Laser sheds light on AF treatment

The cause and treatment of atrial fibrillation (AF) is a developing area of study, but the only true cure remains the surgical Cox-MAZE procedure. More recently cardiac tissue ablation has become an accepted treatment for supraventricular arrhythmias and atrial fibrillation.

The traditional curative treatment for AF is the Cox-MAZE procedure, which consists of an invasive surgical technique requiring a sternotomy, cardiopulmonary bypass and a series of full-thickness incisions made through the atrial tissue. Today, several variants of the procedure have evolved, but the underlying principles remain unchanged. Scar tissue is formed in the atria in a very specific maze lesion pattern in order to electrically isolate atrial paths and prevent the uncontrolled electrical impulse propagation that is characteristic of AF.

Alternative energy sources

Methods using alternative energy sources for cardiac tissue ablation have evolved as a substitute for complex incision techniques. These in turn minimise procedural time and operative morbidity. The goal of these devices is to desiccate cells, causing cellular death and disabling electrical signal propagation, while maintaining the structural integrity of the tissue itself. This can be achieved by raising tissue temperature to approximately 55°C or, alternatively, lowering the temperature to below -10°C. The ideal treatment would allow controlled ablation on a beating heart through small incisions, producing minimal patient trauma.

Laser is a unique energy source for tissue ablation because it is a form of light. While traditional energy sources focus on applying heat-based elements to the tissue’s surface, allowing temperature to propagate across the width of the tissue, or cryothermy, which propagates freezing temperatures, laser is an innovative, tissue-specific energy for tissue ablation.

Because laser is a form of light, its interaction with cardiac tissue is a sum of four types of light propagation: transmission, absorption, scatter and reflection. For ablation of atrial tissue, a wavelength like laser with high transmission and low absorption in water is ideal. So laser energy can penetrate the tissue while slowly being absorbed and converted into thermal energy. The high transmissibility and low absorbtion of the selected wavelength in cardiac tissue produces transmural lesions with a reduced risk of tissue perforation.

In sharper focus

	Figure 2. Atrial lesion (Endocardial view created from Epicardial ablation).
	Figure 3. Sub-millimeter optical fiber.

In addition to wavelength-dependent absorption and transmission of laser energy through tissue, the focused nature of the energy is critical. In other words, if the light is not maintained coherently as a means of delivery the energy to the myocardium and is excessively scattered or reflected, the effect of the laser is less specific and defined.This is why the ideal ablation energy source for atrial lesions would be laser energy at a wavelength of low water absorption being applied in a coherent manner.

Leveraging these physical properties, MedicalCV Inc, has developed a laser-based system called the ATRILAZE™ surgical ablation system. The ATRILAZE system implements coherent 810nm-wavelength diode laser, operating at low water absorption, for deep, full-thickness atrial lines of ablation. (See Figures 1 and 2) The hand-held delivery device is a low-profile tool that is ergonomically similar to a surgeon's scalpel. The first generation device is for use by cardiovascular surgeons in open-heart surgical settings. However, the company is developing a system that will potentially enable a stand-alone, minimally invasive – closed chest and beating heart – procedure. Coherent laser delivery through the device’s sub-millimeter optical fibre will enable thoracoscopic introduction. (See Figure 3)

Figure 1. The Water Absorption/Wavelength Relationship Curve.

Author profiles

Gregory G Brucker, PhD, principal scientist at MedicalCV Inc, has over 15 years’ experience in lasers for treatment of cardiovascular disease and 20 years in medical device development, including extensive work with arrhythmia ablation technologies.

Adam L Berman, MSE, vice president of R&D at MedicalCV Inc, has extensive experience in medical devices, specifically cardiovascular anastomotic devices and robot-assisted minimally invasive cardiac surgery. Berman has also held bioengineering research positions in mathematical modelling applied to cardiovascular disease.

Further information

MedicalCV Inc
Tel: +1 651 452 3000
Fax: +1 651 452 4948
Email: info@medcvinc.com
Website: www.medcvinc.com