RESOURCES

BACKGROUND: Acute myocardial infarction remains a leading cause of chronic heart failure. Excessive myocardial oxygen demand relative to supply is the fundamental mechanism of myocardial infarction. We thus hypothesized that left ventricular (LV) mechanical unloading by the total support of transvascular LV assist device Impella could minimize oxygen
demand, thereby reducing infarct size and preventing subsequent heart failure.

METHODS AND RESULTS: In 20 dogs, we ligated the left anterior descending coronary artery for 180 minutes and then reperfused. We introduced Impella from 60 minutes after the onset of ischemia to 60 minutes after reperfusion. In the partial support group, Impella supported 50% of total cardiac output. In the total support group, systemic flow totally depends on Impella flow. Four weeks after ischemia/reperfusion (I/R), we compared LV function and infarct size among 4 groups: sham (no I/R), I/R (no Impella support), partial support, and total support. Compared with I/R, total support lowered LV end-diastolic pressure (15.0±3.5 versus 4.7±1.7 mm Hg; P<0.001), increased LV end-systolic elastance (4.3±0.8 versus 13.9±5.1 mm Hg/mL; P<0.001), and decreased NT-proBNP (N-terminal pro-B-type natriuretic peptide) level (4081±1123 versus 1773±390 pg/mL; P<0.05). Furthermore, total support markedly  reduced infarct size relative to I/R, whereas partial support decreased infarct size to a lesser extent (I/R, 16.3±2.6; partial support, 8.5±4.3; and total support, 2.1±1.6%; P<0.001).

CONCLUSIONS: LV mechanical unloading by the total support of Impella during the acute phase of myocardial infarction reduced infarct size and prevented subsequent heart failure in dogs.

Background-—Delivering therapeutic materials, like stem cells or gene vectors, to the myocardium is difficult in the setting of ischemic heart failure because of decreased coronary flow and impaired microvascular perfusion (MP). The aim of this study was to determine if mechanical left ventricular (LV) unloading with the Impella increases coronary flow and MP in a subacute myocardial infarction.

Methods and Results-—Anterior transmural myocardial infarction (infarct size, 26.0
3.4%) was induced in Yorkshire pigs. At 2 weeks after myocardial infarction, 6 animals underwent mechanical LV unloading by Impella, whereas 4 animals underwent pharmacological LV unloading using sodium nitroprusside for 2 hours. LV unloading with Impella significantly reduced end-diastolic volume (16
11%, P=0.02) and end-diastolic pressure (EDP; 32
23%, P=0.03), resulting in a significant decrease in LV enddiastolic wall stress (EDWS) (infarct: 71.6
14.7 to 43.3
10.8 kdynes/cm2 [P=0.02]; remote: 66.6
20.9 to 40.6
13.3 kdynes/cm2 [P=0.02]). Coronary flow increased immediately and remained elevated after 2 hours in Impella-treated pigs. Compared with the baseline, MP measured by fluorescent microspheres significantly increased within the infarct zone (109
81%, P=0.003), but not in the remote zone. Although sodium nitroprusside effectively reduced LV-EDWS, 2 (50%) of sodium nitroprusside–treated pigs developed profound systemic hypotension. A significant correlation was observed between the infarct MP and EDWS (r2=0.43, P=0.03), suggesting an important role of EDWS in regulating MP during LV unloading in the infarcted myocardium.

Conclusions-—LV unloading using an Impella decreased EDWS and increased infarct MP without hemodynamic decompensation. Mechanical LV unloading is a novel and efficient approach to increase infarct MP in patients with subacute myocardial infarction.

Background-—Delivering therapeutic materials, like stem cells or gene vectors, to the myocardium is difficult in the setting of ischemic heart failure because of decreased coronary flow and impaired microvascular perfusion (MP). The aim of this study was to determine if mechanical left ventricular (LV) unloading with the Impella increases coronary flow and MP in a subacute myocardial infarction.

Methods and Results-—Anterior transmural myocardial infarction (infarct size, 26.0
3.4%) was induced in Yorkshire pigs. At 2 weeks after myocardial infarction, 6 animals underwent mechanical LV unloading by Impella, whereas 4 animals underwent pharmacological LV unloading using sodium nitroprusside for 2 hours. LV unloading with Impella significantly reduced end-diastolic volume (16
11%, P=0.02) and end-diastolic pressure (EDP; 32
23%, P=0.03), resulting in a significant decrease in LV enddiastolic wall stress (EDWS) (infarct: 71.6
14.7 to 43.3
10.8 kdynes/cm2 [P=0.02]; remote: 66.6
20.9 to 40.6
13.3 kdynes/cm2 [P=0.02]). Coronary flow increased immediately and remained elevated after 2 hours in Impella-treated pigs. Compared with the baseline, MP measured by fluorescent microspheres significantly increased within the infarct zone (109
81%, P=0.003), but not in the remote zone. Although sodium nitroprusside effectively reduced LV-EDWS, 2 (50%) of sodium nitroprusside–treated pigs developed profound systemic hypotension. A significant correlation was observed between the infarct MP and EDWS (r2=0.43, P=0.03), suggesting an important role of EDWS in regulating MP during LV unloading in the infarcted myocardium.

Conclusions-—LV unloading using an Impella decreased EDWS and increased infarct MP without hemodynamic decompensation. Mechanical LV unloading is a novel and efficient approach to increase infarct MP in patients with subacute myocardial infarction.

BACKGROUND: Acute myocardial infarction remains a leading cause of chronic heart failure. Excessive myocardial oxygen demand relative to supply is the fundamental mechanism of myocardial infarction. We thus hypothesized that left ventricular (LV) mechanical unloading by the total support of transvascular LV assist device Impella could minimize oxygen
demand, thereby reducing infarct size and preventing subsequent heart failure.

METHODS AND RESULTS: In 20 dogs, we ligated the left anterior descending coronary artery for 180 minutes and then reperfused. We introduced Impella from 60 minutes after the onset of ischemia to 60 minutes after reperfusion. In the partial support group, Impella supported 50% of total cardiac output. In the total support group, systemic flow totally depends on Impella flow. Four weeks after ischemia/reperfusion (I/R), we compared LV function and infarct size among 4 groups: sham (no I/R), I/R (no Impella support), partial support, and total support. Compared with I/R, total support lowered LV end-diastolic pressure (15.0±3.5 versus 4.7±1.7 mm Hg; P<0.001), increased LV end-systolic elastance (4.3±0.8 versus 13.9±5.1 mm Hg/mL; P<0.001), and decreased NT-proBNP (N-terminal pro-B-type natriuretic peptide) level (4081±1123 versus 1773±390 pg/mL; P<0.05). Furthermore, total support markedly  reduced infarct size relative to I/R, whereas partial support decreased infarct size to a lesser extent (I/R, 16.3±2.6; partial support, 8.5±4.3; and total support, 2.1±1.6%; P<0.001).

CONCLUSIONS: LV mechanical unloading by the total support of Impella during the acute phase of myocardial infarction reduced infarct size and prevented subsequent heart failure in dogs.