Pre-emptive conditioning of the ischemic heart

Myocardial viability and microvascular obstruction: role of cardiac magnetic resonance imaging

Established coronary artery disease has a prevalence of 7% in adult Americans, accounting for 16 million people. As morbidity and mortality rates have risen, research efforts to identify the pathophysiologic mechanisms of systolic dysfunction have risen in parallel. The current goal is to develop new therapeutic strategies with the potential to reverse systolic dysfunction in patients with established coronary artery disease. Cardiac magnetic resonance imaging has gained a key role in cardio vascular medicine. We will comment on the potential pivotal role of cardiac magnetic resonance imaging for the assessment of myocardial viability, including hibernating and stunned myocardium and microvascular obstruction.

Preemptive conditioning of the swine heart by H11 kinase/Hsp22 provides cardiac protection through inducible nitric oxide synthase

The second window of ischemic preconditioning (SWOP) provides maximal protection against ischemia through regulation of the inducible nitric oxide synthase (iNOS), yet its application is limited by the inconvenience of the preliminary ischemic stimulus required for prophylaxis. Overexpression of H11 kinase/Hsp22 (Hsp22) in a transgenic mouse model provides cardioprotection against ischemia that is equivalent to that conferred by SWOP. We hypothesized that short-term, prophylactic overexpression of Hsp22 would offer an alternative to SWOP in reducing ischemic damage through a nitric oxide (NO)-dependent mechanism. Adeno-mediated overexpression of Hsp22 was achieved in the area at risk of the left circumflex (Cx) coronary artery in chronically instrumented swine and compared with LacZ controls (n = 5/group). Hsp22-injected myocardium showed an average fourfold increase in Hsp22 protein expression compared with controls and a doubling in iNOS expression (both P < 0.05). Four days after ischemia-reperfusion, regional wall thickening was reduced by 58 ± 2% in the Hsp22 group vs. 82 ± 7% in the LacZ group, and Hsp22 reduced infarct size by 40% (both P < 0.05 vs. LacZ). Treatment with the NOS inhibitor N(G)-nitro-L-arginine (L-NNA) before ischemia suppressed the protection induced by Hsp22. In isolated cardiomyocytes, Hsp22 increased iNOS expression through the transcription factors NF-κB and STAT, the same effectors activated by SWOP, and reduced by 60% H(2)O(2)-mediated apoptosis, which was also abolished by NOS inhibitors. Therefore, short-term, prophylactic conditioning by Hsp22 provides NO-dependent cardioprotection that reproduces the signaling of SWOP, placing Hsp22 as a potential alternative for preemptive treatment of myocardial ischemia.

Cardiac stunning in the clinic: the full picture

Cardiac stunning refers to different dysfunctional levels occurring after an episode of acute ischemia, despite blood flow is near normal or normal. The phenomenon was initially identified in animal models, where it has been very well characterized. After being established in the experimental setting, it remained unclear, whether a similar syndrome occurs in humans. In addition, it remained controversial, whether stunning was of any clinical relevance as it is spontaneously reversible. Hence, many studies continue to focus on the properties and mechanisms of stunning, although therapies seem more relevant for attenuating and treating myocardial ischemia/reperfusion (I/R) injury, i.e. to bridge until recovery. This article reviews the different facets of cardiac stunning, i.e. myocardial, vascular/microvascular/endothelial, metabolic, neural/neuronal, and electrical stunning. This review also displays where these facets exist and which clinical relevance they might have. Particular attention is directed to the different therapeutic interventions that the various facets of this I/R-induced cardiac injury might require. A final outlook considers possible alternatives to further reduce the detrimental consequences of brief episodes of ischemia and reperfusion.