Comparison of conventional and transesophageal echocardiography with magnetic resonance imaging for anatomical mapping of thoracic aortic dissection. A dual noninvasive imaging study with anatomical and/or angiographic validation.

Thirty-five consecutive patients with clinically suspected aortic dissection were subjected to a dual noninvasive imaging protocol using comprehensive echocardiography and ECG-triggered MRI with multi-slice spin echo and cine sequences in random order. The purpose of this dual imaging study was to compare the diagnostic accuracy of two-dimensional and color-coded Doppler echocardiography using the conventional transthoracic (TTE) and the transesophageal approach (TEE) with magnetic resonance imaging (MRI) for the exact morphologic evaluation and anatomical mapping of the thoracic aorta. The results of each diagnostic method were validated independently against the 'gold standard' of intraoperative findings (n = 17), necropsy (n = 4) or contrast angiography (n = 22). Compared to conventional transthoracic echocardiography both TEE and MRI were more reliable in detecting aortic dissections (TTE vs TEE: p < 0.02; TTE vs MRI: p < 0.01) and associated epiphenomena. Moreover, the reliability of TTE decreased significantly from proximal to distal segments of the aorta, e.g. from the ascending segment to the arch (p < 0.05) and to the descending aorta (p < 0.005), whereas the sensitivities of both TEE and MRI were excellent irrespective of the site of dissection. With regard to epiphenomena such as thrombus formation and entry location, MRI emerged as the optimal method for detailed morphologic information in all segments of the aorta. No serious side effects were encountered with either method. Thus, in patients with suspected acute or subacute aortic dissections the echocardiographic assessment should include the transesophageal approach for significant improvement of the moderate sensitivity and specificity of TTE. Both TEE and MRI are non-traumatic, safe and diagnostically accurate to identify and classify acute and subacute dissections of the thoracic aorta irrespective of their location. MRI provides superb anatomical mapping of all type A and B dissections and more detailed information on the site of entry and thrombus formation than TEE. These features of TEE and MRI may render retrograde contrast angiography obsolete in the setting of thoracic aortic dissection and may encourage surgical interventions exclusively on the basis of noninvasive imaging.

Impedance spectroscopy: a method for surveillance of ischemia tolerance of the heart.

UNLABELLED: During myocardial ischemia the phase angle phi of the complex electric impedance of myocardial tissue at 5 kHz AC exhibits a characteristic behaviour, the progress of which depends on the cardioplegic method applied. By extending the frequency range to 200 Hz and 10 MHz and by analyzing in addition to phase and magnitude also real and imaginary part of the impedance it was possible to elucidate which ischemic changes in the myocardium are responsible for the course of phi (5 kHz). This method we call impedance spectroscopy. Canine hearts were cardioplegically perfused with either the standard solution HTK[4] or the solution HTK[4] + 50 mumol/l Ca++. During the following ischemia at 25 degrees C energy-rich phosphate level, the ultrastructure, the real part, imaginary part and phase angle of the impedance between 200 Hz and 10 MHz were analyzed. RESULTS: phi (5 kHz) displays very similar characteristics during the ischemic period to those of the real part of the impedance at 200 Hz, Re (200 Hz). Re (200 Hz) increases, when--according to electron microscopic findings--an intracellular myocardial edema begins to develop. The changes of Re(200 Hz) are always smaller, however, than those of phi (5 kHz). This indicates that phi (5 kHz) increases in the course of ischemia not only as a consequence of confinement of the extracellular space by myocardial cellular edema but also because of changes of passive electrical characteristics of the myocardial cell membranes.(ABSTRACT TRUNCATED AT 250 WORDS)