A narrative review of intravascular catheters in therapeutic hypothermia

Therapeutic hypothermia (TH) has been regarded as a promising neuroprotective method for acute ischemic stroke (AIS) for decades. During the development of TH, most researchers focused on improving hypothermic benefits by optimizing treatment processes and conditions. Intravenous thrombolysis and endovascular thrombectomy, for instance, have been introduced into AIS treatment. However, the lack of specialized intervention consumables, especially intervention catheter, led to inaccurate and uncontrolled hypothermic temperature, limited the efficacy of TH. In this review, intervention catheters as well as accessory equipment utilized in TH treatment has been summarized. Hopefully, this review may inspire the future development of TH specialized intervention catheter, enhance the outcome of TH, and neuroprotective efficacy in AIS.

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.

Heat transfer analysis of catheters used for localized tissue cooling to attenuate reperfusion injury

Recent revascularization success for ischemic stroke patients using stentrievers has created a new opportunity for therapeutic hypothermia. By using short term localized tissue cooling interventional catheters can be used to reduce reperfusion injury and improve neurological outcomes. Using experimental testing and a well-established heat exchanger design approach, the ɛ-NTU method, this paper examines the cooling performance of commercially available catheters as function of four practical parameters: (1) infusion flow rate, (2) catheter location in the body, (3) catheter configuration and design, and (4) cooling approach. While saline batch cooling outperformed closed-loop autologous blood cooling at all equivalent flow rates in terms of lower delivered temperatures and cooling capacity, hemodilution, systemic and local, remains a concern. For clinicians and engineers this paper provides insights for the selection, design, and operation of commercially available catheters used for localized tissue cooling.

A hemolysis study of an intravascular blood cooling system for localized organ tissue cooling

Therapeutic hypothermia can reduce both ischemic and reperfusion injury arising after strokes and heart attacks. New localized organ cooling systems offer a way to reduce tissue damage more effectively with fewer side effects. To assess initial blood safety of our new organ cooling system, the CoolGuide Cooling System (CCS), we investigated safe operating conditions and configurations from a hemolysis perspective. The CCS consists of a peristaltic pump, a custom-built external heat exchanger, a chiller, biocompatible polyvinyl cellulose (PVC) tubing, and a control console. The CCS cools and circulates autologous blood externally and re-delivers cooled blood to the patient through a conventional catheter inserted directly into the organ at risk. Catheter configurations used included: a 7F guide catheter only, a 7F guide with a 0.038” wire inserted through the center and advanced 2 cm distal to the catheter distal tip, a 6F guide catheter only and a 6F guide with a 0.014” guidewire similarly inserted through the center. Using porcine blood, an in vitro test rig was used to measure the degree of hemolysis generation, defined as the percentage change in free hemoglobin, adjusted for total hemoglobin and hematocrit, between exiting and entering blood. The highest degree of hemolysis generation was 0.11±0.04%, based on the average behavior with a 6F catheter and a 0.014” guidewire configuration at a blood flow rate of approximately 130 mL/min. In terms of average percentage free hemoglobin exiting the system, based on total hemoglobin, the highest value measured was 0.17%±0.03%, using this 6F and 0.014” guidewire configuration. This result is significantly below the most stringent European guideline of 0.8% used for blood storage and transfusion. This study provides initial evidence showing hemolysis generation arising from the CoolGuide Cooling System is likely to be clinically insignificant.

Improved Ease of Use Designs for Rapid Heart Cooling

Mild hypothermia has been shown to reduce heart tissue damage resulting from acute myocardial infarction (AMI). In previous work we developed a trilumen cooling catheter to deliver cooled blood rapidly to the heart during emergency angioplasty. This paper describes two alternative designs that seek to maintain tissue cooling capability and improve “ease of use.” The first design was an autoperfusion design that uses the natural pressure difference between the aorta and the coronary arteries to move blood through the trilumen catheter. The second design used an external cooling system, where blood was cooled externally before being pumped to the heart through a commercially available guide catheter. Heat transfer and pressure drop analyses were performed on each design. Both designs were fabricated and tested in both in vitro and in vivo settings. The autoperfusion design did not meet a cooling capacity target of 20 W. Animal tests, using swine with healthy hearts, showed that the available pressure difference to move blood through the trilumen catheter was approximately 5–10 mmHg. This differential pressure was too low to motivate sufficient blood flow rates and achieve the required cooling capacity. The external cooling system, however, had sufficient cooling capacity and reasonable scalability. Cooling capacity values varied from 14 to 56 W over a flow range of 30–90 ml/min. 20 W and 30 W were achieved at 38 ml/min and 50 ml/min, respectively. Animal testing showed that a cooling capacity of 30 W delivered to the left anterior descending (LAD) and left circumflex arteries (LCX) of a healthy 70 kg swine can reduce heart tissue temperatures rapidly, approximately 3 °C in 5 min in some locations. Core temperatures dropped by less than 0.5 °C during this cooling period. An autoperfusion design was unable to meet the target cooling capacity of 20 W. An external cooling design met the target cooling capacity, providing rapid (1 °C/min) localized heart tissue cooling in a large swine model. Future animal testing work, involving a heart attack model, will investigate if this external cooling design can save heart tissue.