5

Clinical Indications and Quality Assurance

Basic Principles

1. ▪ The value of echocardiography for a specific diagnosis depends on the reliability of the echocardiographic data and integration with other clinical information.
   
2. ▪ The framework for echocardiographic data acquisition and reporting is a structured diagnostic approach to the question posed by the requesting physician.

Key Points

• □ The echocardiographic study seeks to provide the appropriate data for clinical decision making depending on the patient’s symptoms, signs, and known diagnoses.
  
• □ The list of possible diagnoses that might explain the clinical findings, called the differential diagnosis, is mentally constructed at the beginning of the echocardiographic study.
  
• □ As the study proceeds, some diagnoses are excluded, whereas others may be suggested by specific findings.
  
• □ Pertinent positive data include abnormal echocardiographic findings.
  
• □ Pertinent negative data include normal echocardiographic findings that help narrow the differential diagnosis.

Understand the Reliability of Echocardiography for the Specific Diagnosis

1. ▪ The accuracy of echocardiography describes the agreement between an echocardiographic measurement or diagnosis and an external reference standard, such as another imaging approach or clinical outcomes (Fig. 5.1).
   
2. ▪ The precision of an echocardiographic measurement is affected by variability in recording, measuring, and interpreting the echocardiographic data.
   
3. ▪ Expertise in image acquisition and interpretation affect the reliability of echocardiographic data.

Key Points

• □ Sensitivity is the percent of patients with the diagnosis correctly identified by echocardiography.
  
• □ Specificity is the percent of patients without the diagnosis correctly identified by echocardiography.
  
• □ Positive predictive value is the percent of patients with a positive echocardiogram who actually have the diagnosis.
  
• □ Negative predictive value is the percent of patients with a negative echocardiogram who do not actually have the diagnosis.
  
• □ Accuracy indicates what proportion of all studies indicated a correct diagnosis.
  
• □ The positive and negative predictive value of a test depends on the prevalence of disease in addition to sensitivity and specificity.
  
• □ Each laboratory should periodically review the reproducibility of the echocardiographic measurements.
  
• □ The effect of variability is minimized when images from sequential studies are compared side by side.

Integrate the Clinical Data and the Echocardiographic Findings (Fig. 5.2)

1. ▪ The likelihood ratio indicates the probability of disease in a patient with a positive or negative echocardiographic finding; a positive likelihood ratio greater than 10 or a negative likelihood ratio less than 0.1 indicates an excellent diagnostic test.
   
2. 
   
3. ▪ Pre- and posttest probability estimates integrate the likelihood of disease before the echocardiogram is performed with the echocardiographic results.
   
4. ▪ The threshold approach to clinical decision making indicates that diagnostic testing (such as, echocardiography) is most helpful in patients where the results will change either one of the following:
   
5. 
   
   
   
   • ○ Treatment strategy
     
   • ○ Diagnostic strategy

Key Points

• □ The positive likelihood ratio is calculated as the true positive rate divided by the false-positive rate. The negative likelihood ratio is the false-negative rate divided by the true-negative rate.
  
• □ The pretest probability of disease is the probability of disease before echocardiography is done—for example, consideration of cardiac risk factors and symptoms in a patient scheduled for stress echocardiography provides an estimate of the probability of coronary artery disease.
  
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• □ Echocardiography is most helpful when the pretest likelihood of disease is intermediate and echocardiography has a high accuracy for the diagnosis.
  
• □ When the pretest likelihood of disease is very low, an abnormal echocardiographic finding often is a false-positive result.
  
• □ Conversely, when the pretest likelihood of disease is very high, the failure to demonstrate the disease on echocardiography often is a false negative.
  
• □ With the threshold approach, the upper threshold is the point where the risk of the test is higher than the risk of treating the patient; for example, additional diagnostic testing should not delay surgical intervention for an acute ascending aortic dissection.
  
• □ The lower threshold for transthoracic echocardiography (TTE) occurs only with a very low probability of disease; the major potential adverse effect is a false-positive result leading to further inappropriate testing or therapy.

Recommend Additional Diagnostic Testing as Appropriate

1. ▪ The interpretation of the echocardiogram lists the pertinent positive and negative findings along with any confirmed diagnoses.
   
2. ▪ The differential diagnosis of equivocal findings is indicated and appropriate additional diagnostic testing is recommended when the echocardiographic results are not diagnostic.

Key Points

• □ Echocardiography provides qualitative and quantitative information on cardiac structure and function and often provides a definitive diagnosis.
  
• □ Positive findings are more helpful than negative findings; for example, a dissection flap seen on TTE is diagnostic for a dissection, but its absence does not exclude this possibility.
  
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• □ A noncardiac cause for symptoms is likely when the appropriate echocardiographic study is normal. For example, normal resting echo in a patient with a systolic murmur is consistent with a benign flow murmur. A normal stress echo in a patient with chest pain indicates that coronary disease is not a likely cause of symptoms.
  
• □ The echocardiographer often needs to assist in choosing the optimal diagnostic approach (e.g., TTE or transesophageal echocardiography [TEE], stress echocardiography, contrast study) based on the indication for the study.
  
• □ Additional diagnostic studies, with either another echocardiographic modality or an alternate imaging approach, are recommended after review of the echocardiographic exam.

Diagnostic Thinking for the Echocardiographer

1. ▪ The echocardiographer needs:
   
2. 
   
   
   
   1. ▪ Clinical data to estimate the pretest likelihood of disease before starting the exam
      
   2. ▪ An understanding of pertinent positive and negative findings for each clinical indication
      
   3. ▪ Knowledge of the reliability of echocardiography for each diagnosis
      
   4. ▪ The ability to integrate the echocardiographic findings with the clinical data
   
   
3. ▪ The “Echo Exam” section summarizes the approach by anatomic diagnosis.
   
4. ▪ Examples of the approach to common clinical indications for echocardiography are discussed in the next section.

Echocardiography for Common Signs and Symptoms

Murmur

1. ▪ The echocardiographic differential diagnosis for a murmur is based on an anatomic approach with evaluation of all four valves and a search for an intracardiac shunt (Fig. 5.3).
   
2. ▪ Many patients referred to echocardiography for a murmur on auscultation have no significant structural heart disease. In this setting, the physical exam finding is most likely a benign flow murmur.

Key Points

• □ The echocardiography request form may not specify the type of murmur (e.g., systolic or diastolic), so a systemic echocardiographic exam is essential.
  
• □ Normal physiologic regurgitation rarely accounts for an audible murmur.
  
• □ The most common pathologic causes for a murmur in adults are aortic valve stenosis and mitral valve regurgitation.
  
• □ Murmurs typically are due to high-velocity intracardiac flows (e.g., aortic stenosis or mitral regurgitation), because low-velocity flows (e.g., tricuspid regurgitation with normal pulmonary pressures) are not usually audible with a stethoscope.
  
• □ Conditions that cause increased cardiac output (e.g., anemia or pregnancy) may cause a murmur due to high velocity transvalvular flow in patients with otherwise anatomically normal valves.
  
• □ Congenital heart disease may first be diagnosed in an adult based on finding a murmur. In patients with an atrial septal defect, the murmur is due to increased pulmonary blood flow volume, not to flow across the atrial septum.

Chest Pain

1. ▪ The echocardiographic differential diagnosis for chest pain is based on the major clinical diagnoses that are of immediate clinical concern (Fig. 5.4).
   
2. ▪ When the echocardiogram does not establish a diagnosis, further evaluation may be needed emergently.

Key Points

• □ Acute chest pain is a medical emergency, because the differential diagnosis includes acute coronary syndromes and aortic dissection, both of which require immediate treatment.
  
• □ An abnormal echocardiographic finding (such as anterior wall hypokinesis) may prompt further diagnostic and therapeutic interventions (such as coronary angiography).
  
• □ An acute pulmonary embolism, if large enough, may show signs of right heart strain and increased pulmonary pressures. A smaller pulmonary embolism may have no significant findings on echocardiography.
  
• □ Even when the transthoracic echocardiogram is normal, further evaluation may be needed—for example, TEE or chest computed tomography (CT) in a patient with suspected aortic dissection.
  
• □ Normal resting wall motion does not exclude the possibility of significant coronary artery disease. Wall motion is abnormal only after infarction or with ongoing myocardial ischemia.
  
• □ The presence of a pericardial effusion is consistent with pericarditis, although not all patients with pericarditis have an effusion.
  
• □ In a patient with aortic dissection, pericardial fluid may be due to rupture of the aorta into the pericardial space.
  
• □ With significant left ventricle (LV) outflow obstruction, the increase in LV myocardial wall stress and oxygen demand results in angina-type chest pain.

Heart Failure or Dyspnea

1. ▪ Symptoms of dyspnea, edema, and decreased exercise tolerance are nonspecific, with a wide differential diagnosis that includes cardiac and noncardiac conditions.
   
2. ▪ Heart failure, defined as the inability of the heart to supply adequate blood flow at a normal filling pressure, is the clinical consequent of several types of heart disease (Fig. 5.5).

Key Points

• □ Heart failure may be due to systolic dysfunction (called heart failure with reduced ejection fraction [HFrEF]) or may occur with a preserved ejection fraction (HFpEF).
  
• □ HFrEF may be due to a cardiomyopathy, coronary disease with prior infarction, long-standing valvular heart disease, or congenital heart disease.
  
• □ HFpEF, associated with diastolic dysfunction, is seen with hypertensive heart disease, hypertrophic cardiomyopathy, and infiltrative myocardial disease.
  
• □ Constrictive pericarditis often presents as right heart failure, with ascites and peripheral edema.
  
• □ Heart failure occurs in patients with valvular heart disease, even when LV function is normal, due to obstruction of blood flow (e.g., mitral stenosis) or elevated pulmonary diastolic pressure (e.g., mitral regurgitation).
  
• □ Pulmonary hypertension due to left heart disease, pulmonary vascular disease, or underlying lung disease leads to right heart failure with a dilated hypokinetic right ventricle (RV), sometimes called cor pulmonale.
  
• □ Heart failure in patients with congenital heart disease may be due to ventricular dysfunction, obstructive or regurgitant lesions, or intracardiac shunts.
  
• □ When heart failure is present with a normal echocardiographic study, noncardiac causes for the patient’s symptoms should be considered.

Palpitations

1. ▪ Palpitations are the patient’s awareness of a forceful, rapid, or irregular heart rhythm.
   
2. ▪ The primary approach to evaluation of palpitations includes resting and ambulatory electrocardiogram (ECG) monitoring.
   
3. ▪ Echocardiography allows evaluation of any underlying anatomic abnormalities associated with the cardiac arrhythmia.

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Related

Related posts:

1. Principles of Echocardiographic Image Acquisition and Doppler Analysis
2. Endocarditis
3. Pericardial Disease
4. Valvular Regurgitation

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