title: Early detection of acute transmural myocardial ischemia by the phasic systolic-diastolic changes of local tissue electrical impedance.
abstract: 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 Ω·cm·mmHg, P < 0.01, 41 kHz) and 2) a subsequent (5-10 min ischemia) progressive mean resistivity rise (325 ± 23 vs. 438 ± 37 Ω·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.
authors.affiliation: Department of Cardiology, Hospital de la Santa Creu i Sant Pau, Institute of Biomedical Research Sant Pau, Universitat Autonoma de Barcelona, Barcelona, Spain; and ejorge@santpau.cat.
authors.forename: Esther
authors.initials: E
authors.lastname: Jorge
authors.affiliation: Department of Cardiology, Hospital de la Santa Creu i Sant Pau, Institute of Biomedical Research Sant Pau, Universitat Autonoma de Barcelona, Barcelona, Spain; and.
authors.forename: Gerard
authors.initials: G
authors.lastname: Amorós-Figueras
authors.affiliation: Electronic and Biomedical Instrumentation Group, Department of Electronics Engineering, Universitat Politecnica de Catalunya, Barcelona, Spain.
authors.forename: Tomás
authors.initials: T
authors.lastname: García-Sánchez
authors.affiliation: Electronic and Biomedical Instrumentation Group, Department of Electronics Engineering, Universitat Politecnica de Catalunya, Barcelona, Spain.
authors.forename: Ramón
authors.initials: R
authors.lastname: Bragós
authors.affiliation: Electronic and Biomedical Instrumentation Group, Department of Electronics Engineering, Universitat Politecnica de Catalunya, Barcelona, Spain.
authors.forename: Javier
authors.initials: J
authors.lastname: Rosell-Ferrer
authors.affiliation: Department of Cardiology, Hospital de la Santa Creu i Sant Pau, Institute of Biomedical Research Sant Pau, Universitat Autonoma de Barcelona, Barcelona, Spain; and.
authors.forename: Juan
authors.initials: J
authors.lastname: Cinca
mesh_terms: D000818:Animals; D003971:Diastole; D004195:Disease Models, Animal; D042241:Early Diagnosis; D017097:Electric Impedance; D004562:Electrocardiography; D006439:Hemodynamics; D017202:Myocardial Ischemia / Q000175:diagnosis*; D034421:Sus scrofa; D013552:Swine; D013599:Systole
keywords: animal model; bioelectrical impedance; hemodynamics; myocardial ischemia.