Chapter 5: Transthoracic Echocardiography

INTRODUCTION

Transthoracic echocardiography (TTE) is the gold standard for the diagnosis of many cardiac abnormalities. Cardiac point-of-care ultrasound (POCUS), performed and interpreted by clinicians, was described in the Emergency Medicine literature 30 years ago.^1–3 Since then, there has been a significant amount of accumulated data to demonstrate that POCUS changes management and improves patient care.^4–73 POCUS is now a well-accepted part of the practice of emergency and critical care medicine.^43,74,75

Although many clinicians use POCUS in a very simple manner (such as determining the presence or absence of a pericardial effusion), others use it in a more advanced fashion, but with the same goal of optimizing patient management decisions in real time.⁷⁶

CLINICAL CONSIDERATIONS

TTE is an ideal diagnostic tool for detecting life-threatening conditions at the point of care.^3,53,55–57 Other diagnostic tests are too slow and involve moving patients around the hospital, which is not ideal for unstable patients. Invasive monitors can provide important data in patients who are critically ill or injured, but much of the same data can be obtained more quickly and easily by POCUS.

Without POCUS, clinicians are left to manage critically ill patients with just indirect information about cardiac structure and function. “Classic” physical examination findings are often absent and unreliable for making critical diagnoses. Electrocardiograms (ECG) are very helpful in some cases, but the majority of critically ill patients have nonspecific ECG findings. Chest radiographs are of limited use for diagnosing cardiovascular life threats.

In cardiac arrest with pulseless electrical activity (PEA), it is critical to determine whether the patient has true electromechanical dissociation (EMD) with cardiac standstill or pseudo-EMD with mechanical cardiac contractions too weak to generate a palpable blood pressure.⁷⁷ Many patients with PEA have severe hypovolemia, while others have cardiac tamponade, massive pulmonary embolism (PE), or severe left ventricular (LV) dysfunction. All of these conditions can be detected rapidly with POCUS. Echocardiography can be performed serially during a critical resuscitation as long as the examination itself does not interfere with resuscitative efforts. Transesophageal echocardiography (TEE) is becoming more common in the emergency medicine and critical care settings and allows continuous assessment of cardiac function while chest compressions, defibrillation, and other therapies are ongoing.^{7, 78–81}

For stable patients, it is reasonable to use POCUS to screen for clinically silent cardiac abnormalities. These patients often present with vague symptoms such as malaise, dizziness, or dyspnea, and POCUS is the only reasonable way to screen such patients for significant abnormalities. Heart failure (HF) is a global pandemic affecting at least 26 million people worldwide and is increasing in prevalence.⁸² In one study, almost 9% of the adult population age 45 years or older had moderate or severe systolic or diastolic LV dysfunction, but less than half of those patients ...