Previous angina alters in-hospital outcome in TIMI 4. A clinical correlate to preconditioning?

Association of preceding angina with in-hospital life-threatening ventricular tachyarrhythmias and late potentials in patients with a first acute myocardial infarction

We studied 140 patients with a first acute myocardial infarction to examine the effect of preceding angina as a marker of ischemic preconditioning on clinical ventricular arrhythmias and late potentials. Preceding angina was defined as the presence of ischemic chest pain within 24 hours before onset of myocardial infarction lasting no longer than 30 minutes and seen three or more times per day or at rest. Clinical features, angiographic findings, and late potentials were compared between patients with and without preceding angina. Thirty-four (24%) patients had preceding angina. Although the incidence of life-threatening ventricular tachyarrhythmias significantly differed (p = 0.0219), other clinical findings, including presence of late potentials, were not different between the two groups. Of 14 patients with life-threatening ventricular tachyarrhythmias, five events were considered as reperfusion arrhythmias. In patients who had successful reperfusion therapy, the incidence of life-threatening ventricular tachyarrhythmias had a tendency to be lower in patients with preceding angina than in those without preceding angina (p = 0.0586). Severe angina within 24 hours of onset of acute myocardial infarction is suggested to reduce occurrence of life-threatening ventricular tachyarrhythmias mainly associated with reperfusion during hospitalization.

Clinical, angiographic and hemodynamic predictors of recruitable collateral flow assessed during balloon angioplasty coronary occlusion

OBJECTIVES

We sought to determine the predictive value of factors influencing coronary collateral vascular responses in humans.

BACKGROUND

There is limited information on the factors responsible for coronary collateral vascular development, despite the protective effect of collateral vessels in ischemic syndromes.

METHODS

Angiography of the contralateral artery was performed during balloon coronary occlusion in 105 patients with single-vessel disease (left anterior descending coronary artery in 69 patients, left circumflex coronary artery in 4 patients, right coronary artery in 32 patients) and normal left ventricular function. Collateral vessels were graded according to the classification of Rentrop. The relative collateral vascular resistance was calculated in a subgroup of 34 patients by means of aortic pressure, coronary wedge pressure and collateral flow, defined as the transient increase of coronary blood flow velocity of the contralateral artery during balloon coronary occlusion. Ischemia during coronary occlusion was evaluated by the ST segment shift (mV) in a 12-lead electrocardiogram (ECG).

RESULTS

A multivariate logistic analysis of clinical and angiographic variables revealed duration of angina (> or = 3 months, p < 0.0001), lesion severity (> or = 75% diameter stenosis, p < 0.0001) and proximal lesion location (p = 0.02) as independent factors positively associated with recruitability of collateral vessels, whereas the use of nitrates exerted an independent negative effect (p = 0.01). The regression equation yielded an overall predictive accuracy of 80%. The presence of recruitable collateral vessels during coronary occlusion resulted in a higher coronary wedge/aortic pressure ratio (mean [+/- SD] 0.35 +/- 0.13 vs. 0.27 +/- 0.12, p < 0.005), a lower relative collateral vascular resistance (6.7 +/- 7.4 vs. 21.3 +/- 10, p < 0.001) and a reduction of ECG signs of ischemia (0.14 +/- 0.19 vs. 0.38 +/- 0.33 mV, p < 0.001). The relative collateral vascular resistance was the best predictor for recruitability of collateral vessels compared with the other variables related to collateral vascular growth (p < 0.05).

CONCLUSIONS

Clinical and angiographic variables predict recruitability of collateral vessels with an 80% overall accuracy. These findings are important for risk stratification of patients undergoing interventions for ischemic coronary syndromes.

Improvement in ischemic parameters during repeated exercise testing: a possible model for myocardial preconditioning

Repeated short episodes of coronary occlusion in experimental animals, and in humans during balloon angioplasty, cause myocardial preconditioning. This study examines whether myocardial ischemia induced by repeated exercise testing can reduce the extent of ischemia induced by subsequent exercise tests. Twenty-six patients with positive stress tests underwent 3 treadmill exercise tests at 30-minute intervals. Two additional tests were performed on each of the previous 2 days in order to eliminate and/or reduce the training effect. All 3 exercise tests were of similar work load. In spite of that, total ischemic time was markedly shortened from 633 to 399 seconds (p <0.0001) as well as the recovery time from 259 to 126 seconds (p <0.0001) between the first and the second tests. There was no further improvement on the third test. Time to 1-mm ST depression was prolonged from 487 to 593 seconds (p = 0.004) and double product at 1-mm ST depression was increased in the second test from 20,322 to 22,325 mm Hg/second (p = 0.008), implying a higher ischemic threshold. An improvement of > or = 10% in < or = 1 ischemic parameter was observed in 25 of the 26 patients and in > or = 2 of the ischemic parameters in 76% of the patients. Improvement in ischemic parameters develops during repeated exercise induced ischemia in most patients. We suggest that this phenomenon, which was previously known as "warm up," is the clinical counterpart of myocardial preconditioning which develops not only during ischemia caused by reduction in coronary flow, but also during demand-induced ischemia.

Pharmacologic myocardial protection during percutaneous transluminal coronary angioplasty by intracoronary application of dipyridamole: impact on hemodynamic function and left ventricular performance

OBJECTIVES

The aim of this study was to investigate whether intracoronary infusion of dipyridamole represents a suitable tool for preventing deterioration of left ventricular performance and hemodynamic function during percutaneous transluminal coronary angioplasty (PTCA).

BACKGROUND

Coronary angioplasty represents a suitable model for establishing myocardial ischemia in humans. Balloon inflation is usually accompanied by significant deterioration in left ventricular systolic and diastolic properties. A brief episode of ischemia followed by reperfusion, termed preconditioning, has been identified as a mechanism for rendering the myocardium more resistant to ischemia. Adenosine is considered an important mediator of preconditioning. Dipyridamole is an important drug that interferes with myocardial adenosine metabolism by inhibiting its cellular reuptake.

METHODS

In 20 patients undergoing elective coronary angioplasty of a major vessel, assessment of angiographic left ventricular performance and hemodynamic variables was performed before, during and after PTCA. Patients were randomly allocated to pretreatment with intracoronary infusion of dipyridamole before percutaneous transluminal coronary angioplasty (10 patients) or conventional pretreatment without dipyridamole (10 patients).

RESULTS

Dipyridamole pretreatment resulted in significant preservation of systolic and diastolic left ventricular performance during percutaneous transluminal coronary angioplasty, as documented by an unaffected global ejection fraction (vs. a deterioration of 29.2% with conventional pretreatment, p < 0.01) and an increment in diastolic stiffness of only 12.7% (vs. an increment of 57.3% with conventional pretreatment, p < 0.01). Apart from one instance of coronary steal phenomenon, no significant side effects of dipyridamole infusion could be detected.

CONCLUSIONS

It is concluded that intracoronary application of dipyridamole may result in the induction of myocardial preconditioning by improving systolic and diastolic ventricular performance during percutaneous transluminal coronary angioplasty, thereby potentially reducing the risk of the angioplasty procedure.

The slowing of ischemic energy demand in preconditioned myocardium

One or several brief episodes of myocardial ischemia (ischemic preconditioning; IP) rapidly induces tolerance to a later ischemic challenge. This endogenous cardioprotective effect is characterized by a slower onset of cell death. A key feature and probable proximate mechanism of IP is reduced ischemic energy demand which is evident by slower use of ATP and slower accumulation of ischemic catabolites. Several mechanisms for IP and the associated metabolic slowing have been studied: The mitochondrial ATPase is a major cause of ATP hydrolysis in ischemic myocardium but slower ATP depletion in preconditioned myocardium is not due to persistent inhibition of this ATPase. Brief episodes of ischemia in dogs induce stunning as well as IP. Stunning, however, is neither necessary nor sufficient to establish the protective effects of IP. Release of norepinephrine from adrenergic cardiac nerves causes beta adrenergic receptor-mediated stimulation of adenylate cyclase, which stimulates energy-dependent processes. However, IP in dogs that were depleted of catecholamines by pretreatment with reserpine was less effective than IP in control hearts. Thus, an antiadrenergic mechanism does not fully account for the preconditioned state. Another proposed mechanism involves earlier or more complete opening of ATP-sensitive potassium (KATP+) channels. Which of these (or other) pathways mediate the energy sparing effects of ischemic preconditioning remains unknown.

Delayed protection of the ischemic heart--from pathophysiology to therapeutic applications

Preconditioning the heart with brief episodes of ischemia paradoxically increases its resistance to subsequent ischemic episodes, and markedly limits infarct size. Although preconditioning is now considered as the most powerful antiischemic intervention known, its beneficial effects are short-lived since they are lost if the reperfusion period after preconditioning is extended past 2-3 h. There is, however, some evidence of a delayed phase of protection, manifest 24 h after the initial preconditioning stimulus, associated with a decrease in infarct size, a prevention of postischemic contractile dysfunction (stunning) and a reduction in endothelial injury. The delayed beneficial effects of preconditioning resemble those induced by prior heat stress, and might be related to the expression of stress proteins (heat shock proteins or HSP). Evidence for a role of HSP derives from observations showing that brief ischemia is a potent stimulus for HSP expression. Moreover, transfection of isolated cells with HSP or overexpression of HSP in transgenic mice renders the myocytes more resistant to ischemia. Once produced, HSP are believed to facilitate protein synthesis, stabilize newly formed proteins and repair denatured ones. Alternatively, delayed preconditioning may be mediated by antioxidant enzymes such as superoxide dismutase or catalase, which are also upregulated by ischemia and this could lead to a lesser production of oxygen-derived free radicals during reperfusion. Indeed, in isolated myocytes, prevention of hypoxia-induced expression of superoxide dismutase (using an antisense oligonucleotide) abolished the delayed protective effect of preconditioning. Importantly, recent in vivo evidence suggests that the delayed protection may be mediated by adenosine, through activation of A1-receptors, and by stimulation of protein kinase C. Finally, although the exact mechanisms by which preconditioning induces delayed protection are still mostly unknown, the fact that the expression of protective proteins such as HSP can be induced by many other means than ischemia suggests that it is possible to pharmacologically stimulate this expression and thus possibly mimic the endogenous protective pathway. This could lead to the development of new pharmacological interventions which induce delayed myocardial protection in clinical situations such as angioplasty, coronary bypass surgery or even in patients at high risk of infarction.

Intramyocardial infusion of tool drugs for the study of molecular mechanisms in ischemic preconditioning

Many of the new tool drugs useful for the study of molecular mechanisms of ischemic preconditioning (IP) are very valuable in in vitro systems but produce undesired side-effects after systemic injection in intact animals that limit their applicability. Our aim was to develop an experimental in vivo model that allows the use of said drugs in sufficiently high local concentrations, but avoiding at the same time the systemic side-effects. Several techniques were combined to study regional damage or protection as a result of local drug infusion such as nuclear staining, NADH fluorescence, fluorescent microspheres and tetrazolium salts. In open-chest pigs, the intramyocardial infusion (20 microliters/min) of the adenosine A1-receptor agonist N6-cyclohexyladenosine (0.3 mmol) for 10 min prior to a 60-min LAD-occlusion and 120-min reperfusion mimicked IP by exerting a local protection (n = 9, p < 0.001). Krebs-Henseleit buffer (negative control) was without protective effect. IP's cardioprotection was locally prevented by the intramyocardial application of the adenosine A1-receptor antagonist cyclopentyltheophylline (1 mmol, infused during IP; n = 6, p < 0.001) but not by KHB. The protein kinase C (PKC)-inhibitors staurosporine (100 nmol, n = 6) or bisindolylmaleimide (BIS, 25 mumol, n = 9) did not prevent IP locally. The PKC activator phorbol myristate acetate (PMA, 1 mumol, n = 6) was ineffective in preventing ischemic injury and increased the amount of necrosis in IP, whereas BIS exerted a local myocardial protection (n = 9, p < 0.001). In conclusion, the new model of intramyocardial infusion appears to be useful for the investigation of IP's signal transduction. Our data support the role of the adenosine A1-receptor in IP, but suggest that inhibition instead of activation of PKC may protect ischemic myocardium from infarction.

Cardiac preconditioning with calcium: clinically accessible myocardial protection

Cardiac preconditioning is mediated by protein kinase C. Although endogenous calcium is a potent stimulus of protein kinase C, it remains unknown whether preischemic administration of exogenous calcium can induce protein kinase C-mediated myocardial protection against ischemia-reperfusion injury. To study this, calcium chloride was administered retrogradely through the aorta at a rate 5 nmol/min for 2 minutes to isolated perfused rat hearts 10 minutes before a 20-minute ischemia and 40-minute reperfusion insult. Calcium-mediated cardioadaptation was then linked to protein kinase C by means of the protein kinase C inhibitor chelerythrine (20 mumol.L-1.2 min-1). To determine whether exogenous calcium administration induces protein kinase C translocation and activation, immunohistochemical staining for the calcium-dependent protein kinase C isoform alpha was performed on adjacent 5 microns myocardial sections with and without calcium chloride treatment. Results indicated that preischemic calcium chloride administration improved myocardial functional recovery, as determined by enhanced developed pressure, improved coronary flow, reduced end-diastolic pressure, and decreased creatine kinase leakage during reperfusion. Beneficial effects of calcium chloride were eliminated by concurrent protein kinase C inhibition. Immunohistochemical staining for the alpha isoform of protein kinase C demonstrated that calcium chloride induces translocation of this isoform from the cytoplasm to the sarcolemma, indicating that exogenous calcium administration activates this isoform. These results suggest that calcium chloride, a safe and routinely administered agent, can induce protein kinase C-mediated cardiac preconditioning. Calcium-induced cardioadaptation to ischemia-reperfusion injury may be promising as a clinically feasible therapy before planned ischemic events such as cardiac allograft preservation and elective cardiac operations.

Distortion of the terminal portion of the QRS on the admission electrocardiogram in acute myocardial infarction and correlation with infarct size and long-term prognosis (Thrombolysis in Myocardial Infarction 4 Trial)

Previous studies have shown an association between distortion of the terminal portion of the QRS (QRS[+] pattern: emergence of the J point > or = 50%. of the R wave in leads with qR configuration or disappearance of the S wave in leads with an Rs configuration) on admission and in-hospital mortality in acute myocardial infarction (AMI). However, the mechanism for this association is not known. We assessed the relation between QRS(+) pattern and coronary angiographic findings, infarct size, and long-term prognosis in the Thrombolysis In Myocardial Infarction 4 trial. Patients were allocated into 2 groups based on the presence (QRS[+], n = 85) or absence (QRS[-], n = 293) of QRS distortion. The QRS(+) patients were older (mean +/- SD: 61.1 +/- 10.6 vs 57.5 +/- 10.6 years, p = 0.004), had more anterior AMI (49% vs 37%, p = 0.04), and less previous angina (42% vs 54%, p = 0.05). QRS(+) patients had larger infarct size as assessed by creatine kinase release over 24 hours (209 +/- 147 vs 155 +/- 129, p = 0.003), and predischarge sestamibi (MIBI) defect (17.9 +/- 15.9% vs 11.2 +/- 13.4%, p <0.001). When adjusting for difference in baseline characteristics, p values for the differences in 24-hour creatine kinase release were 0.03 and 0.64 for anterior and nonanterior AMI, respectively, and for MIBI defect size 0.03 and 0.02, respectively. One-year mortality (18% vs 6%, p = 0.03) was higher and the weighted end point of death, reinfarction, heart failure, or left ventricular ejection fraction <40% (0.33 +/- 0.37 vs 0.24 +/- 0.32, p = 0. 13), tended to be higher in the anterior AMI patients with QRS(+). No difference in clinical outcome was found in patients with non-anterior AMI. These findings suggest that this simple electrocardiographic definition of presence of QRS(+) pattern on admission may provide an early estimation of infarct size and long-term prognosis, especially in anterior AMI.

The obligate role of protein kinase C in mediating clinically accessible cardiac preconditioning

BACKGROUND

Cardiac preconditioning is an adaptation of cardiomyocytes that promotes tolerance to a subsequent ischemic insult. Adenosine receptor signaling is proposed as a mediator of preconditioning, but its mechanism of protection remains unknown. We hypothesized that protection against hypoxia-reoxygenation (H/R) injury could be conferred in a rat ventricle by adenosine-mediated protein kinase C (PKC) activation and that adenosine-mediated cardioprotection could be extended to human ventricular muscle.

METHODS

Isolated rat and human ventricular muscle (VM) strips were subjected to 30 minutes of hypoxia and 60 minutes of reoxygenation (H/R control). The VM was pretreated with 125 mumol/L adenosine, an adenosine antagonist ((p-Sulfophenyl) theophylline [SPT] 50 mumol/L) and adenosine (adenosine + SPT), or with a PKC inhibitor (chelerythrine, 10 mumol/L) and adenosine (adenosine + chelerythrine) before H/R Developed force (DF) and tissue creatine kinase (CK) activity were assessed at end reoxygenation. Human trabeculae were obtained from diseased explanted hearts at cardiac transplantation and were also subjected to H/R injury. Human VM was pretreated with adenosine (125 mumol/L) before H/R injury. Results are expressed as mean +/- standard error of mean.

RESULTS

In the rat, adenosine pretreatment conferred protection of DF against H/R injury (adenosine, 62% +/- 6%; H/R control, 27% +/- 2%, p < 0.05). Adenosine + SPT or adenosine + chelerythrine eliminated the functional recovery conferred by adenosine. This recovery of contractile function was associated with greater tissue CK activity (adenosine, 415 +/- 40 units/gm; H/R control, 78 +/- 13 units/gm, p < 0.05). The protective effects of adenosine against H/R were present in the human ventricle and with recovery of DF in adenosine (66% +/- 5%) and H/R control (24% +/- 4%), p < 0.05.

CONCLUSIONS

Adenosine, a clinically accessible agonist, induces protection against H/R injury through a PKC-mediated mechanism in the rat ventricle. Further, the protection conferred by adenosine against H/R extends to the human ventricle.

No evidence for ischemic preconditioning during repeated vessel occlusion in coronary angioplasty

Coronary angioplasty has been the favoured model in studying ischemic preconditioning in humans, but results have remained controversial, possibly due to some artefacts related to coronary balloon angioplasty as an ischemia model. We examined this issue by monitoring the sequential metabolic, functional and neurohumoral changes during repeated vessel occlusion in coronary angioplasty performed in patients with chronic angina pectoris. Two groups of patients undergoing two successive balloon inflations of approximately 2 min duration were studied. These balloon inflations were preceded by a short inflation performed immediately after introduction of the balloon into the stenosis. The aim of this primary inflation was to establish adequate coronary blood flow with the deflated balloon in the stenosis and to guarantee that the subsequent two balloon inflations were truly comparable in time. Group I consisted of 23 patients, in whom the changes in the degree of angina, pulmonary capillary wedge pressure (PCWP), atrial natriuretic peptide (ANP) and circulating catecholamines during the procedure were studied. The sequential changes in myocardial metabolism were monitored in group II of nine patients by determining the lactate extraction ratios and femoroarterial coronary sinus (Fa-CS) differences in pH and pCO2 before and after each balloon inflation. In group I, PCWP and total catecholamines increased similarly during both balloon inflations, but ANP remained unchanged. In group II patients the lactate extraction ratios turned negative, the Fa-CS pH-differences increased and the pCO2-differences decreased during vessel occlusions, the changes being somewhat more prominent during the second balloon inflation. To study adaptation to ischemia, the group I patients were divided into two subgroups with and without signs of ischemic dysfunction during balloon inflations (PCWP increase > 5 mmHg and < 5 mmHg, respectively), and the group II patients were divided into two subgroups with and without metabolic ischemia (lactate-producers and non-producers). The ANP levels were constantly higher in the patients demonstrating ischemic dysfunction during balloon inflations, but catecholamine levels increased only after the second balloon inflation. The anginal pain experienced by the patients and the signs of metabolic ischemia were identical during both balloon inflations. We conclude that acute ischemic preconditioning does not occur in patients with repeated vessel occlusions of approximately 2 min duration. The patients without ischemia during the procedure had more critical stenoses and pre-existing collaterals. However, other protective mechanisms, such as chronic adaptation at the cellular level or recruitment of new collaterals, cannot be excluded.

Salvage of jeopardized myocardium by ischemic preconditioning: is the quest over?

Helmholtz is quoted to have said that if he'd had any influence in creation he would have returned the human eye to its maker for revisions. The same could be said of the heart with its only very rudimentary ability to defend itself against ischemia. Ischemia was obviously not a problem during evolution: Early man did not live much longer than prime time for reproduction and no selection bias existed to prevent vascular diseases, an affliction of later life. In spite of this natural disadvantage of aged males the number of existing although not very efficient defense mechanisms is surprisingly large. It is the general belief that the knowledge of these mechanisms may lead to the development of new therapies that hopefully improve the imperfect product of natural selection.

Repeated coronary artery occlusions during routine balloon angioplasty do not induce myocardial preconditioning in humans

OBJECTIVES

The purpose of the present study was to assess whether brief, repeated coronary artery occlusions during balloon angioplasty induce a myocardial ischemic protective effect.

BACKGROUND

In animals, brief coronary artery occlusions preceding a more prolonged occlusion result in reduced infarct size. Whether myocardial protection against ischemia could also occur in humans during angioplasty remains controversial.

METHODS

Thirteen patients with a proximal left anterior descending coronary artery stenosis with no angiographic collateral circulation underwent percutaneous transluminal coronary artery balloon angioplasty. Three 120-s balloon inflations separated by a 5-min equilibration period were performed. For each inflation, intracoronary ST segment modifications, septal wall thickening (M-mode echocardiography), left ventricular pressures and time derivatives were measured at baseline and at 30, 60 and 90 s after balloon inflation and 120 s after balloon deflation.

RESULTS

Intracoronary electrocardiographic analysis showed that the time course of the maximal ST segment elevation was identical at each inflation, as were wall motion changes assessed by the decrease in septal wall thickening. For the first and last inflations, peak positive dP/dt decreased significantly by 13 +/- 9% (mean +/- SD) and 14 +/- 13%, whereas peak negative dP/dt increased by 23 +/- 15% and 22 +/- 10%, respectively (all p < 0.01 from baseline values). The relaxation time constant, tau, was altered similarly during the different inflations, from 44 +/- 6 to 74 +/- 13 ms and from 57 +/- 13 to 77 +/- 13 ms (all p < 0.001) for the first and last inflations, respectively. Left ventricular end-diastolic pressure increased to the same level after each inflation. In contrast to other hemodynamic variables, tau and left ventricular end-diastolic pressure did not return to baseline values in between the inflations, which may be due to myocardial stunning.

CONCLUSIONS

In patients with proximal left anterior descending coronary artery stenosis and no evidence of collateral circulation, brief periods of ischemia, such as those used during routine coronary balloon angioplasty, do not provide any protection against myocardial ischemia.

Adaptation to myocardial ischemia during repeated dynamic exercise in relation to findings at cardiac catheterization

It has been suggested that the myocardium is able to recruit endogenous protective mechanisms in response to repeated ischemia and reperfusion. We set out to study whether this is manifested in patients with coronary artery disease in the form of fewer signs of myocardial ischemia during the second of two successive exercise tests and whether any relations exist between ischemia adaptation and findings at cardiac catheterization. Twenty-one patients with typical angina pectoris symptoms underwent two repeated bicycle exercise tests with identical protocols, followed by cardiac catheterization and coronary angiography the next day. The first exercise test was discontinued whenever a 2 mm ST depression in the electrocardiogram (ECG) was achieved or further exercise was limited by symptoms. The second exercise test was performed after disappearance of the symptoms or ST depression or both. Kaplan-Meier survival analysis for the appearance of a 1 mm ST depression demonstrated improved ischemia tolerance during the second test, when the required time for its appearance was significantly longer (6.5 +/- 0.8 min vs 4.5 +/- 0.5 min; p = 0.005). The maximal intensity of anginal pain was lower during the second exercise (2.2 +/- 1.0 min vs 0.7 +/- 0.3 min in Borg's scale; p < 0.001), and the time required for disappearance of the ST depression was shorter after this exercise (3.0 +/- 0.8 min vs 6.2 +/- 0.9 min; p = 0.003), with a similar tendency in the disappearance of angina. The rate-pressure product on the appearance of a 1 mm ST depression was significantly higher during the second test (17,990 +/- 1210 mm Hg x min-1 vs 15,960 +/- 869 mm Hg x min-1; p = 0.009). Eighteen of the patients had three-vessel disease, as evidenced by coronary angiography, and the change in the time required for the appearance of a 1 mm ST depression in the repeated exercise tests was inversely correlated with the severity of the left anterior descending (LAD) coronary artery obstruction (r = -0.61; p = 0.006) and left ventricular end-diastolic pressure (r = -0.50; p = 0.03). No significant correlation with the degree of collateral vessels was found. We conclude that most patients with extensive coronary artery disease are able to increase their tolerance of ischemia during repeated dynamic exercise and that increased vasodilation and oxygen delivery are the major mechanisms for this warm-up phenomenon. On the other hand, collaterals visible in routine resting anglography do not predict the degree of adaptation to ischemia during repeated dynamic exercise.

Creatine kinase and creatine kinase-MB release after nontraumatic cardiac arrest

The aim of the study was to describe the course of serum creatine kinase (CK) and its MB fraction (CK-MB) in patients surviving cardiac arrest, and to identify factors influencing CK and CK-MB release. The study was set in the community of Vienna, Austria. Data concerning cardiopulmonary resuscitation, collected within a period of 33 months, were evaluated retrospectively and compared with laboratory blood investigations collected prospectively (on admission and after 6, 12, and 24 hours) in 107 adult patients surviving a witnessed cardiac arrest for 24 hours. CK and CK-MB were elevated in >75% of the patients within 24 hours. Release of CK and CK-MB was mainly associated with electrocardiographic evidence of acute myocardial infarction (AMI) cumulative energy administered during defibrillation, and duration of chest trauma by compression. The CK-MB/CK ratio was elevated in 32% of the patients. Of patients with electrocardiographic evidence of AMI, only 49% had an elevated CK-MB/CK ratio. In conclusion, the elevation in serum CK and CK-MB fraction in patients after nontraumatic cardiac arrest is a frequent finding, and is associated with ischemic myocardial injury, as well as physical trauma to the chest. This should be considered when interpreting the course of CK and CK-MB fraction for the diagnosis of AMI.

Myocardial preconditioning promises to be a novel approach to the treatment of ischemic heart disease

In the phenomenon termed "ischemic preconditioning," a brief period of ischemia prior to a more prolonged one improves myocardial function (after reperfusion) and diminishes infarction. This phenomenon has been described extensively in experimental animals and now in humans. It is triggered by several agents released by ischemic cells and can be reproduced by infusion of agonists coupled to protein kinase C (PKC), e.g. adenosine, angiotensin, phenylephrine, bradykinin, and endothelin. The intracellular signaling pathway involves a phospholipase, either C or D, which metabolizes membrane phospholipids to produce diacylglycerol, a necessary endogenous cofactor for PKC activation. Which protein(s) is phosphorylated by PKC is not yet known, nor is the identity of the end-effector that actually mediates protection of the ischemic cell. Identification of the end-effector may make it possible in the routine treatment of patients with ischemic heart disease to precondition and thereby salvage ischemic myocardium and improve survival.

Effect of repetitive ischemia on myocardial oxygen tension in isolated perfused and hypoperfused rat hearts

The objective of this study was to determine the effects of repetitive ischemia on myocardial oxygen tension (pO2), consumption, and delivery in crystalloid normoperfused (perfusion pressure>70 mmHg) and hypoperfused (perfusion pressure approximately 50 mmHg) constant flow isolated rat hearts. EPR oximetry with lithium phthalocyanine was used to measure myocardial pO2. Baseline myocardial pO2 (means +/- SE) was 185 +/- 13 mmHg (normoperfused) and 162 +/- 14 mmHg (hypoperfused). Myocardial pO2 fell to < 1 mmHg during no-flow ischemia. After recovery from repetitive ischemia, myocardial pO2 and coronary resistance increased significantly in all hearts; oxygen consumption and left ventricle work decreased in normoperfused hearts, although not significantly compared with controls, and did not change significantly in hypoperfused hearts. Increased myocardial pO2 in the normoperfused group may be due to decreased oxygen consumption and/or increased local delivery, while increased myocardial pO2 in the hypoperfused hearts is due to increased local oxygen delivery.

Optimal myocardial preservation: cooling, cardioplegia, and conditioning

Myocardial preservation techniques have evolved in conjunction with cardiac surgery and currently offer substantial protection against myocardial injury. We propose that cardiac preconditioning, a robust, endogenous mechanism of cardioprotection, is emerging as an important adjunct to current cardioplegic techniques. By reviewing the physiologic basis for current cardioplegic strategies, and understanding the cardioprotective benefits of preconditioning, we postulate that cardiac preconditioning may represent an important, clinically accessible component of myocardial protection.

Preinfarction angina as a predictor of more rapid coronary thrombolysis in patients with acute myocardial infarction

BACKGROUND

When a myocardial infarction is preceded by angina, the infarct tends to be smaller than when there is no preinfarction angina. Prompt recanalization of the occluded infarct-related artery is crucial in limiting the size of the infarct. We prospectively studied the relation among preinfarction unstable angina, the speed of coronary reperfusion, and the size of the infarct in patients with acute myocardial infarction receiving thrombolytic therapy.

METHODS

We compared 14 patients who had unstable angina during the week before myocardial infarction with 9 patients who had no preinfarction angina. Coronary arteriograms were obtained at base line and 15, 35, 55, and 90 minutes and 24 hours after the start of thrombolytic therapy. The size of the infarct was estimated on the basis of creatine kinase and creatine kinase MB levels, which were measured every 4 hours during the first 24 hours.

RESULTS

Complete reperfusion (a flow of grade 3 according to the Thrombolysis in Myocardial Infarction classification) was achieved at 35 minutes in 64 percent of the patients with preinfarction angina but in none of those without preinfarction angina (P = 0.006); at 55 minutes in 86 percent and 38 percent, respectively (P = 0.05); and at 90 minutes in 86 percent and 50 percent, respectively (P = 0.14). The mean (+/- SD) time to reperfusion was 27 +/- 16 minutes in the group with preinfarction angina and 48 +/- 17 minutes in the group without preinfarction angina (P = 0.04); the peak creatine kinase levels were 1118 +/- 783 and 2395 +/- 1615 U per liter, respectively (P = 0.03); the peak creatine kinase MB levels were 102 +/- 67 and 251 +/- 186 U per liter, respectively (P = 0.009); and the 24-hour integrated creatine kinase MB levels were 1716 +/- 1171 and 4267 +/- 3252 U.liter-1 x 24 hours, respectively (P = 0.009). The time to reperfusion was positively correlated with the indexes of infarct size (r > or = 0.53, P < or = 0.02).

CONCLUSIONS

In patients with acute myocardial infarction preceded by unstable angina, as compared with those without preinfarction angina, thrombolytic therapy resulted in more rapid reperfusion and smaller infarcts. Earlier myocardial reperfusion may thus account for the smaller infarct size in patients with preinfarction angina.

Protection of the myocardium by ischaemic preconditioning: mechanisms and therapeutic implications

Preconditioning of the heart with brief periods of ischaemia protects the myocardium for up to 90 min against a more sustained ischaemic injury. A "second window of protection" occurs 24 hr after preconditioning with ischaemia. The cardioprotective effects of ischaemic preconditioning involve the release of mediators (adenosine, bradykinin, catecholamines, prostaglandins, endothelin-1), which either alone or in concert activate protein kinase C, which translocates to the cell membrane. This manuscript reviews (i) the cardioprotective effects of ischaemic preconditioning, (ii) the underlying mechanisms, (iii) the effects of ischaemic preconditioning of other tissues (skeletal muscle, brain and kidney), and (iv) the clinical implications.

Ischemic preconditioning against infarction: its mechanism and clinical implications

Exposing the myocardium to brief ischemia followed by reperfusion enhances myocardial resistance to infarction from a subsequent sustained ischemia. This phenomenon, termed preconditioning, is most likely to be triggered by adenosine A1 receptor activation, and the dependence of the preconditioning effect on the duration of preconditioning ischemia and the number of its repetition is probably through the interstitial adenosine level achieved by each preconditioning protocol. Our studies support the theory that activation of protein kinase C subsequent to stimulation of the A1 receptor enhances myocardial ischemic tolerance. The ATP-sensitive potassium channel may be involved in preconditioning, but its relation with protein kinase C is unclear, and the relative importance of this channel might be species dependent. The mechanism of preconditioning needs to be further elucidated in animal models and preconditioning in the human heart needs to be further characterized before we can adapt its biochemical basis to clinical therapy.

Preconditioning the human myocardium: recent advances and aspirations for the development of a new means of cardioprotection in clinical practice

Ischemic preconditioning has been shown to be one of the most powerful means of protecting the myocardium from ischemic injury in experimental animal models, although the mechanism is incompletely understood. In this review we discuss the evidence for preconditioning occurring in ischemic syndromes in humans, whether the human myocardium can be preconditioned, and whether preconditioning would have a place as a therapeutic tool in clinical practice. Some studies evaluating patients after acute myocardial infarction have shown a better outcome in patients reporting angina before the onset of the infarction, but this is not a universal finding, and it is difficult to exclude other confounding factors, such as collateral flow, from influencing the results. More controlled prospective studies have evaluated patients undergoing percutaneous transluminal coronary angioplasty and have found less ST-segment change and less reported angina during the second balloon inflation when compared with the first. Again, it is impossible to completely exclude other causes for this effect, but the dependence on mechanisms that are known to be important for preconditioning in animal models does suggest the phenomena are the same. Further experiments using isolated human atrial muscle have shown that human myocardium can be preconditioned and that the mechanisms involved are similar to those elucidated in animal models (adenosine, protein kinase C, and ATP-dependent potassium channels). In clinical medicine preconditioning is most likely to benefit patients when it is used to protect against the ischemia induced by cardiac surgery. In this respect, a study has shown that in patients undergoing coronary artery bypass grafts, the reduction in ATP occurring during the first ischemic period is attenuated in those given an ischemic preconditioning protocol beforehand. Despite these advances, it is likely that the full potential of preconditioning in clinical practice will not be realized until the whole mechanism of protection is understood and a safe pharmacological "preconditioning" agent becomes available.

Adaptation mechanisms during myocardial ischemia in chronic unstable angina pectoris

Unstable angina with a clinical duration of < 2 months is characterized angiographically by a high incidence of complex lesions. Some patients have ischemic rest pain syndromes of longer duration. Thus, we retrospectively analyzed, in blinded fashion, the clinical and angiographic findings in 52 patients with unstable angina of < 2 months' duration (group A), and compared the results with those of 32 patients with unstable angina of > 6 months' duration (group B). Group B had a greater number of diseased vessels and better collateral circulation, but had fewer eccentric lesions. There were no differences in age, left ventricular function, or history of prior myocardial infarction. Thus, chronic unstable angina is associated with more extensive coronary disease than unstable angina of shorter duration. The role of different anatomic substrata and collateral circulation is discussed.

Clinical aspects of preconditioning and implications for the cardiac surgeon

Ischemic preconditioning is one of the most powerful means to reduce myocardial ischemic cell death in the experimental laboratory. Data are now emerging suggesting that ischemic preconditioning also can occur in the human heart. Studies performed on human myocardial biopsies, angioplasty studies, clinical studies assessing acute tolerance to angina, and some studies evaluating the effect of angina prior to myocardial infarction, lend support to the concept that the human heart can be preconditioned. The ultimate objective is to develop preconditioning-mimetic agents that can be administered prophylactically prior to the time of cardiopulmonary bypass surgery or administered to hearts that have been harvested for transplant in order to better preserve the ischemically jeopardized myocyte.

Basic view on the pathobiology of myocardial ischemia during coronary angioplasty: implications for cardiac protection

PTCA is not only an effective therapeutic tool but a unique opportunity to study the pathobiology of the human myocardium during ischemia and reperfusion. In addition, it is a good model to assess potential therapeutic interventions. Studies performed during PTCA contributed significantly to the understanding of the metabolic, electrophysiologic, hemodynamic, and coronary perfusion changes in the human heart following coronary occlusion. Combining the data from experimental models and human patients may lead to better techniques for myocardial protection during PTCA and consequently reduce the risk of patients undergoing mechanical revascularization.