MKSAP primer: Heart failure
Adapted from ACP's latest Medical Knowledge Self-Assessment Program
From the November ACP Hospitalist, copyright © 2007 by the American College of Physicians
Diagnosis and evaluation
Initial diagnostic testing of the patient with heart failure includes obtaining an electrocardiogram, a chest radiograph, and an echocardiogram, as well as blood chemistry evaluation. The electrocardiogram may reveal prior myocardial infarction, ventricular hypertrophy, arrhythmias or conduction abnormalities. The chest radiograph may demonstrate pulmonary edema, but beyond a gross estimate of the presence of cardiomegaly, does not provide a precise measurement of cardiac size. Any patient with a new diagnosis of heart failure warrants an echocardiographic evaluation, which provides information regarding cardiac structure and function. Unlike other imaging modalities, such as radionuclide ventriculography, echocardiography provides additional information regarding valve function and regional wall motion. Additional testing may include cardiac catheterization or exercise testing, as indicated.
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As many as 40% to 60% of patients with symptoms of heart failure actually have diastolic heart failure, although the estimated prevalence varies widely. |
As many as 40% to 60% of patients with symptoms of heart failure actually have diastolic heart failure, although the estimated prevalence varies widely because of heterogeneous diagnostic criteria. Diastolic heart failure is generally diagnosed when signs and symptoms of systolic heart failure are present, but the echocardiogram reveals normal left ventricular ejection fraction and the absence of significant valvular abnormalities. Doppler echocardiography is important in diagnosing and determining prognosis in patients with diastolic heart failure.
B-type natriuretic peptide
B-type natriuretic peptide (BNP) is a hormone synthesized by the cardiac ventricle in response to increased wall stress due to pressure or volume overload. BNP assays have become a useful tool in the diagnosis of acute heart failure and for following treatment effectiveness over time. In conjunction with clinical information, BNP assay significantly improves the accuracy of diagnosis of acute heart failure in patients presenting to the emergency department with dyspnea. Patients with a BNP concentration below 100 pg/mL are unlikely to have acute heart failure, whereas those with a concentration higher than 500 pg/mL are likely to have acute heart failure. At a cutoff of 100 pg/mL, BNP in isolation of clinical factors has a sensitivity of 90% and specificity of 73% for diagnosing heart failure. Interpretation of the significance of BNP findings should be made in the context of the clinical scenario, and with the knowledge of factors that affect BNP results independent of heart failure status (including generally higher concentrations in women, in patients with renal failure and in the setting of acute coronary syndrome or myocardial infarction). BNP cannot be used to differentiate between systolic and diastolic heart failure. Levels of BNP correlate with severity of heart failure symptoms and prognosis, including risk for rehospitalization and mortality. Outpatient treatment guided by BNP assay may reduce the combined outcome of death, hospital admission and heart failure decompensation. Currently, the utility of other cardiac biomarkers, such as troponin, for the diagnosis of heart failure is limited to evaluating for other conditions, such as acute coronary syndrome or myocardial infarction, that may be complicating the clinical picture.
Ischemia
Ischemia is a major cause of left ventricular dysfunction. Given the potential significant benefits of revascularization in appropriate candidates, including improved ventricular function and reduced morbidity and mortality, diligent evaluation for revascularizable coronary artery disease (CAD) should be undertaken for most patients with heart failure. The American College of Cardiology/American Heart Association (ACC/AHA) guidelines recommend coronary angiography for heart failure patients with angina or significant ischemia who are candidates for revascularization. This procedure is also reasonable to evaluate patients presenting with heart failure and no contraindications to revascularization who have chest pain less typical for angina and who have not had their coronary anatomy evaluated. Angiography is also a reasonable approach for heart failure patients without chest pain but with known or suspected CAD. For patients with known CAD who present with heart failure, noninvasive imaging to assess for myocardial ischemia and viability is also reasonable.
Right-heart catheterization
In cases in which the severity of heart failure needs to be clarified, such as evaluation for cardiac transplantation, or in which volume status is difficult to determine, right-heart catheterization is useful to assess pulmonary and right-heart chamber pressures. Exercise testing helps to quantify functional limitation and can be performed with a six-minute walk test or with formal cardiopulmonary exercise testing. With cardiopulmonary exercise testing, functional limitation due to cardiac versus other causes can be differentiated. Formal quantification of functional limitation becomes important in risk stratification for the purposes of cardiac transplantation listing.
Endomyocardial biopsy
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Biopsy reveals a specific diagnosis in fewer than 10% of patients with cardiomyopathy, it has been estimated. |
On occasion, endomyocardial biopsy may need to be performed to diagnose etiology of heart failure if routine evaluation does not. The most common approach is via the right internal jugular vein to obtain tissue from the right ventricle under echocardiographic or fluoroscopic guidance. Because of the heterogeneity of disease involvement in the myocardium, endomyocardial biopsy is rarely diagnostic in the setting of heart failure—it has been estimated that biopsy reveals a specific diagnosis in fewer than 10% of patients with cardiomyopathy. Because of the low diagnostic yield, most heart failure patients do not need to undergo endomyocardial biopsy as part of their diagnostic evaluation. It remains controversial which patients should undergo biopsy, but the procedure is most frequently used to diagnose infiltrative diseases of the myocardium. In heart transplant recipients, endomyocardial biopsy to monitor for rejection is the standard of care.
Disease classification systems
For the purposes of grading heart disease severity, making treatment decisions and judging prognosis, disease classification systems have been developed. The most commonly used currently are those developed by the New York Heart Association (NYHA) and those developed by the ACC/AHA. The basic difference between these two classification systems is that the NYHA classification is based on symptoms, while the ACC/AHA classification is based on the presence of or potential to develop structural heart disease. The NYHA functional classes are I (asymptomatic), II (symptomatic with ordinary activity), III (symptomatic with less than ordinary activity) and IV (symptomatic at rest). Occasionally, the subclassification IIIb is used, indicating a recent history of dyspnea at rest. The ACC/AHA classification scheme includes stage A (at high risk for heart failure but without structural heart disease or symptoms of heart failure), stage B (structural heart disease but without symptoms of heart failure), stage C (structural heart disease with prior or current symptoms of heart failure) and stage D (refractory heart failure requiring specialized interventions).
Treatment of systolic heart failure
Despite the impressive advances in medical and device therapy for the treatment of heart failure in the past few decades, all heart failure patients can still benefit from simple interventions, including limiting fluid and sodium intake, avoiding toxins such as alcohol and nicotine, performing regular aerobic exercise and closely monitoring their weight as a measure of volume status.
Pharmacotherapy
Medications commonly used for the treatment of heart failure include loop diuretics, angiotensin-converting enzyme inhibitors, β-blockers, aldosterone antagonists and angiotensin-receptor blockers. ACC/AHA treatment strategies for heart failure are outlined in the figure.
Device therapies and cardiac transplantation for heart failure
Implantable cardioverter-defibrillators
The most common cause of sudden death in patients with heart failure is arrhythmia, including both ventricular tachyarrhythmia and bradyarrhythmia. In heart failure patients with reduced left ventricular systolic function, CAD and asymptomatic nonsustained ventricular tachycardia, prophylactic use of implantable cardioverter-defibrillators (ICDs) improves survival. In patients with left ventricular dysfunction and hemodynamically significant ventricular tachycardia or resuscitated sudden death, ICDs have been shown to improve survival, regardless of the presence or absence of CAD. More recently, the Multicenter Automatic Defibrillator Implantation Trial II (MADIT II) demonstrated a survival benefit of prophylactic ICD use in patients with prior myocardial infarction (30 days or more in the past) and reduced ejection fraction (<30%), regardless of the presence of arrhythmia. Recent trials also suggest that prophylactic use of ICDs in patients with nonischemic cardiomyopathy may reduce mortality.
Biventricular pacemakers (cardiac resynchronization therapy)
Interventricular conduction delay is common in patients with heart failure and results in poor coordination of ventricular contraction, contributing to the hemodynamic consequences of chronic left ventricular systolic dysfunction. Patients with heart failure who have severe symptoms (NYHA class III or IV) and evidence of ventricular dyssynchrony (left ventricular enlargement and QRS prolongation) benefit from implantation of a biventricular pacemaker for cardiac resynchronization therapy. (Note that in studies, QRS prolongation has included left bundle-branch block, not right bundle-branch block.) A biventricular pacemaker includes three leads: one lead located in and pacing the right ventricle, one lead in the coronary sinus to pace the left ventricle and one lead in the right atrium to sense intrinsic rhythm to ensure an appropriate atrioventricular timing interval. Indications for ICD and biventricular pacemaker placement in patients with heart failure are shown in the table.
Mechanical circulatory support, cardiac transplantation
For patients with end-stage heart failure that is refractory to therapy, mechanical circulatory support and cardiac transplantation remain potentially life-saving options of last resort. The mechanical circulatory support device most commonly used currently is the left ventricular assist device (VAD), which offloads the left ventricle via a cannula in the left ventricular apex and returns blood to the systemic circulation via a cannula into the ascending aorta. VADs are used as a bridge to cardiac transplantation, for recovery from severe cardiogenic shock or as an alternative to medical therapy for patients not eligible for transplantation. A patient with end-stage heart failure should be considered for referral for VAD implantation if cardiac transplantation is being considered and he or she remains refractory to medical and nonsurgical methods of hemodynamic support. In these cases, the VAD functions as a bridge to stabilize the patient until cardiac transplantation, which may occur weeks to months later. Patients with end-stage heart failure should be considered for referral for cardiac transplantation evaluation in conjunction with VAD evaluation or, in cases of less severe end-stage heart failure, if they display evidence of refractory heart failure, including poor functional status, persistent hypotension, recurrent hospitalizations due to heart failure or renal failure due to poor perfusion.
Approximately 2,700 cardiac transplantations are performed in the U.S. annually. The average one-year survival rate is 80% after cardiac transplantation. Early mortality is mainly due to infection or acute graft failure, while later mortality is associated with transplant vasculopathy, the accelerated CAD frequently found in transplanted hearts. Other problems inherent to cardiac transplantation are primarily those associated with the need for lifelong immunosuppression, including increased risk for infection, side effects from medications and increased risk for certain skin and lymphoproliferative cancers. Contraindications include advanced age; significant pulmonary vascular hypertension; inadequate social support system; and severe renal, pulmonary or hepatic dysfunction.
Treatment of diastolic heart failure
There are significantly fewer clinical trials in diastolic heart failure than in systolic heart failure. The angiotensin-receptor blocker candesartan has been shown to reduce heart failure-related hospitalizations, but not mortality, in patients with diastolic heart failure. Otherwise, the primary treatment goals in diastolic heart failure are to treat the underlying etiology if possible, to manage any potentially exacerbating factors and to optimize diastolic filling. As such, treatment for diastolic heart failure often consists of management of systolic and diastolic hypertension, cardioversion or rate-control of atrial fibrillation and judicious use of diuretics to relieve pulmonary congestion and edema, while avoiding hypovolemia and tachycardia.
Cardiogenic shock
Severe acute heart failure causing hypotension and systemic hypoperfusion is termed cardiogenic shock. The approach to cardiogenic shock includes treatment of hemodynamic derangements and diagnosis of etiology, which may determine treatment method. Initial evaluation includes an electrocardiogram and, in most cases, an echocardiogram. An electrocardiogram and echocardiogram may be helpful in diagnosing the etiology—and thus determining the treatment—of cardiogenic shock, as in the case of acute myocardial infarction, acute mitral regurgitation, ventricular rupture or tamponade. Acute myocardial infarction requires urgent revascularization, acute mitral regurgitation or ventricular rupture requires emergent corrective surgery and cardiac tamponade requires pericardiocentesis.
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Elevated intracardiac filling pressures will likely be improved with a combination of diuresis and afterload reduction. |
In addition to etiology-specific interventions, treatment of cardiogenic shock includes correcting hypotension, improving intracardiac filling pressures and improving end-organ perfusion. Placement of a pulmonary artery catheter in selective cases can assist in assessing volume status, intracardiac filling pressures and cardiac output, although use of a pulmonary artery catheter does not ultimately appear to affect survival in critically ill patients or those with decompensated heart failure. This information assists in the diagnosis of hemodynamic abnormalities and the accurate titration of vasoactive medications. If hypovolemia is present, volume resuscitation with intravenous fluid is indicated, whereas if volume overload is present (which is more often the case in patients with heart failure), intravenous diuretics administered using intermittent dosing or as a continuous infusion are warranted. Elevated intracardiac filling pressures will likely be improved with a combination of diuresis and afterload reduction. A low cardiac output indicates primary cardiogenic shock; depending on the severity of systemic hypoperfusion, inotropic agents may be needed to augment myocardial contractility and thus cardiac output. Positive inotropic agents such as dobutamine or milrinone can be used to correct hypotension and improve perfusion. If the patient’s systemic pressure is acceptable, nitroprusside or nesiritide can be added to inotrope therapy to reduce afterload.
If the patient remains refractory or minimally responsive to medical therapy, placement of an intra-aortic balloon pump is generally indicated. This device inflates during diastole and deflates during systole, thereby improving coronary perfusion and reducing afterload, respectively. Finally, if cardiogenic shock is refractory to these measures, VAD implantation and/or cardiac transplantation can be considered.
The information included herein should never be used as a substitute for clinical judgment and does not represent an official position of ACP. View further information on MKSAP.
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