Imaging of the cardiovascular system Flashcards
Indications for CV imaging
Cough
Dyspnoeas: tachypnoea, orthopnoea
Exercise intolerance
Murmurs heard on examination
Pre-treatment checks (doxorubicin, pre-anaesthesia is disease suspected)
Imaging techniques for CV system
Thoracic radiography
Echocardiography
Angiography
Scintigraphy
Computed tomography
Pneumopericardiography (rarely used)
Which radiographic projections are best for imagng the heart?
The dorsoventral and right lateral projections are best because the heart lies in a more consistent position.
Contrast techniques for imaging CV system
Angiocardiography
Pneumopericardiography (following drainage of a pericardial effusion (rarely used)
What can thoracic radiographs provide information about (CV)?
Heart size
Cardiac chamber enlargement
Pulmonary vasculature changes
Lung patterns associated with cardiac disease
Great vessels
Normal heart size in dogs
Varies greatly between different breeds of dog
deep-chested breeds the heart is tall, narrow and upright whereas in barrel-chested breeds it is globular
Lateral
- width 2.5 - 3.5 times intercostal space
- height two-thirds height of thoracic cavity
- short axis + long axis = 9.7 ± 0.5 thoracic vertebral body lengths in most breeds
Dorsoventral
- width two-thirds of width of thoracic cavity
Normal heart size in cats
Lateral - short axis dimension is 2 intercostal spaces
○ vertebral scale system (VHS) 7.5 ± 0.3 vertebral body lengths
○ height two-thirds height of thoracic cavity
Dorsoventral - width two-thirds width of thoracic cavity
Normal variations of heart size on radiograph
Due to technique
○ Cardiac cycle
○ Respiratory cycle
Breed related in dogs
○ Globoid in retrievers
○ Elongated in … ?
Cats: older cats can have a ‘redundant aorta’
○ 30-40% of cats
Position of individual heart chambers on lateral radiograph
cranial and caudal cardiac waists
right chambers cranial
left chambers caudal
12-2 o’clock: left atrium
2-5 o’clock: left ventricle
5-9 o’clock: MPA and right auricular appendage
10-11 o’clock: aortic arch
Position of individual heart chambers on DV radiograph
11 to 1 o’clock - the aortic arch
1 to 2 o’clock- the pulmonary artery
2 to 3 o’clock - the left auricular appendage
2 to 5 o’clock - the left ventricle
5 to 9 o’clock - the right ventricle
9 to 11 o’clock - the right atrium
Pulmonary vasculature on radiography
arteries and veins should be of similar size and run on either side of the bronchi
arteries are dorsal and the veins ventral in the lateral view
diameter of the cranial lobe vessels should be smaller than the proximal third of the 4th rib
CdVC on radiographs
0.75 ± 0.13 vertebral lengths.
CdVC: aorta < 1.5
Cranial mediastinum on radiograph
In dogs, normally no wider than 1-1.5 times the width of vertebral column, except in brachycephalic breeds where it is often larger. In cats, it is normally no wider than the vertebral column.
Concentric hypertrophy
Increased systolic pressure (pressure overload)
Ventricular wall becomes thicker
Chamber size remains the same
Eccentric hypertrophy
Increased diastolic pressure and volume (volume overload)
Dilatation
Lumen size increases
Ventricular size initially the same, then thins
Eccentric is more easily seen radiographically
Left sided cardiomegaly on lateral radiograph
Taller heart resulting in tracheal and bronchial elevation
Splitting of the mainstem bronchi - left dorsal to right
Caudal border straighter and more upright
Left atrium bulges caudiodorsally
Loss of caudal cardiac waist and elevation of the caudal vena cava
Left-sided cardiomegaly in DV radiograph
Increased width of the cardiac silhouette
Rounding of left ventricular border
Heart apex may be displaced to the right
Enlarged left auricular appendage 2 to 3 o’clock
Dilated LA superimposed on cardiac silhouette
Left atrial enlargement on radiograph
Straightening caudo-dorsal cardiac waist
Dorsal deviation of the mainstem bronchi on DV
Elevation of the left caudal mainstem bronchus (separation of the two mainstem bronchi on lateral)
Increased height of the heart
Enlargement of the pulmonary veins
Left ventricle enlargement on radiograph
Hypertrophy = can be radiographically normal
Dilation:
○ Tracheal elevation (entire trachea)
○ Loss of normal dipping of the carina
○ Straight caudal border of the heart
○ In DV view: increased length of the cardiac silhouette, can see rounding of the apex
Secondary features of left sided cardiomegaly on radiographs
Engorgement and tortuosity of pulmonary veins compared to the arteries
Patchy increase in lung density particularly in perihilar region
Right-sided cardiomegaly on lateral radiograph
Heart is enlarged craniocaudally
Rounding of the cranial border
Increased sternal contact
Loss of cranial cardiac waist
Elevation of cranial lobe bronchi and vessels
Elevation of trachea just cranial to carina
Right-sided cardiomegaly on DV radiograph
Increased width of heart
Rounding of right cardiac border, reversed ‘D’ shape
Heart apex may be displaced left
Right ventricle enlargement on radiograph
Often over-diagnosed
Rare
Reverse D shape
Elevation of the apex from the sternum on the left lateral view
Elevation of the trachea without loss of the dipping of the trachea
Often concurrent with left ventricular dilation (DCM cases)
Right atrial enlargement on radiograph
Uncommon in isolation
Focal bulge on cranial aspect of the cardiac silhouette
Deviation of the trachea at the focal bulge
Secondary features of right sided cardiomegaly on radiograph
Engorgement and enlargement of CdVC.
CdVC: Ao > 1.5
CdVC: vertebral length > 1.30
CdVC: rib 4 > 3.50
Hepatic enlargement
Ascites
Generalised cardiomegaly on radiograph
Radiological signs of both left- and right-sided enlargement will be present.
Globoid appearance of the heart, more valentine shaped heart in cats
Enlargement of the cardiac silhouette in all chambers
Radiographic signs of both left and right sided enlargement
Signs of congestive heart failure
○ Pulmonary oedema
○ Hepatomegaly
○ Ascites
Pericardial effusion causes
neoplasia (haemangiosarcoma, heart base tumour, mesothelioma)
idiopathic,
left atrial rupture,
haemorrhage,
infection,
chronic uraemia
right-sided heart failure.
In cats, cardiomyopathy and FIP are most commonly involved.
Radiological signs of pericardial effusion
Gross enlargement of cardiac silhouette
Appears globular in both views
Sharp borders, effacement of the cardiac waists
No individual chamber enlargement identified
Under perfusion of the lung fields usually
Evidence of right sided heart failure can be present
Right-sided failure due to cardiac tamponade – ascites can be seen in the abdomen
Pleural and mediastinal fluid may be present
Pericardiocentesis followed by pneumopericardiography can be used for differential diagnosis, although ultrasound is now the method of choice
Echocardiography signs of pericardial effusion
Echolucent space between the epicardium and pericardium
There may be abnormal cardiac motion
Fluid space is greatest at the cardiac apex
Fluid may contain echodense material - fibrin, clots or tumour
Differentials for left sided cardiomegaly
Mitral incompetence
§ Mitral dysplasia
§ Chronic valvular disease
§ Endocarditis
Sub-aortic stenosis
Dilated cardiomyopathy
DIfferentials for right sided cardiomegaly
Tricuspid incompetence
§ Tricuspid dysplasia
§ Chronic valvular disease
Pulmonic stenosis
Tetralogy of fallot
Chronic pulmonary disease
Heartworm disease
Differentials for generalised cardiomegaly
Chronic valvular disease
Patent ductus arteriosus
Ventricular septal defect
Dilated cardiomyopathy
Chronic anaemia
Pericardial cysts
Rare.
They occur in the costophrenic angles and may be caused by incarcerated omentum or abnormal development of mesenchymal tissue during fetal life.
The history, clinical signs, pathophysiology and diagnosis are similar to those of pericardial effusion.
Peritoneo-pericardial diaphragmatic hernia
Congenital defect with abdominal viscera displaced into pericardial sac resulting in gastrointestinal or respiratory signs, which can occur at any age.
Weimaraners over-represented.
Radiological signs of Peritoneo-pericardial diaphragmatic hernia
Large round cardiac silhouette with dorsal displacement of the trachea
Enlarged cardiac silhouette merges with the diaphragm - the dorsal peritoneopericardial mesothelial remnant has been shown to be an aid to diagnosis in the cat
Different densities within the cardiac silhouette
Gas-filled intestine may be superimposed on cardiac shadow
‘Empty abdomen’
Barium can be used to confirm diagnosis
Sternal abnormalities
Absence of radiographic signs of heart failure
Incidental finding
When is reduced cardiac size seen?
Microcardia is seen in hypovolaemic shock and hypoadrenocorticism.
Radiological signs of reduced cardiac size
Heart size is reduced in all directions
Apex may be raised from the sternum
Cardiac shape appears triangular
Hyperlucent lung fields due to pulmonary undercirculation
Caudal vena cava reduced in size
Pulmonary circulation on DV radiograph
Artery lateral to the vein
Artery = vein in diameter
Diameter < diameter 9th rib
Pulmonary circulation on lateral radiograph
Artery dorsal to vein
Diameter <proximal third of 4th rib
Artery = vein in size roughly
Radiological signs of pulmonary undercirculation
Lung field more lucent
Pulmonary arteries smaller than normal and smaller than corresponding pulmonary vein.
Aetiology of pulmonary undercirculation
Right to left shunting (eg. tetralogy of Fallot)
Pulmonic stenosis
Hypovolaemic shock (+ microcardia)
Hypoadrenocorticism (+ microcardia)
Differential diagnoses when radigraphic signs of pulmonary undercirculation
Emphysema, overinflation, overexposure
Aetiology of pulmonary overcirculation
Left to right shunting (eg. PDA, VSD)- both arteries and veins enlarged
Congestive heart failure - veins > arteries
Heartworm disease (Dirofilaria immitis, Angiostrongylus vasorum) arteries > veins
Iatrogenic fluid overload - both arteries and veins enlarged
Radiological signs of pulmonary overcirculation
Increased vascular pattern
Pulmonary arteries and veins larger than normal
Differentials of pulmonary overcirculation signs on radiograph
Underexposure, expiratory radiograph
Technique for echocardiography
Should be imaged from the right and left sides.
Occasionally suprasternal and subcostal views are also required.
A small area of hair should be clipped extending for several intercostal spaces over the palpable apex beat of the heart on each side of the thorax, usually i/c space 3 to 6.
A generous quantity of coupling gel is applied to the thorax to eliminate air
2-D (B-mode - 2D real time), M-mode and Doppler studies may then be undertaken.
Simultaneous ECG is essential for producing accurate timings within the cardiac cycle.
Contrast echocardiography can be performed by injecting a bolus of contrast into a peripheral vein while imaging the heart.
Saline, blood and Gelofusion have been used after agitation to produce microbubbles.
The left cardiac chambers are not normally opacified as the microbubbles do not pass through the pulmonary circulation.
2D echocardiography assessment
Provides anatomical and functional information.
A systematic approach is essential to ensure nothing is missed.
Assessment includes:
* Overall size
* Cardiac motion
* Normal anatomy
* Atrioventricular valves
* Semilunar valves
* Chamber size
* Great vessels
Right parasternal long axis view (echocardiography)
(3rd-6th i/c space)
left ventricle apex and mitral valve
LV apex, LV outflow tract, aortic valve and proximal ascending aorta
left atrium and pulmonary veins
interventricular septum, LV outflow, aortic valve, mitral valve and left ventricular free wall (a plane between previous view and next)
aortic annulus, valve cusps and sinuses of Valsalva
Display with cardiac apex to the left and the base (atria or aorta) to the right
Right parasternal short axis view (echocardiography)
(3rd-6th i/c space)
LV, high papillary muscle level
chordae tendinae of the left ventricle
mitral valve
aortic root and valve
Display with cranial part of the image (RV outflow) to the right with the right heart encircling the LV and aorta clockwise
Left parasternal apical long axis view (echocardiography)
(5th-7th i/c space)
LV, mitral valve and left atrium, with slight counterclockwise rotation the LV outflow can be seen
Display with LV apex to the left and LA or aorta to the right
LV, LA, RV, and RA (four chamber view)
Display with left heart to the right and the right heart to the left
Left parasternal long axis view (echocardiography)
(3rd-4th i/c space)
LV outflow tract, aortic valve and ascending aorta
Display with LV apex to the left and aorta to the right
right ventricular inflow and tricuspid valve, angle beam ventrally
RV outflow tract, pulmonary valve and pulmonary artery, angle beam dorsally
Left parasternal short axis view (echocardiography)
right ventricular inflow and outflow with short axis view of aorta
Display with right heart encircling the aorta clockwise (RV inflow to the left, RV outflow and PA to the right
M-mode echocardiography
Allows measurement of chamber size and wall thickness and provides characterisation and timing of motion, relative to the ECG, during the cardiac cycle.
Correct alignment of the M-mode cursor is required in both the long and short axis planes for accurate and reproducible measurements to be made.
The left ventricular dimensions should be obtained when the ultrasonic beam is directed between the papillary muscles in the short axis view at the level of the chordae tendineae.
M-mode measurements are affected by body weight, breed, heart rate, age and physical training.
Measurements from the M-mode tracing are made from leading edge to leading edge.
Doppler echocardiography
Assess:
○ Quality of flow
○ Velocity of flow
○ Pressure gradients
○ Cardiac output
○ Blood flow
A few diagnoses
○ Valvular stenosis
○ Valvular regurgitation
○ Intracardiac shunts
