Double Outlet Right Ventricle With Normally Related Great Arteries 

Updated: Sep 07, 2018
Author: Maggie L Likes, MD; Chief Editor: Stuart Berger, MD 

Overview

Background

Double outlet right ventricle (DORV) was first pathologically described in the late 19th century as partial transposition. In 1957, Witham first used the term double outlet right ventricle to describe a partial transposition of the great arteries.[1] He described 4 hearts with 2 varieties of "complete aortic transposition with the pulmonary artery in normal position."

Double outlet right ventricle is defined as a form of ventriculoarterial connection in which both great arteries arise completely or predominantly from the morphologic right ventricle. This definition is still controversial. For example, some researchers require that the aorta and the pulmonary artery arise entirely from the right ventricle. Others require that 90% of the great vessels arise from the morphologic right ventricle. Alternatively, the 50% rule states that more than one half of both arterial trunks must arise from the morphologic right ventricle. Some require only the presence of fibrous discontinuity between the mitral and semilunar valves. This is present in most specimens and is referred to as subpulmonic and subaortic conus.

Pathophysiology

Double outlet right ventricle, with a large variability in anatomy, represents a continuum of congenital heart defects (CHDs) that includes ventricular septal defect (VSD) with significant override of the aorta, origin of both great arteries from the right ventricle, and transposition of the great arteries with pulmonary override of the VSD. A common arterial trunk may also arise completely from the right ventricle. This is actually a type of truncus arteriosus.

Pathophysiologic description and classification is accomplished by relating the location of the VSD to the arrangement of the great vessels. Each combination results in a physiologic behavior similar to that of other CHDs. The VSD in double outlet right ventricle can be subaortic, subpulmonary, noncommitted, or doubly committed. Most VSDs are nonrestrictive, but as many as 17% of patients may require VSD enlargement during repair to allow unrestricted systemic blood flow.

The most common type of VSD found in double outlet right ventricle is a subaortic type. The aortic orifice is usually posterior and to the right of the pulmonary orifice, with a spiral arterial relationship. Because the great arteries are normally related, the left ventricular outflow is directed toward the aorta, resulting in aortic oxygen saturations that exceed pulmonary saturations. Associated pulmonary stenosis is present in as many as 50% of patients with double outlet right ventricle. The resulting physiology is similar to tetralogy of Fallot, in which the aorta completely overrides the right ventricle.

Systolic pressures are equal in both ventricles and in the aorta. In the absence of pulmonary stenosis, the physiology resembles that of a large isolated VSD, in which the ratio of pulmonary to systemic blood flow is determined by the pulmonary vascular resistance. Systemic and pulmonary saturations are also affected by the degree of mixing in the right ventricle. This anatomy may result in congestive heart failure (CHF) and pulmonary vascular disease.

In double outlet right ventricle with subpulmonary VSD (Taussig-Bing anomaly), the left ventricular outflow is directed toward the pulmonary artery. This preferential streaming results in pulmonary artery saturations greater than aortic saturations. The aortic and pulmonary orifices are usually positioned side by side but are described as transposed or malposed. The rare presence of pulmonary stenosis results in physiology similar to tetralogy of Fallot. However, in the absence of pulmonary obstruction or stenosis, patients with double outlet right ventricle and subpulmonary VSD have physiology similar to transposition of the great arteries and VSD. In this case, pulmonary vascular resistance (PVR) determines pulmonary blood flow. Early-onset pulmonary obstructive vascular disease commonly develops because of increased pulmonary blood flow and pressures, yet cyanosis may be absent with high pulmonary blood flow. This type of double outlet right ventricle is frequently associated withsubaortic stenosis and arch obstruction.

Double outlet right ventricle with noncommitted or remote VSD has anatomy and physiology similar to that of an isolated VSD or atrioventricular canal defect. To meet the criteria for double outlet right ventricle with noncommitted VSD, some have suggested that the distance between the VSD and the aortic and pulmonary outflow tracts should be at least equal to the aortic valve diameter. Most commonly, the great arteries are normally related in this type of double outlet right ventricle. Pulmonary and systemic blood flow and saturations are determined by the ratio of pulmonary to systemic vascular resistance and by the degree of right ventricular mixing.

Finally, double outlet right ventricle with doubly committed VSD displays physiology in which the left ventricular outflow is equally shared by the aorta and pulmonary artery. The systemic and pulmonary vascular resistances determine the ratio of pulmonary-to-systemic blood flow. This is a relatively rare form of double outlet right ventricle that typically has normally related great arteries. Right ventricular mixing affects oxygen saturations.

Because double outlet right ventricle is the only defect in less than 50% of patients with double outlet right ventricle, classification and description may also take into consideration obstruction of the systemic circulation, ventricular anomalies, coronary artery anomalies, and conduction system abnormalities. Upon further investigation, findings of additional VSDs, anomalies of ventricular rotation, and anomalies of insertion of the subvalvar apparatus of atrioventricular valves are not uncommon.

Systemic circulation may be obstructed at the aortic valve or the obstruction may be subaortic; subaortic obstruction develops in approximately 10% of patients. Aortic valve anomalies are usually associated with mitral valve anomalies that may also be present in the form of a restrictive VSD. Coarctation of the aorta is the most common associated lesion, and interrupted aortic arch may also be present.

Patients with double outlet right ventricle can have coexisting ventricular anomalies. Left ventricular inflow anomalies are less frequent yet can be severe. Mitral stenosis or atresia is often associated with a hypoplastic left ventricle and intact ventricular septum. Left ventricular hypoplasia is present if decreased pulmonary venous return, restrictive VSD, and large atrial septal defect (ASD) are present. Misalignment of atrioventricular valves is also visible. This is very important for surgical correction and must be investigated. Finally, straddling of the atrioventricular valve annuli or straddling of the chordae may be present. Right ventricular abnormalities including tricuspid regurgitation, tricuspid stenosis, and Ebstein malformation may develop.

Coronary artery abnormalities are related to the relationship of the great arteries with several variations, including anomalous origin of the right coronary artery (RCA) from the left main coronary artery (LMCA), duplication of left anterior descending coronary artery (LAD), anomalous origin of LAD from RCA (associated with a subaortic VSD and pulmonary stenosis), anterior origin of LAD, RCA immediately beneath pulmonary annulus (seen with L-malposed aorta), and RCA from the posterior sinus of Valsalva/LMCA from the left sinus, which is seen with an anterior aorta and subpulmonary VSD and is similar to transposition of the great arteries.

Conduction system abnormalities develop because of alterations in anatomy. Anatomy of the atrioventricular node and His-Purkinje system is similar to that in an isolated perimembranous VSD. In subaortic, subpulmonary, and doubly committed VSD, conduction tissues are displaced from the superior margin of the VSD.

Other abnormalities and associations are rare and can include dextrocardia and atrioventricular discordance, superior and inferior ventricles, and single atrioventricular valve connection.

Epidemiology

United States data

Double outlet right ventricle accounts for 1-1.5% of all CHDs, with an incidence of 1 per 10,000 live births.

International data

Incidence is the same internationally as in the United States.

Morbidity/mortality

One review found early in-hospital mortality after operation to be 4.8%.[2] The rate was significantly higher in patients with complex lesions. Late mortality was 3.2% with a mean follow-up time of 5.3 years. Overall 15-year survival ranged from 89.5-95.8%, with more complex lesions exhibiting higher mortality rates. Reoperation was required in 11.2% of surviving patients. This occurred a mean of 4.1 years after the original definitive repair. The most likely cause of reoperation was right ventricular outflow tract obstruction. Fifteen-year freedom from reoperation rates in surviving patients ranged from 72-100%. The reoperation rate was higher in patients with subpulmonary VSDs.

Race-, sex-, and age-related demographics

No race predilection has been reported.

No sex predilection has been reported.

Most cases of double outlet right ventricle are diagnosed in the first month of life.

Prognosis

The long-term survival rate for children who undergo repair for a subaortic VSD type of double outlet right ventricle is 80-95%.

A retrospective study analyzed the pregnancy outcome of patients with previous biventricular repair of double outlet right ventricle. The study, which included 19 pregnancies, found a premature labor rate of 44% at a median of 32 weeks' gestation.[3] Other complications included diminished fertility, menstrual disorders, and a higher than expected rate of neonates that were small for gestational age. However, despite these complications, 17 of the 19 pregnancies resulted in live births.

Patient Education

Educate parents regarding anatomic defect, surgical repair, and postoperative course. Prior to repair, parents should learn about medical therapy and signs and symptoms of CHF.

Institute a specific nutritional program to attain adequate weight gain.

For patient education resources, see the Heart Health Center and Tetralogy of Fallot.

 

Presentation

History

History of double outlet right ventricle (DORV) varies based on type of anatomy.

  • Subaortic or subpulmonary ventricular septal defect (VSD) with pulmonary stenosis

    • These children present with histories similar to those of children with tetralogy of Fallot.

    • If pulmonary oligemia is present, severe cyanosis is seen in the newborn period, and the condition is recognized early.

    • Beyond the newborn period, cyanosis may be accompanied by hypercyanotic spells, polycythemia, and failure to thrive.

    • These children are less likely to develop pulmonary obstructive vascular disease due to limitation of blood flow and pressure by pulmonary stenosis.

  • Subaortic VSD without pulmonary stenosis

    • These children present with histories similar to those of children with a large VSD and pulmonary hypertension.

    • Oxygenation is relatively normal, and patients usually present with congestive heart failure (CHF) and failure to thrive.

    • Referral usually occurs later unless associated left heart lesions are present.

    • These children may have associated chromosomal abnormalities such as trisomy 13 or 18.

    • These children are likely to acquire pulmonary obstructive vascular disease without surgical repair, especially if the VSD is large.

  • Subpulmonary VSD without pulmonary stenosis

    • These children present with histories similar to those of children with transposition of the great arteries.

    • Cyanosis varies, with oxygen saturations ranging from 40-80%.

    • If associated coarctation or interruption of the aorta is present, earlier onset of CHF can be expected to result in earlier referral.

Physical Examination

Physical examination findings vary with the anatomy.

  • Subaortic or subpulmonary VSD with pulmonary stenosis: Physical examination reveals prominent right ventricular impulse, systolic thrill at left upper sternal border, harsh systolic murmur, and a single second heart sound.

  • Subaortic VSD without pulmonary stenosis

    • Physical examination reveals hyperdynamic precordial impulse, a grade III-IV/VI holosystolic murmur, a loud pulmonary component of the second heart sound, an apical diastolic rumble, and, sometimes, a palpable thrill.

    • Once these children acquire pulmonary obstructive vascular disease, they exhibit decreased pulmonary blood flow with subsequent loss of the diastolic rumble and attenuation of systolic murmur. They may also develop a loud second heart sound and a diastolic decrescendo murmur of pulmonary insufficiency.

  • Subpulmonary VSD without pulmonary stenosis

    • Physical examination reveals cyanosis, tachypnea, grunting, and signs of CHF.

    • Examination also reveals a loud pulmonary component of the second heart sound, a III/VI systolic murmur, and an apical diastolic rumble.

    • If coarctation of aorta is present, the examination also reveals diminished femoral pulses.

Causes

As with other conotruncal heart defects, the cause of double outlet right ventricle may be of neural crest origin.[4] The neural crest is involved in the development of the cardiac septum. Studies indicate removal of the neural crest during development results in outflow tract malformations, and total removal of cardiac neural crest usually results in truncus arteriosus abnormality. Deletions of smaller parts of the cardiac neural crest result in malformations such as double outlet right ventricle, tetralogy of Fallot, and Eisenmenger complex. Interestingly, neural crest ablation rarely results in transposition of the great arteries. Most changes in heart morphology occur while the heart is still in the looped tube stage.

In addition to formation of cardiac structures, this area of neural crest cells participates in formation of the thymus and the thyroid and parathyroid glands, serving as the basis for association of congenital heart diseases (CHDs) with DiGeorge syndrome. The combination of velocardiofacial syndrome, DiGeorge syndrome (facial anomalies and parathyroid/thymus aplasia or hypoplasia), and a chromosome band 22q11 deletion is known as CATCH 22.[5, 6, 7]

The most common types of CHD associated with the band 22q11 deletion include tetralogy of Fallot, truncus arteriosus, VSDs, and aortic arch abnormalities.[5, 6, 7] Research has shown that 22q11 deletions are rare in double outlet right ventricle. In one study, only 1 in 20 patients with double outlet right ventricle had the deletion; double outlet right ventricle was defined only by lack of fibrous continuity between mitral and aortic valves and an aorta that arises more than 50% above the right ventricle.[7] However, because double outlet right ventricle encompasses such a large spectrum of anomalies, recommendations are to continue to test patients for the 22q11 deletion, especially when they display other features of velocardiofacial syndrome.

 

DDx

 

Workup

Laboratory Studies

Routine laboratory studies are not required for the initial diagnosis and management in children with double outlet right ventricle (DORV). Assess hemoglobin and hematocrit if children are thought to have polycythemia. Monitor serum electrolyte levels after treating children with diuretics, glycosides, and afterload-reducing agents.

Imaging Studies

Chest radiography

Chest radiography findings usually correlate with clinical presentation, but do not differentiate double outlet right ventricle from other forms of congenital heart disease (CHD).

The presence or absence of pulmonary stenosis and pulmonary vascular resistance determines if cardiomegaly and increased pulmonary vascularity are present. Patients with subaortic ventricular septal defect (VSD) and severe pulmonary stenosis demonstrate diminished pulmonary vascularity and concave left heart border (similar to appearance associated with tetralogy of Fallot). If pulmonary obstructive vascular disease is present, peripheral pulmonary vascularity may be reduced and proximal pulmonary arteries may be dilated.

The appearance in patients with subpulmonary VSD is similar to that in patients with transposition of the great arteries, revealing increased pulmonary vascularity and cardiomegaly.

In patients in whom the aorta is anterior and to the left, radiography may reveal the leftward position of the aorta.

Echocardiography

Echocardiography is the imaging technique most often used to diagnose double outlet right ventricle. The principle diagnostic feature is appearance of both great arteries primarily committed to the right ventricle. Parasternal long-axis and short-axis views reveal the degree of commitment to the right ventricle. Subcostal and apical 4-chamber views reveal the separation between semilunar and atrioventricular valves (ventriculoinfundibular fold).

Use multiple views to determine the relationship between the ventricular septum and the outlet septum.

Features that must be established with echocardiography include the primary commitment of both great arteries to the right ventricle, the spatial relationship of both great arteries, the location of the VSD and its relationship to semilunar valves, and the presence of associated anomalies such as coarctation, the straddle/override of atrioventricular valve in relation to the VSD, and the presence of restrictive VSD.

In addition, fetal echocardiography has been used to prenatally diagnose cases of double outlet right ventricle. This imaging modality can also reveal other congenital cardiac anomalies that may be present in addition to double outlet right ventricle. Prenatal quantification of left ventricular size is important. One study noted that, in patients with double outlet right ventricle and borderline left ventricular size, only 33% of pregnancies proceeded to live birth.[8] Of those patients, only 25% successfully underwent biventricular repair. Patients with double outlet right ventricle may demonstrate other abnormalities on fetal ultrasonography. However, even in patients with isolated double outlet right ventricle, diagnosis is possible based solely on limited fetal echocardiography, provided a long-axis view is included.[9]

MRI

MRI can help clarify ambiguities that remain after echocardiography.

MRI reveals the relationship between the great arteries, the anatomy of the outlet septum relative to the ventricular septum, and the relationship of the VSD to the great arteries.

One study reported that, in patients with doubly committed or noncommitted VSDs, MRI more reliably predicted the feasibility of a biventricular repair than did echocardiography.[10]

Limitations include the need for prolonged evaluation, deeper sedation, and incomplete atrioventricular valve definition. MRI may also fail to reveal the presence of aberrant chordae tendineae.

Other Tests

Abnormalities are often present on electrocardiography (ECG) but are not diagnostic of double outlet right ventricle.

If obtained after the newborn period, ECG reveals right ventricular hypertrophy. Left ventricular hypertrophy may develop in the presence of a restrictive VSD that leads to left ventricular pressure overload or an increased pulmonary venous return that leads to left ventricular volume overload.

Right atrial enlargement is common. Left atrial enlargement may be present if pulmonary venous return or mitral stenosis/atresia is increased.

Usually, left axis deviation of the frontal plane QRS is present because of displacement of the bundle of His posterior to VSD.

Procedures

Cardiac catheterization may delineate anatomy and hemodynamics. Objectives of catheterization include the following:

  • Evaluation of right and left ventricular volumes

  • Evaluation for possible gradient across VSD and pulmonary vascular resistance (PVR)

  • Evaluation of relationship between VSD and great arteries

  • Evaluation of coronary artery and aortic arch anatomy

  • Assessment of degree of mixing of the 2 circulations

If a restrictive atrial septal defect (ASD) is present, increased pulmonary blood flow with aortic saturations below 70%, or 10% less than pulmonary saturations, indicates the possibility of improvement with atrial septostomy (termed transposition physiology).

Diagnostic angiographic features of double outlet right ventricle include the following:

  • Opacification of both great arteries following right ventriculography

  • Similarity of aortic and pulmonary valve horizontal planes

  • Frequent anterior malposition of the aorta

  • Presence of a filling defect dividing the 2 outflow tracts

Histologic Findings

Findings vary depending on the clinical presentation; various physiologic effects determine histology of cardiac structures.

 

Treatment

Medical Care

Initial evaluation and treatment are usually performed in an outpatient setting. Treatment varies depending on the anatomy of the lesion. Direct medical treatment of infants with double outlet right ventricle (DORV) at control of congestive heart failure (CHF). Hospitalize children who present with severe heart failure and treat them with fluid restriction and reduction of physical stress. Monitor children to ensure adequate weight gain because CHF can decrease oral intake and increase caloric expenditure. Provide inpatient care if congestive heart failure (CHF) is severe. Treat patients initially with fluid restriction and alleviation of temperature and physical stress. Sedation may be required with opioids. Other therapies include the following:

  • Oxygen therapy may be required if pulmonary edema is present.

  • Use oxygen only to relieve hypoxemia because it is a pulmonary vasodilator and can exacerbate left-to-right shunt and CHF.

  • Promptly initiate diuretic therapy with furosemide.

  • Glycoside therapy with digoxin can be initiated in a maintenance dose if severe CHF is not present.

Systemic afterload reduction is important in treating infants with CHF. ACE inhibitors (ie, captopril, enalapril) are the most commonly used afterload-reduction agents.[11]

Transfer may be required for further diagnostic testing and medical/surgical treatment. 

Surgical Care

In 1957, Kirkland reported the first surgical repair of double outlet right ventricle (DORV) using an intraventricular tunnel to establish left ventricular-aortic continuity via subaortic ventricular septal defect (VSD). Surgical repair usually requires cardiopulmonary bypass with moderate hypothermia. Many double outlet right ventricles have been repaired with a period of circulatory arrest.

Most transpositions are repaired using a biventricular approach with placement of an intraventricular baffle; this is more difficult without 2 well-developed ventricles or if the anatomy precludes a biventricular repair.[12] An alternative repair is a Fontan procedure, which deteriorates with time.

In general, procedures depend on the location of the VSD and the size of the left ventricle. A significant number of patients undergo palliative procedures prior to definitive repair, especially when the patients have borderline or hypoplastic left ventricles. These procedures include pulmonary artery banding, Blalock-Taussig shunt, coarctation repair, or a stage I Norwood procedure.

Observe and manage ventricular function for patients in immediate postoperative period. Arrhythmias may develop after repair and may require medical intervention.

After repair, children with DORV are often treated with systemic afterload reduction using ACE inhibitors for several months to assist in cardiac remodeling.

Double outlet right ventricle with subaortic VSD

Double outlet right ventricle with subaortic VSD is repaired by VSD closure to baffle the left ventricular outflow to the aorta. It is typically repaired in patients younger than 6 months to prevent pulmonary vascular disease. If severe pulmonary stenosis is present, the condition and repair are similar to those of tetralogy of Fallot. Pulmonary stenosis often occurs with hypoplasia of the pulmonary arteries and coronary artery anomalies, making repair more difficult. Historically, this condition often was treated with initial shunting and definitive repair in patients aged 4-5 years.

Double outlet right ventricle with subpulmonary VSD

Double outlet right ventricle with subpulmonary VSD can be repaired using the following 3 methods:

  • The first procedure involves construction of a left ventricle–to–subpulmonary outflow tract tunnel with a subsequent arterial switch. This is the preferred method when the aorta is malposed anteriorly. Coronary artery transfer is similar to that in transposition of the great arteries.

  • The second method consists of construction of a long intraventricular tunnel to establish continuity between the left ventricle and the aorta and between the right ventricle and pulmonary artery.

  • The third method involves closure of the VSD with baffling of the left ventricular outflow to the pulmonary artery with a subsequent atrial baffle (eg, Senning procedure, Mustard procedure). This method is associated with high operative and late mortality rates.

Doubly committed or noncommitted VSD

Doubly committed or noncommitted VSDs often require a complex repair with a Fontan procedure and possibly reoperation for secondary subaortic stenosis. For example, a patient with double outlet right ventricle, complete atrioventricular septal defect (AVSD), and valvar pulmonary stenosis underwent repair involving patching the ventricular portion of the AVSD and translocating it into a subaortic position. A left ventricular–to–aortic tunnel was then created. Nine years after primary repair, the patient required right ventricle–to–pulmonary artery conduit replacement. 

One case series studied 50 children with double outlet right ventricle and adequate left ventricular size.[13] Eleven patients in the study had double outlet right ventricle with transposition of the great vessels. Biventricular repair was performed in 48 of the children, and the overall mortality rate was 6%. Actual surgical mortality rate in patients with biventricular repair was 4.3%.

In contrast, surgical and overall morbidity and mortality rates increase with more complex types of double outlet right ventricle. Takeuchi et al recently reported a case series of 96 patients with double outlet right ventricle and heterotaxy syndrome and/or complete atrioventricular canal defect.[14] Only 8 patients had biventricular repair. Nine of the 17 neonatal patients survived. Of the 79 patients older than 30 days, 71 survived. The overall mortality rate was 17% in all patients.

 

Consultations

Refer patients with heart murmurs and physical findings suggestive of double outlet right ventricle to a pediatric cardiologist.

Consult a pediatric cardiac surgeon for possible repair following diagnosis of double outlet right ventricle.

Consult pediatric critical care personnel. Following surgical repair, postoperative care normally occurs in the pediatric ICU.

Involve a geneticist in the care of patients diagnosed with double outlet right ventricle who may have associated genetic syndromes, including velocardiofacial syndrome and DiGeorge syndrome.[15, 16]

Diet

Children with CHF due to double outlet right ventricle often require increased caloric intake supplemented by the addition of medium-chain triglyceride or carbohydrate preparations to conventional infant formulas.

Some children may require overnight, bolus, or continuous feeds by nasogastric tubes.

Activity

Activity is not limited for infants initially diagnosed with double outlet right ventricle, unless they have CHF. For patients with CHF, reduce physical stress until the heart failure can be controlled.

Advance the activity of patients in the postoperative period as tolerated, until a normal level of activity is achieved.

Complications

If patients undergo surgery for repair at an older age, they often develop ventricular dysfunction and elevation of pulmonary artery pressures.

Operative and postoperative complications depend on anatomy of lesion and type of repair. Note the following:

  • Some patients develop restrictive ventricular septal defect (VSD) and require reoperation.

  • In patients with subaortic and subpulmonary VSD, the VSD diameter can decrease by 20% in the immediate postoperative period. These patients can sometimes develop subaortic obstruction.

  • Patients, especially those undergoing complex repair, can develop postoperative ventricular dysfunction associated with residual VSD, aortic insufficiency, atrioventricular valve insufficiency, and prolonged circulatory arrest at repair.

  • Some patients are at risk for late postoperative arrhythmias and sudden death.

  • Patients may develop persistent atrial tachycardia, complex ventricular ectopy, or syncope requiring electrophysiologic studies.

 

Medication

Medication Summary

The overall goal of medical therapy in patients with double outlet right ventricle (DORV) is to prevent or control congestive heart failure (CHF). Commonly used medications include furosemide, digoxin, captopril, and enalapril.

Diuretic agents

Class Summary

These agents promote excretion of water and electrolytes by the kidneys. They are used to treat heart failure or hepatic, renal, or pulmonary disease when sodium and water retention has resulted in edema or ascites. They are also used to reduce plasma volume and, thus, improve CHF.

Furosemide (Lasix)

Titrate treatment dose to produce initial diuresis and subsequently to control symptoms.

Increases excretion of water by interfering with chloride-binding cotransport system, which, in turn, inhibits sodium and chloride reabsorption in ascending Henle loop and distal renal tubule.

Inotropic agents

Class Summary

Positive inotropic agents increase the force of myocardial contraction and are used to treat acute and chronic CHF. Some agents may also increase or decrease the heart rate (ie, positive or negative chronotropic agents), provide vasodilatation, or improve myocardial relaxation. These additional properties influence the choice of drug for specific circumstances. Agents used predominantly for their inotropic effects include cardiac glycosides and phosphodiesterase inhibitors.

Digoxin (Lanoxin)

Used to increase contractility of the left ventricle. Inhibits Na/K-ATPase, which causes intracellular calcium in the sarcoplasmic reticulum of cardiac cells to increase. This leads to a sustained but modest positive inotropic effect on the heart. Some question the inotropic effect of these medications on immature myocardium, while others have demonstrated improved left ventricular contractility without symptomatic improvement.

ACE inhibitors

Class Summary

These agents are used to reduce afterload and left-to-right shunting. ACE inhibitors are beneficial in all stages of chronic heart failure. Pharmacologic effects result in a decrease in systemic vascular resistance, reducing blood pressure, preload, and afterload. Dyspnea and exercise tolerance are improved.

Captopril (Capoten)

Prevents conversion of angiotensin I to angiotensin II, a potent vasoconstrictor, resulting in increased levels of plasma renin and a reduction in aldosterone secretion. Shown to increase systemic flow by reducing left-to-right shunting in patients with relatively low pulmonary vascular resistance.

Enalapril (Vasotec)

Decreases pulmonary-to-systemic flow ratio in the catheterization laboratory and increases systemic blood flow in patients with relatively low pulmonary vascular resistance. It has a favorable clinical effect when administered over a long period.

Phosphodiesterase Enzyme Inhibitor

Class Summary

This agent is used for short-term treatment of acute decompensated heart failure.

Milrinone (Primacor)

Positive inotropic agent and vasodilator. Selectively inhibits phosphodiesterase type III (PDE III) in cardiac and smooth vascular muscle, resulting in reduced afterload, reduced preload, and increased inotropy. Several studies that have compared milrinone with dobutamine demonstrated that milrinone showed greater improvements in preload and afterload and improvements in cardiac output, without significant increases in myocardial oxygen consumption.