© 1998 by European Society of Cardiology
Copyright © 1998, European Society of Cardiology
Passive transmission of ischemic ST segment changes in low electrical resistance myocardial infarct scar in the pig
éguez-Sinovasa
aLaboratorio de Cardiologéa Experimental, Servicio de Cardiologéa, Hospital General Universitari Vall d'Hebron, Universitat Autònoma de Barcelona, 08035 Barcelona, Spain
bDepartament d'Enginyeria Electrònica, UPC, Barcelona, Spain
* Corresponding author. Tel.: +34-93-4894031; Fax: +34-93-2746063; E-mail:jcinca@hg.vhebron.es
Objectives: To analyze the passive electrical properties of a healed infarction and assess their role on transmission of contiguous ischemic ST segment potential changes. Methods: We measured tissue resistivity (
cm) at 1 kHz and the epicardial ST segment during 1 h of proximal reocclusion of the left anterior descending (LAD) coronary artery in 12 anesthetized pigs with one-month-old transmural infarction elicited by LAD ligature below the first branch. The impedance spectrum (1 to 1000 kHz) of normal and infarcted myocardium was measured in seven other pigs with similar infarctions. Electrical transmission of current pulses (30 µA) in infarcted tissue and in test solutions was also investigated. Results: The infarct scar has a lower than normal resistivity (110±30 cm vs. 235±60 cm, p<0.0001) and, unlike the normal myocardium, resistivity and phase angle of the scar did not change at increasing current frequencies, reflecting no capacitative response. LAD reocclusion induced a resistivity rise (510±135 cm, p<0.01) and a ST segment elevation (0.6±0.7 to 9.5±5.1 mV, p=0.002) in the ischemic peri-infarction zone, whereas the infarcted area showed ST segment elevation (0.5±0.5 to 3.8±2.6 mV, p=0.03) with no resistivity changes. Potential decay of both ST segment and current pulses in the scar and in 0.9% NaCl solution was less than 1 mV/mm. Transmural deposition of connective tissue was seen in the center of the infarction. Conclusions: A one-month-old transmural infarction is a low resistance, noncapacitative medium that allows a good transmission of current pulses and of ST segment potential changes generated by contiguous peri-infarction ischemia.
KEYWORDS Electrophysiology; Connective tissue; ECG; Infarction; Ischemia; Necrosis
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