Contributors: Alison Dickie

 Species: Canine   |   Classification: Miscellaneous

Introduction

Uses

Advantages

  • Low cost.
  • Non-invasive.
  • Straightforward.
  • Rarely requires sedation.
  • No known biological risk.
    Time requirement will reduce with operator experience.

Disadvantages

  • Usually requires patient's coat to be clipped.
  • Normal sonographic appearance does not exclude disease.
  • Abnormal sonographic appearance does not always indicate significant disease.
  • Similar sonographic findings with different diseases.
  • Must be familiar with normal anatomy before can reach meaningful clinical conclusions.

Potential problems

  • Poor transducer-skin contact:
    • Inadequate clipping.
    • Insufficient coupling medium.
  • Inadequate patient restraint.
  • Operator inexperience.
  • Lung may interfere with image quality.
  • Inadequate equipment.

Alternatives

Equipment

Ultrasound machine

  • Most veterinary ultrasound machines have M-Mode Cardiac ultrasound video 03: ultrasound machine setup.
  • Colorflow and spectral Doppler are desirable but not commonly available.
  • Enter patient identification, date and other relevant information on the screen.
  • Alter time-gain, depth and focal point settings throughout the examination to optimize the images obtained.
  • Keep power setting low to reduce noise.

Transducer

  • High frequency (5 - 7.5 MHz).
  • Curvilinear or sector.
  • Small scan face essential to image between ribs.
  • High resolution equipment is required.
  • Doppler is useful.

Image production and storage

  • Any of the following are acceptable:
    • Thermal printer.
    • Video recorder.
    • Multiformat camera.
    • Disk drive.

Skin preparation

  • Clippers.
  • Coupling medium:
    • Ultrasound gel.
    • Alcohol or spirit.

Environmental factors

  • Quiet room with reduced lighting.
  • Assistant to restrain patient.
  • Table with comfortable surface, eg blanket or foam pad.
    A relaxed patient will avoid the need for sedation.
  • Table with hole or semi-circle cut from the edge.

Patient preparation

Prior to examination

  • Sedation is rarely required.
    Sedatives with cardiovascular effects may influence assessment of cardiac function.

Where to clip

  • Palpate apical heart beat and clip over this region.
  • Usually corresponds with ventral third of ribcage from level of 3rd to 5th rib.
  • Clip both sides of thorax.

Positioning

Technique: B-Mode

  • Swab the clipped region with alcohol.
  • Apply ultrasound gel to the skin surface and transducer before commencing examination.
  • Place transducer against skin surface from beneath animal through the hole in table.
  • Place transducer over the palpable apical beat midway between sternum and costochondral junction.
  • The heart falls towards the dependant thoracic wall where the transducer is located and into the cardiac notch of the lung field. This displaces the lung and allows the heart to be imaged.
  • A series of standard views are obtained to ensure repeatability.

Right parasternal views

  • Obtained with patient in right lateral recumbency and transducer applied to right thoracic wall.

Short axis views

Long axis views

Left parasternal views

  • Obtained with the patient in left lateral recumbency and transducer applied to left thoracic wall.

Long axis views

  • Place the transducer onto the intercostal space over the apical beat.
  • Use a longtitudinal imaging plane with the beam parallel to the long axis of the heart.
  • Angle the transducer craniodorsally towards the base of the heart.
  • The cardiac apex falls towards the left of the thorax and the transducer. The beam therefore passes through the heart in long axis from apex to base.
  • The beam passes through both ventricles and both atria giving the 'four chamber' view Heart normal left side 4-chamber view - ultrasound Heart: normal right 4-chamber view – ultrasound.
  • If the angle of the beam is altered slightly, the aorta will become visible leaving the left ventricle between the two atria in the far field of the image. This view is known as the 'five chamber' view.

Normal anatomy: B-Mode

  • B-Mode assesses gross appearance of heart.
  • Cardiac chambers are fluid filled so appear anechoic.
  • Myocardium is echogenic.
  • Pericardium appears as hyperechoic layer around periphery of myocardium.
  • Cardiac valves are hyperechoic structures separating cardiac chambers.
  • Motion of valves and contraction of myocardium throughout cardiac cycle is visible.
  • Convention states that:
    • The left side of the heart should be to the right of the screen.
    • The base of the heart should be to the right of the screen.

Right parasternal views

  • Image quality in the near field of the image is often poor especially if a sector transducer is used.
  • The right side of the heart is in the near field when the right parasternal approach is used and so is often poorly visualized in these views.

Short axis views

  • Left ventricle:
    • Left ventricular lumen is anechoic and keyhole shaped.
    • Two papillary muscles are symmetrical echogenic structures protruding into lumen.
    • Right ventricle is curved and wraps around left ventricle in near field of image.
  • Mitral valve:
    • The 'fishmouth view' through the mitral valve demonstrates the movement of mitral valve cusps.
    • Has similar appearance to mouth of fish opening and closing hence name.
  • Heart base Heart normal right side short axis view - ultrasound :
    • Aorta appears as an anechoic circle in the center of the image.
    • Three cusps of aortic valve in short axis resemble `Mercedes-Benz' emblem.
    • The right ventricle is in the near field of the image and curves round the aorta.
    • The pulmonic outflow tract is visible running down the screen and the pulmonic valves may be visible.
    • The left atrium is located in the far field.

Long axis views

  • Left atrium Heart normal right side long axis for left atrium - ultrasound :
    • Left ventricle is elongated chamber to left of image and left atrium is round chamber to right of image.
    • Cusps of mitral valve are hyperechoic structures separating the two chambers which open and close with the cardiac cycle.
    • Echogenic protrusions from ventricular wall distal to mitral valve represent papillary muscles.
    • Hyperechoic strands running from cusps of mitral valve to papillary muscles represent chordae tendinae.
    • Right ventricle and atrium are located in the near field.Their image quality depends on the near field resolution of the transducer.
  • Aorta:
    • The left ventricle is located to the left of the image and the aorta is imaged in long axis running towards the right of the image Heart: normal 5-chambered view for aorta 02 - ultrasound.
    • The cusps of the aortic valve are visible.
    • The interventricular septum is well visualized.
    • The left atrium and mitral valve are not visible.
  • Left atrium and aorta:
    • The left ventricle is to the left of the image.
    • The aorta is imaged in long axis running towards the right of the image.
    • The left atrium is located beyond and adjacent to the aorta.
    • Both the aortic and mitral valves are visible.

Left parasternum
Long axis views

  • Four chamber view:
    • The two ventricles are located in the near field.
    • The two atria are located in the far field.
    • The hyperechoic atrioventricular valve cusps are visible separating the chambers.
    • The left ventricular wall is thicker than the right.
  • Five chamber view:
    • The chambers are located as described for the four chamber view.
    • The aorta is imaged in long axis leaving the left ventricle in the far field.

Common problems or artifacts

  • Appearance of heart can be confusing so familiarity with normal anatomy should be achieved before attempting a clinical echocardiographic examination.
  • Ultrasound cannot penetrate air-filled lung resulting in reverberation artefact and acoustic shadowing. Lung located between the transducer and the heart will prevent images being obtained.
  • Presence of concurrent chronic lung disease or panting will significantly reduce image quality.
  • Imaging restricted to intercostal spaces. Ribs appear as hyperechoic structures with distal acoustic shadows which interefere with image quality.

Technique: M-Mode

  • Allows objective assessment of cardiac function.
  • Allows movement of structures to be measured at various stages of cardiac cycle.
  • Standardized parameters can be compared to published data tables.
  • Allows monitoring of cardiac function over a series of examinations.
  • Standard B-Mode right parasternal views used to perform M-Mode examinations.
  • Where possible, an ECG trace should be established on the ultrasound machine prior to performing M-Mode.
  • There are many parameters which can be assessed using M-Mode. Only the most common ones are described here.

Left ventricle

  • Left ventricular short axis view obtained.
  • M-Mode cursor line placed between two papillary muscles.

Mitral valve

  • Short axis view through mitral valve or `fishmouth' view obtained Heart: normal mitral valve 02 - ultrasound (M-mode).
  • M-Mode cursor line placed across valve leaflets.

Left atrium and aorta

  • Two options. Most suitable depends on particular patient:
    • Long axis view through both left atrium and aorta obtained.
    • Short axis view through heart base at level of aortic valves.
  • M-Mode cursor line placed across aorta and left atrium.

Normal anatomy: M-Mode

Left ventricle

  • M-Mode trace demonstrates Heart: normal with mitral valve 01 - ultrasound (M-mode) Heart: endocardiosis CHF hyperdynamic septum – ultrasound (M-mode) :
    • Left ventricular free wall (LVFW).
    • Left ventricular lumen (LV).
    • Interventricular septum (IVS).
  • Each of these structures is measured at:
    • End of diastole which corresponds with QRS complex on ECG.
    • End of systole which corresponds with T-wave on ECG.
  • If ECG not available:
    • End of diastole corresponds approximately with widest diameter of LV.
    • End of systole corresponds approximately with narrowest diameter of LV.
  • Measurements repeated over several cardiac cycles and averaged.
  • Measurements can be compared with published tables to determine if within normal limits compared to weight of patient.
  • LV dimensions can be used to calculate shortening fraction:
    • END DIASTOLIC - END SYSTOLIC/END DIASTOLIC X 100/1.
  • Normal limits in dogs 25-50%.

Mitral valve

  • M-Mode trace demonstrates motion of mitral valve leaflets.
  • Anterior cusp produces M-shape.
  • Posterior cusp produces W-shape.
  • Maximum excursion of valve occurs at E-point which corresponds with end of passive filling.
  • Distance between E-point and IVS is known as E-Point to Septal Separation (EPSS).
  • Normal distance should be <6 mm.
  • A value greater than this indicates left ventricular dilation.

Aorta and left atrium

  • M-Mode trace demonstrates left atrium and aorta.
  • Measure:
    • Aorta at end diastole.
    • Left atrium at maximum systolic motion (widest point).
  • Ratio between aorta and left atrium should be <1:1.2.

Common problems or artifacts

  • Poor B-Mode image quality will produce inferior M-Mode trace.
  • Inaccurate cursor placement will result in misleading results.