Incidence of diabetic retinopathy in people with type 2 diabetes mellitus attending the Diabetic Retinopathy Screening Service for Wales: retrospective analysis.

OBJECTIVES: To determine the incidence of any and referable diabetic retinopathy in people with type 2 diabetes mellitus attending an annual screening service for retinopathy and whose first screening episode indicated no evidence of retinopathy. DESIGN: Retrospective four year analysis. SETTING: Screenings at the community based Diabetic Retinopathy Screening Service for Wales, United Kingdom. PARTICIPANTS: 57,199 people with type 2 diabetes mellitus, who were diagnosed at age 30 years or older and who had no evidence of diabetic retinopathy at their first screening event between 2005 and 2009. 49,763 (87%) had at least one further screening event within the study period and were included in the analysis. MAIN OUTCOME MEASURES: Annual incidence and cumulative incidence after four years of any and referable diabetic retinopathy. Relations between available putative risk factors and the onset and progression of retinopathy. RESULTS: Cumulative incidence of any and referable retinopathy at four years was 360.27 and 11.64 per 1000 people, respectively. From the first to fourth year, the annual incidence of any retinopathy fell from 124.94 to 66.59 per 1000 people, compared with referable retinopathy, which increased slightly from 2.02 to 3.54 per 1000 people. Incidence of referable retinopathy was independently associated with known duration of diabetes, age at diagnosis, and use of insulin treatment. For participants needing insulin treatment with a duration of diabetes of 10 years or more, cumulative incidence of referable retinopathy at one and four years was 9.61 and 30.99 per 1000 people, respectively. CONCLUSIONS: Our analysis supports the extension of the screening interval for people with type 2 diabetes mellitus beyond the currently recommended 12 months, with the possible exception of those with diabetes duration of 10 years or more and on insulin treatment.

Can moderate alcohol intake limit the size of myocardial infarction?

Several observational and epidemiologic analyses suggest that moderate drinking of alcohol (usually two drinks per day) may have beneficial effects on the heart. Specifically it may reduce the incidence of ischemic heart disease and improve the outcome after a myocardial infarction. The purpose of this study was to test the hypothesis that long-term, moderate consumption of alcohol has a direct cardioprotective effect, reducing myocardial infarct size in rats subjected to ischemia/reperfusion. Two groups of rats were given alcohol in their drinking water at concentrations of 15% or 36%; control rats received water (n = 10 for all groups). After 16 weeks of treatment, the rats were anesthetized and subjected to 60 min of coronary artery occlusion and reperfusion. The ischemic risk region (% LV) was not significantly different among groups. Infarct size (% risk zone) was 49+/-7%, 44+/-4%, and 50+/-8%, respectively (p = 0.79). Thus no significant differences in infarct size between control and alcohol-fed rats were observed. There was no correlation between alcohol level and infarct size in alcohol-treated rats (r = 0.20, p = 0.45). Arterial pressures were lower in the 36% group at baseline and throughout the study compared with the control and 15% groups, but heart rates were similar in all groups. Moderate consumption of alcohol failed to alter infarct size compared with control and thus it is unlikely that alcohol drinking has a direct myocardial-protecting effect on the outcome of ischemia and reperfusion.

Ethanol does not exert myocardial preconditioning in an intact rabbit model of ischemia/reperfusion.

Some epidemiologic analyses suggest that moderate drinking of alcohol may have beneficial effects on the heart. An experimental in vitro study also indicated that acute alcohol administration may precondition myocardium against ischemia, but only if it is washed out before ischemia. The goal of this study was to test whether alcohol + washout preconditions the myocardium to ischemia, reducing necrosis after ischemia/reperfusion in an in vivo model. Two groups of anesthetized open-chest rabbits received ethanol (0.5 mL/kg, intravenously) at 90 minutes before (Group 1, alcohol preconditioning, n = 8) or 5 minutes before (Group 2, acute, n = 8) coronary artery occlusion (CAO); control rabbits received saline (Group 3, n = 8). All rabbits received 30 minutes of CAO and 3 hours of reperfusion. Blood alcohol level at the time of CAO in Group 1 had returned to control level (< 10 mg/dL). Alcohol level in Group 2 was 162 +/- 9 mg/dL. There were no differences in hemodynamics, ischemic risk region size, or collateral blood flow among groups. Alcohol, with or without washout, failed to reduce necrosis. Infarct size (% risk region) was 45 +/- 5% in control rabbits, 48 +/- 6% with acute administration, and 53 +/- 7% with washout (P = 0.57). These data indicate that alcohol + washout did not precondition hearts against ischemia in this model, adding evidence to the theory that acute alcohol administration has no direct beneficial effect on ischemic myocardium.

Combination therapy for maximal myocardial infarct size reduction.

The aim of this study was to test whether myocardial infarct size reduction would be optimized by combining three known effective therapies: cariporide, regional hypothermia, and ischemic preconditioning (CHIP). Before coronary artery occlusion (CAO), treated rabbits (CHIP, n = 7) received cariporide (0.3 mg/kg), ischemic preconditioning (7 minutes ischemia and 5 minutes reperfusion), then 20 minutes of mild regional hypothermia (34 degrees C). Control rabbits (n = 7) received saline and a 34-minute waiting period. All received 30 minutes of CAO and reperfusion. In another study, rabbits (n = 8 in each group) received 90 minutes of CAO. In the 30-minute protocol, the authors found that hearts in both groups were equally ischemic during CAO. Mean ischemic risk zones were similar in both groups; however, in CHIP hearts, infarct size was 4 +/- 1% of risk zone, a reduction of 91% compared with control rabbits (44 +/- 7% of the risk zone, P = 0.001). In the 90-minute protocol, risk zone size was similar in both groups, but infarct size in control hearts was 76 +/- 3% of the risk zone compared with 34 +/- 7% in CHIP treated hearts (P = 0.0003). In summary, the combined treatment provided extraordinary protection. Infarct comprised only 4% of the risk region after 30-minute ischemia-a far greater reduction than was previously observed in the same laboratory using any single intervention. After 90 minutes of ischemia, infarct was 55% lower in CHIP hearts, suggesting that this therapeutic approach dramatically reduces ischemia/reperfusion cell death, even during long occlusions.

Effects of resveratrol, a flavinoid found in red wine, on infarct size in an experimental model of ischemia/reperfusion.

OBJECTIVE: Resveratrol is a potent anti-inflammatory and anti-oxidant flavinoid found in red wine. Resveratrol has been shown to improve ventricular function and decrease lactic dehydrogenase release after ischemia in rats. The aim of this study was to test whether resveratrol could provide direct cardioprotection to myocytes during acute myocardial infarction. METHOD: Anesthetized, open-chest rabbits (N= 24) were subjected to 30 minute coronary artery occlusion followed by 3 hr reperfusion. Before the onset of ischemia (15 minutes), the rabbits were randomly assigned (n = 8 in each group) to either high-dose (1.5 mg/kg) resveratrol, low-dose (0.15 mg/kg) resveratrol or ethanol vehicle, and the effects on infarct size and regional myocardial blood flow (RMBF) were tested. RESULTS: Hemodynamic parameters and size of ischemic risk region (29% to 35% of the left ventricle) were similar in all groups. Infarct size, expressed as a mean (SEM) percentage of the risk region, was 46% (5%) of the risk region in controls, 46% (7%) in the low-dose group and 54% (3%) in the high-dose group (p = .53). Thus, treatment with resveratrol had no effect on infarct size at either dose. There were no differences in RMBF in the risk zone or in nonischemic tissue, during either occlusion or reperfusion. CONCLUSIONS: In this intact model of ischemia and reperfusion, resveratrol fails to provide cardioprotection. The mechanism of other beneficial effects (e.g., improvement of function) that are observed with resveratrol probably do not result from increased RMBF or a reduction in myocardial necrosis.

Effect of combined K(ATP) channel activation and Na(+)/H(+) exchange inhibition on infarct size in rabbits.

We tested if combining treatment with cariporide, an Na(+)/H(+) exchange inhibitor, and diazoxide, a mitochondrial ATP-sensitive K(+) (K(ATP)) channel opener, would reduce myocardial infarct size (IS) to a greater extent than either intervention alone. Four groups of rabbits were studied (n = 10 each): cariporide (0.3 mg/kg), diazoxide (10 mg/kg), both drugs, and saline control, given 15 min before a 30-min coronary artery occlusion and 3 h reperfusion. IS in controls comprised 47 +/- 6% of the risk region. Cariporide reduced IS by 55% compared with control (21 +/- 3%), but diazoxide did not significantly reduce IS compared with controls (37 +/- 6%). Combined treatment resulted in an IS of 18 +/- 5%. Also we determined that diazoxide did not potentiate a subthreshold dose of cariporide nor did a mitochondrial K(ATP) channel blocker, 5-hydroxydecanoate (5-HD), prevent cariporide from reducing IS. Thus cariporide reduced necrosis by >50% in this model, both in the presence and absence of K(ATP) channel blockade. There was no significant difference in IS reduction between the group receiving cariporide alone and the group receiving combined treatment. Because the effect of cariporide was not blocked by 5-HD, it is unlikely that K(ATP) channels play a role as an end effector in cariporide's mechanism.

What is the required reperfusion period for assessment of myocardial infarct size using triphenyltetrazolium chloride staining in the rat?

Measurements of infarct size by use of tripenyltetrazoliumchloride (TTC) is a widely accepted method used to delineate the extent of myocardial necrosis following coronary occlusion and reperfusion in various animal experiments. There is controversy, however, regarding the optimal reperfusion time for estimating the maximally infarcted area by TTC staining in the rat. We tested six different reperfusion times following 90 minutes of regional myocardial ischemia. Group 1 had 5 minutes of reperfusion (n=6), group 2 had 30 minutes of reperfusion (n=6), group 3 had 1 hour of reperfusion (n=6), group 4 had 2 hours of reperfusion (n=6), group 5 had 3 hours of reperfusion (n=6), group 6 had 4.5 hours of reperfusion (n=6). Risk areas, measured by the use of blue dye, were similar among the 6 study groups. Infarct size as a percent of risk area was 57+/-11% in group 1, 74+/-7% in group 2, 61+/-9% in group 3, 71+/-5% in group 4, 70+/-5% in group 5, and 64+/-9% in group 6 (x+/-standard error [SE]). There was no significant difference in infarct size between the groups. However, prior to 60 minutes of reperfusion, patches of pink and white areas were observed within the risk regions, indicating a more difficult assessment of proper delineation of outer regions of necrotic tissue. For acute assessment of infarct size, reperfusion for 60 minutes or more is optimal because the infarct does appear homogeneous at that time and does not become larger with longer reperfusion periods.

Location as a determinant of myocardial infarction in rabbits.

Determinants of infarct size in the rabbit heart include risk zone size, regional myocardial blood flow (RMBF), temperature and duration of ischemia. However, other factors might contribute, such as the location of the risk zone (apex to base), independent of known factors. Occlusion of a large marginal branch of the circumflex artery in the rabbit produces a risk region that typically comprises the entire apex of the left ventricle with decreasing area involvement from apex to base. In a retrospective study of 65 rabbit hearts (subjected to 30 min of coronary artery occlusion) which had been sliced into six to eight cross-sectional slices, average area at risk (AR) comprised 86+/-3% of the apical level, 68+/-2% of the middle level and 39+/-2% near the site of occlusion at the base of the heart. If necrosis were dependent on AR alone, then infarct size (area of necrosis/area at risk, AN/AR) would not vary by site. However, AN/AR in the apex was 54+/-3% while AN/AR near the base was 27+/-2%, P<0.0001. To test if this salvage of tissue at risk near the base was due to differences in regional myocardial blood flow, we measured RMBF during occlusion in additional rabbits (n=4). Average RMBF in the risk zone was 0.025 ml/min/g in the apex and 0.010 in the base, P=N.S. Nor was the salvage due to differences in temperature. During occlusion, temperature in the risk zone (n=5) was 38.1 degrees C+/-0.3 in the apex and 38.4+/-0.2 in the base (P=N.S.). When we examined this phenomenon in hearts that received a non-pharmacological intervention that decreases overall infarct size (ischemic preconditioning) and in hearts that received a pharmacological intervention that decreases overall infarct size, a similar pattern of decreasing infarct size as a percentage of the area at risk from apex to base was observed. In conclusion, infarct size as a percentage of the AR depends on whether the AR is at the apex or base of the heart. A larger part of the AR undergoes necrosis toward the apex of the heart. This phenomenon is independent of collateral flow or temperature, and suggests that other as yet unknown factors contribute to infarct size.

Adenosine A1 agonist at reperfusion trial (AART): results of a three-center, blinded, randomized, controlled experimental infarct study.

Adenosine A1 receptor agonists given prior to myocardial ischemia limit ischemic injury in several species. However, the ability of adenosine receptor agonists to limit infarct size when given at reperfusion has proved controversial. We designed a three-center experimental study using a blinded, randomized treatment protocol to test the hypothesis that adenosine A1 receptor activation during early reperfusion can attenuate lethal reperfusion injury, thereby reducing infarct size. Sixty anesthetized rabbits (20 in each laboratory) underwent 30 minutes coronary artery occlusion followed by 120 minutes reperfusion. The selective adenosine A1 receptor agonist GR79236 (10.5 microg/kg, a dose shown to limit infarction in this model when given before ischemia) or vehicle were administered IV 10 minutes before reperfusion. Infarct size was assessed by tetrazolium staining and, after the randomization code was revealed, data from the three laboratories were pooled for statistical analysis. Infarct size was not modified by administration of GR79236. In the vehicle-treated group, the infarct-to-risk ratio was 28.9 +/- 2.7% (n = 24) compared with 31.9 +/- 2.6% (n = 26) in the GR79236-treated group (not significant). Risk zone volume was similar in the two groups (1.06 +/- 0.05 cm3 vs 1.00 +/- 0.05 cm3, respectively). A modest reduction in rate-pressure product was noted following the administration of GR79236, but this effect was transient. The same dose of GR79236 was found to limit infarct size when given prior to coronary artery occlusion. We conclude that A1 receptor activation does not modify lethal reperfusion injury in myocardium.

Ischemic preconditioning and myocardial hypothermia in rabbits with prolonged coronary artery occlusion.

This study tests whether combining regional hypothermia and ischemic preconditioning (IP) provides greater myocardial protection during prolonged coronary artery occlusion (CAO) than either intervention alone, and whether increasing the duration of IP from 5 to 7 min extends the window of protection to include a 2-h CAO. Anesthetized rabbits were randomized to four groups (n = 8 rabbits/group): control (C), hypothermia alone (H), IP alone for two 7-min episodes (IP7), and IP plus hypothermia (H + IP7). To compare differences in IP for 5 versus 7 min, additional rabbits (n = 6) received one 5-min episode of ischemia (IP5). All rabbits got 2 h of CAO and 3 h of reperfusion. In comparison with the infarct size in the control group (72 +/- 4% of the risk zone), infarct size was significantly reduced in H (50 +/- 7%), IP7 (49 +/- 5%), and H + IP7 (42 +/- 6%) (all P < 0.05 vs. control group). IP5 failed to confer protection (67 +/- 5% of the risk zone). Therefore, IP can protect against a 2-h CAO if the IP regimen is increased from 5 to 7 min. The combination therapy significantly improved regional myocardial blood flow in the previously ischemic region to a greater extent than either treatment alone.

Myocardial hypothermia: a potential therapeutic technique for acute regional myocardial ischemia.

The importance of temperature in the development of necrosis after myocardial ischemia in the beating heart is becoming apparent. Recent studies have shown that the proportion of the ischemic risk zone that becomes necrotic is directly correlated with temperature. This fact suggests the potential therapeutic benefits of reducing myocardial temperature after coronary artery occlusion. We have shown in a number of experimental protocols in the rabbit model of myocardial infarction that topical regional hypothermia reduces infarct size even when instituted after coronary artery occlusion. The reduction in myocardial temperature required to obtain this benefit is modest ( 30 degrees C to 34 degrees C). Topical regional hypothermia allows targeted cooling of a zone of the heart. Myocardial cooling can also be achieved by perfusing the pericardial sac with a chilled fluid by using a closed-circuit catheter system that does not cause cardiac tamponade. This technique also protects myocardium during ischemia. Myocardial hypothermia might be a useful technique to limit ischemic damage during infarction or as adjunctive therapy during minimally invasive cardiac surgery.

Hypothermic, closed circuit pericardioperfusion: a potential cardioprotective technique in acute regional ischemia.

OBJECTIVES: This study sought to determine whether infarct size can be reduced by hypothermic pericardioperfusion. BACKGROUND: We have shown that myocardial infarct size can be reduced by topical cooling of the heart. The present study tests whether myocardial cooling and protection can be produced by hypothermic pericardioperfusion using a catheter. METHODS: The catheter was sutured into the pericardial space of anesthetized rabbits. Beginning 30 min before coronary artery occlusion, the space was perfused with either chilled (n = 10) or body temperature (n = 10) fluid. The artery was occluded for 30 min and reperfused for 3 h. RESULTS: After 30 min of pericardioperfusion, myocardial temperature was reduced to 34.1 +/- 0.9 degrees C in chilled hearts compared with 38.9 +/- 0.4 degrees C in control hearts, p < 0.001, a reduction in myocardial temperature of approximately 5 degrees C. Risk areas were similar in both groups (32 +/- 4% left ventricle in cooled and 31 +/- 3% in control hearts, p = NS). However, infarct size in cooled hearts was significantly reduced by 49% (18 +/- 3% of risk area vs. 35 +/- 6%, p = 0.025). Tamponade did not develop, and there were no significant differences in heart rate, arterial pressure or body temperature between groups. CONCLUSIONS: A significant reduction in myocardial temperature, without the development of cardiac tamponade, can be attained using a pericardial catheter to cool the pericardial space. This reduction in temperature causes a significant reduction in necrotic damage. This technique might be used to cool and protect the heart as an adjunct to thrombolysis or during minimally invasive cardiac surgery.

Myocardial temperature reduction attenuates necrosis after prolonged ischemia in rabbits.

OBJECTIVE: Previously we observed that a large reduction in infarct size was attained by cooling the risk region of the heart, either before or early after the onset of a 30-min coronary artery occlusion. While this is a standard duration of ischemia used in the rabbit model of infarction, it may not reflect the situation of patients who are reperfused late. The effects of regional hypothermia with a longer duration of ischemia, and when the intervention is applied later, are unknown. This study tests the hypothesis that a local reduction in cardiac temperature protects myocardium during prolonged ischemia (2 h) even if begun well after coronary artery occlusion. METHODS: Anesthetized rabbits received 2 h of coronary artery occlusion and 3 h of reperfusion. Rabbits were randomly assigned to a treated group: topical myocardial cooling starting 30 min after coronary occlusion (n = 14), or control group, no intervention (n = 12). Myocardial temperature in the risk zone, hemodynamics and regional myocardial blood flow were measured. RESULTS: Ischemic zone temperature was similar in both groups at 30 min post occlusion, but the cooling maneuver produced a reduction in temperature in the risk region of the treated group such that myocardial temperature was reduced an average of 10 degrees C between 30 and 60 min of coronary artery occlusion. Myocardial temperature in the control group remained within 0.3 degree C of baseline during coronary artery occlusion and into reperfusion. Core temperatures were similar in both groups. Hemodynamic parameters and collateral blood flow during occlusion were also equivalent in both groups. After 120 min of coronary occlusion, necrosis in the control group comprised 72 +/- 3% of the ischemic risk region. However, in cooled hearts, infarct size, expressed as a fraction of the risk region was significantly lower. Infarct size in this group averaged 59 +/- 3% of the risk region (p < 0.004 vs. controls), and thus cooling resulted in a salvage of approximately 18% of the risk region. CONCLUSION: These results show that reducing myocardial temperature protects ischemic myocardium during a long duration of ischemia even if initiated after coronary artery occlusion.

Ischemic preconditioning at a distance: reduction of myocardial infarct size by partial reduction of blood supply combined with rapid stimulation of the gastrocnemius muscle in the rabbit.

BACKGROUND: Limitation of myocardial infarct size by an earlier brief complete occlusion of a coronary artery is defined as ischemic preconditioning. However, myocardial protection also can be achieved by partial reduction of coronary flow, rapid cardiac pacing, or brief ischemia-reperfusion of a remote region of the heart. Our study assesses the effect on myocardial infarct size of preconditioning at a distance induced by partial reduction of blood flow to a hind limb with or without increase of demand by electrical stimulation of a skeletal muscle. METHODS AND RESULTS: Anesthetized rabbits were randomized to 30 minutes of waiting period (controls), 55% to 65% reduction of femoral artery blood flow (stenosis), electrical stimulation of the gastrocnemius muscle at a rate of one per second (stimulation), or stenosis+stimulation. Thereafter, rabbits underwent 30 minutes of coronary artery occlusion and 4 hours of reperfusion. Each group included 8 rabbits. Risk zones were comparable among groups. However, the ratio of infarct size to risk zone was smaller in the stenosis+stimulation group (0.09+/-0.02) compared with the control (0.26+/-0.03), stenosis (0.36+/-0.05), and stimulation (0.30+/-0.05) groups (P=.0006). ANCOVA performed on the fraction of infarction (infarct size/left ventricular weight) and the fraction of risk zone revealed a significant group effect (P=.0004). CONCLUSIONS: Remote ischemia of a skeletal muscle induced by muscle stimulation combined with restriction of blood flow preconditioned the myocardium. The combination of muscle stimulation with reduction of femoral arterial blood flow but not muscle stimulation without blood flow restriction or of flow restriction without muscle stimulation reduced myocardial infarct size considerably.

Myocardial temperature in acute myocardial infarction: protection with mild regional hypothermia.

This study tests the hypothesis that a 2-4 degrees C reduction in myocardial temperature, obtained by using topical regional hypothermia (TRH), reduces infarct size. Anesthetized rabbits received coronary artery occlusion and reperfusion. We cooled hearts in the TRH group by applying an ice bag directly over the risk zone; the control group received no intervention. Risk zone myocardial temperature (MT) in the TRH group was reduced at occlusion by 2 degrees C from baseline and after 5 min of occlusion by 3.6 degrees C. In the control group, MT in the risk region remained within 0.3 degree C of baseline. The ischemic area was similar in both groups, yet infarct size in the TRH group was reduced by an average of 65% compared with the control group. Infarct size closely correlated with MT in the risk region at the time of occlusion. In a second protocol in which all hearts were paced, infarct size was 21% of the risk region in TRH hearts compared with 44% in controls. These results strongly support the important role of MT in the progression of necrosis and demonstrate that the application of local cooling to the risk region profoundly reduces myocardial infarct size.

Changes in R wave amplitude: ECG differentiation between episodes of reocclusion and reperfusion associated with ST-segment elevation.

This study assesses the electrocardiographic (ECG) differences between episodes of increased ST-segment amplitude induced by coronary artery occlusion and by reperfusion in the open-chest rabbit model. Nine anesthetized open-chest male New Zealand White rabbits were subjected to four episodes of 5 minutes of coronary artery occlusion followed by 5 minutes of reperfusion. The ST-segment and R wave amplitudes were measured from an ECG lead attached to the pericardium overlying the ischemic myocardium. In 10 out of 35 (29%) of the episodes, reperfusion resulted in a transient increase in ST-segment amplitude. While episodes of coronary artery occlusion were associated with increase in R wave amplitude (69% and 97% of the episodes after 1 and 5 minutes, respectively), all reperfusion episodes were associated with prompt decrease in R wave amplitude. There was no difference between the repeated episodes in the occurrence of ST-segment elevation during reperfusion. However, ST-segment elevation during reperfusion could be distinguished from the ischemic episodes by the prompt decline in the R wave amplitude in the former compared with no change or increase in the latter.

Differences in reperfusion length following 30 minutes of ischemia in the rabbit influence infarct size, as measured by triphenyltetrazolium chloride staining.

Assessment of myocardial infarct size in acute experimental models is usually done by triphenyltetrazolium-chloride (TTC) staining. A certain period of reperfusion is mandatory for discrimination of the infarct zone, especially after relatively short ischemic periods. However, it is unclear what the optimal reperfusion time is for full delineation of the infarct following 30 min of myocardial ischemia in the rabbit. This study compares infarct size, assessed by TTC, in anesthetized open-chest rabbits subjected to 30 min of coronary artery occlusion followed by either 2 (n = 14) v 4 (n = 14) (protocol 1), or 3 (n = 8) v 6 (n = 7) h of reperfusion (protocol 2). Area at risk was assessed by blue dye and necrotic zone by TTC staining. Protocol 1: heart rate and mean blood pressure were comparable in both groups throughout the protocol. Regional myocardial blood flows in both the ischemic and non-ischemic zones during ischemia and after 2 h of reperfusion were comparable between the groups. Regional myocardial blood flow in the post-ischemic zone deteriorated between 2 and 4 h (1.11 +/- 0.15 v 0.58 +/- 0.09 ml/min/g, respectively, P = 0.0004) of reperfusion. The size of the area at risk was comparable (0.31 +/- 0.03 v 0.33 +/- 0.03 of the LV weight in the 2 and 4 h reperfusion groups). However, the ratio of the necrotic zone to the ischemic zone at risk was 63% larger in the 4 compared to the 2 h of reperfusion group (0.31 +/- 0.04 v 0.19 +/- 0.05, respectively, P = 0.02). Analysis of covariance performed on the weight of tissue that developed necrosis and the weight of ischemic zone at risk revealed a significant effect of the reperfusion time (P = 0.014). Protocol 2: there was no difference in infarct size between rabbits subjected to three (0.38 +/- 0.05 of the area at risk) v 6 h (0.41 +/- 0.07) of reperfusion (P = 0.72). Analysis of covariance performed on the weight of tissue that developed necrosis and the weight of ischemic zone at risk did not reveal a significant effect of the reperfusion time. Infarct size as assessed by TTC following 30 min of myocardial ischemia, is smaller when measured 2 h after reperfusion than after 4 h of reperfusion. At least 3 h of reperfusion is needed to delineate infarct size by tetrazolium staining following 30 min of ischemia.

Is warm retrograde blood cardioplegia better than cold for myocardial protection?

BACKGROUND: This study tests the hypothesis that continuous normothermic retrograde blood cardioplegia is superior to cold intermittent blood cardioplegia in protecting the left and right side of the heart transmurally during an extended cross-clamping period. METHODS: Twelve anesthetized, open chest dogs were placed on cardiopulmonary bypass and randomized to receive continuous warm (n = 6) or intermittent cold cardioprotection (n = 6) during a 3-hour aortic cross-clamp period. Transmural left ventricular muscle biopsy specimens were taken before the initiation of cardiopulmonary bypass and 90 and 180 minutes after cross-clamping. Right ventricular (RV) biopsy specimens were taken 180 minutes after aortic cross-clamping. Biopsy specimens were analyzed for adenosine triphosphate, creatine phosphate, and lactate levels and for morphologic changes via electron microscopy. RESULTS: At the end of 180 minutes of cardiopulmonary bypass, the adenosine triphosphate contents of endocardial and epicardial halves of the left ventricular myocardium were only slightly degraded in both cardioplegia groups; a significantly greater reduction in adenosine triphosphate levels occurred in the RV of the warm compared with the cold group (p < 0.02). The difference in creatine phosphate values in the left ventricle between the cold group (35.2 +/- 23.4 nmol/mg cardiac protein) and the warm animals (64.4 +/- 24.9 nmol/mg cardiac protein) was not statistically significant, but the RV creatine phosphate stores were significantly better preserved in the warm compared with the cold cardioplegia group (p < 0.02). Lactate levels increased to a similar extent in both groups, but both values rose significantly over baseline (p < 0.03). Importantly the electron microscopic score of the left ventricle and RV indicated that cells were reversibly and not irreversibly damaged with both cardioplegic protections. CONCLUSIONS: These results suggest the following: (1) Chemical arrest is a major contributor of myocardial preservation during diastolic arrest as used in clinical cardiac surgery. (2) Both methods preserve the ultrastructure of the myocytes transmurally during 3 hours of aortic cross-clamping. (3) Both techniques protect the RV and left ventricle; however, to provide optimal protection of the RV, alternated retrograde and antegrade perfusion might be beneficial over retrograde cardioplegia flow alone, in particular with warm cardioplegia.

Regional hypothermia reduces myocardial necrosis even when instituted after the onset of ischemia.

UNLABELLED: Previously, we observed that reducing myocardial temperature in the risk region before coronary artery occlusion caused a profound reduction in infarct size. It is unknown whether lowering myocardial temperature after ischemia has already begun, or just before reperfusion, is also effective in reducing infarct size. This study tests the hypothesis that reducing myocardial temperature locally, after coronary occlusion, reduces infarct size. METHODS: Anesthetized rabbits received 30 min of coronary artery occlusion and three hours of reperfusion. Myocardial temperature in the risk zone was monitored. Rabbits were randomly assigned to one of three groups: group 1, topical myocardial cooling starting 10 min after coronary occlusion (n = 11); group 2, cooling starting 25 min after coronary occlusion (n = 11); or group 3, control, no intervention (n = 10). RESULTS: Hemodynamic parameters and regional myocardial blood flow were equivalent in all groups. Risk zone temperature was similar in all groups at occlusion. The cooling maneuver produced a rapid reduction in temperature in the risk region. In group 1, myocardial temperature was reduced an average of 6.3 degrees C between 10 and 15 min of coronary artery occlusion; myocardial temperature in group 2 was reduced an average of 5.9 degrees C between 25 and 30 min of coronary artery occlusion. Cooling was maintained until 15 min of reperfusion. Myocardial temperature in group 3 remained within 0.3 degree C of baseline during coronary artery occlusion and into reperfusion. Core temperature was similar in all groups. Although the ischemic risk region was comparable in all groups, early cooling (group 1) resulted in a significant reduction in infarct size, expressed as a fraction of the risk region, compared with the control group (0.23 +/- 0.04 vs. 0.44 +/- 0.04 of the risk region); however, cooling just before reperfusion (group 2) failed to modify infarct size compared with the controls (0.43 +/- 0.04 and 0.44 +/- 0.04 of the risk region, respectively). CONCLUSION: These results support our hypothesis that reducing myocardial temperature reduces infarct size. However, it is important the reduction in temperature be produced as early as possible following coronary artery occlusion.

Direct evidence that ischemic preconditioning does not cause protein kinase C translocation in rabbit heart.

OBJECTIVE: Indirect pharmacological evidence suggests that myocardial protection conferred by ischemic preconditioning in rabbit myocardium is mediated through the translocation of protein kinase C (PKC). To test this hypothesis, we performed direct biochemical measurements of subcellular distribution of PKC in rabbit hearts. METHODS: Two protocols were utilized. In Protocol I the preconditioned group (PC) underwent two 5-min episodes of brief coronary artery occlusion each followed by 5 min of reperfusion, while the control group consisted of time-matched, sham-operated (non-ischemic) animals (SO). Tissue samples were homogenized and cytosolic and particulate fractions were obtained by ultracentrifugation. In Protocol II one group of rabbits received ischemic preconditioning as in Protocol I followed by 10 min of sustained ischemia (PC + IS); a second control group was subjected to 10 min of sustained ischemia (IS); and the third group was time-matched, sham-operated (non-ischemic) animals (SO). Homogenized tissue samples were separated into cytosolic, nuclear and membrane fractions. RESULTS: In Protocol I, no differences in the subcellular distribution of PKC between the SO and PC groups were observed. In Protocol II, when samples were obtained at 10 min of sustained ischemia, no changes in the subcellular distribution of PKC were observed between SO, IS and PC + IS groups. CONCLUSION: Our results indicate that translocation of protein kinase C is not an important mediator of ischemic preconditioning in the rabbit ischemia model.