INVASIVE ULTRASOUND TRANSDUCER TESTING

TEE EXAMINATIONS - TRANSESOPHAGEAL ECHOCARDIOGRAPHY (TEE)

Transesophageal echocardiography (TEE), also known as "swallowing echo", is an ultrasound examination of the heart. It enables better visualization, for example for assesing of cardiac structures. By inserting an endoscope with an ultrasound probe into the oesophagus,close proximity to the heart can be achieved. The ultrasound examination through the esophagus enables particularly high-resolution imaging of the heart valves and the atria. Heart valve defects, the smallest blood clots and deposits in the case of inflammation (endocarditis) can be examined precisely in this way.

In contrast to transthoracic echocardiography (TTE), TEE examinations are not performed through the chest wall, but through the oesophagus using an endoscope-like examination tool. The esophagus runs directly behind the heart, so that the distance to cardiac structures is significantly less than by conventional echocardiography. The structures in front of the heart (e.g. ribs, fatty and connective tissue, etc.) are omitted in TTE, so that interference signals are minimized. This means that particularly high-resolution transducers can be used, which make even the smallest structures and changes visible. However, as these transducers only have a very low penetration depth, a transthoracic examination is not possible.

WHY DO ULTRASOUND TRANSDUCERS NEED TO BE TESTED?

Many types of diagnostic ultrasound transducers come into close contact with patients and should therefore be tested regularly in order to evaluate the integrity of the isolation between the transducer's internal circuit and the external environment. Due to the close proximity to the heart during a typical medical application, TEE (transesophageal echocardiography) ultrasound transducers are of high importance in terms of safety and containment of potentially dangerous electrical leakage currents. A small leak caused by a bite during a previous use of TEE can result in an increased risk of potentially dangerous electrical leakage currents for the next patient, which are inducted with the TEE transducers.

DANGER TO THE PATIENT FROM DAMAGED TEE TRANSDUCERS

All leading manufacturers recommend testing as a preventive measure (predictive maintenance). A TEE probe that has a faulty electrical leak creates a potentially dangerous path to ground directly behind the patient's heart.

Holes or bites in the probe pose the greatest risk to patient safety as they damage the probe's insulation. As a result of this damage, the TEE probe does not operate electrically any more. This also increases the risk of infection and cross-contamination. Liquids that have entered the probe sheath, such as the disinfectant used to clean the probe, can leak out of the probe while it is being inserted into the patient, which can lead to burns in the patient's esophagus and illness after a TEE examination.

The disinfectant solutions generally used to reprocess TEE probes are both highly corrosive and electrically conductive and can sometimes lead to immediate probe failure by penetration. However, the corrosive effect can also cause long-term damage.

It is therefore important that the integrity of the insulation is checked after every examination in which the probe is used. If there is any damage, the probe should not be disinfected until a leakage current test has been carried out by a specialist. A probe that does not pass this test must be taken out of operation immediately.

1 Medical Dictionairy 2009 ('davisTab', 'e05.jpg')