Block 13: Cardiology Board Review: q & A

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Myocarditis involves inflammation of the myocardium that causes some degree of tissue damage or necrosis. Causes may be infectious, the result of toxic exposures, or associated with connective tissue diseases. Numerous viral and bacterial agents have been associated with myocarditis, but Coxsackievirus B is the most common causative viral pathogen. Infants and young children are affected more commonly than older children, and there may be a seasonal distribution of cases, with occurrence in the spring and summer being more common.
Myocarditis is suspected when there is a new murmur, sudden cardiac failure, arrhythmia, or some combination of these following a flulike illness. Symptoms may be subtle, with subclinical changes in the myocardial performance, or severe, with cardiovascular collapse and shock. Most affected infants have the signs and symptoms of congestive heart failure, the typical result of significant myocardial inflammation. Young children may appear pale, diaphoretic, and irritable. With increasingly diminished cardiac output, there can be somnolence and lethargy.
Findings on physical examination in infants typically include tachycardia and tachypnea as well as a holosystolic murmur of mitral regurgitation on auscultation, which is believed to result from distortion of the mitral valve supporting structure as the left ventricle dilates. Pulses and perfusion may be diminished, depending on the degree of myocardial dysfunction. Hepatomegaly may result if there is increased filling pressure in the atria.
The child described in the vignette has fatigue, anorexia, irritability, and a fever. Her clinical examination findings are most consistent with moderate congestive heart failure, and her new murmur of mitral regurgitation suggests the diagnosis of myocarditis. Dehydration and meningitis are not associated with hepatomegaly or a new cardiac murmur. Kawasaki disease and rheumatic fever may be associated with myocarditis, but both are systemic diseases that require the presence of other findings for diagnosis.
15. Included in your rounds today is a 36-hour-old boy who was born at term by normal, spontaneous vaginal delivery. His respiratory rate is 80 breaths/min and heart rate is 168 beats/min. He has easily palpable, bounding pulses in all four extremities, and his blood pressure is 72/30 mm Hg. Precordial examination reveals a lift and a 3/6 systolic ejection murmur at the upper left sternal border. You also note a murmur over the anterior fontanelle.
Of the following, the MOST likely diagnosis is

A. aortic coarctation with congestive heart failure

B. aortic insufficiency

C. large ventricular septal defect with congestive heart failure

D. left-to-right extracardiac shunting with congestive heart failure

E. right-to-left extracardiac shunting with right heart failure

Preferred Response: D
Systemic arteriovenous malformations constitute an extracardiac left-to-right shunt (system to venous). Blood flow always moves from high to low resistance when given the opportunity. When an arteriovenous communication occurs, as might be seen in the brain or in the liver, blood from the high-pressure, high-resistance systemic circulation can move directly into the low-pressure, low-resistance venous circulation, bypassing the capillary bed of the affected organ.
In so doing, the volume of blood entering the venous system is increased, as is the oxygen content of the blood because the tissues have not been exposed to the oxygenated blood. With the passage of time and decreasing blood viscosity as physiologic anemia of the newborn ensues, the volume of blood “shunted” through the arteriovenous malformation becomes greater. Such excess blood flow “loads” the venous pool, which is delivered to the right atrium.
As a result, the right atrium and right ventricle become dilated, and congestion may occur. If such congestion is significant, jugular venous distension and hepatomegaly may become evident on physical examination. Other signs of the right heart volume overload include a prominent precordial lift on palpation and a systolic ejection murmur or relative pulmonary stenosis as the excess blood from the right heart makes its way across the pulmonary valve. The murmur is termed “relative” because the pulmonary valve annulus does not dilate despite dilation of the right ventricle. However, because more blood is ejected from the right ventricle, it must travel with greater velocity as it crosses the pulmonary valve, leading to turbulence, which produces the audible murmur on auscultation. The excess right heart output enters the pulmonary vascular bed, often leading to some level of congestion, with the resulting sign of tachypnea on examination.
Similarly, because arterial blood has a “run-off” into the low-pressure veins, there is a pronounced pulse pressure with a typically low diastolic pressure that produces bounding pulses on examination. In some patients, a continuous murmur can be heard over the area of the arteriovenous malformation, such as the fontanelle, as in the patient described in the vignette, or the liver.
The newborn described in the vignette has physical findings and blood pressure that suggest a run-off lesion from the aorta, which could be significant aortic insufficiency, a large-volume ductus arteriosus, or an arteriovenous malformation. There is no diastolic murmur to suggest aortic insufficiency, and at 36 hours of age, a ductus arteriosus would not be expected to lead to symptoms. Similarly, a large ventricular septal defect might present with a holosystolic murmur and rarely leads to symptoms in the first few days after birth. Coarctation often leads to narrowed blood pressure and is associated with a pressure load on the left ventricle rather than a volume load, as in this patient. Right-to-left extracardiac shunting can occur only when pressure in the venous (right) vessel exceeds that in the arterial (left) vessel. This is a situation that does not exist.
16. You care for a 6-month-old boy who was born with pulmonary atresia and ventricular septal defect. He received a modified Blalock-Taussig (systemic-to-pulmonary artery) shunt 5 days after birth. His oxygen saturations have ranged between 70% and 84% at office visits over the past 2 months. During a health supervision visit, you record a hematocrit of 57% (0.57).
Of the following, this child’s polycythemia puts him at INCREASED risk for

A. acute leukemia

B. bacteremia

C. cerebrovascular accident

D. congestive heart failure

E. necrotizing enterocolitis

Preferred Response: C
Cyanosis is the term given to the observation of a blue, maroon, or purple discoloration of the skin. A number of clinical conditions can lead to this finding, and cyanotic congenital heart disease is an important cause in the pediatric age group. Heart diseases that limit effective pulmonary blood flow or allow for shunting of desaturated blood from the right to left side result in desaturation and cyanosis. Until the underlying condition is corrected or palliated, the desaturation of arterial blood can cause increased erythropoietin secretion from specialized cells in the kidney, resulting in increased erythrocyte production and polycythemia.
Polycythemia leads to an increase in blood viscosity that has a direct relationship to vascular blood flow resistance. In addition, polycythemia increases oxygen-carrying capacity because of greater numbers of red blood cells (RBCs) and a greater concentration of hemoglobin. Because of the increased resistance to blood flow and oxygen-carrying capacity, blood flow at rest is reduced in those who have polycythemia.
Polycythemia is associated with significant clinical morbidity, particularly as the hematocrit increases to values well beyond normal. Complications may involve virtually any organ, but the infant, child, and adolescent typically present with headache, lethargy, irritability, joint pain, anorexia, and dyspnea. More serious complications can include thrombosis of the lungs, kidneys, or the brain. Thus, the balance of the benefit from the increased oxygen-carrying capacity and the risk from increased blood viscosity for the patient who has cyanotic heart disease is precarious. If the underlying congenital heart disease cannot be corrected, consideration should be given to partial volume exchange transfusion as the hematocrit exceeds 65% or at lower values if signs and symptoms are present.
The patient described in the vignette is at risk for a cerebrovascular accident because he has developed polycythemia and its attendant hyperviscosity as a result of his pulmonary atresia with a ventricular septal defect (VSD). As he outgrows his Blalock-Taussig shunt, his oxygen saturations will decrease further because he will have decreased pulmonary blood flow and continued right-to-left shunting at the VSD. If not corrected, this can lead to more pronounced polycythemia and greater risk for its complications. Polycythemia does not increase the risk for acute leukemia, bacteremia, congestive heart failure, or necrotizing enterocolitis.
17. A 1-week-old infant presents to the emergency department with a 1-day history of poor feeding, pallor, diaphoresis, and increasing somnolence. She was born at term, and the delivery was uncomplicated. On physical examination, her heart rate is 180 beats/min, respiratory rate is 90 breaths/min, and blood pressure is 50/30 mm Hg. Her breath sounds are shallow, and cardiac evaluation reveals no murmurs but a gallop rhythm. Her liver is palpable at 3 cm below the costal margin. Her extremities are cool, pale, and mottled, and she has poor distal pulses. After you administer normal saline at 20 mL/kg, her heart rate is 194 beats/min.
Of the following, the MOST appropriate next step is

A. adenosine infusion at 50 mcg/kg

B. computed tomography scan of the head

C. dopamine infusion at 10 mcg/kg per minute

D. lumbar puncture followed by antibiotics

E. normal saline infusion at 20 mL/kg

Preferred Response: C
The newborn described in the vignette has the clinical signs and symptoms of diminished systemic perfusion and shock. Causes of shock in the neonate may include hypovolemia, sepsis, metabolic imbalance, and cardiogenic problems. The tachypnea described for the child likely results from pulmonary congestion caused by decreased filling of the failing left ventricle.
The auscultatory corollary is the presence of the gallop rhythm caused by the abnormal filling of the noncompliant left ventricle. Abnormal filling of the left ventricle results from the chamber’s inability to eject contents adequately, which may be caused by an acute afterload (left heart obstruction with a closing ductus arteriosus) or a cardiomyopathy (genetic, metabolic, or intrinsic). As filling of the left ventricle diminishes, pressure increases in the left atrium and subsequently the pulmonary veins, capillaries, and arteries. This pressure is transmitted back to the right ventricle, which becomes progressively hypertensive and may begin to fail. When right ventricular failure occurs, the systemic veins must drain at higher pressure into the failing right heart, which leads to hepatic congestion and enlargement, with the liver edge becoming palpable well below the costal margin, as described for the infant in the vignette.
The tachypnea exacerbates the poor feeding that results from the infant’s inability to generate a prolonged suck while maintaining nasal breathing. When poor intake is coupled with increased water losses through the respiratory tree, hypovolemia, dehydration, and decreased urine output ensue. Lethargy may reflect decreased perfusion to the brain and may be exacerbated by the metabolic acidosis that results from inadequate tissue perfusion. The tachycardia is often compensatory to maintain cardiac output (cardiac output = heart rate x stroke volume). As the ability to maintain cardiac output fails, the blood pressure falls, as reported for this infant, and the compensated shock becomes uncompensated.
Administration of colloid or crystalloid often improves the cardiac output of patients who have shock due to hypovolemia or sepsis by allowing for increased stroke volume as the patient’s “tank” becomes filled. The tachycardia may begin to resolve following initiation of this therapy.
Conversely, those who suffer from cardiogenic causes of shock may not improve with the addition of volume, which may exacerbate further congestion in the pulmonary circuit and volume in the already dilated left ventricle. The Frank-Starling mechanism, which relates cardiac muscle fiber shortening to left ventricular end-diastolic volume, demonstrates that beyond a certain volume, when the heart is significantly dilated, the addition of volume may lead to diminished fiber shortening and reduced function and stroke volume. This can be characterized by an increase in tachycardia as attempts continue to maintain cardiac output in the face of the diminished stroke volume. The increase in heart rate after the administration of fluids reported for the patient in the vignette signals a cardiogenic cause for her shock.
Immediate management of this critically ill infant includes the administration of inotropic medications to improve cardiac muscle fiber shortening, thereby increasing stroke volume and cardiac output. Dopamine is an excellent drug for patients who have cardiogenic shock with hypotension. Dopamine has both inotropic effects on the heart and vasoconstrictive properties that can help to maintain or improve systemic blood pressure.
Adenosine, a fast-acting atrioventricular node blocker, is used to treat supraventricular tachycardia, commonly characterized in infants by heart rates greater than 240 beats/min. Administering more intravenous fluids can lead to progression of the cardiac failure. Transporting a patient such as the one described in the vignette for computed tomography scan or placing her in the positions necessary for lumbar puncture may lead to further hemodynamic compromise. Administering empiric antibiotics in such cases and obtaining cultures as the shock is being treated is appropriate.
18. A 7-month-old female has undergone the second stage of surgical palliation (Glenn operation) for hypoplastic left heart syndrome. She was discharged from the hospital 1 week ago, and her mother brings her to the office because of irritability that began this morning. On physical examination, the infant is awake and irritable, with a heart rate of 150 beats/min and a respiratory rate of 50 breaths/min. She has cyanosis of the face and mucosal surfaces and swelling of the arms and head.
Of the following, the BEST explanation for this patient’s clinical presentation is

A. polycythemia

B. postpericardiotomy syndrome

C. protein-losing enteropathy

D. superior vena cava syndrome

E. thoracic duct injury

Preferred Response: D
The child described in the vignette has had surgery involving her superior vena cava, which has been sewn by an end-to-side anastomosis to her right pulmonary artery (Glenn operation). She is at risk for stenosis at the surgical site, thrombosis within the superior vena cava, and altered hemodynamics if the pulmonary vascular resistance (and, thus, the pulmonary artery pressure) increases, which raises the pressure against which the venous drainage must occur. Her symptoms and physical findings are consistent with superior vena cava syndrome, and she should undergo an aggressive evaluation and rapid institution of treatment.
Obstruction of the systemic venous return may result from one of three primary causes: extrinsic compression of either the superior or inferior vena cava, intrinsic obstruction of systemic return, or abnormal hemodynamics with significantly elevated right atrial pressures. The systemic veins are thin-walled vascular structures that typically drain at low pressure into the superior and inferior vena cavae. Normally, these large veins drain into the right atrium at low pressure. Flow in any system moves from high to low pressure, and the cardiovascular system

is no exception. The right atrium in the healthy individual typically has a pressure of less than 10 mm Hg, often less than 5 mm Hg. Mechanisms that facilitate venous drainage to the right atrium include gravity for the vessels of the upper body and muscular contraction of the lower extremities, which serves to "push blood up" the valved veins of the caudal portion of the body. As long as the pressure in the right atrium ("downstream") remains lower than the pressures in the veins, forward flow ensues. Any process that increases the pressure in the right atrium raises the pressure needed to ensure forward drainage of the systemic veins.

Similarly, any obstruction of the superior or inferior vena cava raises the pressure "upstream" and may limit normal venous drainage. Extrinsic compression can result from a mediastinal mass or tumor that physically compresses the vena cava, thereby raising the pressure needed to pass blood through the narrowing and into the right atrium. Intrinsic obstructions can result from surgical anastomotic sites, baffle stenosis, thrombosis (eg, from an indwelling catheter), or cardiac tumors that physically obstruct blood return through the vena cava.
When blood return from the superior vena cava into the right atrium is obstructed significantly, patients may demonstrate signs of superficial venous distention, venous congestion, and facial and upper body edema, as described for the infant in the vignette. As the venous pressure increases proximal to the obstruction, the venous drainage of the brain may become engorged, leading to discomfort, irritability, and seizure and brain injury.

Polycythemia (elevated hemoglobin concentrations) might lead to sluggish blood flow through the small capillaries, but would not cause the findings described in this child. Postpericardiotomy syndrome, which can occur in children who have had cardiac surgery, generally presents with fever and systemic symptoms. Protein-losing enteropathy is a serious complication that can occur in patients who have increased pressure in the venous drainage of the gut, including those who undergo single ventricle palliation. Such patients typically present with diarrhea and edema of the entire body, not localized to the upper compartments, as in this patient. Thoracic duct injury can occur in any patient undergoing cardiac surgery and often leads to a chylothorax.

19. You are evaluating a 12-year-old boy who has been fatigued for 2 weeks. His mother reports that he had an upper respiratory tract infection 2 weeks ago, and his appetite has been decreased since then. On physical examination, he is afebrile and has a heart rate at rest of 110 beats/min. His respiratory rate is 22 breaths/min. His lungs are clear, and he has a gallop rhythm without murmurs on cardiac auscultation. You discern hepatomegaly and mild jugular venous distention.
Of the following, the MOST likely diagnosis is

A. anemia

B. dilated cardiomyopathy

C. Kawasaki disease

D. primary pulmonary hypertension

E. pulmonary embolism

Preferred Response: B
The gallop rhythm, hepatomegaly, and jugular venous distention described for the boy in the vignette support the diagnosis of congestive heart failure (CHF), most likely due to myocardial dysfunction associated with dilated cardiomyopathy. Generally, CHF is a clinical syndrome that reflects the inability of the myocardium to meet the metabolic requirements of the body, including those for growth. The presentation in the older child differs from that of the young infant. In the former, CHF usually presents with signs and symptoms of fatigue, particularly with exercise or activity. In addition, children may present with shortness of breath, palpitations, diaphoresis, and

in the most acute cases, extremis. Almost invariably, the left ventricle is affected, and as its systolic and diastolic function diminishes, its filling pressures increase. Clinically, this may manifest during auscultation as a gallop rhythm. The increased left ventricular filling pressures results in rising pressures in the pulmonary veins, pulmonary capillaries, pulmonary arteries, right ventricle, and right atrium. When the right-sided filling pressures increase, the systemic veins that drain into the right atrium, including those of the hepatic system and the jugular system, become congested. Congestion of the former leads to hepatomegaly and that of the latter may manifest with jugular venous distention discernible on examination.
Laboratory support for the myocardial failure seen in patients who have CHF can be demonstrated by an elevation in the brain natriuretic peptide value. Results of this test almost always are abnormal in patients who have significant CHF. Among the many causes of CHF are large-volume left-to-right shunts with pulmonary overcirculation, pressure load on the myocardium, inadequate blood flow to the myocardium, infection or infiltration of the myocardium, or genetic or idiopathic diseases of the myocardium.
CHF from large-volume shunting lesions is seen almost exclusively during infancy. The other causes may manifest any time throughout infancy, childhood, or adolescence. Anemia can lead to a "high-output" state but does not present with the right heart failure demonstrated by the patient in the vignette. Although Kawasaki disease can present in some cases with CHF due to acute myocarditis, the patient in the vignette has no other physical findings to support this diagnosis. Primary pulmonary hypertension is seen more typically in females during adolescence or adulthood and includes the presence of a loud second heart sound with or without a gallop rhythm. Pulmonary embolism typically presents more acutely with chest pain, hypoxemia, and tachypnea in addition to the findings of acute right heart failure.
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