Mechanics of porcine coronary arteries ex vivo employing impedance planimetry: a new intravascular technique.

Our objective was to evaluate methodological aspects of impedance planimetry, a new balloon catheter-based technique, for the investigation of coronary artery mechanical wall properties. We used a four ring-electrode electrical impedance measuring system that was located inside a balloon. Two of the electrodes were used for excitation and connected to a generator producing a constant alternating current of 250 mA at 5 kHz. The other two electrodes for detection were placed midway between the excitation electrodes. The balloon was distended with electrically conducting fluid through an infusion channel. The vessel cross-sectional area (CSA) was measured according to the field gradient principle by measuring the impedance of the fluid inside the balloon. Impedance planimetry was applied in the three major branches of the coronary arteries of seven extracted porcine hearts to assess luminal CSAs in response to internal pressurization. The biomechanical wall properties were evaluated by computing the strain [(r - r0) x r0(-1), where r is the vessels inner radius computed as (CSA x pi-1)1/2 and r0 is the radius of the vessel at a minimal distension pressure], the tension [(r x dP), where dP is the transmural pressure difference], and the pressure elastic modulus (delta P x r x delta r-1). We found that in vitro testing demonstrated that impedance planimetry was accurate and reproducible. The technique has controllable sources of error. Measurements were performed with consecutively increasing pressures in the range 1-25 kPa (8-188 mmHg, 0.01-0.25 atm). The CSAs increased nonlinearly and were significantly larger in the left anterior descendent coronary artery (LAD) (1 kPa, mean 5.0 mm2; 25 kPa, mean 21.8 mm2) than in both the left circumflex (Cx) (4.5-16.0 mm2) and the right coronary artery (RCA) (2.8-15.6 mm2) (analysis of variance, P < 0.001 for both). The circumferential wall tension-strain relation showed exponential behavior. For a given strain, tension values for LAD were significantly lower than those of Cx (P < 0.01). The pressure elastic modulus-strain relation also was exponential, and values for Cx were significantly lower than values for LAD (P < 0.001) and RCA (P < 0.05). Impedance planimetry was applied to the study of coronary artery biomechanics ex vivo. The LAD had the largest CSA, and the Cx was the least compliant. Methodological aspects of an in vivo introduction of the method require additional evaluation.