Alden H. Harken

Preconditioning of Isolated Rat Heart Is Mediated by Protein Kinase C

Catecholamines have been implicated in the phenomenon of ischemic preconditioning. We have previously demonstrated that ischemic preconditioning against postischemic mechanical dysfunction in the isolated rat heart is mediated by the alpha 1-adrenergic receptor. The purpose of this study was to delineate the signal transduction of preconditioning distal to the alpha 1-adrenergic receptor. Our results suggest that (1) transient ischemia and alpha 1-adrenergic receptor-induced preconditioning is inhibited by protein kinase C (PKC) antagonists, (2) functional protection against global ischemia/reperfusion injury can be induced by infusion of diacylglycerol, the second messenger of the alpha 1-adrenergic pathway, and (3) transient ischemia and alpha 1-adrenergic preconditioning are both characterized by similar translocation of PKC-delta to the sarcolemma of myocardium. These findings suggest that PKC is an effector of preconditioning in the isolated rat heart.

Preconditioning against myocardial dysfunction after ischemia and reperfusion by an alpha 1-adrenergic mechanism.

Preconditioning may find ready applicability in humans facing scheduled global cardiac ischemia-reperfusion (IR) during bypass or transplantation, where such a maneuver is feasible before arrest. Our objective was to delineate and exploit the endogenous preconditioning mechanism triggered by transient ischemia (TI) and thereby attenuate myocardial postischemic mechanical dysfunction by clinically acceptable means. Preconditioning by 2 minutes of TI followed by 10 minutes of normal perfusion protected isolated rat left ventricle function assessed after 20 minutes of global, 37 degrees C ischemia and 40 minutes of reperfusion. Final recovery of developed pressure (DP) was improved (91.5 +/- 1.9% of equilibration DP versus unconditioned IR control, 57.4 +/- 2.4%, P < .01) and was accompanied by increased contractility (+/- dP/dt). Norepinephrine release increased after TI, and reserpine pretreatment abolished TI preconditioning. This suggests that endogenous norepinephrine mediates functional preconditioning in rat. Brief pretreatment (2 minutes) with exogenous norepinephrine reproduced the protection (89.1 +/- 1.4%) of postischemic function. Functional protection persisted after the hemodynamic effects had resolved. Norepinephrine-induced preconditioning was simulated by phenylephrine and blocked by alpha 1-adrenergic receptor antagonist. TI preconditioning was similarly lost after selective alpha 1-adrenergic receptor blockade. We conclude that transient ischemic preconditioning is mediated by the sympathetic neurotransmitter release and alpha 1-adrenergic receptor stimulation. Although the postreceptor mechanism remains unclear, functional protection after IR does not seem related to the magnitude of ATP depletion and elevation of resting pressure during ischemia. Rather, the endogenous mechanisms facilitate both recovery of mechanical function and ATP repletion during reperfusion.

Endocardial excision: a new surgical technique for the treatment of recurrent ventricular tachycardia.

SUMMARYTwelve patients with medically refractory ventricular tachycardia secondary to ischemic heart disease underwent surgery for cure of their arrhythmia. Preoperatively, the tachycardia could be reproducibly initiated and terminated in each patient by programmed stimulation. In all instances, intraoperative mapping localized the tachycardia to the border of the aneurysm, a site not routinely resected during aneurysmectomy. In nine instances, the area of origin involved the septum. During bypass the tachycardia could still be induced after standard aneurysmectomy or ventriculotomy in 11 of 12 patients. On the basis of intraoperative mapping, resection of endocardium in the area of origin (25–40% the circumference of the aneurysmectomy) up to normal muscle was performed. In one patient without a discrete aneurysm, endocardial excision alone through a ventriculotomy was performed. There was one operative death due to cardiogenic shock (preoperative ejection fraction 5%) and one late death due to rupture of a mycotic aneurysm in the pulmonary artery. Before discharge, all patients underwent a repeat electrophysiologic study off antiarrhythmic agents and in none could ventricular tachycardia be initiated. Hemodynamic and angiographic catheterization showed improved hemodynamics and ejection fractions in all. The 10 survivors remained free of sustained ventricular tachycardia for 9–20 months, with one late nonarrhythmic death.

Relation Between Late Potentials on the Body Surface and Directly Recorded Fragmented Electrograms in patients With Ventricular Tachycardia

The relation between low-amplitude, late potentials on the body surface and directly recorded electrograms in 8 patients with and 11 patients without ventricular tachycardia (VT) was studied. Bipolar X,Y,Z leads were signal-averaged and filtered with a digital technique. All patients had catheter endocardial left ventricular maps. The VT group had medically intractable VT and an endocardial excision was performed for control of VT. Before bypass, epicardial maps were obtained in the operating room. All studies were performed during normal sinus rhythm. Four patients without VT, each with a previous myocardial infarction, had fragmented endocardial electrograms recorded at 2.0 +/- 1.2 sites. The latest electrogram for each patient ended 87 +/- 8 ms after QRS onset, within the high-amplitude portion of the filtered QRS complex. All patients with VT had fragmented electrograms recorded at 6.1 +/- 3.1 sites/patient. Eighty-eight percent of the fragmented electrograms were endocardial. The latest fragmented electrogram for each patient ended 161 +/- 43 ms after QRS onset, significantly later than the fragmented electrograms from the patients without VT (p = 0.002). Six VT patients had low-amplitude, late potentials at the end of the filtered QRS complex. In these patients, the last 40 ms of the filtered QRS complex contained a higher proportion of fragmented electrograms compared with earlier segments of the QRS complex (68% versus 27%, p less than 0.001). Two patients with VT did not have late potentials. One patient with left bundle branch block had delayed left ventricular epicardial activation which masked the fragmented electrograms. The other had fragmented electrograms of brief duration which ended 80 +/- 12 ms after QRS onset, during the time of normal ventricular activation. It is concluded that the late potential corresponds to delayed, fragmented electrographic activity. Failure to record a late potential may arise from delayed ventricular activation at other sites from bundle branch block or fragmented electrograms of a brief duration.

Tumor necrosis factor-alpha and interleukin-1 beta synergistically depress human myocardial function

OBJECTIVE Proinflammatory cytokines such as tumor necrosis factor (TNF)-alpha and interleukin (IL)-1beta have been implicated in the pathogenesis of myocardial dysfunction in ischemia-reperfusion injury, sepsis, chronic heart failure, viral myocarditis, and cardiac allograft rejection. Although circulating TNF-alpha and IL-1beta are both often elevated in septic shock, it remains unknown whether TNF-alpha or IL-1beta are the factors induced during sepsis that directly depress human myocardial function, and if so, whether the combination synergistically depresses myocardial function. Furthermore, the mechanism(s) by which these cytokines induce human myocardial depression remain unknown. We hypothesized the following: a) TNF-alpha and IL-1beta directly depress human myocardial function; b) together, TNF-alpha and IL-1beta act synergistically to depress human myocardial function; and c) inhibition of ceramidase or nitric oxide synthase attenuates myocardial depression induced by TNF-alpha or IL-1beta by limiting proximal cytokine signaling or production of myocardial nitric oxide (NO). DESIGN Prospective, randomized, controlled study. SETTING Experimental laboratory in a university hospital. SUBJECTS Freshly obtained human myocardial trabeculae. INTERVENTIONS Human atrial trabeculae were obtained at the time of cardiac surgery, suspended in organ baths, and field simulated at 1 Hz, and the developed force was recorded. After a 90-min equilibration, TNF-alpha (1.25, 12.5, 125, or 250 pg/mL for 20 mins), IL-1beta (6.25, 12.5, 50, or 200 pg/mL for 20 mins), or TNF-alpha (1.25 pg/mL) plus IL-1beta (6.25 pg/mL) were added to the bath, and function was measured for the subsequent 100 mins after the 20-min exposure. To assess the roles of the sphingomyelin and NO pathways in TNF-alpha and IL-1beta cross-signaling, the ceramidase inhibitor N-oleoyl ethanolamine (1 microM) or the NO synthase inhibitor N(G)-monomethyl-L-arginine (10 microM) was added before TNF-alpha (125 pg/mL) or IL-1beta (50 pg/mL). MEASUREMENTS AND MAIN RESULTS TNF-alpha and IL-1beta each depressed human myocardial function in a dose-dependent fashion (maximally depressing to 16.2 + 1.9% baseline developed force for TNF-alpha and 25.7 + 6.3% baseline developed force for IL-1beta), affecting systolic relatively more than diastolic performance (each p < .05). However, when combined, TNF-alpha and IL-1beta at concentrations that did not individually result in depression (p > .05 vs. control) resulted in contractile depression (p < .05 vs. control). Inhibition of myocardial sphingosine or NO release abolished the myocardial depressive effects of either TNF-alpha or IL-1beta. CONCLUSIONS TNF-alpha and IL-1beta separately and synergistically depress human myocardial function. Sphingosine likely participates in the TNF-alpha and IL-1beta signal leading to human myocardial functional depression. Therapeutic strategies to reduce production or signaling of either TNF-alpha or IL-1beta may limit myocardial dysfunction in sepsis.

Oral Sulfonylurea Hypoglycemic Agents Prevent Ischemic Preconditioning in Human Myocardium Two Paradoxes Revisited

BACKGROUND Patients receiving oral hypoglycemic agents for diabetes mellitus are at increased risk of cardiovascular mortality. Oral hypoglycemic agents are inhibitors of the ATP-sensitive potassium (KATP) channel. Ischemic preconditioning is mediated by KATP channel activation. We therefore hypothesized that myocardium from patients taking long-term oral hypoglycemic agents would be resistant to the protection by ischemic preconditioning. METHODS AND RESULTS Isolated human right atrial trabeculae were suspended in an organ bath at 37 degrees C, with field stimulation at 1 Hz. Control trabeculae were then subjected to 45 minutes of simulated ischemia (hypoxic, glucose-free buffer with pacing at 3 Hz) and 120 minutes of reperfusion. Ischemic preconditioned (IPC) trabeculae from patients without oral hypoglycemic therapy and from patients taking insulin (Ins+IPC) were given 5 minutes of simulated ischemia before this injury. Trabeculae (Oral Hypo+IPC) were obtained from patients taking long-term oral hypoglycemic agents and were also exposed to 5 minutes of simulated ischemia before this injury. Developed force (DF) was recorded. Recovery of DF relative to preischemic values was 28 +/- 4% in control trabeculae, whereas IPC trabeculae showed 52 +/- 5% recovery (P < .05 versus control). In patients receiving long-term oral hypoglycemic agents (Oral Hypo+IPC), recovery of DF was 27 +/- 3%, but in trabeculae from insulin-treated patients (Ins+IPC), it was 45 +/- 6%. CONCLUSIONS Human myocardium from patients without long-term exposure to oral hypoglycemic agents is functionally protected by preconditioning. Long-term oral hypoglycemic intake blocks the protection by preconditioning. These data suggest that ischemic preconditioning in human myocardium relies on KATP channels, and long-term inhibition of KATP channels with oral hypoglycemic agents may explain the excess cardiovascular mortality in these patients.

Early kidney TNF-α expression mediates neutrophil infiltration and injury after renal ischemia-reperfusion

The purpose of this study was to determine whether isolated renal ischemia and reperfusion (I/R) induces renal tumor necrosis factor (TNF) mRNA production, TNF protein expression, or TNF bioactivity and, if so, whether local/early TNF production acts as mediator of ischemia-induced, neutrophil-mediated renal injury. After rats were anesthetized, varying periods of renal ischemia, with or without reperfusion, were induced. Kidney mRNA content (RT-PCR), TNF protein expression (ELISA), TNF bioactivity (WEHI-164 cell clone cytotoxicity assay), and neutrophil infiltration [myeloperoxidase (MPO) assay] were determined. In other animals, renal MPO and serum creatinine were assessed after TNF was neutralized [binding protein (TNF-BP)]. Thirty minutes of ischemia induced renal TNF mRNA. TNF protein expression and bioactivity peaked after 1 h ischemia and 2 h reperfusion, whereas neutrophil infiltration peaked at 4 h reperfusion. TNF-BP neutralized TNF bioactivity, reduced neutrophil infiltration, and protected postischemic function. These results constitute the initial demonstration that 1) early renal tissue TNF expression contributes to neutrophil infiltration and injury after I/R and 2) TNF-BP may offer a new adjunctive therapy in renal preservation prior to planned ischemic insults.The purpose of this study was to determine whether isolated renal ischemia and reperfusion (I/R) induces renal tumor necrosis factor (TNF) mRNA production, TNF protein expression, or TNF bioactivity and, if so, whether local/early TNF production acts as mediator of ischemia-induced, neutrophil-mediated renal injury. After rats were anesthetized, varying periods of renal ischemia, with or without reperfusion, were induced. Kidney mRNA content (RT-PCR), TNF protein expression (ELISA), TNF bioactivity (WEHI-164 cell clone cytotoxicity assay), and neutrophil infiltration [myeloperoxidase (MPO) assay] were determined. In other animals, renal MPO and serum creatinine were assessed after TNF was neutralized [binding protein (TNF-BP)]. Thirty minutes of ischemia induced renal TNF mRNA. TNF protein expression and bioactivity peaked after 1 h ischemia and 2 h reperfusion, whereas neutrophil infiltration peaked at 4 h reperfusion. TNF-BP neutralized TNF bioactivity, reduced neutrophil infiltration, and protected postischemic function. These results constitute the initial demonstration that 1) early renal tissue TNF expression contributes to neutrophil infiltration and injury after I/R and 2) TNF-BP may offer a new adjunctive therapy in renal preservation prior to planned ischemic insults.

Ventricular Resection Guided by Epicardial and Endocardial Mapping for Treatment of Recurrent Ventricular Tachycardia

Recurrent, medically refractory ventricular tachycardia is usually associated with ventricular aneurysms after myocardial infarction, but aneurysmectomy alone has not been consistently effective in abolishing this dangerous arrhythmia. Therefore, we have used endocardial and epicardial mapping during induced ventricular tachycardia in 30 consecutive patients to identify the probable site where arrhythmia originated in the endocardial tissue. Complete resection of the site was possible in 27 patients, and partial resection in three. In addition aneurysmectomy was performed in 27 patients, and coronary-bypass grafting in 21. There were two operative and three late nonarrhythmic deaths. None of the 25 surviving patients have had ventricular tachycardia during follow-up of four to 28 months; three patients, who had incomplete resections, have required antiarrhythmic drugs. We conclude that surgical therapy of recurrent ventricular tachycardia can be improved through identification of the endocardial origin of the arrhythmia followed by appropriately guided resection.

The Automatic Implantable Cardioverter-Defibrillator: Efficacy, Complications, and Device Failures

Twenty-six patients with refractory ventricular arrhythmias received the automatic implantable cardioverter-defibrillator. A patch lead only was placed during arrhythmia surgery in 7 other patients. During 13 +/- 6 (SD) months, the device discharged in 10 patients because of a sustained ventricular arrhythmia. No sudden deaths occurred. There were 31 complications in 17 patients, including postoperative refractory heart failure, coronary artery erosion, subclavian vein thrombosis, postoperative stroke after conversion of atrial fibrillation, atelectasis with pneumonia, symptomatic pleural effusions, and infection at the generator site. The cardioverter-defibrillator discharged in 9 asymptomatic patients, failed to terminate ventricular fibrillation during postoperative testing in 3 patients, and had premature battery failure in 4 patients. Tachycardia slowing during chronic amiodarone therapy and unipolar ventricular pacing during ventricular fibrillation precluded or delayed arrhythmia sensing. Thus, the cardioverter-defibrillator can be life saving, but its potential complications and interactions with antiarrhythmic drugs and pacemakers must be considered at patient selection.

REVIEW ARTICLE: THE ROLE OF TUMOR NECROSIS FACTOR IN RENAL ISCHEMIA-REPERFUSION INJURY

Renal ischemia-reperfusion injury induces a cascade of events leading to cellular damage and organ dysfunction. Tumor necrosis factor-alpha (TNF), a potent proinflammatory cytokine, is released from the kidney in response to, and has been implicated in the pathogenesis of, renal ischemia-reperfusion injury. TNF induces glomerular fibrin deposition, cellular infiltration and vasoconstriction, leading to a reduction in glomerular filtration rate (GFR). The signaling cascade through which renal ischemia-reperfusion induces TNF production is beginning to be elucidated. Oxidants released following reperfusion activate p38 mitogen activated protein kinase (p38 MAP kinase) and the TNF transcription factor, NFkappaB, leading to subsequent TNF synthesis. In a positive feedback, proinflammatory fashion, binding of TNF to specific TNF membrane receptors can reactivate NFkappaB. This provides a mechanism by which TNF can upregulate its own expression as well as facilitate the expression of other genes pivotal to the inflammatory response. TNF receptor binding can also induce renal cell apoptosis, the major form of cell death associated with renal ischemia-reperfusion injury. Anti-TNF strategies targeting p38 MAP kinase, NFkappaB, and TNF itself are being investigated as methods of attenuating renal ischemic injury. The control of TNF production and activity represents a realistic goal for clinical medicine.