Cardiac Ultrasound


Article Author:
Meghan Herbst


Article Editor:
Maria O'Rourke


Editors In Chief:
Anne Kennedy


Managing Editors:
Orawan Chaigasame
Carrie Smith
Abdul Waheed
Frank Smeeks
Kristina Soman-Faulkner
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Radia Jamil
Sobhan Daneshfar
Saad Nazir
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Matthew Varacallo
Ahmad Malik
Mark Pellegrini
James Hughes
Beata Beatty
Hajira Basit
Phillip Hynes


Updated:
3/28/2019 11:48:09 PM

Introduction

Cardiac ultrasound, or echocardiography, is a noninvasive diagnostic modality that can provide detailed hemodynamic information in a short period at the patient bedside. It was first adopted by cardiologists for diagnostic purposes in the 1960s, and later by emergency physicians as one of several point-of-care ultrasound applications spanning from head to toe. As a result of these two temporally and specialist independent adaptations, there are two different conventions used to perform a cardiac ultrasound exam, which will be discussed further under “Technique.”

Anatomy

The heart sits obliquely behind and slightly to the left of the sternum, with the atria more superiorly positioned in the direction of the right shoulder, and the ventricles anterior and inferior ending approximately at the left nipple. The right ventricle (RV) is the most anterior chamber of the heart typically at the fourth intercostal space. The right atrium sends blood to the right ventricle in a right-to-left and superior-to-inferior direction via the tricuspid valve. The left atrium simultaneously sends blood to the left ventricle (LV) in parallel via the mitral valve. The ascending aorta takes off anteriorly from the left ventricle heading behind the sternum to the right before it courses superiorly and to the patient’s left.

Indications

1. Chest pain[1]:

  • LV wall motion abnormalities, or failure of certain parts of the LV wall to contract, suggests acute coronary syndrome in the appropriate clinical setting.
  • RV dilation (RV as large or larger than the LV) suggests right heart strain. If there is associated RV free wall thickness greater than 5 mm or tricuspid regurgitation with velocities higher than 4 m/s, this supports chronic right heart strain. However, an RV or right atrial thrombus ( the echogenic mass that has movement independent of the ventricle/atrium), and or a McConnell sign (RV hypokinesis with apical sparing) in the setting of chest pain and/or shortness of breath suggests a pulmonary embolism.
  • Visualization of an intimal flap in the ascending aorta (highly specific) or dilation of the aortic outflow tract greater than 4cm (leading edge to leading edge) with or without a pericardial effusion suggests a Stanford type A aortic dissection[2][3].

2. Shortness of breath[4]

  • A pericardial effusion explains undifferentiated dyspnea in up to 13% of cases[5].
  • Depressed LV ejection fraction less than 50% (less than 30% fractional shortening, or an E-point septal separation of greater than 7 mm) supports congestive heart failure or myocarditis[6].
  •  Acute coronary syndrome
  •  Pulmonary embolism
  •  Endocarditis[7]
  •  Valvular heart disease[8]

3. Hypotension

  • Massive or submassive pulmonary embolism[9]
  • Cardiogenic shock
  • Pericardial effusion with tamponade physiology
  • Aortic dissection
  • Hyperdynamic squeeze may suggest sepsis or hemorrhagic shock

4. Penetrating trauma or significant blunt trauma to the chest[10] [11]

  • Pericardial effusion with or without tamponade physiology
  • Left ventricular wall motion abnormalities may be appreciated in the setting of a cardiac contusion

5. Cardiac arrest

  • Organized cardiac activity seen on ultrasound following PEA arrest is associated with survival compared to disorganized activity
  • Detection of reversible causes such as pericardial effusion or pulmonary embolism can be identified
  • Cardiac ultrasound may offer guidance/feedback to medical providers delivering chest compressions regarding the quality of compressions. For this particular indication, transesophageal echocardiography is preferred as it can better visualize the heart during cardiopulmonary resuscitation (CPR) to see if the ventricles are adequately being compressed.[12]

Contraindications

Parasternal cardiac ultrasound should not be done during CPR, but other views are appropriate if feasible. Parasternal views can take place during the pulse check and towels should be nearby to clean off the gel immediately before CPR resumes. Care should be taken not to scan over a wound or incision to avoid contamination and infection.[13]

Equipment

Cardiac ultrasound should be performed with a low-frequency probe that has a small footprint that can fit between the ribs (phased array is ideal), using a cardiac setting.

Personnel

A trained provider can perform a cardiac ultrasound[14]. Emergency physicians are required to correctly perform and interpret a minimum of 25 to 50 cardiac ultrasound exams upon residency graduation. Many nurse practitioners and physician assistants are also skilled in this examination.

Preparation

The patient should be lying supine on a stretcher with the head of the bed approximately 30 degrees upright. For males, the chest should be completely exposed. For females, the hospital gown can be gathered at the level of the breast and towels tucked around the gown edges to keep it dry from the ultrasound gel. Alternatively, a towel can be draped over this area if the patient isn’t wearing a gown. For dominant right-hand operators, the ultrasound machine should be positioned at the patient’s anatomic right, plugged in (if applicable) and turned on. The lights should be dimmed if possible.

Technique

There are historically two conventions used when performing a cardiac ultrasound[15][1]. The first was established by cardiologists in the 1960s where the operator stands at the patient’s anatomic left, the indicator on the probe is directed either to the patient’s anatomic left or anatomic right depending on the view, and the indicator on the screen is on the right side. When emergency physicians adopted ultrasound, it was for multiple applications spanning from head to toe and included procedural guidance. Having a convention where the indicator on the screen is always to the left side, and the indicator on the probe is to the operator’s left (and up to 90 degrees clockwise from that position) keeps orientation consistent for the operator to perform and interpret, and is more practical for procedures. For this reason, the technique will be described with the latter convention.

  • A low-frequency phased array probe is best for a cardiac ultrasound. There are four key views: 

Subxiphoid: The phased array probe is placed inferior to the xiphoid process, indenting the skin one to two centimeters, with the indicator directed to the patient’s anatomical right, and footprint of the probe directed up towards the patient’s heart (handle of the probe parallel with the patient’s skin). Structures closest to the probe appear at the top of the screen, and structures further away appear towards the bottom of the screen, so in this view, the top of the screen is both anterior and inferior, and the bottom of the screen is more posterior and superior. For this reason, the left lobe of the liver is often visualized at the top of the screen, followed by the right atrium and right ventricle, and finally the left atrium and left ventricle near the bottom of the screen. Adjust the depth to see the entire heart, and interrogate for a pericardial effusion. Pericardial effusions are anechoic (black), and usually, encircle the heart when clinically significant. This view is often easy to obtain in thin patients, as well as patients with chronic obstructive pulmonary disease. It is more difficult in obese patients. Rotating the probe clockwise 90 degrees (so the indicator is pointing cephalad) allows visualization of the inferior vena cava emptying into the right atrium.

Parasternal long axis[16]: The phased array probe is placed just to the anatomic left of the sternum at the four intercostal space, with the handle of the probe perpendicular to the chest wall, an indicator to the patient’s right shoulder. The footprint of the probe is aligned with the long axis of the patient’s heart in this view. The chamber closest to the footprint at the top of the screen (anterior aspect of the patient) is the right ventricle. The additional chambers include the left atrium, left ventricle, and aortic outflow tract. Posterior to the left atrium and left ventricle at the bottom of the screen is a cross-section of the descending thoracic aorta. This view is helpful to confirm the presence of a pericardial effusion, evaluate the aortic outflow tract, and assess the left ventricle function. A circumferential pericardial effusion should track anterior to the descending thoracic aorta in this view (whereas a left pleural effusion will track posterior to the descending thoracic aorta). A dilated aortic outflow tract greater than 4cm measured from leading edge to leading edge, especially in the presence of a pericardial effusion, may indicate a type A aortic dissection in the appropriate clinical context. Left ventricular function can be assessed by how well the LV myocardium comes together, where a fractional shortening [(LV end-diastolic diameter – LV end-systolic diameter) / LV end-diastolic diameter] of about 30% to 45% correlates with a good squeeze. An indirect way to assess LV function is via the E-point septal separation (EPSS), which is the smallest distance between the anterior leaflet of the mitral valve and the interventricular septum during early diastole. The EPSS should be less than 7 mm, and a distance 7 mm or greater indicates depressed left the ventricular function. Diastolic dysfunction may cause falsely lower this distance, and mitral valve dysfunction may falsely increase this distance. 

Parasternal short axis: The phased array probe is rotated 90 degrees counterclockwise from the parasternal long axis position so that the indicator is pointing towards the right hip. Otherwise, the position of the probe is unchanged (still approximately the 4 intercostal space, just lateral to the sternum, with the handle of the probe at a perpendicular angle to the chest). The footprint of the probe is aligned with the short axis of the patient’s heart in this view, where the majority of the screen displays the circular left ventricle, and anteriorly (top left of the screen) is the RV, which should appear as a crescent shape. This view is ideal for assessing the left ventricle function, but can also confirm the presence of a pericardial effusion, or signs of right heart strain such as paradoxical septal motion and RV enlargement. The overall function of the left ventricle is best assessed concentrically at the level of the papillary muscles. The operator can also look for wall motion abnormalities and correlate with the ECG in this view. The walls of the LV in a parasternal short axis are septal, anterior, lateral, posterior, and inferior, in clockwise order.

Apical 4-Chamber[3]: The phased array probe is positioned at the apex of the heart, usually at approximately 5 o’clock on a male patient’s left nipple, or laterally beneath the left breast at the apex of the heart on a female. Palpating the pulse of maximal impulse (PMI) and placing the probe there will usually result in a perfect apical four-chamber view. Similar to the subxiphoid view, the footprint of the probe should be directed up towards the patient’s heart (handle of the probe parallel with the patient’s skin), but in this view, the footprint is facing the right shoulder, and the indicator is pointing towards the right superior iliac crest. In this view, the ventricles are closest to the probe at the top of the screen, and the atria are furthest away from the probe at the bottom of the screen with the right ventricle and atrium on the left of the screen, and the left ventricle and atrium on the right of the screen. This view is ideal for comparison of the right and left ventricles to look for evidence of right heart strain, but also to confirm the presence of a pericardial effusion. The normal RV to LV ratio is 0.6 to 1, but to keep the assessment of the RV specific for right heart strain as well as rapid and easy to perform, the binary assessment is whether the RV is smaller than the LV (no significant right heart strain), or if it is as big or bigger than the LV (evidence of right heart strain). This is particularly helpful in the setting of acute onset chest pain or shortness of breath when a pulmonary embolism is in the differential diagnosis[17]. A patient with no significant past medical history who has a large RV on cardiac ultrasound has a pulmonary embolism until proven otherwise. Even more specific for pulmonary embolism is a McConnell sign, where the RV is large and hypokinetic with apical sparing (the apex is not hypokinetic like the rest of the RV). These ultrasound findings for an otherwise healthy patient younger than the age of 65 yours may benefit from thrombolytics.

Complications

Cardiac ultrasound, like most diagnostic ultrasound applications, is associated with little if any risk. There may be some associated discomfort when acquiring certain views, such as the apical four-chamber view, with the pressure of the probe pressing against the ribs.

Clinical Significance

Cardiac ultrasound is a non-invasive, rapid, inexpensive application that expedites diagnosis and management of imminently life-threatening disease, including pericardial tamponade, acute coronary syndrome, cardiomyopathy, pulmonary embolism, and Stanford type A aortic dissection. Cardiac ultrasound can also differentiate shock states and guide resuscitative measures.[18]

Enhancing Healthcare Team Outcomes

Cardiac ultrasound, or echocardiography, is a procedure the multidisciplinary team should perform as needed to evaluate patients. It is a noninvasive diagnostic modality that can provide detailed hemodynamic information in a short period at the patient bedside. Nurses should be prepared to assist the provider in point-of-care ultrasound applications spanning from head to toe. [Level V]


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Cardiac Ultrasound - Questions

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What orthogonal plane is closest to the vertical long-axis view of the heart?



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Which is the best view to assess left ventricular function?



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Which of the following is not a sign of right heart strain?



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Ultrasound is defined as a sound wave above what frequency?



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A 50-year-old female with history of end-stage renal disease on hemodialysis presents to the emergency department with shortness of breath. Her vital signs are temperature 98.9 F, blood pressure 110/70 mmHg, heart rate 90 bpm, respiratory rate 20/minute, oxygen saturation 99% on room air. Which of the following is highest on the differential and what cardiac view would one start with to find it?



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A 50-year-old female with history of end-stage renal disease on hemodialysis presents to the emergency department with shortness of breath. She is in moderate respiratory distress, but her lungs are clear. Her vital signs are temperature 98.9 F, blood pressure 110/70 mmHg, heart rate 90 bpm, oxygen saturation 99% on room air. Her EKG does not show any abnormality. Which of the following choices fits the ultrasound approach?



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Cardiac Ultrasound - References

References

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Emergency department point-of-care ultrasound in out-of-hospital and in-ED cardiac arrest., Gaspari R,Weekes A,Adhikari S,Noble VE,Nomura JT,Theodoro D,Woo M,Atkinson P,Blehar D,Brown SM,Caffery T,Douglass E,Fraser J,Haines C,Lam S,Lanspa M,Lewis M,Liebmann O,Limkakeng A,Lopez F,Platz E,Mendoza M,Minnigan H,Moore C,Novik J,Rang L,Scruggs W,Raio C,, Resuscitation, 2016 Dec     [PubMed]
Common pitfalls in point-of-care ultrasound: a practical guide for emergency and critical care physicians., Blanco P,Volpicelli G,, Critical ultrasound journal, 2016 Dec     [PubMed]
Point-of-Care Clinical Ultrasound for Medical Students., Heiberg J,Hansen LS,Wemmelund K,Sørensen AH,Ilkjaer C,Cloete E,Nolte D,Roodt F,Dyer R,Swanevelder J,Sloth E,, Ultrasound international open, 2015 Nov     [PubMed]
Cardiac Imaging of Infective Endocarditis, Echo and Beyond., Iung B,Rouzet F,Brochet E,Duval X,, Current infectious disease reports, 2017 Feb     [PubMed]
[Real-time 3D echocardiography for estimation of severity in valvular heart disease : Impact on current guidelines]., Buck T,Bösche L,Plicht B,, Herz, 2017 Feb 22     [PubMed]
Current issues with emergency cardiac ultrasound probe and image conventions., Moore C,, Academic emergency medicine : official journal of the Society for Academic Emergency Medicine, 2008 Mar     [PubMed]
Point of care cardiac ultrasound applications in the emergency department and intensive care unit--a review., Arntfield RT,Millington SJ,, Current cardiology reviews, 2012 May     [PubMed]
Evaluation of Myocardial Injury using Standard Diagnostic Tools and Tissue Doppler Imaging in Blunt Trauma Chest., Gautam PL,Luthra N,Kaur M,Singh J,Wander GS,Tandon R,Namrata,Gautam N,, Journal of clinical and diagnostic research : JCDR, 2017 Jun     [PubMed]
Focused Transesophageal Echocardiography by Emergency Physicians is Feasible and Clinically Influential: Observational Results from a Novel Ultrasound Program., Arntfield R,Pace J,Hewak M,Thompson D,, The Journal of emergency medicine, 2016 Feb     [PubMed]
Right ventricular dilatation on bedside echocardiography performed by emergency physicians aids in the diagnosis of pulmonary embolism., Dresden S,Mitchell P,Rahimi L,Leo M,Rubin-Smith J,Bibi S,White L,Langlois B,Sullivan A,Carmody K,, Annals of emergency medicine, 2014 Jan     [PubMed]
Can junior emergency physicians use E-point septal separation to accurately estimate left ventricular function in acutely dyspneic patients?, Secko MA,Lazar JM,Salciccioli LA,Stone MB,, Academic emergency medicine : official journal of the Society for Academic Emergency Medicine, 2011 Nov     [PubMed]
The "5Es" of emergency physician-performed focused cardiac ultrasound: a protocol for rapid identification of effusion, ejection, equality, exit, and entrance., Kennedy Hall M,Coffey EC,Herbst M,Liu R,Pare JR,Andrew Taylor R,Thomas S,Moore CL,, Academic emergency medicine : official journal of the Society for Academic Emergency Medicine, 2015 May     [PubMed]
Incidence of pericardial effusion in patients presenting to the emergency department with unexplained dyspnea., Blaivas M,, Academic emergency medicine : official journal of the Society for Academic Emergency Medicine, 2001 Dec     [PubMed]
Modeling of predissection aortic size in acute type A dissection: More than 90% fail to meet the guidelines for elective ascending replacement., Rylski B,Branchetti E,Bavaria JE,Vallabhajosyula P,Szeto WY,Milewski RK,Desai ND,, The Journal of thoracic and cardiovascular surgery, 2014 Sep     [PubMed]
Diagnostic performance of emergency transthoracic focus cardiac ultrasound in suspected acute type A aortic dissection., Nazerian P,Vanni S,Castelli M,Morello F,Tozzetti C,Zagli G,Giannazzo G,Vergara R,Grifoni S,, Internal and emergency medicine, 2014 Sep     [PubMed]
Recommendations for cardiac chamber quantification by echocardiography in adults: an update from the American Society of Echocardiography and the European Association of Cardiovascular Imaging., Lang RM,Badano LP,Mor-Avi V,Afilalo J,Armstrong A,Ernande L,Flachskampf FA,Foster E,Goldstein SA,Kuznetsova T,Lancellotti P,Muraru D,Picard MH,Rietzschel ER,Rudski L,Spencer KT,Tsang W,Voigt JU,, European heart journal cardiovascular Imaging, 2015 Mar     [PubMed]

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