavian vein near its junction with the internal jugular vein.
(Choice B) The cystic duct drains bile from the gallbladder into the common bile duct. The gallbladder is typically visualized just below the liver in the anterior right abdomen but is not well seen in this image.
(Choice C) The image reveals the abdominal aorta giving rise to the right and left renal arteries at the L1 vertebral level. The abdominal aorta lies posteromedial to the IVC within the abdomen.
(Choice E) The superior mesenteric vein joins the splenic vein to form the portal vein. The portal vein can be seen vaguely near the head of the pancreas in this cross-sectional image.
Educational objective:
The inferior vena cava is formed by the union of the right and left common iliac veins at the level of L4-L5. The renal arteries and veins lie at the level of L1. The inferior vena cava returns venous blood to the heart from the lower extremities, portal system, and abdominal and pelvic viscera.
Answer E
Evolution of a myocardial infarction occurs in several stages. The final stage of the healing process begins approximately 2 weeks after infarction and involves increased deposition of type I collagen. Fibrosis continues until about 2 months after infarction, resulting in a dense collagenous scar composed primarily of type I collagen. The scar can be identified grossly as a firm, gray-white lesion or microscopically as collagenous tissue replacing myocardium (as in this patient).
In addition to its role in wound healing, type I collagen (the most abundant type) provides strength and support for a variety of cellular tissues and organs (eg, tendons, ligaments, skin). It is also the major organic component in bones and significantly contributes to overall bone strength. Defects in type I collagen can occur in osteogenesis imperfecta, an autosomal dominant disorder that may present with fragile bones and ligament laxity.
(Choices A, C, and D) Basement membrane contains type IV collagen; hyaline cartilage (eg, articular surfaces) and nucleus pulposus contain type Il collagen.
(Choice B) Granulation tissue is a capillary-rich fibroblastic proliferation composed primarily of type Ill collagen. Although granulation tissue is seen approximately 7 days after an acute myocardial infarction, it is eventually replaced by type I collagen as the infarct heals. Type Ill collagen is involved in the structural maintenance of extensible connective tissues and is often found alongside type I collagen.
Educational objective:
Type I collagen is the primary collagen in mature scars (eg, remote myocardial infarction). It is the most prevalent type of collagen and provides strength and support throughout the human body, particularly in bones, tendons, ligaments, and skin.
Answer B
Postmortem histopathology of this patient’s myocardium reveals a dense neutrophilic infiltrate surrounded by relatively normal myocytes consistent with the morphologic changes expected in the border zone of ischemic injury 1-3 days after myocardial infarction (MI). Myocardial cells are highly metabolically active and susceptible to schemic injury after as little as 3-4 minutes of oxygen deprivation due to coronary artery blockage.
After irreversible myocardial injury, a series of characteristic microscopic changes occur over predictable time frames due to coagulative necrosis of myocardial fibers and infiltration of Inflammatory cells, which play an essential role in the healing process:
* During the first 4 hours post-MI, no visible change occurs although cardiac-specific enzymes can be detected in the patient’s bloodstream (Choice A).
* From 4 to 24 hours post-Mi, changes due to digestion of cytoplasmic organelles, denaturation of proteins, and loss of RNA become visible (eg, wavy, hypereosinophilic myocytes with shrunken nuclei), especially in the central portion of the infarct.
* From 1 to 3 days post-MI, neutrophils infiltrate the** border zone** of the injured tissue in response to proinflammatory cytokines (eg, IL-6, IL-8), eventually migrating to the central portion of the infarct. These neutrophils phagocytize dead myocytes and release lysosomal enzymes, reactive oxygen species, and cytokines (eg, IL-1, TNF-a) that can prevent infiltration by pathogens and facilitate wound healing.
* From 3 to 10 days post-MI, macrophages infiltrate and phagocytize dead myocytes and neutrophils while initiating the formation of granulation tissue by producing cytokines (eg, IL-10) and growth factors (TGF-ß) (Choice C).
* From 10 to 14 days post-MI, prominent fibroblast proliferation, collagen deposition, and neovascularization of granulation tissue are present.
* From 2 weeks to 2 months post-MI, collagen remodeling and fibroblast differentiation into myofibroblasts drive the formation of scar tissue (Choice D).
* After 2 months post-MI, remodeling continues to a slower rate as the scar matures and contracts (Choice E).
Educational objective:
Irreversible myocardial ischemic injury initiates a series of predictable morphologic changes over the hours to weeks after the initial injury. From 1 and 3 days after the initial injury, neutrophils infiltrate the border zone of the injured tissue (where myocytes are relatively normal) in response to proinflammatory cytokines (eg, IL-6, IL-8), eventually migrating to the central portion of the infarct.
Answer B
Acute cardiac transplant rejection typically occurs within 6 months of transplantation and can be diagnosed via endomyocardial biopsy. Acute rejection can be cell-mediated (ie, acute cellular rejection [ACR]) or, less commonly, antibody-mediated (ie, acute antibody-mediated rejection).
In ACR, host T-lymphocytes are sensitized against foreign human leukocyte antigens (HLA) in the cardiac allograft, which leads to inflammation and injury to the transplanted organ. Microscopic features of ACR include an **interstitial lymphocytic infiltrate ** (primarily T-lymphocytes) and damaged myocytes.
Symptoms consistent with progressive rejection include those found in systolic dysfunction (eg, dyspnea on exertion). However, cardiac transplant recipients undergo close surveillance with regular endomyocardial biopsies, and acute rejection is often diagnosed before patients become symptomatic.
(Choice A) Concentric intimal thickening of the coronary arteries can be seen in cardiac allograft vasculopathy, an important cause of ischemic damage and long-term graft dysfunction. The pathogenesis is complex and includes the release of cytokines that cause smooth muscle cell proliferation in the vessel wall.
(Choice C) Patchy necrosis with granulation tissue is indicative of ischemic damage to the donor heart. Ischemia in a donor heart can occur in a variety of situations including during attempted resuscitation of the donor patient, during transport of the organ from the donor to the recipient, and acutely during initial perfusion of the organ after transplantation.
(Choice D) Perivascular infiltrate with abundant eosinophils is a histopathologic feature of hypersensitivity myocarditis.
Hypersensitivity myocarditis often represents an immunologic response to a newly initiated drug.
(Choice E) Interstitial fibrosis with scant inflammation can be seen in chronic rejection of solid organ transplants. Chronic rejection is mediated by host T-lymphocytes as well as antibodies and classically occurs months to years following transplantation.
Educational objective:
Acute cardiac transplant rejection usually occurs weeks to months following transplantation and is primarily a cell-mediated process. In acute cellular rejection, endomyocardial biopsy shows an interstitial lymphocytic infiltrate with myocyte damage.
