Author(s): Crastina A, Pokreisz P, Schnitzer JE
We describe a novel model of myocardial infarction (MI) in rats induced by percutaneous transthoracic low-energy laser-targeted photodynamic irradiation. The procedure does not require thoracotomy and represents a minimally invasive alternative to existing surgical models. Target cardiac area to be photodynamically irradiated was triangulated from the thoracic X-ray scans. The acute phase of MI was histopathologically characterized by the presence of extensive vascular occlusion, hemorrhage, loss of transversal striations, neutrophilic infiltration, and necrotic changes of cardiomyocytes. Consequently, damaged myocardium was replaced with fibrovascular and granulation tissue. The fibrotic scar in the infarcted area was detected by computer tomography imaging. Cardiac troponin I (cTnI), a specific marker of myocardial injury, was significantly elevated at 6 h (41 ± 6 ng/ml, n = 4, P < 0.05 vs. baseline) and returned to baseline after 72 h. Triphenyltetrazolium chloride staining revealed transmural anterolateral infarcts targeting 25 ± 3% of the left ventricle at day 1 with a decrease to 20 ± 3% at day 40 (n = 6 for each group, P < 0.01 vs. day 1). Electrocardiography (ECG) showed significant ST-segment elevation in the acute phase with subsequent development of a pathological Q wave and premature ventricular contractions in the chronic phase of MI. Vectorcardiogram analysis of spatiotemporal electrical signal transduction revealed changes in inscription direction, QRS loop morphology, and redistribution in quadrant areas. The photodynamically induced MI in n = 51 rats was associated with 12% total mortality. Histological findings, ECG abnormalities, and elevated cTnI levels confirmed the photosensitizer-dependent induction of MI after laser irradiation. This novel rodent model of MI might provide a platform to evaluate new diagnostic or therapeutic interventions.