Echo On-Call: Echocardiographic Emergencies

Introduction

Echocardiography can be used appropriately to diagnose and triage emergent situations. The life-threatening pathologies in which real-time assessment by echocardiography can be critical include pericardial tamponade, aortic dissection, acute myocardial infarction (MI), acute pulmonary embolus (PE), and cardiac trauma. These conditions may cause severe chest pain, dyspnea with hypoxia, hypotension, and ultimately cardiogenic and respiratory shock. Even in cases where the primary cause of a patient’s deteriorating condition is unclear, such as isolated profound hypotension, the importance of echocardiography in rapidly assessing heart function and ruling out these critical abnormalities in an unstable patient cannot be understated.

This chapter is intended to be a guide to echocardiography in the acute scenario, that is, “echo on-call,” or “STAT” requests. In these situations, the sonographer must quickly grasp (1) the clinical scenario, (2) the indication for the exam, that is, the specific question being asked, and (3) key pathologies that must be ruled in or out. If a specific pathology is found, the ensuing clinical management decisions may be beyond the scope of the specific sonographer and this text, but they are touched upon in the interests of facilitating rapid patient care.

Cardiovascular Emergencies

Cardiogenic shock is heralded by profound hypotension and often respiratory failure. Specifically, systolic blood pressure falls below 80 mm Hg, with signs of end-organ insufficiency (cool extremities, altered mentation) and there is dyspnea, tachypnea, and hypoxia. This is a common and compelling scenario for emergency echocardiography.

From the broadest perspective, there are four very common acute life-threatening emergencies in which echocardiography may assist with diagnosis and/or triage: MI (and its related complications), tamponade, aortic dissection, and PE . Each has specific clinical settings, signs, and symptoms that would lead a clinician to suspect their occurrence in a given patient; although the sonographer may assess for echocardiographic signs of all in one exam, it is best to have an idea of the most likely suspected condition(s) to hasten the relevant imaging and patient care.

Acute MI and mechanical complications of MI are discussed fully in Chapter 18, Chapter 19 . For rapid reference, the most salient echocardiographic diagnoses are reproduced here in Table 13.1 . To be clear, in a patient who clearly has acute symptoms of myocardial infarct and ST elevations on electrocardiogram (ECG), coronary angiography and urgent revascularization is the first-line treatment, and obtaining an echocardiogram to confirm wall motion abnormalities would only be an impediment to appropriate treatment. Once the patient is stabilized or revascularized, if acute decompensation occurs, the key findings to assess on echocardiography are detailed below.

TABLE 13.1

Echocardiographic Emergencies

	Mechanical	Other Causes
Complications of MI	Acute MR (ruptured papillary muscle	Global LV failure
	VSD	RV failure/RV infarct
	Pseudoaneurysm Free wall rupture Hemopericardium and tamponade	LVOT obstruction
Tamponade	LV rupture or RV puncture Postcardiac surgery Aortic dissection	Pericarditis Malignant Renal
Aortic dissection	Traumatic (recent instrumentation, deceleration injury)	Spontaneous Aortic aneurysm
Pulmonary embolus

LV, Left ventricle; LVOT, left ventricular outflow tract; MI, myocardial infarction; MR, mitral regurgitation; RV, right ventricle; VSD, ventricular septal defect.

Note that these mechanical complications tend to occur 5–14 days after the actual coronary artery occlusion. All represent varying degrees of tissue necrosis, of papillary muscle versus ventricular wall, due to hypoxia. They typically occur in patients who have had large infarcts, or delayed or unsuccessful revascularization. The mortality rate of all is high and depends on rapid identification, stabilization, and repair.

Acute Mitral Regurgitation (Flail Leaflet) ( Fig. 13.1 , , , )

Mitral regurgitation (MR) may occur both acutely and chronically in patients with MI. When there is sudden hypotension and respiratory distress in the days after a large MI, one potential cause could be rupture of the papillary muscle trunk, tip, or chordae causing acute severe MR.

To assess for flail mitral valve:

1.
Obtain a standard parasternal long-axis view showing the mitral valve. Ask:
- Do the mitral valve leaflet tips meet normally (i.e., touch each other just below the annulus)?
- Or does the tip of one prolapse or “flail” back into the left atrium in systole? (see Fig. 13.1 and )
2.
Place a color Doppler sector over the mitral valve and left atrium. Ask:
- Is there a jet of MR (high velocity or turbulent speckled flow in systole)? In many cases, this will be directed eccentrically towards either the anterior or the posterior wall of the left atrium. Typically, a flail leaflet will direct the MR jet away, that is, in the opposite direction, from the damaged leaflet itself (refer to Fig. 19.2 ; see , ).
3.
Repeat two-dimensional (2D) imaging and color Doppler scans of the mitral valve in apical four-chamber and apical three-chamber windows. For technical reasons, it is not unusual for poor image quality to preclude an absolute determination of whether there is a flail leaflet or not, but an eccentric jet of brisk MR or a chordal structure oscillating in the left atrium proximal to the mitral valve ( , ) raises the strong possibility of ruptured mitral apparatus.
- The figures in this chapter show an example of posterior mitral leaflet flail. Examples of anterior mitral leaflet flail are shown in Chapter 19 , Figs. 19.1 and 19.3, and , , , , .
- Urgent management: Even the suspicion of flail mitral leaflet should generally trigger immediate cardiac surgical consultation. If needed, a transesophageal echocardiography (TEE) may be performed in the operating room (OR), or if the patient is in an intensive care unit with ventilator and pressor support providing enough stabilization, bedside TEE may be considered to confirm or refute the diagnosis. Pressors and an intraaortic balloon pump (IABP) may allow enough stabilization preoperatively to get the patient to the operating room.

Ventricular Septal Defect

Another cause of sudden hypotension and pulmonary edema in a patient in the peri- and post-MI period is rupture of the interventricular septum. This causes oxygenated blood to flow from the left to the right ventricle and mix with deoxygenated blood. Ventricular Septal Defects (VSDs) may occur in the anteroseptum (best seen in parasternal windows) due to anterior MIs or in the inferoseptum (best seen in apical four-chamber and subcostal windows) as a result of inferior MIs. Both types of VSDs may be screened for using parasternal short-axis windows. Using color Doppler is essential to detecting these ruptures, because the tissue discontinuity is often slit-like or serpentine and may not be readily visible on 2D imaging alone.

To assess for VSD:

1.
Obtain a standard parasternal long-axis view showing the left ventricle (LV) and right ventricle (RV). Ask:
- Is the interventricular septum of normal thickness and contracting during systole?
2.
Place a color Doppler window over the interventricular septum, particularly any akinetic sections or segments with echo drop-out.
- Color flow from left to right penetrating through the septum indicates a VSD. (See Chapter 19 , Fig. 19.4 A and .)
- Place a continuous wave (CW) Doppler cursor line through the color flow. If one measures the peak velocity of the CW Doppler flow envelope, the interventricular pressure gradient (Δ P ) = 4 × peak gradient (where peak gradient is expressed in m/s) ( Fig. 13.2B ; see also Fig. 13.3E , later).
- The narrower the neck of the color flow and the higher the peak velocity of the flow, the smaller or more restrictive the VSD is.
3.
Rotate the transducer clockwise 90 degrees and obtain parasternal short-axis windows of the LV and interventricular septum. Tilt the transducer apically to sweep the imaging plane from base to apex. Look for akinetic areas or focal echo dropout. Turn the color Doppler sector to cover the interventricular septum, and similarly sweep from base to apex looking for color flow from left-to-right. (See Chapter 19 , Fig. 19.4 B and .)
4.
In apical four-chamber view, examine the interventricular septum on 2D images, then position a color Doppler sector over the septum. Fig. 13.2 and show an example of an inferoseptal VSD.
5.
In subcostal four-chamber view, turn the color Doppler sector on and position it over the interventricular septum. Again, look for color flow through the septum from left to right.
- Urgent management: The treatment of choice is early surgical closure, which reduces mortality. Basal septal rupture is technically more difficult to repair fully, in part due to proximity to the mitral valve. In poor operative candidates, percutaneous closure may be considered (shown in ).