Echocardiogram

Indications

Diagnosis of Cardiogenic Shock (see Cardiogenic Shock, [[Cardiogenic Shock]])

Clinical Features

  • Left Ventricular Failure
    • Global: severely diminished contraction of all left ventricular walls
    • Focal: hypokinesis (decreased contraction) or akinesis (no contraction) of specific LV segments
  • Right Ventricular Failure
    • Decreased RV Contraction in Longitudinal Aspect
    • Decreased Movement of Tricuspid Valve Toward Apex

Diagnosis of Pulmonary Hypertension (see Pulmonary Hypertension, [[Pulmonary Hypertension]])

  • Clinical Efficacy
    • Study of Echocardiogram Compared to Swan-Ganz Catheterization in the Diagnosis of Pulmonary Hypertension (J Am Soc Echocardiogr, 2016) [MEDLINE]
      • Echocardiogram Reliably Estimates Right Ventricular Systolic Pressure, Assuming Attention is Given to Simple Quality Metrics

Diagnosis of Ventricular Assist Device (VAD) Pump Thrombosis (see Ventricular Assist Device, [[Ventricular Assist Device]])

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Evaluation of Acute Pulmonary Embolism (PE) (see Acute Pulmonary Embolism, [[Acute Pulmonary Embolism]])

Clinical Features

  • Direct Signs
    • Clot in Transit
    • Clot in Main PA: seen primarily on transesophageal echocardiogram (TEE)
  • Indirect Signs
    • Dilated RV
    • Impaired RV Free Wall Function (with/without Intact Apical Function)
    • Systolic Septal Flattening (with “D-Shape” of LV)

Evaluation of Hypovolemic Shock (see Hypovolemic Shock, [[Hypovolemic Shock]])

Clinical Features

  • Small LV End-Diastolic and End-Systolic Area
  • Small, Collapsible IVC
    • Greater than 50% Inspiratory Collapse: suggests that CVP is <8
  • LV Cavity Obliteration (“Kissing” Papillary Muscles)

Evaluation for Pericardial Tamponade (see Tamponade, [[Tamponade]])

Clinical Features

  • Pericardial Effusion (see Pericardial Effusion, [[Pericardial Effusion]])
  • Chamber Collapse
    • Diastolic RV and LV Collapse
    • Systolic RA and LA Collapse
  • Inflow Velocity Variablity
    • Increased Variability in Mitral (>25%) Inflow Velocity
    • Increased Variability in Tricuspid (>40%) Inflow Velocity

Evaluation of Volume Status in Septic Shock (see Sepsis, [[Sepsis]])

  • Physiology
    • Mechanical Ventilation in the Passive Patient
      • Inspiration -> Increases Intrathoracic Pressure and RA Pressure, Resulting in IVC Distention
      • Expiration -> Decreases Intrathoracic Pressure and RA Pressure, Resulting in IVC Collapse
  • Rationale
    • A Fluid-Responsive Circulation Will Demonstrate Significant Cyclic Respiratory Variation in IVC Volume and Left Ventricular Stroke Volume
    • In Contrast, if Circulation is Not Fluid-Responsive, Only Small Respirophasic Changes Will Be Seen in the IVC or Left Ventricular Stroke Volume
    • Caveats
      • Lung Distention Increases the Pressure Around Pulmonary Capillaries, Increasing RV Afterload
        • Normally, this Doesn’t Have Significant Consequence for the Circulation
        • However, in the Setting of RV Failure, this will Result in Fluid-Unresponsiveness Despite Significant Respiratory Variation in the Left Ventricular Stroke Volume
  • Technique of IVC Diameter Measurement
    • IVC is Imaged in a Subxiphoid, Long-Axis View (Either off the Frozen Image with Caliper Function or with M-Mode Imaging)
    • IVC Diameter is Measured 2-3 cm Below the Right Atrium or Just Caudad to the Inlet of the Hepatic Veins: allows an estimation of right atrial pressure
    • IVC Diameter Should Be Measured at End-Expiration
  • Clinical Efficacy
    • Minimal/Maximal IVC Diameter as a Guide to Fluid Responsiveness in Sedated, Mechanically-Ventilated Patients (Intensive Care Med, 2004) [MEDLINE]
      • Correlations: r = 0.58 (minimal IVC diameter) and r = 0.44 (maximal IVC diameter)
      • Variation in IVC Diameter = Max Diameter-Min Diameter/Mean Diameter
      • Respiratory Variation in IVC Diameter was Greater in Fluid Responders than in Fluid Non-Responders
      • Threshold Variation in IVC Diameter of 12% (Max Diameter-Min Diameter/Mean Diameter) or 18% (Max Diameter-Min Diameter/Min Diameter) Separated Fluid Responders (Positive Predictive Value: 93%) from Fluid Non-Responders (Positive Predictive Value: 92%)
    • In Spontaneously Breathing Patient, A Dilated IVC (>2 cm) without a >50% Decrease in IVC Diameter with Gentle Sniffing Usually Indicates an Elevated Right Atrial Pressure (Chest, 2005) [MEDLINE]
      • However, this is Less Specific in Mechanically-Ventilated Patients, Since there is a High Prevalence of IVC Dilation in These Patients
  • General Features of Echocardiogram Which Predict Fluid Responsiveness (Chest, 2012) [MEDLINE]
    • Assumptions: patient is either on mechanical ventilation with respiratory efforts or is breathing spontaneously
    • If the Left Ventricle is Hyperdynamic with End-Systolic Effacement, There is a High Probability of Fluid Responsiveness
    • If the IVC is <1 cm in Diameter, There is a High Probability of Fluid Responsiveness
    • If the IVC is Between 1-2.5 cm, There is an Indeterminate Probability of Fluid Responsiveness
    • If the IVC is >2.5 cm in Diameter, There is a Low Probability of Fluid Responsiveness

Technique

Background-Normal Echocardiogram

Assessment of RV Size

  • RV is normally 60% of the LV size at end-diastole (best seen in apical 4-chamber view)
    • End-Diastolic RV Cavity Size >60% of the End-Diastolic LV Cavity Size Indicates Moderate-Severe RV Enlargement

Assessment of RV Wall Thickness

  • RV wall is normally <4 mm thick
    • RV Wall Thickness >5 mm is Abnormal

Assessment of Septal Kinetics

  • Rationale: the septum normally moves toward the LV during ventricular systole
  • Interpretation
    • Pressure overload of the right ventricle causes a straightening of the interventricular septum during systole: results in a D-shape of the LV during LV during systole
    • Volume overload of the RV causes a straightening of the septum during diastole: results in a D-shape of the LV during LV during diastole

Assessment of RV Systolic Function

  • Rationale: the RV has more longitudinal rather than transverse motion during systole, so the degree of longitudinal systolic movement of the tricuspid annulus correlates with overall RV systolic function
  • Technique
    • Tricuspid annular plane systolic excursion (TAPSE): M-mode interrogation in apical 4-chamber view using a line through the tricuspid annulus
  • Interpretation
    • Normal TAPSE: >17 mm (values below this indicate decreased RV systolic function)

Estimation of Pulmonary Artery Systolic Pressure

  • Technique: pulmonary artery systolic pressure assessment requires the presence of a tricuspid regurgitation (TR) jet
    • Continuous wave Doppler interrogation line is placed along the main axis of the TR jet to measure the blood flow velocity of the regurgitant jet
    • With use of the modified Bernoulli equation, the pressure gradient across the valve is calculated
    • Once the pressure gradient is known, adding the RA pressure to this gradient yields an estimate of pulmonary artery systolic pressure
      • The RA pressure may be measured directly if a central venous catheter is in place or estimated from the size and respiratory variation of the inferior vena cava (IVC

Assessment of Preload Sensitivity

  • Clinical Efficacy
    • Change in Stroke Volume After Passive Leg Raising Identifies Preload Sensitivity (Intensive Care Med, 2007) [MEDLINE]

References

  • The respiratory variation in inferior vena cava diameter as a guide to fluid therapy. Intensive Care Med. 2004;30(9):1834-1837 [MEDLINE]
  • Bedside ultrasonography in the ICU: part 1. Chest. 2005 Aug;128(2):881-95 [MEDLINE]
  • Passive leg raising predicts fluid responsiveness in the critically ill. Crit Care Med. 2006;34(5):1402-1407 [MEDLINE]
  • Diagnosis of central hypovolemia by using passive leg raising. Intensive Care Med. 2007;33(7):1133-1138 [MEDLINE]
  • Shock: Ultrasound to guide diagnosis and therapy.  Chest  2012; 142(4):1042-1048. Doi:10.1378/chest.12-1297 [MEDLINE]
  • Focused critical care echocardiography. Crit Care Med. 2013;41:2618–2626 [MEDLINE]
  • Advanced echocardiography for the critical care physician: Part 1. Chest. 2014;145:129–134 [MEDLINE]
  • Advanced echocardiography for the critical care physician: Part 2. Chest. 2014;145:135–142 [MEDLINE]
  • Bedside ultrasonography for the intensivist. Crit Care Clin. 2015 Jan;31(1):43-66. doi: 10.1016/j.ccc.2014.08.003. Epub 2014 Oct 3 [MEDLINE]
  • Addressing the Controversy of Estimating Pulmonary Arterial Pressure by Echocardiography. J Am Soc Echocardiogr. 2016 Feb;29(2):93-102. Epub 2015 Dec 11 [MEDLINE]