The treatment of the coronary heart disease (CHD) at present is implemented using either drug therapy or surgery. The surgical approach implies execution of operations aimed at revascularization (recovery of tissue blood supply) of the cardiac muscle.
The most wide-spread method of indirect revascularization of myocardium is the transmyocardial revascularization (TMR) that consists in producing channels in the cardiac wall with subsequent formation of blood vessels. Various surgical techniques can be used to produce such channels, including the transmyocardial laser revascularization (TMLR). In the process of such operation within the depth of the cardiac muscle of the left ventricle the channels opening into the cardiac cavity are formed using laser radiation.
TMRL is widely used for sufficiently long time and is officially permitted by the Food and Drug Administration (FDA), USA, for treatment of refractory angina pectoris in patients with CHD, for which it is impossible to perform direct revascularization of myocardium.
In our country the most significant experience of treating the coronary heart disease by means of TMLR is accumulated in the Bakulev Research Center of Cardiovascular Surgery of the Russian Academy of Medical Sciences.
In the developed instrument the solid-state laser, operating at the wavelength 1.44 µm and having the output radiation pulse energy up to 4 J, variable pulse duration 2—20 ms, the pulse shape close to rectangular, and the pulse repetition rate up to 3 Hz is exploited. The instrument allows implementing perforation of myocardium during a single cardiac cycle, with the possibility of electrocardiographic synchronization and simultaneous injection of medicinal preparations.
Due to the fact that the emitting face of the silica optical fiber in the process of operation is located at the surface of the cardiac muscle, the TMLR instrument provides the formation of a channel 20—25 mm long and nearly a millimeter in diameter penetrating through the myocardium during a single laser pulse (up to 20 ms long). The efficiency of the radiation action during the whole pulse time is provided by continuous mechanical displacement of the optical fiber in the direction of the radiation action. In this case the operating part of the optical fiber is moved into the myocardium tissue depth through the channel produced by laser radiation. The possibility of simultaneous injection of medical preparations into the zone of TMLR execution is also provided.
In the course of pre-clinical testing of the TMLR instrument the fine-tuning of the instrument’s operating modes was carried out in biological tissues (the porcine myocardium postmortem).
The goal of the studies was to evaluate the possibility of using the TMLR instrument in medical practice within the territory of Russian Federation, as well as the operating convenience and technological effectiveness of the instrument.
The tissue samples were subjected to the action of laser radiation with different pulse durations and energies.
The following studies have been performed:
- The work has been carried out on the effect of laser radiation on the porcine myocardium at different duration, energy, and shape of the radiation pulse;
- The work has been carried out on establishing the relation between the energy and duration of the laser pulse, on the one hand, and the velocity of the translational movement of the perforating segment of fiber and the perforation depth, on the other hand;
- The histological studies have been performed in order to determine the total perforation depth and the diameter and the zone of the myocardium channel lesion, produced as a result of the action of laser radiation on the porcine myocardium tissue.
As a result of testing the regimes of the instrument operation it was shown that the optimal values of the duration and energy of the pulse lie within the limits 10—20 ms and 2—3 J, respectively, while the move of the perforator is within 10—15 mm.
As a result of testing the regimes of the instrument operation it was also shown that the channels produced within the myocardium depth may have the following parameters:
- total lesion depth 12—15 mm;
- channel diameter 0.63—0.9 mm;
- coagulation zone 50--300 µm;
- carbonization zone is minimal.
Recommendations were developed that have been used in developing the software for the control system of the instrument. These recommendations allow simplification of using the instrument in executing surgical operations.
The material presented in the paper demonstrates the possibility of using the instrument in transmyocardial laser revascularization operations. To approve clinical use of the developed instrument it is needed to perform experimental studies in clinic and to evaluate their efficiency.
The most important result of the resented paper is the creation of operating hardware-software complex, capable of extension of its functional capabilities.
An instrument is developed that allows essential reduction of myocardium injuring during the TMLR operation. This reduction is due to using significantly smaller necessary values of the supplied energy of laser radiation. The instrument also allows application of a number of additional terminal units (applicators) for joint action of laser radiation and medicinal preparations, injected into the zone of the TMLR performance.
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