Journal
AMERICAN JOURNAL OF PHYSIOLOGY-HEART AND CIRCULATORY PHYSIOLOGY
Volume 310, Issue 3, Pages H436-H443Publisher
AMER PHYSIOLOGICAL SOC
DOI: 10.1152/ajpheart.00754.2015
Keywords
animal model; bioelectrical impedance; hemodynamics; myocardial ischemia
Funding
- Spanish Ministerio de Economia y Competitividad
- Instituto de Salud Carlos III
- Fondo Europeo de Desarollo Regional (FEDER): Red de Investigacion Cardiovascular (Redes Tematicas de Investigacion Cooperativa en Salud-RETICS) [FIS-PI13/00765, RIC-RD12/0042/0002]
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Myocardial electrical impedance is influenced by the mechanical activity of the heart. Therefore, the ischemia-induced mechanical dysfunction may cause specific changes in the systolic-diastolic pattern of myocardial impedance, but this is not known. This study aimed to analyze the phasic changes of myocardial resistivity in normal and ischemic conditions. Myocardial resistivity was measured continuously during the cardiac cycle using 26 different simultaneous excitation frequencies (1 kHz-1 MHz) in 7 anesthetized open-chest pigs. Animals were submitted to 30 min regional ischemia by acute left anterior descending coronary artery occlusion. The electrocardiogram, left ventricular (LV) pressure, LV dP/dt, and aortic blood flow were recorded simultaneously. Baseline myocardial resistivity depicted a phasic pattern during the cardiac cycle with higher values at the preejection period (4.19 +/- 1.09% increase above the mean, P < 0.001) and lower values during relaxation phase (5.01 +/- 0.85% below the mean, P < 0.001). Acute coronary occlusion induced two effects on the phasic resistivity curve: 1) a prompt (5 min ischemia) holosystolic resistivity rise leading to a bell-shaped waveform and to a reduction of the area under the LV pressure-impedance curve (1,427 +/- 335 vs. 757 +/- 266 Omega.cm.mmHg, P < 0.01, 41 kHz) and 2) a subsequent (5-10 min ischemia) progressive mean resistivity rise (325 +/- 23 vs. 438 +/- 37 Omega.cm at 30 min, P < 0.01, 1 kHz). The structural and mechanical myocardial dysfunction induced by acute coronary occlusion can be recognized by specific changes in the systolic-diastolic myocardial resistivity curve. Therefore these changes may become a new indicator (surrogate) of evolving acute myocardial ischemia.
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