Intracoronary Hypothermia Before Reperfusion to Reduce Reperfusion Injury in Acute Myocardial Infarction: A Novel Hypothesis and Technique

Recent advances in the diagnosis and management of acute myocardial infarction

With the discovery of new biomarkers for the early detection of acute myocardial infarction (AMI), advancements in valid medication, and percutaneous coronary intervention (PCI), the overall prognosis of AMI has improved remarkably. Nevertheless, challenges remain which require more difficult work to overcome. Novel diagnostic and therapeutic techniques include new AMI biomarkers, hypothermia therapy, supersaturated oxygen (SSO 2 ) therapy, targeted anti-inflammatory therapy, targeted angiogenesis therapy, and stem cell therapy. With these novel methods, we believe that the infarction size after AMI will decrease, and myocardial injury-associated ventricular remodeling may be avoided. This review focuses on novel advances in the diagnosis and management of AMI.

Therapeutic Hypothermia in STEMI

In this review article we tried to find an answer to the question, should local coronary hypothermia be a part of the early reperfusion strategy in patients with STEMI to prevent reperfusion injury, no-reflow phenomenon, and to reduce the infarct size and mortality. Hypothermia can save cardiomyocytes if achieved in a timely fashion before reperfusion. Intracoronary hypothermia can be adjunct to PCI by lessening ischemia/reperfusion injury on cardiomyocytes and reduction in infarct size. Reperfusion induced Calcium overload, generation of ROS and subsequent activation of Mitochondrial permeability transition pore (MPT) are major contributors to reperfusion injury. Hypothermia reduces calcium loading of the cell and maintains cellular energy and tissue level glucose which can scavenger ROS. Hypothermia reduces MPT activation and thus reduces infarct size. Systemic cooling trials failed to reduce infarct size, perhaps because the target temperature was not reached fast enough, and it was associated with systemic side effects. The need for rapid induction of hypothermia to <35 °C with the ethical concern of delaying reperfusion while cooling the patient and the inconsistency of endovascular cooling results lead to a belief that endovascular cooling may exceed the acceptable level of invasiveness in the context of other novels cardioprotective, regenerative and reperfusion therapies. Clinical trials showed the safety and feasibility of novel intracoronary hypothermia with rapid induction and maintenance of hypothermia using routine PCI equipment ahead of reperfusion. Two phases of cooling were applied without significant delay in the door to balloon time. Cooling of the coronary artery leads to cooling of its dependant myocardium without affecting adjacent myocardium. Heat transfer occurred by heat conduction during the occlusion phase and heat convention during the reperfusion phase. Fine-tuning of saline temperature and infusion rate helped to improve the protocol. The best duration of hypothermia before and after reperfusion is not known and needs further investigation. A balance between the undoubted cardioprotective effects of hypothermia with iatrogenic prolongation of ischemia time needs to be established. A reduction in infarct size was observed but needs to be validated with large randomized trials. Furthermore, it might be possible to augment the cardioprotective effects of intracoronary hypothermia by combination with other cardioprotective approaches such as antioxidant drugs and afterload reducing agents.

Hypothermia in patients with acute myocardial infarction: a meta-analysis of randomized trials

BACKGROUND

In patients with acute myocardial infarction (MI) receiving percutaneous coronary intervention (PCI), the role of systemic therapeutic hypothermia remains controversial. We sought to investigate the role of systemic therapeutic hypothermia versus standard of care in patients with acute MI treated with PCI.

METHODS

This is a study-level meta-analysis of randomized trials. The primary outcome was all-cause death. The main secondary outcome was infarct size. Other secondary outcomes were recurrent MI, ischemia-driven target vessel revascularization (TVR), major adverse cardiovascular events, and bleeding.

RESULTS

A total of 1012 patients with acute MI receiving a PCI in nine trials (503 randomly assigned to hypothermia and 509 to control) were available for the quantitative synthesis. The weighted median follow-up was 30 days. As compared to controls, patients assigned to hypothermia had similar risk of all-cause death (risk ratio, [95% confidence intervals], 1.25 [0.80; 1.95], p = 0.32), with a trend toward higher risk of ischemia-driven TVR (3.55 [0.80; 15.87], p = 0.09) mostly due to acute or subacute stent thrombosis. Although in the overall cohort, infarct size was comparable between groups (standardized mean difference [95% Confidence intervals], 0.06 [- 0.92; 1.04], p = 0.92), patients effectively achieving the protocol-defined target temperature in the hypothermia group had smaller infarct size as compared to controls (p for interaction = 0.016). Treatment strategies did not differ with respect to the other outcomes.

CONCLUSIONS

As compared to standard of care, systemic therapeutic hypothermia in acute MI patients treated with PCI provided similar mortality with a signal toward more frequent repeat revascularization. Among patients assigned to hypothermia, those effectively achieving the protocol-defined target temperature displayed smaller infarct size.

TRIAL REGISTRATION

PROSPERO, CRD42019138754.

Myocardial tissue salvage is correlated with ischemic border region temperature at reperfusion

OBJECTIVES

Our pilot study investigated the association between region-specific myocardial tissue temperature and tissue salvage using a novel tri-lumen cooling catheter to provide rapid localized cooling directly to the heart in an open-chest porcine model of ischemia-reperfusion.

BACKGROUND

Therapeutic hypothermia remains a promising strategy to limit reperfusion injury following myocardial ischemia.

METHODS

Large swine underwent 60 min of coronary occlusion followed by 3 hr of reperfusion. Prior to inducing ischemia, six temperature probes were placed directly on the heart, monitoring myocardial temperatures in different locations. Hemodynamic parameters and core temperature were also collected. Approximately 15 min prior to reperfusion, the cooling catheter was inserted via femoral artery and the distal tip advanced proximal to the occluded coronary vessel under fluoroscopic guidance. Autologous blood was pulled from the animal via femoral sheath and delivered through the central lumen of the cooling catheter, delivering at 50 ml/min, 27°C at the distal tip. Cooling was continued for an additional 25 min after reperfusion followed by a 5-min controlled rewarming. Hearts were excised and assessed for infarct size per area at risk.

RESULTS

Although cooling catheter performance was consistent throughout the study (38 W), the resulting tissue cooling was not. Our results show a correlation between myocardial tissue salvage and ischemic border region (IBR) temperature at the time of reperfusion (R² = 0.59, p = 0.027). IBR tissue is the tissue located at the boundary between healthy and ischemic tissues.

CONCLUSIONS

Our findings suggest that localized, rapid, short-term myocardial tissue cooling has the potential to limit reperfusion injury in humans.