Percutaneous cardiac support during myocardial infarction drastically reduces mortality: perspectives from a swine model

Abstract

Background/aims: Acute myocardial infarction (AMI) with cardiogenic shock (CS) remains the leading cause of in-hospital death in acute coronary syndromes. In the AMI-CS pig model we tested the efficacy of temporary percutaneous cardiorespiratory assist device (PCRA) in rescuing the failing heart and reducing early mortality.

Methods: In open-chest pigs we induced AMI by proximal left anterior descending coronary artery (LAD) ligation. Eight animals without PCRA (C group) were compared with 12 animals otherwise treated with PCRA (T group), starting approximately at 60 minutes post-occlusion and lasting 120-180 minutes. In 3 animals of the T group, regional myocardial oxygen content was also imaged by two-dimensional near infrared spectroscopy (2D-NIRS) with and without PCRA, before and after LAD reperfusion.

Results: All animals without PCRA died despite unrelenting resuscitation maneuvers (120 minutes average survival time). Conversely, animals treated with PCRA showed a reduction in life-threatening arrhythmia and maintenance of aortic pressure, allowing interruption of PCRA in all cases early in the experiments, with sound hemodynamics at the end of the observation period. During LAD occlusion, NIRS showed severe de-oxygenation of the LAD territory that improved with PCRA. After PCRA suspension and LAD reperfusion, the residual de-oxygenated area proved to be smaller than the initial risk area.

Conclusions: In AMI, PCRA initiated during advanced CS drastically reduced early mortality from 100% to 0% in a 4-5 hour observation period. PCRA promoted oxygenation of the ischemic area during LAD occlusion. Results support the use of PCRA as first line of treatment in AMI-CS, improving myocardial rescue and short-term survival.

Fig. 1

Time (minutes) to death following proximal left anterior descending coronary artery (LAD) occlusion in control group (n = 8). Time 0 corresponds to LAD occlusion. Dark segments (resuscitation) indicate the time-periods spent in repeated manual cardiac massage in an unsuccessful attempt to restore left ventricular systolic pressure. Mortality rate was 100%, average survival time was 60 minutes (max. 125 minutes) without resuscitation and 120 minutes (max. 235 minutes) including resuscitation time.

Fig. 2

Time (minutes) to death following proximal left anterior descending coronary artery (LAD) total occlusion and the application of percutaneous cardiorespiratory assistance (PCRA) in treated group (n = 12). Time 0 corresponds to LAD occlusion. As in Figure 1, resuscitation (cardiac massage) was started when the left ventricle was no longer able to develop pressure. PCRA application restored left ventricle ability to develop pressure and all animals survived during a 205-295-minute observation period. In 3 additional animals of the treated group we performed two-dimensional near infrared spectroscopy (2D-NIRS) imaging of the LAD myocardial territory. In these animals reperfusion of the ischemic area was accomplished by LAD reopening at the end of the experiment.

Fig. 3

Mean ± SD values of left ventricular systolic pressure, left ventricular diastolic pressure and positive and negative dp/dt in treated group during the different phases of the study. Values were obtained before left anterior descending coronary artery (LAD) occlusion (contr) and, in periods free of sustained arrhythmias and relatively far from life-support interventions, 30 ± 15 minutes after LAD occlusion (isch), 30 ± 15 minutes from onset of cardiorespiratory assistance (PCRA) and 10 ± 5 minutes following PCRA discontinuation with LAD still occluded (post-PCRA). The resuscitation period is missing because of the absence, by definition, of developed ventricular pressure during this period.

Fig. 4

2D-NIRS imaging of HbO₂ & MbO₂ content of exposed superficial myocardium. (A). Control condition: RV = right ventricle; LV = left ventricle. Predominant red color indicates heart is well oxygenated. (B). 2-minute left anterior descending coronary artery (LAD) occlusion: the blue area indicates deoxygenated myocardium in the LAD territory and delineates the ‘risk area’. (C). 60 minutes following LAD occlusion, just before the onset of cardiorespiratory assistance: the blue area expands to the anterior right ventricular wall. (D). Following 60 minutes of cardiorespiratory assistance (PCRA) the reduction of de-oxygenation signal in the LAD territory becomes evident. (E). After PCRA discontinuation and immediately after LAD reopening (reperfusion): only mildly oxygenated (green) areas are visible during reactive hyperemia. (F). Final picture at 10 minutes from reperfusion: residual deoxygenated area following 3 hours of LAD occlusion proves to be much smaller than the ‘risk area’ outlined in the initial minutes of ischemia (see frame (B)).