Recognition of Fibrotic Infarct Density by the Pattern of Local Systolic-Diastolic Myocardial Electrical Impedance

Abstract

Myocardial electrical impedance is a biophysical property of the heart that is influenced by the intrinsic structural characteristics of the tissue. Therefore, the structural derangements elicited in a chronic myocardial infarction should cause specific changes in the local systolic-diastolic myocardial impedance, but this is not known. This study aimed to characterize the local changes of systolic-diastolic myocardial impedance in a healed myocardial infarction model. Six pigs were successfully submitted to 150 min of left anterior descending (LAD) coronary artery occlusion followed by reperfusion. 4 weeks later, myocardial impedance spectroscopy (1–1000 kHz) was measured at different infarction sites. The electrocardiogram, left ventricular (LV) pressure, LV dP/dt, and aortic blood flow (ABF) were also recorded. A total of 59 LV tissue samples were obtained and histopathological studies were performed to quantify the percentage of fibrosis. Samples were categorized as normal myocardium (<10% fibrosis), heterogeneous scar (10–50%) and dense scar (>50%). Resistivity of normal myocardium depicted phasic changes during the cardiac cycle and its amplitude markedly decreased in dense scar (18 ± 2 Ω·cm vs. 10 ± 1 Ω·cm, at 41 kHz; P < 0.001, respectively). The mean phasic resistivity decreased progressively from normal to heterogeneous and dense scar regions (285 ± 10 Ω·cm, 225 ± 25 Ω·cm, and 162 ± 6 Ω·cm, at 41 kHz; P < 0.001 respectively). Moreover, myocardial resistivity and phase angle correlated significantly with the degree of local fibrosis (resistivity: r = 0.86 at 1 kHz, P < 0.001; phase angle: r = 0.84 at 41 kHz, P < 0.001). Myocardial infarcted regions with greater fibrotic content show lower mean impedance values and more depressed systolic-diastolic dynamic impedance changes. In conclusion, this study reveals that differences in the degree of myocardial fibrosis can be detected in vivo by local measurement of phasic systolic-diastolic bioimpedance spectrum. Once this new bioimpedance method could be used via a catheter-based device, it would be of potential clinical applicability for the recognition of fibrotic tissue to guide the ablation of atrial or ventricular arrhythmias.

Endocardial infarct scar recognition by myocardial electrical impedance is not influenced by changes in cardiac activation sequence

“…The first intervention aimed to induce acute myocardial infarction by occluding the left anterior descending coronary artery during 150 minutes with a catheter balloon, followed by reperfusion, as previously described. 10 Animals were premedicated with midazolam 0.6 mg/kg and ketamine 12 mg/ kg, and then they were submitted to general anesthesia with propofol 2-4 mg/kg and maintained with sevoflurane inhalation (2.5%-3.5%). Fentanyl (5 mg/kg) was administered for analgesia.…”

“…Although we analyzed the entire impedance spectra in all sites, we preferentially reported the data at 1, 41, 307, and 1000 kHz because we previously verified that these frequencies were highly discriminative. 10,13 To characterize the curve of phasic impedance changes elicited during the cardiac cycle, we measured the amplitude of the curve and the time interval elapsed from the peak of the electrocardiographic R wave to the moment of maximum impedance magnitude (R wave impedance peak time).…”

“…More recently, with the use of fast broadband electrical impedance spectroscopy, 11 it has been possible to measure the impedance changes throughout the cardiac cycle using a wide range of current frequencies from 1 to 1000 kHz. 10,17 Using intramural needle electrodes, one of these studies 10 showed that the infarcted regions with greater fibrotic content had the lower mean impedance values and the more depressed systolic-diastolic impedance curve. The present data confirm that compared to the healthy myocardium, the impedance curve of the infarct scar has a reduced amplitude and a delayed peak value.…”

Comparison of four different FIM configurations—a simulation study

“…Unfortunately, the equipment presented by Jorge et al is not suitable to use on human subjects. The same instrumentation was used by Amorós-Figueras et al in the work presented in Recognition of Fibrotic Infarct Density by the Pattern of Local Systolic-Diastolic Myocardial Electrical Impedance [32]. This work demonstrates that there are changes in the myocardial tissue after an infarct, and they suggest that it can be used in ablation procedures via a catheter to detect scar tissue.…”

Orthogonal Multitone Electrical Impedance Spectroscopy (OMEIS) for the Study of Fibrosis Induced by Active Cardiac Implants

“…Preliminary studies conclude that there is a correlation between the measured resistance and the morphology of the tissue next to the electrode [8]. Amorós-Figueras et al [9] show that in situ impedance measurements in myocardium or epicardium allowed discriminating healthy and infarcted tissue. These results suggest that the tissue remodeling occurring in fibrosis has an EIS signature.…”