Endothelial activation through brain death?

Excitation and contraction of cardiac muscle and coronary arteries of brain-dead pigs

Excitability and contraction of cardiac muscle from brain-dead donors critically influence the success of heart transplantation. Membrane physiology, Ca²⁺-handling, and force production of cardiac muscle and the contractile properties of coronary arteries were studied in hearts of brain-dead pigs. Cardiac muscle and vascular function after 12 h brain death (decapitation between C2 and C3) were compared with properties of fresh tissue. In both isolated cardiomyocytes (whole-cell patch clamp) and trabecular muscle (conventional microelectrodes), action potential duration was shorter in brain dead, compared to controls. Cellular shortening and Ca²⁺ transients were attenuated in the brain dead, and linked to lower mRNA expression of L-type calcium channels and a slightly lower I_Ca,_L, current, as well as to a lower expression of phospholamban. The current-voltage relationship and the current above the equilibrium potential of the inward K⁺ (I_K1) channel were altered in the brain-dead group, associated with lower mRNA expression of the Kir2.2 channel. Delayed K⁺ currents were detected (I_Kr, I_Ks) and were not different between groups. The transient outward K⁺ current (I_to) was not observed in the pig heart. Coronary arteries exhibited increased contractility and sensitivity to the thromboxane analogue (U46619), and unaltered endothelial relaxation. In conclusion, brain death involves changes in cardiac cellular excitation which might lower contractility after transplantation. Changes in the inward rectifier K⁺ channel can be associated with an increased risk for arrhythmia. Increased reactivity of coronary arteries may lead to increased risk of vascular spasm, although endothelial relaxant function was well preserved.

Peritransplant Cardiometabolic and Mitochondrial Function: The Missing Piece in Donor Heart Dysfunction and Graft Failure

Primary graft dysfunction is an important cause of morbidity and mortality after cardiac transplantation. Donor brain stem death (BSD) is a significant contributor to donor heart dysfunction and primary graft dysfunction. There remain substantial gaps in the mechanistic understanding of peritransplant cardiac dysfunction. One of these gaps is cardiac metabolism and metabolic function. The healthy heart is an "omnivore," capable of utilizing multiple sources of nutrients to fuel its enormous energetic demand. When this fails, metabolic inflexibility leads to myocardial dysfunction. Data have hinted at metabolic disturbance in the BSD donor and subsequent heart transplantation; however, there is limited evidence demonstrating specific metabolic or mitochondrial dysfunction. This review will examine the literature surrounding cardiometabolic and mitochondrial function in the BSD donor, organ preservation, and subsequent cardiac transplantation. A more comprehensive understanding of this subject may then help to identify important cardioprotective strategies to improve the number and quality of donor hearts.

The pathophysiology of chronic graft failure in the cardiac transplant patient

Following cardiac transplantation, many patients develop chronic deterioration of graft function, which may lead to a clinical syndrome similar to native chronic heart failure (CHF). This condition of chronic cardiac graft failure (CGF) may also share pathophysiological processes comparable with that of CHF. However, the unique environment following cardiac transplantation may also contribute with a variety of unique mechanisms, deserved of special attention. This review article discusses the complex pathophysiology of CGF after cardiac transplantation, an important yet neglected condition of transplant medicine.

Brain Death Does Not Change Epicardial Action Potentials and Their Response to Ischemia–Reperfusion in Open-chest Pigs

BACKGROUND

It is debated whether brain death (BD) causes transient functional ischemia. In this investigation we used monophasic action potential (AP) recording during BD as a sensitive means to assess: (i) whether ischemia was present; and (ii) the effect of BD on a subsequent ischemia-reperfusion challenge.

METHODS

In Period 1, BD was induced (BD group, 6 pigs) or not induced (sham maneuver, control [C] group, 6 pigs), and effects were followed for 3 hours. In Period 2, left anterior descending (LAD) coronary artery ligation ischemia was applied for 20 minutes to all hearts, followed by 60-minute reperfusion.

RESULTS

In Period 1, plasma norepinephrine was 3.1-, 6.3- and 5-fold greater in BD than in C at 1, 120 and 180 minutes, respectively, and systolic blood pressure was 26% greater at 1 minute and 35% at 120 minutes. The arteriovenous difference in lactate was similar or lower in BD than in C. In both groups, at all time-points, the action potential recording had a rectangular plateau shape and action potential duration (APD50) had a linear relationship to the cardiac inter-beat (RR) interval (R2 = 0.89 and 0.73, slope = 0.42 +/- 0.02 and 0.46 +/- 0.06 in BD and C, respectively). In Period 2, ischemia caused a similar (50%) APD shortening in BD and C. Restoration of the APD upon reperfusion was complete in both groups.

CONCLUSIONS

Our findings suggest that BD does not cause direct cardiac ischemia and does not change the response of the heart to subsequent ischemia-reperfusion challenge.

Aturdimiento miocárdico neurogénico

The existence of stunned myocardium and reversible myocardial dysfunction is widely described and accepted in patients suffering ischemic heart disease. However, it cannot be exclusive to coronary disease. Classically, the appearance of electrocardiographic changes in the critical neurological disease has been described. However, at present, it seems to be observed that some of these patients with critical neurological disease could have variable grades of myocardial dysfunction, which is generally reversible in the surviving patients. This myocardial dysfunction, which could affect critically ill neurological patients, has traits similar to stunned myocardium generated in coronary patients since: a) it is generally associated to electrocardiographic changes, b) it can be accompanied by segmental contractility disorders and even c) it may be accompanied by a certain increase of cardiac biomarkers. Although its etiopathogeny is unknown, it could be related with the severity of the primary neurological disease. Its prophylaxis and prognosis are also unknown. It could be related with neurogenic edema, with hemodynamic instability, and could also play a very important role in brain death and in organ donation.

Increased cardiac expression of tissue inhibitor of metalloproteinase-1 and tissue inhibitor of metalloproteinase-2 is related to cardiac fibrosis and dysfunction in the chronic pressure-overloaded human heart

BACKGROUND

Alterations in the balance of matrix metalloproteinases (MMPs) and their specific tissue inhibitors (TIMPs) are involved in left ventricular (LV) remodeling. Whether their expression is related to interstitial fibrosis or LV dysfunction in patients with chronic pressure overload-induced LV hypertrophy, however, is unknown.

METHODS AND RESULTS

Therefore, cardiac biopsies were taken in 36 patients with isolated aortic stenosis (AS) and in 29 control patients without LV hypertrophy. Microarray analysis revealed significantly increased mRNA expression of collagen types I, III, and IV and transcripts involved in collagen synthesis, including procollagen endopeptidase and lysine and proline hydroxylases, in AS compared with control patients. Collagen deposition was greater in AS than in control patients and was most pronounced in AS patients with severe diastolic dysfunction. Cardiac mRNA expression of TIMP-1 and TIMP-2 was significantly increased in AS compared with control patients (mRNA transcript levels normalized to GAPDH: TIMP-1, 0.67+/-0.1 in AS versus 0.37+/-0.08 in control patients; TIMP-2, 9.5+/-2.6 in AS versus 1.6+/-0.4 in control patients; P<0.05 for both) but did not differ significantly for MMP-1, -2, or -9. Cardiac TIMP-1 and -2 transcripts were significantly related to the degree of interstitial fibrosis and proportional to diastolic dysfunction in AS patients.

CONCLUSIONS

Cardiac expression of TIMP-1 and TIMP-2 is significantly increased in chronic pressure-overloaded human hearts compared with controls and is related to the degree of interstitial fibrosis.