10 Contrast and bubble contrast studies Flashcards
What are the indications for bubble contrast studies?
Diagnosis of intracardiac and intrapulmonary shunts, assessment of TR and pulmonary hypertension, assessment of LV size and function including RWMAs, assessment of cardiomyopathies (e.g. ARVC, LVNC, HCM), differentiation of masses (e.g. thrombi and tumours) and guidance in pericardiocentesis.
How is an agitated bubble contrast study performed and what are the variations?
An agitated saline bubble contrast study is performed during a TTE or TOE.
Draw 8.5ml of normal saline and 0.5ml of air into a 10ml Luer lock syringe. Use a 3 way tap to connect the first syringe to a second empty 10ml Luer lock syringe. Attach the 3 way tap to the intravenous cannula in the patient’s antecubital vein. Withdraw 1ml of the patient’s blood into the first syringe containing the saline and air. Turn off the 3 way tap to the patient and repeatedly squirt the saline, blood and air mixture between the two syringes for a few seconds until a suspension of small air bubbles is created in the mixture. Visualise the A4C view. Start recording and instruct the patient to perform the Valsalva manoeuvre and inject the 10 mL mixture. When the bubbles are visualised in the RA, instruct the patient to stop the Valsalva manoeuvre and watch for the air bubbles crossing from the RA into the LA.
Which manoeuvres can be performed during a bubble contrast study?
The Valsalva manoeuvre causes compression of the heart and the great veins so increases right sided pressures. This causes blood to flow from right to left. The other manoeuvres include coughing and leg elevation.
The bubbles can be injected via veins in the arms or veins in the legs.
The contrast can be injected via a bolus or infusion.
How are intracardiac and intrapulmonary shunts diagnosed with bubble contrast?
Normally, bubbles are only visible in the right heart. If bubbles are visible in the left heart, it indicates the presence of a right to left cardiac shunt.
In the presence of an intracardiac shunt, a minimum of 3 bubbles will be visualised in the LA 3-5 cycles after they are visible in the RA.
In the presence of an intrapulmonary shunt, a minimum of 3 bubbles will be visualised in the LA >5 cycles after they are visible in the RA.
What are the contraindications and possible complications of a bubble contrast study?
The contraindications include severe pulmonary hypertension, known right to left shunt with severe hypoxaemia and severe HF.
The complications include infection and possible air emboli and embolic events.
What are the characteristics of echo contrast agents?
The contrast bubbles are small and the structure is a shell holding the gas.
If the contrast bubbles are hit by ultrasound, the bubbles resonate and oscillate. The bubbles amplify the ultrasound signal and emit an ultrasound signal intensity (higher harmonic). If the contrast bubbles are hit by ultrasound, the bubbles can distort and fracture, emitting a harmonic signal.
Echo contrast agents are able to pass from the right heart, to the lungs, to the left heart, unlike agitated saline bubbles.
How do bubbles distort and fracture to create harmonic signals?
At low mechanical indexes, contrast bubbles oscillate and emit harmonic signals. At high mechanical indexes, contrast bubbles fracture and emit harmonic signals which are strong but short.
How is the echo machine optimised during bubble contrast studies?
A low mechanical index is used to prevent bubble fracture but a high mechanical index is used to assess myocardial perfusion. Harmonic imaging settings improve the visualisation of bubbles. Gain and focus settings improve the image quality.
