A minimally invasive method for induction of myocardial infarction in an animal model using tungsten spirals.

Most animal models use surgical thoracotomy with ligation of a coronary artery to induce myocardial infarction. Incision of the chest wall and myocardium affect remodeling after myocardial infarction. The aim of our study was to evaluate a new minimally invasive technique for inducing acute myocardial infarction in pigs. To this end, coronary angiography using a 6-F cardiac catheter was performed in 20 pigs. The cardiac catheter was advanced into the left circumflex artery (LCX) under electrocardiographic monitoring and small tungsten spirals were deployed in the vessel. LCX occlusion was verified by coronary angiography. Two days later, magnetic resonance imaging (MRI) was performed to estimate the extent of infarction. Thereafter, all animals were euthanized and the hearts stained with 2,3,5-triphenyltetrazolium chloride for histologic measurement of infarct size. Tungsten spirals were successfully placed in the LCX in all 20 pigs. About 13 of the 20 animals survived until the end of the experiment. The mean infarct size in the area supplied by the LCX was 4.4 +/- 2.3 cm(3) at MRI and 4.3 +/- 2.2 cm(3) at histology (r = 0.99, P < 0.001). No other myocardial regions showed infarction in any of the 13 pigs. Five of nine pigs requiring defibrillation due to ventricular fibrillation died because defibrillation was unsuccessful. One animal each died from pericarditis and pneumonia. Our results show that the minimally invasive method presented here enables reliable induction of myocardial infarction in a fairly straightforward manner. The 25% mortality rate associated with induction of myocardial infarction in our study is comparable to that reported by other investigators.

3D and 2D delayed-enhancement magnetic resonance imaging for detection of myocardial infarction: preclinical and clinical results.

RATIONALE AND OBJECTIVES: The purpose was to verify whether myocardial viability can be detected by a delayed enhancement magnetic resonance imaging (MRI) approach using a rapid three-dimensional inversion-recovery fast low-angle shot (3D IR-FLASH) sequence in a preclinical and clinical setting. MATERIALS AND METHODS: Nonreperfused myocardial infarctions were induced in eight minipigs. Both the pigs and 15 patients with suspected myocardial infarction underwent MRI using a rapid 3D IR-FLASH sequence and a two-dimensional IR-FLASH sequence as the reference standard. RESULTS: In the pigs, a total of 52 segments with myocardial infarction were identified with both sequences and there was good agreement in transmurality of 99.5%. The infarction volume determined with the 3D IR-FLASH in the animal study (2.4 +/- 1.5 cm(3)) showed a good correlation with the histomorphometrically determined volume using triphenyltetrazolium chloride (2.3 +/- 1.2 cm(3), r = 0.98, P < .001) and the two-dimensional IR-FLASH sequence (2.3 +/- 1.4 cm(3), r = 0.99, P < .001). Eleven of 15 patients were found to have myocardial infarction in 37 myocardial segments with both sequences and there was a good agreement in transmurality of 98.8%. There was also a good correlation in the clinical study between the 3D and 2D sequences (6.9 +/- 6.7 cm(3) vs. 6.8 +/- 6.5 cm(3), r = 0.98, P < .001). In Bland-Altman analysis there was no significant under- or overestimation of the myocardial infarction volume using the 3D IR-FLASH sequence in comparison to the two-dimensional reference standard in both the preclinical and clinical study. The contrast-to-noise ratios were not significantly different between 3D and 2D sequences in the animal (34.7 +/- 1.5 vs. 33.8 +/- 2.6; P = .51) and clinical study (31.4 +/- 12.5 vs. 36.7 +/- 11.5; P = .31). The breathhold time for the 3D IR-FLASH sequence in the clinical study (20.4 +/- 2.2 s) was significantly shorter than that of the 2D IR-FLASH sequence (190.1 +/- 20.8 s, P < .001). CONCLUSIONS: The rapid 3D IR-FLASH sequence detects myocardial infarction with high accuracy and allows a relevant reduction in acquisition time.

Improved evaluation of myocardial perfusion and viability with the magnetic resonance blood pool contrast agent p792 in a nonreperfused porcine infarction model.

OBJECTIVES: To investigate whether a magnetic resonance (MR) blood pool contrast agent enables both evaluation of myocardial perfusion and viability in nonreperfused infarction in pigs. MATERIALS AND METHODS: An optimized MR protocol using the blood pool contrast agent P792 (0.026 mmol/kg, twice the clinical dose, Guerbet, France) was investigated to evaluate nonreperfused myocardial infarction in an animal model. P792 was compared with the extracellular contrast agent Gd-DOTA (0.1 mmol/kg). The MRI findings were compared with histomorphometry performed with microspheres to evaluate perfusion and triphenyltetrazolium chloride (TTC) to evaluate viability. Contrast-enhanced MR imaging of the heart was performed on a 1.5-Tesla scanner 2 days after instrumentation in 6 minipigs. A saturation recovery steady-state free precession sequence was used for perfusion imaging and an inversion recovery fast low-angle shot sequence for evaluation of myocardial viability. RESULTS: P792 tended to depict areas of reduced perfusion more accurately than Gd-DOTA (17.2% +/- 11.1% versus 13.7% +/- 8.0%) in comparison to the gold standard of histomorphometry with microspheres (18.2% +/- 9.8%). Moreover, P792, but not Gd-DOTA, depicted ischemic areas for 30 minutes after intravenous injection. The change in myocardial signal intensity during first pass was not significantly different after P792 compared with Gd-DOTA (140.3% +/- 64.4% versus 123.3% +/- 22.5%, P = 0.56). P792 was highly accurate in depicting infarcted areas (11.1% +/- 7.1%) compared with Gd-DOTA (12.1% +/- 8.2%, r = 0.98, P < 0.001) and histomorphometry with TTC (12.2% +/- 8.0%, r = 0.99, P < 0.001). CONCLUSIONS: Unlike Gd-DOTA, the blood pool contrast agent P792 allows evaluation of myocardial perfusion for a period of 30 minutes and shows good agreement with histomorphometry. P792 must be examined in further studies to evaluate its potential in evaluating early myocardial lesions and reperfusion. In addition, P792 also allows for evaluation of myocardial viability.