Bubble studies are useful for identifying intracardiac shunts. In my experience, there are several major ingredients to doing a great one…
Bubble studies have been considered contraindicated in Eisenmenger’s syndrome.
Take note of any respiratory variation. If you have an awake patient, consider getting them to Valsalva as a test run and see if it wrecks your views. I recommend the apical 4 chamber view for bubble studies. A subcostal 4 chamber, though ideal for interrogating the interatrial septum for a PFO, may be associated with acoustic shadowing of the left atrium when the swarm of bubbles opacifies the right atrium.
Plan your capture
This can be prospective or retrospective, with the aim of recording a loop with a beat or two prior to bubbles entering the right atrium, then at least 5 more beats – a total of 10 beats is my usual approach. If you are injecting centrally, starting prospective capture at, or just before, injection of saline contrast is suitable. However, I prefer to use retrospective capture for bubble studies, and start counting beats from the time I first see bubbles in the right atrium. I capture after 8 beats have elapsed, so I get 1-2 bubble free beats, then 8-9 beats with bubbles.
The right stuff
Especially for peripheral injection, it’s ideal to have nice stable bubbles. This can be achieved by including about 1 ml of blood in the agitated saline – but that requires Luer lock syringes and secure connections to avoid the risk of disconnection at injection covering staff and patient in diluted blood. Of course, you’ll need a 3 way tap. I use 1 mL of blood, 20 ml of saline and 0.5 ml of air, drawn into my syringes which I then attach to the 3 way tap. I turn the tap so only the syringes communicate with each other, and connect these to my IV, ideally a central line which offers predictable timing of bubble arrival in the right atrium and rapid opacification. Make sure any taps on the central line are turned the right way to allow injection into the patient – and know what is in the line you are flushing! If you’re using a peripheral line, make sure it’s a drip that allows, and a vein that can tolerate, a rapid injection – the more proximal, the better.
You can get good help …
Almost anyone can be a good assistant – the onus is on you to give clear instructions and maybe play through the sequence with the assistant and patient as a dry run first to avoid misunderstandings about timing. My sequence for bubble studies is:
- Get your windows, set your capture interval (e.g. 10 beats) and know which button to press for capture
- If using Valsalva, ask the patient perform the manoeuvre (e.g. “take a big breath and use it to push your stomach out like you’re bursting a belt around your waist”)
- Get your assistant to agitate the saline between the syringes 5-10 times and then rotate the tap, permitting rapid injection into the patient.
- If using Valsalva, ask the patient to release Valsalva (e.g. “breath out”) when the bubbles enter the right atrium
- Capture prospectively, or retrospectively, as planned.
Depending on the reference you look at, bubbles in the left heart within 3-4 beats after opacification of the right atrium constitute a positive study suggesting intracardiac shunt.
Cover image: Blue bubbles by Tim Fields
Tags: ASD bubble studies Eisenmenger's PFO shunt