When should I consider giving contrast?
There are numerous scenarios in which a contrast agent may prove useful and these are discussed in chapters 2 and 3. However, in summary, they include:
- Enhancement of LV endocardial border delineation (EBD – when 2 or more contiguous segments are sub-optimally visualised) for assessment of global and regional systolic function, LV volumes and ejection fraction.
- LV opacification (LVO) for improved visualisation of structural abnormalities
- Enhanced visualisation of wall thickening during stress echocardiography
- Determination of myocardial ischaemia and viability using myocardial contrast echocardiography (MCE)
- Quantification of the coronary flow reserve, which has prognostic value in various disease conditions
The most important absolute contra-indication is known allergy to any of the constituent ingredients (e.g. sulphur allergy for Sonovue® contrast agent). Sonovue® should not be given in the following situations:
Unstable angina or acute coronary syndrome in past 7 days
Unstable (NYHA Class IV) heart failure
Right-to-left intra-cardiac shunt
Significant pulmonary hypertension
The first two restrictions above do not apply to Optison or Luminity.
Does it matter which contrast agent I choose?
The choice of agent will be influenced by both non-clinical factors (e.g. those that are available in each individual country, cost of contrast agent) as well as clinical factors (e.g. patient allergies, indication for contrast use). For enhancement of endocardial borders or LV opacification, all currently licensed 2nd generation agents are adequate. For assessment of myocardial perfusion, this should be done using a continuous intravenous infusion rather than repeated bolus injections (see below and chapter 2 for more details). Thus, at present, we recommend whichever agent can be given by continuous infusion in your department if MCE is being performed.
How do you decide on a bolus or infusion of contrast?
A bolus injection of contrast is suitable for enhancing the left ventricle so that one can assess overall cardiac structure as well as assess wall motion at a global and segmental level. Bolus injections are not suitable for the destruction-replenishment process in MCE studies (see chapter 2 for further details on this) and thus, for those cases, continuous infusion is required. A continuous infusion can also be used simply for LVO and some prefer this due to increased homogeneity of the images obtained.
What causes the “swirling” artefact I sometimes see after I give contrast?
There are several potential artefacts to watch out for when using contrast agents, but one often seen when first starting with contrast-enhanced imaging is “swirling” near the apex. This occurs due to excessive bubble destruction (apex is nearest to the transducer) and can be resolved by reducing the output power (mechanical index) at which one is scanning and also adjusting the focus (move up towards the apex). In patients with significantly impaired LV function this artefact can also be seen and may be improved by increasing the rate of contrast (for infusions) or using larger volume bolus injections.
Yes, absolutely! In fact, contrast use often eases the overall workload by reducing the number of “non-diagnostic studies” for which a patient may have to come back to the department specifically for a contrast-enhanced study. Gaining intravenous access and using contrast takes no more than 5 minutes. In our experience, the biggest obstacle to contrast use is the requirement of an intravenous cannula. Consequently, we strongly advise all our sonographers to undertake the appropriate training so that they may gain intravenous access themselves. Most countries also allow sonographers to inject contrast, though one may well have to attend a training course before being allowed to do so.
Is assessment of perfusion (MCE – Myocardial Contrast Echocardiography) of clinical use or a research tool only?
MCE has been in the research arena for over 25years and has acquired a very large evidence base attesting to its diagnostic utility in a number of clinical scenarios. It is fair to state that MCE is not as widely available or used as some other imaging techniques, but its use is constantly increasing. Routine use of contrast agents for assessment of myocardial perfusion is not always appropriately reimbursed in some countries which has been a limiting factor in uptake of the technique, as well as the steeper learning curve for perfusion assessment as opposed to EBD or LVO contrast use.
Is MCE as accurate in atrial fibrillation as in sinus rhythm?
Yes, both real-time and triggered imaging are perfectly feasible with the varying R-R intervals of AF. However, if there is a rapid ventricular response at rest (rate > 100bpm) it may be wise to defer the study until adequate rate control is achieved.
How long would it take to become trained in perfusion assessment (MCE)?
It is recognised that learning MCE as a technique – both image acquisition as well as interpretation – takes time. We would recommend a minimum period of 3-6months in a centre which regularly performs MCE studies and under the tutelage of a recognised expert in the field.
Why is MCE less widely used than CMR / SPECT imaging?
Nuclear cardiology techniques (e.g. SPECT) are traditional imaging modalities which have been in use for several decades and thus are an established part of some departments in many countries. Cardiac MRI has grown exponentially since its introduction approximately 20 years ago but is still not available in many hospitals and, in many countries, availability is restricted to tertiary referral units only. MCE has been used since the 1980s but learning the acquisition and interpretation of destruction-replenishment imaging takes time and is a new skill which has to be learnt. It is also fundamentally important to understand the physics of microbubbles and how we can harness their interaction with ultrasound for our benefit whilst scanning a patient.
I am interested! How can I become trained in contrast echocardiography?
Excellent! Your first step now should be to identify a centre with much experience in contrast echocardiography. This may be in your own country or overseas. We suggest you contact your national echocardiography society or the European Association of Echocardiography (EAE) offices for further information on whom to approach to gain experience with contrast imaging.