Use of pulsed energy delivery to minimize tissue injury resulting from carbon dioxide laser irradiation of cardiovascular tissues

Abstract

The carbon dioxide (CO2) laser has been utilized for preliminary intraoperative cardiovascular applications, including coronary endarterectomy and ventricular endocardiectomy. CO2 lasers used for these applications have been operated in the continuous wave, chopped or pulsed mode at low peak powers. To evaluate the extent of boundary tissue injury, continuous, chopped and pulsed energy delivery of CO2 laser emission was used to bore through 192 5 mm thick myocardial slices in air. Continuous, chopped and pulsed delivery at a peak power of 500 W or less failed to eliminate light microscopic or ultrastructural signs of thermal injury. Only when a high energy CO2 laser (pulse energy 80 to 300 mJ, pulse duration 1 microseconds) was used at a peak power greater than 80 kW were all signs of thermal injury eliminated; furthermore, high peak power prevented thermal injury only when the beam was focused to achieve a peak power density greater than 60 kW/mm2. Under these conditions, pathologic findings were identical to those observed using excimer wavelengths. The results of these experiments indicate that: conventional CO2 lasers fail to minimize boundary tissue injury, elimination of thermal injury during intraoperative laser ablation requires that CO2 laser energy be focused to achieve a peak power density greater than 60 kW/mm2, and elimination of thermal injury can be achieved at a variety of wavelengths, provided that an appropriate energy profile is employed.

Long- and short-term effects of transmyocardial laser revascularization in acute myocardial ischemia

“…Therefore, higher levels of collateral damage are expected with low-power, very short pulse ablation modalities, due to the thermal and structural components of tissue ablation. This is in agreement with the conclusions of Deckelbaum et al [14], who showed that, at sufficiently high levels of the average power, the collateral damage caused by infrared radiation will be optimally reduced.…”

Tissue adhesives in ocular surgery

“…Noguera et al set up a thermocouple device to monitor the temperature at the tissue interface. Other groups have used pulsed delivery of laser energy as opposed to continuous wave laser delivery, and it has been suggested that pulsed delivery minimizes collateral thermal damage [184]. Other groups have used photo-enhancing dyes and laser wavelengths specific to the chromophore's peak absorption to localize heat at applied areas.…”

Direct myocardial revascularization in ischemic heart disease

“…Unlike the CO 2 laser that is commonly used in surgical DMR, the Ho:YAG laser has profound acoustic effects due to its differences in absorption coefficient and laser pulse parameters (high peak power and short pulse duration). [35][36][37][38][39] The CO 2 laser produces confined photothermal ablative effects with a very thin zone of adjacent thermal injury and precise channel borders, but cannot be transmitted via conventional fiberoptics and cannot be used for catheter-based DMR applications. 36,37 The short pulsed (Ho:YAG or excimer) lasers cause photothermal and predominantly photo-acoustic ('shock-wave') tissue effects.…”

“…[35][36][37][38][39] The CO 2 laser produces confined photothermal ablative effects with a very thin zone of adjacent thermal injury and precise channel borders, but cannot be transmitted via conventional fiberoptics and cannot be used for catheter-based DMR applications. 36,37 The short pulsed (Ho:YAG or excimer) lasers cause photothermal and predominantly photo-acoustic ('shock-wave') tissue effects. These lasers can be transmitted via silicabased fibers, inducing irregular channel borders and large zones of collateral tissue injury.…”