Very early administration of glucose-insulin-potassium by emergency medical service for acute coronary syndromes: Biological mechanisms for benefit in the IMMEDIATE Trial

An Opportune Time to Consider Glucose-Insulin-Potassium Therapy for Takotsubo Syndrome

This viewpoint takes the position that the management of takotsubo syndrome (TTS) should not wait the elucidation of the pathophysiology of this mysterious malady but should move along the direction currently implemented for acute coronary syndromes (ACS). Accordingly, and since there is a current rekindled interest in the salutary effect of glucose-insulin-potassium (GIK) for the management of acute myocardial infarction, and in general of the broad domain of ACS, it is the opinion of this author that it is an opportune time for the same therapeutic principles, including GIK, applied for the broad domain of suspected ACS (in view of the prospective phase 3 IMMEDIATE-2 trial), to be considered for TTS.

EFFICACY-TO-EFFECTIVENESS CLINICAL TRIALS

Efficacy trials, which assess treatments in optimally selected patients under advantageous conditions for relatively short time periods, are necessary to gain regulatory approval for marketing. In contrast, effectiveness trials, which test treatments across a spectrum of patients in real-world conditions with follow-up periods that match typical treatment regimens, provide critical information on drug effects in those patients who may ultimately receive the treatment. We previously proposed a study design that integrates efficacy and effectiveness trials into a 2-component "efficacy-to-effectiveness (E2E) trial," in which if the initial efficacy trial component is positive, then the trial immediately and seamlessly transitions to the effectiveness trial component. However, we believe that total study duration could be even further shortened by simultaneously addressing efficacy and effectiveness too (EE2). An EE2 trial rigorously demonstrates efficacy, but uses broad inclusion characteristics of effectiveness trials. An example of a study using EE2 design, the IMMEDIATE (Immediate Myocardial Metabolic enhancement During Initial Assessment and Treatment in Emergency Care) trial, is provided.

High pre-ischemic fatty acid levels decrease cardiac recovery in an isolated rat heart model of donation after circulatory death

RATIONALE

Donation after circulatory death (DCD) could improve cardiac graft availability. However, strategies to optimize cardiac graft recovery remain to be established in DCD; these hearts would be expected to be exposed to high levels of circulatory fat immediately prior to the inevitable period of ischemia prior to procurement.

OBJECTIVE

We investigated whether acute exposure to high fat prior to warm, global ischemia affects subsequent hemodynamic and metabolic recovery in an isolated rat heart model of DCD.

METHODS AND RESULTS

Hearts of male Wistar rats underwent 20min baseline perfusion with glucose (11mM) and either high fat (1.2mM palmitate; HF) or no fat (NF), 27min global ischemia (37°C), and 60min reperfusion with glucose only (n=7-8 per group). Hemodynamic recovery was 50% lower in HF vs. NF hearts (34±30% vs. 78±8% (60min reperfusion value of peak systolic pressure*heart rate as percentage of mean baseline); p<0.01). During early reperfusion, glycolysis (0.3±0.3 vs. 0.7±0.3μmol*min^-1*g dry^-1, p<0.05), glucose oxidation (0.1±0.03 vs. 0.4±0.2μmol*min^-1*g dry^-1, p<0.01) and pyruvate dehydrogenase activity (1.8±0.6 vs. 3.6±0.5U*g protein^-1, p<0.01) were significantly reduced in HF vs. NF groups, respectively, while lactate release was significantly greater (1.8±0.9 vs. 0.6±0.2μmol*g wet^-1*min^-1; p<0.05).

CONCLUSIONS

Acute, pre-ischemic exposure to high fat significantly lowers post-ischemic cardiac recovery vs. no fat despite identical reperfusion conditions. These findings support the concept that oxidation of residual fatty acids is rapidly restored upon reperfusion and exacerbates ischemia-reperfusion (IR) injury. Strategies to optimize post-ischemic cardiac recovery should take pre-ischemic fat levels into consideration.

Possible increase in insulin resistance and concealed glucose-coupled potassium-lowering mechanisms during acute coronary syndrome documented by covariance structure analysis

Objective

Although glucose-insulin-potassium (GIK) therapy ought to be beneficial for ischemic heart disease in general, variable outcomes in many clinical trials of GIK in acute coronary syndrome (ACS) had a controversial impact. This study was designed to examine whether “insulin resistance” is involved in ACS and to clarify other potential intrinsic compensatory mechanisms for GIK tolerance through highly statistical procedure.

Methods and results

We compared the degree of insulin resistance during ACS attack and remission phase after treatment in individual patients (n = 104). During ACS, homeostasis model assessment of insulin resistance (HOMA-IR) values were significantly increased (P<0.001), while serum potassium levels were transiently decreased (degree of which was indicated by ΔK) (P<0.001). This finding provides a renewed paradox, as ΔK, a surrogate marker of intrinsic GIK cascade activation, probably reflects the validated glucose metabolism during ischemic attack. Indeed, multiple regression analysis revealed that plasma glucose level during ACS was positively correlated with ΔK (P = 0.026), whereas HOMA-IR had no impact on ΔK. This positive correlation between ΔK and glucose was confirmed by covariance structure analysis with a strong impact (β: 0.398, P = 0.015). Intriguingly, a higher incidence of myocardial infarction relative to unstable angina pectoris, as well as a longer hospitalization period were observed in patients with larger ΔK, indicating that ΔK also reflects disease severity of ACS.

Conclusions

Insulin resistance most likely increases during ACS; however, ΔK was positively correlated with plasma glucose level, which overwhelmed insulin resistance condition. The present study with covariance structure analysis suggests that there are potential endogenous glucose-coupled potassium lowering mechanisms, other than insulin, regulating glucose metabolism during ACS.