Analysis of Ischemic Neonatal and Adult Myocardium by Bioelectrical Impedance Spectroscopy

• Published in: The Thoracic and Cardiovascular Surgeon
• Main Authors: Lück, S., Delis, A., Minor, T., Pliquett, U., Martens, S., Preuße, C. J.
• Format: Conference Proceeding
• Language: English
• Published: 20.01.2015
• ISSN: 0171-6425; 1439-1902
• DOI: 10.1055/s-0035-1544494

Objectives: Bioelectrical impedance spectroscopy is a non-invasive method to determine ischemia-induced alterations of various tissues. Therefore, neonatal and adult porcine hearts were examined during ischemia at different temperatures to analyze distinctive myocardial changes properly. Methods: Ischemic piglet hearts ( n  = 12) and adult ones ( n  = 9) were examined at 35°C, 25°C and 15°C. Mean ages were 5 days and 2.7 months, respectively. After sternotomy all hearts were harvested and an epicardial probe was placed on the left ventricle to continuously measure impedance within a frequency range from 100 Hz–1 MHz. All hearts were incubated at constant temperatures (35°C, 25°C, 15°C) for 24 hours. Bioelectrical impedance measurements included two electrical resistances - Ohm (Re) and imaginary resistance (Im). For analysis, resulting phase angle was calculated. Additionally, specimens for ultrastructural studies were taken at certain intervals. Results: The phase angle showed a sigmoid curve in all groups. After an initial “lower” plateau it increased till it started to plateau again (“upper” plateau). At normothermia phase angles of neonates and of adults differed significantly ( p  = 0.009) since changes in neonates started earlier. Absolute values of maximum phase angles in neonates (35°C: −24.74°); 25°C: −28.22°; 15°C: −26.59°) outnumbered the ones in adults (35°C: −21.12°; 25°C: −24.34°). The lower the temperature the later the increase of phase angles occurred. By dividing Re at 300 Hz by Re at 1 MHz the extracellular space index (ESI) was calculated being an indicator for edema formation. In neonates ESI decreased from 54.9% to 10.4% at 35°C, from 60.1% to 8.4% at 25°C and from 54.9% to 10.5% at 15°C. Decreases of ESI of the comparison groups were inferior and occurred later. Ultrastructural alterations correlated with impedance measurements. Conclusion: New insights in intraischemic alterations of myocardial structures and size of the extracellular space can be gained by the use of atraumatic, non-invasive bioelectrical impedance measurements. Our results demonstrate higher sensitivity of neonatal hearts to ischemia. Especially, the development of a myocardial edema was more extensive in neonates with severe clinical impacts. Bioimpedance spectroscopy offers a chance to gain better knowledge about ischemia and myocardial protective strategies of neonatal hearts.