If you have been asked to attend for a contrast echocardiogram, you may be wondering exactly what one is, and why you need one.

Contrast echos tend to be requested for patients who have a moderate or greater level of impairment in their left ventricular systolic function. The left ventricle is (or should be, in normal individuals) the most muscular chamber of the heart, which pumps blood to the whole body, via the aorta. Impairment in your heart's ability to pump blood to your body can cause dyspnoea (shortness of breath), palpitations, fatigue, oedema, to name but a few of the most common symptoms.

Patients referred for a contrast echo will often have an ejection fraction in the 35-45% range, and the procedure may be requested to more accurately assess ejection fraction, given that placement of an ICD (implantable cardio-defibrillator) is indicated when ejection fraction reaches or falls below 35% (for simple handheld ECG monitors suitable for patients with ICDs, click here). A contrast echocardiogram may also be requested following a myocardial infarction (heart attack), if the function of the left ventricle is impaired, and/or the apical segments of the left ventricle are not contracting well, as such patients are at increased risk of thrombus (blood clot) formation. Blood clots in the heart are very dangerous, and can embolise and cause a stroke or necrosis of other tissues.

Less common uses of contrast are to confirm or rule out a pseudoaneurysm (again, following a heart attack), or to check for apical hypertrophic cardiomyopathy where image quality at the apex is poor.

Contrast is needed precisely because not all patients are naturally good imaging subjects. Body habitus plays a big role, with overweight people often being very difficult to image (equally, very small people with narrow rib spaces can be a real challenge). Similarly, chest shape can make imaging very difficult (pectus carinatum or 'pigeon chest'). Contrast may be indicated in these patients, in order to improve endocardial definition (see the walls of the heart more clearly) and come to a more accurate estimation of ejection fraction.

One additional, but very different use of contrast is for looking at communications between chambers or vessels, most frequently in trying to confirm the presence of an ASD (atrial-septal defect) or PFO (patent foramen ovale), i.e. a communcation between the two atria; a PDA (patent ductus arteriosus, a communication between the aoera and pulmonary artery); or a ventricular septal defect (VSD), a communcation between the two ventricles. The former two have a congenital origin, whereas the latter can be either congenital or post-infarction.

A contrast echocardiogram involves the use of two syringes and a three-way tap. For investigating shunts, saline solution is placed in one syringe, and is first exchanged back and forth between the two syringes through the stopcock. Once the saline solution has been agitated in this way, the tap is opened and the agitated saline injected into the patient's vein. Within seconds, it will show up into the heart. You may be asked to perform a valsalva manoever (to strain), in order to encourage the bubbles to pass through the suspected shunt.

When using contrast for opacification of the chambers, a slightly different method may be used. Saline will again be needed, but this time as a flush, injected immediately after administration of a microbubble contrast agent, which is likely to have been hand-agitated prior to administration.

 

Risks of contrast echocardiography

An echocardiogram does not expose your body to radiation, but it does expose it to energy; sound energy, to be precise. In simple terms, this involves rapid pressure changes (areas of compression and rarefraction) as the sound energy travels through the body.

Manufacturers have a responsibility to limit the thermal and mechanical effects of ultrasound, and by law now must display indices for the sonographers to see. An echocardiographer can manually increase the power output of the machine, as well as change other controls (frequency, pulse repetition frequency, and so on) which will adjust the amount of sound energy traveling into the body, but will do so with the ALARA (As Low As Reasonably Achieveable). For this reason, ultrasound has an impeccible safety record, and is the safest imaging modality available for cardiac scanning.

Contrast echocardiography actually involves scanning at an even lower power output than usual, because using too high a power output would burst the bubbles. So in this sense, contrast echo is no greater risk at all than a normal echocardiogram. However, the contrast agent itself does serve as an additional risk factor. Research is still ongoing about the behaviour of microbubbles in the bloodstream, but so far, no adverse effects have ever been documented in humans. Certainly, it seems very unlikely that any permanent damage can be done from a single exposure to contrast.

Given that a contrast echocardiogram will be requested to answer a specific question, and not as a routine examination, the benefits far outweigh the risks.