Transmyocardial holmium-YAG laser channels in an animal model: a preliminary morphologic and histologic study

Laser transmyocardial revascularization (TMR) appears to improve symptoms in patients with refractory angina. However, it remains a controversial treatment modality for relieving ischemia. We conducted our study in dogs and evaluated the changes in morphology and histology of the myocardium after laser TMR.

The hearts of 10 mongrel dogs (20-30 kg each) were treated with a holmiumyttrium aluminum garnet (YAG) laser in vivo. After opening the pericardium, the 1-mm fiberoptic device was used to create an average of 30 transmyocardial channels per heart at approximate intervals of 0.5 to 1 cm through normal left ventricular myocardium. All dogs tested survived the procedure. The dogs were sacrificed on the first and 60th postoperative days.

In the day-1 postoperative group (n = 4), the transmyocardial channels were obliterated at both epicardial and endocardial ends. The channels were totally occupied by necrotic myocytes and did not appear patent under the microscope. In the day-60 postoperative group (n = 6), the epicardial and endocardial scars were identified at each original laser application site. On cross-section, the channels were invaded by fibrous tissue bands extending from the endocardium to the epicardium, without a prominent central passage. Trichrome stained specimens showed that the channels were replaced by collagen fibers, fat tissue and numerous well-developed capillaries or sinusoids in which plenty of red blood cells were found.

We concluded that laser TMR offers no help for acute myocardial ischemia, but results in neovascularization inside the channels by the 60th postoperative day. Angiogenesis induced by laser TMR could possibly play a role in relieving chronic ischemia.