TEE-INVASIVE ULTRASOUND TRANSDUCER TESTING (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.
How transesophageal echocardiography works 1
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 into the patient's chest cavity and a few centimeters into the heart muscle.
Major manufacturers of diagnostic ultrasound systems such as GE Healthcare, Philips Medical Systems, Siemens Healthineers, Sonosite Inc. and Toshiba America Medical Systems recommend to test leakage currents from TEE transducers before each clinical application (or at least between applications). TEE transducers such as the Acuson V510B and V705B, GE Healthcare 6T, Philips Medical Systems miniMulit, OmniPlane III, S7-3t, MPT- 7-4, Siemens Medical Solutions V5M, V5Ms, V7M, Sonosite TEE/8-3, and Toshiba America Medical Systems PEF 510SB are just a few examples of transducers that should be regularly tested for electrical leakage currents as recommended by the manufacturers.
The Intersocietal Accreditation Commission (IAC) refers to this in section 2.2.3B of the new standards for the accreditation of adult echocardiography:
The manufacturer's instructions must ensure that the cleaning and disinfection of the transducer complies with the standards for the prevention and spread of infectious diseases. From 31.12.2015, it must also be ensured that the structural integrity of the transducer is checked before use. "Passed" or "Defective" must be determined and documented as the test result of a TEE transducer, as well as the following measures in the event of a "Defective" result.
During the electrical leakage current test will be checked whether the shaft of a TEE probe is damaged, that could lead to an electrical discharge during the examination.
Given the proximity of the TEE transducer to the heart during a transesophageal echocardiogram, an electrical discharge as a result of damage to the probe can pose a very high risk to the patient2.
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.
Leakage current tester SECULIFE UL with adapters for connecting the TEE probes
1 Medical Dictionairy 2009 ('davisTab', 'e05.jpg')
2 Carr, James D. “On the Proper Care of a Transesophageal(TE) Probe.” Sonora Medical Systems –Longmont, Colorado, 2009.
