Utilizing Echocardiography to Guide Therapy in Heart Failure Patients
ACVIM 2008
Ashley B. Saunders, DVM, DACVIM
College Station, TX, USA

The purpose of this session is to address how and when to use echocardiography to guide therapy in heart failure patients. Echocardiography is useful for determining underlying etiology of heart failure and for providing non-invasive anatomic and functional information that may guide therapeutic decision making. Initial determination whether a patient has left or right sided congestive heart failure and/or evidence of forward heart failure (decreased cardiac output) is beneficial for guiding further evaluation and therapy. Clinical signs that would support echocardiographic evaluation in heart failure patients would include weakness, syncope and dyspnea, especially if there is a lack of response to heart failure therapy. Echocardiographic evaluation is beneficial at initial presentation and if decompensation occurs during management with standard heart failure therapy (ACE I, furosemide, pimobendan). Echocardiographic abnormalities of interest include global or regional myocardial dysfunction, mitral valve leaflet flail, pulmonary hypertension and pericardial effusion. In the presence of left sided congestive heart failure, global or regional myocardial dysfunction and mitral valve leaflet flail may be considered. If there is evidence of right sided congestive heart failure or forward heart failure, pulmonary hypertension or pericardial effusion may be the underlying cause.

Applications

Echocardiography can provide useful information regarding ventricular myocardial function. If a patient has global myocardial dysfunction, clinical signs attributed to a reduction in cardiac output include lethargy, weakness, syncope, hypotension and potentially azotemia. Regional wall motion abnormalities may be detected as well and typically represent areas of myocardial infarction or fibrosis. Positive inotropic therapy (pimobendan, dobutamine) is indicated in the presence of myocardial dysfunction.

Dogs with chronic degenerative valve disease can develop sudden respiratory distress with mitral valve flail. Progressive volume overload and cardiac enlargement cause the chordae tendineae to stretch and rupture resulting in sudden severe mitral regurgitation. Survival is often dependent on left atrial compliance and response to diuretic therapy.

Echocardiography is a useful noninvasive test for diagnosing pulmonary hypertension, present in as many as 72% of dogs with severe degenerative mitral valve disease.1 Echocardiographic evidence of pulmonary hypertension includes right ventricular hypertrophy, pulmonary artery enlargement and elevated tricuspid or pulmonary regurgitation velocities. Pulmonary artery pressures can be estimated indirectly with Doppler echocardiography by documenting (color Doppler) and quantitating (spectral Doppler) tricuspid and/or pulmonary regurgitation velocities and converting them to a pressure gradient with the modified Bernoulli equation (P=4V2). Patients with pulmonary hypertension may have an abnormal transpulmonic velocity profile that demonstrates a rapid acceleration and rapid or abrupt deceleration pattern with notching. The pulmonary acceleration time (AT) to ejection time (ET) ratio may be useful in the diagnosis of pulmonary hypertension in patients without tricuspid or pulmonary regurgitation.2 An AT:ET ratio >0.32 suggests normal pulmonary artery systolic pressure.

If the presence of pericardial effusion causes pericardial pressures to be in excess of right heart pressures, right heart failure develops. Small volume pericardial effusions can occur with left atrial rupture in severe degenerative mitral valve disease and may be indicative of congestive heart failure in cats with heart disease. Pericardiocentesis is indicated with large volume effusions and in the presence of cardiac tamponade or clinical signs of decompensation. When small volume pericardial effusions develop in association with atrial rupture or congestive heart failure, therapeutic management is directed at the underlying heart disease.

While echocardiography can provide useful information, there are potential pitfalls to consider. Obtaining an echocardiographic study may be informative but dangerous if it places an unstable patient at risk and compromises patient care. Underestimation of pulmonary pressures may occur with improper alignment of the tricuspid or pulmonary insufficiency jets. Regional wall motion abnormalities may not be detected without careful examination. In summary, echocardiography provides valuable diagnostic information and is useful for monitoring disease progression and response to therapeutic management in heart failure patients.

References

1.  Serres FJ, et al. J Am Vet Med Assoc 2006;229:1772-1778.

2.  Schober KE, et al. J Vet Intern Med 2006;20:912-920.

Speaker Information
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Ashley Saunders, DVM, DACVIM
Texas A&M University
College Station, TX


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