Determinants of arrhythmic death due to coronary spasm: effect of preexisting coronary artery stenosis on the incidence of reperfusion arrhythmia

Impact of electrical defibrillation on infarct size and no-reflow in pigs subjected to myocardial ischemia-reperfusion without and with ischemic conditioning

Ventricular fibrillation (VF) occurs frequently during myocardial ischemia-reperfusion (I/R) and must then be terminated by electrical defibrillation. We have investigated the impact of VF/defibrillation on infarct size (IS) or area of no reflow (NR) without and with ischemic conditioning interventions. Anesthetized pigs were subjected to 60/180 min of coronary occlusion/reperfusion. VF, as identified from the ECG, was terminated by intrathoracic defibrillation. The area at risk (AAR), IS, and NR were determined by staining techniques (patent blue, triphenyltetrazolium chloride, and thioflavin-S). Four experimental protocols were analyzed: I/R (n = 49), I/R with ischemic preconditioning (IPC; n = 22), I/R with ischemic postconditioning (POCO; n = 22), or I/R with remote IPC (RIPC; n = 34). The incidence of VF was not different between I/R (44%), IPC (45%), POCO (50%), and RIPC (33%). IS was reduced by IPC (23 ± 12% of AAR), POCO (31 ± 16%), and RIPC (22 ± 13%, all P < 0.05 vs. I/R: 41 ± 12%). NR was not different between protocols (I/R: 17 ± 15% of AAR, IPC: 15 ± 18%, POCO: 25 ± 16%, and RIPC: 18 ± 17%). In pigs with defibrillation, IS was 50% larger than in pigs without defibrillation but independent of the number of defibrillations. Analysis of covariance confirmed the established determinants of IS, i.e., AAR, residual blood flow during ischemia (RMBFi), and a conditioning protocol, and revealed VF/defibrillation as a novel covariate. VF/defibrillation in turn was associated with larger AAR and lower RMBFi. Lack of dose-response relation between IS and the number of defibrillations excluded direct electrical injury as the cause of increased IS. Obviously, AAR size and RMBFi account for both IS and the incidence of VF. IS and NR are mechanistically distinct phenomena.NEW & NOTEWORTHY Ventricular fibrillation/defibrillation is associated with increased infarct size. Electrical injury is unlikely the cause of such association, since there is no dose-response relation between infarct size and number of defibrillations. Ventricular fibrillation, in turn, is associated with a larger area at risk and lower residual blood flow.

Ambulatory electrocardiogram-based T-wave alternans in patients with vasospastic angina during asymptomatic periods

T-wave alternans (TWA) is a useful method for evaluating repolarization abnormalities and as a predictor of life-threatening ventricular arrhythmias. Although life-threatening ventricular arrhythmias are occasionally observed during ischemic attacks in patients with vasospastic angina (VSA), there have been no studies to detect repolarization abnormalities using TWA analysis in these patients during the asymptomatic phase. The aim of this study was to analyze modified moving average (MMA) TWA using Holter recordings in 40 patients with VSA and in 40 control subjects. The incidence of positive TWA was higher in the VSA group than in the control group (24 of 40 [60%] vs 0 of 40 [0%], p <0.01). The value of the maximum MMA TWA was also greater in the VSA group than in the control group (68.6 ± 21 vs 34.0 ± 11 μV, p <0.01). In the VSA group, although there was no significant difference in maximum MMA TWA values between patients with multiple- and single-vessel spasm, patients with ventricular tachycardias had higher values than those without (83.0 ± 15 vs 65.9 ± 20 μV, p <0.05). Patients taking calcium channel blockers exhibited decreased values of maximum MMA TWA compared with subjects not taking these drugs (73.8 ± 18 vs 59.5 ± 21 μV, p <0.05). In conclusion, high values and incidences of TWA events were observed in patients with VSA. In the VSA group, maximum values of MMA TWA were high in patients with ventricular tachycardias but decreased in those taking calcium channel blockers. The results suggest that the patients with VSA during asymptomatic phases exhibit repolarization abnormalities leading to a potential risk for life-threatening arrhythmias.

Sevoflurane postconditioning attenuates reperfusion-induced ventricular arrhythmias in isolated rat hearts exposed to ischemia/reperfusion injury

Sevoflurane postconditioning has been proven to protect the hearts against ischemia/reperfusion injury, manifested mainly by improved cardiac function, reduced myocardial specific biomarker release, and decreased infarct size. This study is to observe the effects of sevoflurane postconditioning on reperfusion-induced ventricular arrhythmias and reactive oxygen species generation in Langendorff perfused rat hearts. Compared with the unprotected hearts subjected to 25 min of global ischemia followed by 30 min of reperfusion, exposure of 3% sevoflurane during the first 15 min of reperfusion significantly improved cardiac function, reduced cardiac troponin I release, decreased infarct size and attenuated reperfusion-induced ventricular arrhythmia. Further analysis on arrhythmia during the 30 min of reperfusion showed that, sevoflurane postconditioning decreased both the duration and incidence of ventricular tachycardia and ventricular fibrillation. In the meantime, intracellular malondialdehyde and reactive oxygen species levels were also reduced. These above results demonstrate that sevoflurane postconditioning protects the hearts against ischemia/reperfusion injury and attenuates reperfusion-induced arrhythmia, which may be associated with the regulation of lipid peroxidation and reactive oxygen species generation.

Successful management of intractable coronary spasm with a coronary stent

Although the long-term survival of patients suffering from coronary spasm is usually excellent, serious complications can develop, such as disabling pain, myocardial infarction, ventricular tachyarrhythmias, atrioventricular block and sudden cardiac death. A 40-year-old man who had intractable chest pain from coronary artery spasm suffered ventricular fibrillation and an acute anterior myocardial infarction upon first admission. The patient underwent a coronary angiogram, which revealed a spontaneous focal spasm at the proximal left anterior descending coronary artery (LAD). He was treated by the combination of nitrate and calcium channel blocker, but continued to complain of severe chest pain despite intensive medical therapy and he had to be treated in the emergency room 5 times during an 8-month follow-up period. An ergonovine coronary angiogram was performed and an intracoronary ultrasound examination, which revealed a focal spasm at the same site of the proximal LAD with a small amount of localized eccentric atheromatous plaque. A coronary artery stent was placed in the proximal LAD and his symptoms resolved. A follow-up coronary angiogram was performed 3 years after stenting and the stent remained patent without any in-stent restenosis or spasm.

Racial heterogeneity in coronary artery vasomotor reactivity: differences between Japanese and Caucasian patients

Japanese investigators have provided a substantial contribution in the understanding of coronary vasomotor reactivity. On occasions, their findings have been at variance with those undertaken on caucasian patients, raising speculation that vasomotor differences between races may exist. In a comparative review of the published literature, we evaluated the vasoreactive differences among Japanese and caucasian patients with variant angina or myocardial infarction. In variant angina, Japanese patients appear to have diffusely hyperreactive coronary arteries compared with caucasian people, manifested by their segmental rather than focal spasm, hyperreactive nonspastic vessels and multivessel spasm. These differences may reflect the increased basal tone among Japanese variant angina patients and may relate to controversial differences in endothelial nitric oxide production or autonomic nervous system activity. Provocative vasomotor studies of Japanese patients with a recent myocardial infarction report a higher incidence of inducible spasm than caucasian studies, an observation recently supported by a controlled study. Furthermore, the hyperreactivity was diffuse, occurring in both non-infarct- and infarct-related vessels. These observations support the existence of racial coronary vasomotor reactivity differences but require confirmation in further prospectively conducted studies.

Estrogen diminishes postischemic hydroxyl radical production

Reperfusion of blood flow to an ischemic myocardium is imperative to survival; ironically, it may also manifest several pathophysiological conditions. The most important of these are reperfusion arrhythmias and tissue injury and/or death. The mechanisms involved in reperfusion arrhythmias remain to be fully elucidated; however, increasing evidence indicates that reperfusion-induced arrhythmias are a free radical-mediated phenomenon. Acute administration of conjugated equine estrogen to dogs attenuates ischemia- and reperfusion-induced arrhythmias. The cardioprotective effect of estrogens in postmenopausal women is well documented, and recent studies suggest that estrogens possess strong antioxidant properties, with equine estrogens most potent. In this study we show that administration of conjugated equine estrogen to fully anesthetized dogs abolishes the burst of .OH radicals typically produced on reperfusion of the myocardium. This indicates that estrogen might attenuate reperfusion-induced ventricular arrhythmias by virtue of its antioxidant properties, suggesting a novel cardioprotective effect of the hormone.

Effects of oral administration of different doses of purified micronized flavonoid fraction on microvascular reactivity after ischaemia/reperfusion in the hamster cheek pouch

1. The effects of a purified micronized flavonoid fraction (S5682) on mean internal diameter and blood flow of arterioles and venules, as well as the functional capillary density (FCD) were evaluated in the hamster cheek pouch microvasculature before and after 90 min of total ischaemia. 2. Male hamsters were treated for ten days, twice a day, with oral doses of S5682 (5, 20, 80 and 160 mg kg-1 day-1) or placebo (10% lactose solution). The cheek pouch preparation was placed under an intravital microscope coupled to a closed circuit TV system. Local ischaemia was obtained by a cuff mounted around the neck of the everted pouch where it leaves the mouth of the hamster. 3. Measurements were performed before ischaemia, at the onset of reperfusion and 10, 20, 30, 45 and 60 min thereafter. Diameters were measured by means of an image shearing device. Red blood cell (RBC) velocity was analysed by use of the dual-slit photometric technique. Blood flow was calculated from diameters and RBC velocities. FCD, defined as the number of capillaries with flowing blood per field of observation, was also assessed. 4. During reperfusion, placebo-treated animals showed a significant vasodilatation, a decrease in blood flow and FCD and S5682-treated animals showed a clear trend, dose-dependent, towards maintaining these parameters closer to the value found before ischaemia. 5. In conclusion, our results indicate that S5682 improves the microvascular reactivity and FCD after ischaemia/reperfusion. These data suggest that S5682 could function as an antioxidant, which may explain its beneficial therapeutic effect in chronic venous insufficiency where oxidative stress is involved in the pathological mechanism.

Effects of lidocaine and diltiazem on recovery of electrophysiologic activity during partial reperfusion following severe myocardial ischemia in canine hearts

The effects of lidocaine and diltiazem on recovery of electrophysiologic activity during partial reperfusion following severe myocardial ischemia were investigated in 28 dogs. The left anterior descending artery was ligated, and the distal end was connected to the carotid artery. Myocardial ischemia was induced by retrograde blood flow for 10 minutes, after which flow-limited reperfusion (30-60% of the coronary flow before ischemia) was performed. The dogs were divided according to the agent administered before ischemia into the following three groups: saline (group S, n = 11); lidocaine (group L, n = 8, 0.07 mg/kg/min by intravenous drip infusion following 2 mg/kg intravenous injection); and diltiazem (group D, n = 9, 0.02 mg/kg/min by intravenous drip infusion. There were no significant differences among the three groups in the incidence of ventricular tachyarrhythmia, which occurred as ventricular tachycardia (VT) or ventricular fibrillation (VF). In each group, the occurrence of VT was frequently preceded by delayed potential which was initiated after reperfusion, with depressed conduction in the epicardium, suggesting reentry (82%, 96%, and 87%, not significant). The determining factors for VT with degeneration into VF were long duration of VT in groups S and L (VT with degeneration into VF vs VT without, 1.2 +/- 0.2 seconds vs 0.6 +/- 0.1 seconds, P < .05, in group S and 11.6 +/- 2.5 seconds vs 2.2 +/- 0.4 seconds, P < .05, in group L), and decrease in average R-R interval during VT in groups L and D (195 +/- 8 ms vs 313 +/- 17 ms, P< .01, in group L and 201 +/- 11 ms vs 327 +/- 28 ms, P< 0.01, in group D). In addition, occurrence of epicardial electrophysiologic activity with reduced time from onset of the QRS complex in the surface electrocardiogram to the onset of the activity during VT preceded VF in group L (VT with degeneration into VF vs VT without, 130.0 +/- 15.1 ms vs 185.8 +/- 21.4 ms, P < .05), while that with prolongation of the time had this effect in group D (116.0 +/- 15.7 ms vs 69.0 +/- 10.7 ms, P < .05). It is concluded that, even when partial reperfusion is applied, neither lidocaine nor diltiazem suppresses VT because neither drug decreases delayed potential acting as a triggering factor or suppresses VF, since the alteration of the epicardial conductivity during VT can change the VT circuit to a smaller one.

A rare indication for stenting: persistent coronary artery spasm

A 34-year-old man presenting with angina both at rest and on exertion was investigated. He developed severe ST segment elevation and a brief period of ventricular tachycardia during an exercise tolerance test. On coronary angiography, 60% fixed luminal narrowing was observed in the proximal left anterior descending coronary artery and a severe spasm developed at this site, leading to temporary total occlusion of the vessel. Successful coronary angioplasty (PTCA) was performed on this lesion, with a residual 15% narrowing. However, the patient had a recurrence of angina 3 weeks later, despite being administered high doses of nitrate and calcium antagonist. During control angiography, the lesion severity was unchanged, but spasm developed again following contrast injection. At this time, a Palmaz-Schatz stent was implanted. Calcium antagonist, nitrate, Ticlopidine and low molecular weight heparin therapy was started. There was no recurrence of symptoms during a 3-month follow-up. The exercise tolerance test, and myocardial perfusion scintigraphy findings were normal and the stent was patent without restenosis at the end of the 3-month follow-up. Intracoronary stent implantation for persistent coronary spasm refractory to conventional medical therapy can be considered a feasible and attractive treatment modality for the control of symptoms.

Stenosis severity and the occurrence of ventricular ectopic activity during acute coronary occlusion during balloon angioplasty

To elucidate the incidence and determinants of early ventricular arrhythmias (VA) during acute coronary occlusion, continuous electrocardiographic, heart rate, and blood pressure recordings were performed in 152 patients during standardized balloon occlusions of significant (50% to 95%) coronary artery stenoses. A control group of 13 patients with chronic total occlusion of a coronary artery was also studied. None of them developed VA during balloon inflation in the preexisting total occlusion of the artery. Balloon occlusion of a coronary artery was associated with occurrence of ventricular ectopy in 18 patients (VA group, 12%). The VA group had milder stenosis severity (72% vs 81%, p < 0.001) than the rest of the patients, and none of them had visible collaterals to the occluded vessel. The VA group also had ST-segment deviations more often (p < 0.05) during occlusion than patients with no VA. Occlusion of the left anterior descending artery caused VA more often (p < 0.05) than occlusion of the left circumflex or right coronary artery. No clinical or hemodynamic variable or medication was associated with the occurrence of VA. In stepwise logistic regression analysis, the only significant predictors of ventricular ectopic activity were the stenosis severity and the anterior site of coronary occlusion. Even a nonstenotic plaque can be so fragile that it is prone to rupture. The present findings suggest that such an occlusion may result in electrical instability more easily than occlusion of a more advanced coronary lesion.

Suppression of reperfusion arrhythmia by ischemic preconditioning in the rat: is it mediated by the adenosine receptor, prostaglandin, or bradykinin receptor?

The mechanism for the suppression of reperfusion arrhythmia by preconditioning (PC) remains unknown. This study aimed to examine the roles of the adenosine receptor, prostaglandin (PG), and bradykinin (BK) receptor in PC. Under pentobarbital anesthesia, the coronary artery of the rat was occluded for 5 min and then reperfused. In untreated controls, this protocol induced ventricular tachycardia (VT) in 100% of the rats and ventricular fibrillation (VF) in 60%. PC with 2 min ischemia/5 min reperfusion prior to the 5 min coronary occlusion significantly reduced the incidence of reperfusion VT and VF to 30% and 0%, respectively. This antiarrhythmic effect of the PC was not blocked when rats were pretreated with 8-phenyltheophylline (8-PT, 10 mg/kg), aspirin-DL-lysin (18 mg/kg), or a specific BK receptor antagonist, Hoe140 (20 nmol/kg). None of these agents alone significantly modified the incidence of reperfusion VT or VF. These results suggest that neither the adenosine receptor, endogenous PG, nor BK receptor play a major role in the mechanism of suppression of perfusion arrhythmias by PC in the rat heart.

Gianturco-Roubin stent placement for variant angina refractory to medical treatment

A 43-yr-old man with mild, fixed obstruction of the left anterior descending (LAD) coronary artery and severe, uncontrolled variant angina underwent placement of an endovascular stent to preserve patency of the artery. The decision for stent placement was based on several factors, including refractoriness to medical treatment and standard balloon angioplasty, documented spasm localized to the proximal LAD lesion, and the morbidity, mortality, and costs associated with the surgical approach in this type of patient. At follow-up, there was moderate restenosis of the stented coronary segment; the vasospastic angina syndrome had totally resolved.

A patient in whom self-terminating ventricular fibrillation was a manifestation of myocardial reperfusion

Self-terminating ventricular fibrillation was recorded in a 47 year old woman without coronary artery or other structural heart disease. Reperfusion was thought to be responsible for the ventricular fibrillation because the arrhythmia started while the ST segment was returning to the baseline during an episode of silent ischaemia that was probably caused by coronary spasm. This case shows that potentially lethal arrhythmias can arise during reperfusion and that ventricular fibrillation during reperfusion may be self-terminating.

Cardiac arrest and sudden unexpected death in variant angina: complications of coronary spasm that can occur in the absence of severe organic coronary stenosis

Experiences in 81 patients with variant angina were reviewed with the goal of determining which clinical features were associated with the greatest risk of angina-linked cardiac arrest (13 patients) or sudden unexpected death (9 patients). The risk of occurrence of one of these actually or potentially fatal events was approximately tripled by the presence of either a history of angina-linked syncope or documentation of serious arrhythmia complicating attacks. An unexpected finding was that the risk was increased 1.5-fold by the absence of high-grade organic coronary stenosis. Cardiac arrest and sudden death are important risks of variant angina, which can occur without the presence of severe organic coronary stenosis. These risks can be reduced by adequate vasodilator therapy that includes a calcium channel blocker.

A fast Fourier transform analysis of coronary reperfusion-induced ventricular fibrillation and the modification by dibutyryl cyclic AMP in a cat model

To investigate the effect of dibutyryl cyclic AMP (dbcAMP) on ventricular fibrillation after coronary reperfusion, the proximal portion of the anterior descending branch of left coronary artery was reperfused 20 min after ligation in 24 cats. McFee X Y Z electrocardiograms were recorded and ventricular fibrillation was analyzed using a fast Fourier transform analysis (FFT). Ventricular fibrillation occurred in 20 of 24 cases. Sixty seconds after the occurrence of ventricular fibrillation, an intracardiac infusion of dbcAMP was administered. Nine of the 20 were defibrillated and converted to sinus rhythm or junctional rhythm after the administration of dbcAMP. The amplitude and frequency of the main power spectrum of the ventricular fibrillation waves were analyzed by FFT before and after the infusion of saline or dbcAMP. In the saline group there was no significant change in FFT. However, in the dbcAMP group, the amplitude increased significantly from 0.036 +/- 0.015 (MV--2) to 0.054 +/- 0.013 (MV--2) (p < 0.01) and the frequency decreased significantly from 4.22 +/- 1.37 (Hz) to 1.33 +/- 0.91 (Hz) (p < 0.01). Those results indicate that dbcAMP increased the amplitude and decreased the frequency of the main power spectrum of ventricular fibrillation analyzed by FFT. These distinctive changes in FFT analysis were associated with defibrillation in 9 of 20 cases.

Xanthine oxidase inhibition does not limit canine infarct size

BACKGROUND

Evidence supporting the role of xanthine oxidase in myocardial reperfusion injury is based on studies with pharmacological interventions used to inhibit enzyme function. Controversy exists, however, regarding the true role of xanthine oxidase in reperfusion injury. This study was performed to determine whether xanthine oxidase inhibition limits myocardial injury due to coronary artery occlusion and reperfusion.

METHODS AND RESULTS

Anesthetized dogs underwent coronary artery occlusion (90 minutes) and reperfusion (6 hours). Oxypurinol (28 mg/kg) or amflutizole (30 mg/kg), chemically unrelated inhibitors of xanthine oxidase, or vehicle was infused intravenously 15 minutes before and 3 hours after reperfusion. Regional myocardial blood flow was determined with radiolabeled microspheres. Infarct size was determined with the tetrazolium method. Myocardial infarct size (percent of risk region) was less in oxypurinol-treated dogs, 32 +/- 16%, compared with that of the control group, 46 +/- 15%. Infarct size for the amflutizole-treated dogs, 40 +/- 21%, was not significantly different from that of the control group. There were no differences in rate-pressure product or collateral blood flow to account for differences in infarct size. Uric acid concentration in the coronary venous plasma increased after reperfusion in the dogs treated with vehicle but not in the drug-treated dogs. Xanthine oxidase inhibition was demonstrated in each of the drug treatment groups, but only oxypurinol limited the extent of myocardial injury.

CONCLUSIONS

Previously reported cardioprotective effects of allopurinol, noted to occur only when the drug was administered chronically, may be related to a property of oxypurinol, a major metabolite of allopurinol. The beneficial effect of oxypurinol is unrelated to inhibition of superoxide formation during xanthine oxidase-catalyzed oxidation of xanthine and hypoxanthine.

Reperfusion arrhythmias are rare during acute myocardial infarction and thrombolysis in man

Coronary arterial reperfusion is commonly associated, in anaesthetized animals, with severe arrhythmias, but the clinical relevance of this model remains uncertain. Continuous electrocardiographic ST-segment recording was performed immediately from admission in 38 patients who presented within six (mean 2.5) hours of the onset of acute myocardial infarction and had emergency coronary arteriography and thrombolysis with intracoronary streptokinase. All patients received high doses of isosorbide dinitrate but no prophylactic anti-arrhythmic drugs. In 19 patients, 36 occurrences of intermittent reperfusion were observed. Stable reperfusion was achieved in 32 patients. Only 14 episodes of arrhythmia (11 ventricular) were observed in 6 patients within five minutes of transient or stable reperfusion. No episodes of arrhythmia were documented within five minutes of the other 57 occurrences of reperfusion. In contrast, 215 episodes of arrhythmia (198 ventricular) not associated with reperfusion were recorded in 32 patients. Arrhythmias are commonly observed in patients during evolving acute myocardial infarction and thrombolysis but are an insensitive and rarely specific marker of reperfusion at the time when this occurs.

Ventricular fibrillation during partial reperfusion following severe myocardial ischemia in the canine model

The authors examined whether partial reperfusion protects against reperfusion ventricular fibrillation (VF) following severe acute myocardial ischemia. Fifty-seven dogs were divided into two groups. In group A (n = 21), the left anterior descending coronary artery was occluded for 10 minutes, followed by full reperfusion. In the remaining 36 dogs (group B), myocardial ischemia was induced by retrograde blood flow (RBF) for 10 minutes. Thereafter, these dogs were divided into three subgroups: in group B1 (n = 10), full reperfusion was made by a carotid-left anterior descending coronary artery bypass; in group B2 (n = 13), partial reperfusion was achieved by collateral flow into the ischemic zone due to stopping RBF; in group B3 (n = 13), RBF was continued for an additional 5 minutes. During 10 minute ischemia, the myocardial blood flow at the ischemic zone measured by the H2 gas-clearance method was 12.3 +/- 2.0 ml/min/100 g in A, 3.4 +/- 0.9 ml/min/100 g in B1, 4.7 +/- 0.6 ml/min/100 g in B2, and 4.7 +/- 0.6 ml/min/100 g in B3 (A vs B1, p less than 0.02; A vs B2 and B3, p less than 0.01). Maximal ST-segment elevation was 11.4 +/- 1.8 mV in A, 28.2 +/- 2.7 mV in B1, 25.1 +/- 3.0 mV in B2, and 27.0 +/- 1.9 mV in B3 (A vs B1, B2, and B3, p less than 0.001). Maximal conduction delay was 48.6 +/- 9.4 ms in A, 106.4 +/- 5.2 ms in B1, 101.6 +/- 9.9 ms in B2, and 91.2 +/- 5.1 ms in B3 (A vs B1, B2, and B3, p less than 0.001). The incidence of reperfusion VF was 14% (3/21) in A, 80% (8/10) in B1, and 69% (9/13) in B2 (A vs B1, p less than 0.001; A vs B2, p less than 0.005). In group B3, VF occurred in only 1 of 13 dogs for the additional 5 minutes. It is concluded that reperfusion VF occurred frequently when ischemia was severe even though the duration of ischemia was short (B1), and that reperfusion VF was not prevented by partial reperfusion when the ischemia was severe (B2).

Myocardial protection with preconditioning

Myocardial preconditioning with brief coronary artery occlusions before a sustained ischemic period is reported to reduce infarct size. To determine the number of occlusive episodes required to produce the preconditioning effect, we performed single or multiple occlusions of the left circumflex coronary artery (LCx) followed by a sustained occlusion (60 minutes) of the LCx. Anesthetized dogs underwent one (P1), six (P6), or 12 (P12) 5-minute occlusions of the LCx. Each occlusion period was followed by a 10-minute reperfusion period. A 60-minute occlusion of the LCx followed the preconditioning sequences. A control group received a 60-minute occlusion of the LCx without preconditioning. All groups were subjected to 6 hours of reperfusion after which the heart was removed for calculating infarct size (IS), area at risk (AR), and left ventricular mass (LV). The IS/AR ratio for the control group was 29.8 +/- 4.4% (n = 17), which was substantially greater (p less than 0.001) than that of the preconditioned groups: P1, 3.9 +/- 1.3% (n = 14); P6, 0.4 +/- 0.3% (n = 5); and P12, 2.9 +/- 2.8% (n = 5). There were no significant differences in the IS/AR ratio among the three preconditioned groups. The AR/LV ratio was comparable among all groups and did not differ statistically: control, 40.4 +/- 1.3%; P1, 36.2 +/- 1.7%; P6, 36.1 +/- 1.7%; and P12, 37.3 +/- 2.1%. Collateral blood flow to the inner two thirds of the risk region determined with radiolabeled microspheres during ischemia did not differ significantly between the control group (0.03 +/- 0.01 ml/min/g, n = 8) and single occlusion group (0.06 +/- 0.02 ml/min/g, n = 8), indicating that the marked disparity in infarct size could not be attributed to differences in collateral blood flow. The data indicate that preconditioning with one brief ischemic interval is as effective as preconditioning with multiple ischemic periods.

Combined adenosine and lidocaine administration limits myocardial reperfusion injury

The endogenous compound adenosine may play a role in limiting myocardial ischemia-reperfusion injury through its ability to cause vasodilation, modulate cardiac adrenergic responses, inhibit neutrophil function, or modulate energy supply and demand of the myocardium. The local anesthetic lidocaine has been shown to be protective against myocardial ischemia-reperfusion injury, although its mechanism of action remains unresolved. We hypothesized that administration of exogenous adenosine during reperfusion would limit the size of the infarct that results from a period of ischemia and reperfusion only when the animals are treated with lidocaine. Male, mongrel dogs (13.0-20.0 kg) were anesthetized (30 mg/kg i.v. sodium pentobarbital), and a left thoracotomy was performed. The left circumflex coronary artery (LCx) was isolated and instrumented with an electromagnetic flow probe, a 25-gauge nonobstructing intracoronary catheter, and a critical stenosis. The dogs were allocated randomly to one of four groups: 1) control, n = 13, (saline), 2) adenosine, n = 13, (0.15 mg/kg/ml/min i.c. for the first hour of reperfusion), 3) lidocaine, n = 9, (2.0 mg/kg i.v. given immediately before coronary artery occlusion and just before reperfusion), or 4) adenosine plus lidocaine, n = 11. The LCx was occluded for 90 minutes and reperfused for 6 hours. Regional myocardial blood flow (RMBF) was determined (n = 6 per group) at 80 minutes of occlusion and at 45 minutes of reperfusion with radiolabeled microspheres. RMBF determinations revealed an increase in blood flow to the inner two thirds of the myocardium at 45 minutes of reperfusion only in the presence of the combined treatment. Adenosine treatment alone or lidocaine treatment alone did not affect RMBF. Quantification of infarct size (triphenyltetrazolium method) expressed as a percent of the area at risk revealed a significant limitation of infarct size only in the group treated with both adenosine and lidocaine: control, 47.8 +/- 6.6%; adenosine, 45.0 +/- 3.2%; lidocaine, 46.9 +/- 6.0%; and adenosine and lidocaine, 20.8 +/- 5.6%. Statistical analyses were performed with two-way analysis of variance to account for the two individual drug treatments. The findings show that intracoronary administration of exogenous adenosine, at the dose used, is only effective at limiting myocardial infarct size when administered to lidocaine-treated animals.

Endothelial, platelet and leukocyte interactions in ischemic heart disease: insights into potential mechanisms and their clinical relevance

Recent investigations of the complex interactions among vascular endothelium, platelets and leukocytes have relevance to the pathogenesis of atherosclerosis and ischemic heart disease. Perturbations in the hemodynamic equilibrium maintained by these cellular elements may lead to vasospasm, in vivo thrombosis and a reduction in blood flow. Recent advances in the understanding of these interactions in health and disease states are summarized. The effect of pharmacologic agents on these cell-cell interactions are discussed to provide the reader with a general understanding of the relevance of these interactions in cardiovascular disease.

Effect of a critical coronary stenosis on myocardial neutrophil accumulation during ischemia and early reperfusion in dogs

In many experimental models of ischemia and reperfusion, reperfusion is performed abruptly, allowing full reactive hyperemia to occur. In the clinical setting, however, reperfusion after thrombolysis is often limited by residual stenosis. Some experimental models attempt to mimic this situation with a "critical stenosis" (defined as a coronary constriction sufficient to abolish reactive hyperemia without altering baseline flow). The purpose of this study was to determine whether preventing reactive hyperemia during the initial phase of reperfusion would modify the transmural distribution of myocardial blood flow or the myocardial accumulation of polymorphonuclear leukocytes (PMNs). The left circumflex artery was occluded for 90 minutes and then reperfused for 60 minutes in anesthetized, open-chest dogs. Autologous PMNs were isolated, labeled with 111In, and reinjected 1 hour before coronary occlusion. 125I-labeled albumin was injected simultaneously to correct for 111In associated with plasma proteins and to permit calculation of the number of PMNs in the inner, middle, and outer thirds of nonischemic and ischemic-reperfused tissue. The presence of a critical stenosis abolished reactive hyperemia during the first 5 minutes of reperfusion, but did not substantially affect blood flow measured after 55 minutes of reperfusion. In both groups, there was a significant accumulation of PMNs in all layers of the ischemic-reperfused bed compared with the nonischemic bed, and the magnitude of this PMN accumulation was not altered by the presence of a critical stenosis. Moreover, infarct size, estimated by triphenyl tetrazolium chloride (TTC) loss after 60 minutes of reperfusion, was not affected by the presence of a critical stenosis. Thus, the presence of a critical stenosis abolished the hyperemic blood flow after reperfusion but did not influence the early PMN response to ischemia and reperfusion or the early loss of TTC staining.

Reperfusion arrhythmia: myth or reality?

Early reports of "reperfusion arrhythmia" after experimental temporary coronary occlusion raised concern that these arrhythmias, particularly ventricular fibrillation and ventricular tachycardia, might occur in association with reperfusion of an occluded coronary vessel during thrombolysis. Such an occurrence could increase the risk of transfer of such patients. To provide a more definitive answer to this question, we reviewed hospital and transfer records for all patients with acute myocardial infarction transferred by our critical care transfer service between January 1, 1985, and November 30, 1987, noting the occurrence of five types of arrhythmia: ventricular fibrillation, ventricular tachycardia, premature ventricular contractions, bradycardia, and atrioventricular block, both before and during transfer. Five hundred patients with acute myocardial infarction less than 48 hours old were transferred during this period. Two hundred twenty-five patients received thrombolytic therapy; 270 did not (five unknown). The type of acute myocardial infarction was known for 471 patients: 192 were anterior, 203 were inferior, and 76 were lateral. There were no deaths during transfer. Overall survival through hospitalization was 91%. The incidence of arrhythmia was 36% before transport and 12% during transport. There was no difference in arrhythmias overall, or with respect to any of the five arrhythmias specified, between patients who received thrombolytic therapy before and during transport and those who did not. Reperfusion arrhythmia does not appear to be a clinically significant entity during the transport of patients who are receiving IV thrombolytic therapy.

Identification of a time window for therapy to reduce experimental canine myocardial injury: suppression of neutrophil activation during 72 hours of reperfusion

The cardio-protective effects of neutrophil depletion or inhibition of neutrophil activation early in the course of myocardial reperfusion has been established. Whether these treatments would be effective during extended periods of reperfusion has not been ascertained. Open-chest anesthetized dogs were subjected to left circumflex artery (LCX) occlusion for 90 minutes followed by 72 hours of reperfusion. Dogs were randomized into one of four groups: 1) control; 2) Ilo-2 (iloprost 100 ng/kg/min administered via the left atrium beginning 10 minutes after LCX occlusion and continuing 2 hours into reperfusion); 3) Ilo-48 (iloprost 100 ng/kg/min administered as above until 1 hour after reperfusion then 25 ng/kg/min for 48 hours of reperfusion; or 4) antibody (neutrophil antibody administered before occlusion and 1/2 hourly for 2 hours of reperfusion and then every 24 hours). Myocardial infarct size, as a percentage of the area at risk assessed after 72 hours of reperfusion, was significantly smaller in the antibody-treated group (32.1 +/- 5.0% mean +/- SEM) or Ilo-48 (22.6 +/- 4.0%) treatment group compared with control (48.7 +/- 5.6%) or Ilo-2 (57.6 +/- 5.2%) groups. Regional myocardial blood flow studies demonstrated that all groups developed similar degrees of ischemia. The iloprost-treated groups had lower mean arterial blood pressures during occlusion and reperfusion than groups 1 and 4 (p less than 0.05). Circulating neutrophil counts were increased in groups 1 and 2 at 24 and 48 hours after reperfusion compared to groups 3 and 4 (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of residual stenosis on infarct size and regional transmural myocardial blood flow after reperfusion

This study in dogs was designed to determine the effects of residual stenosis on infarct size and on the transmural distribution of coronary flow in the central and peripheral ischemic perfusion bed. A plastic shunt containing a Doppler flow probe was inserted between the left anterior descending coronary artery and the subclavian artery. The dogs were divided into two groups. Group 1 (N = 7) underwent total shunt occlusion for 2 hours followed by reperfusion at 50% of control flow for 2 hours. Group 2 (N = 8) underwent 2 hours of total occlusion followed by 2 hours of total reperfusion. Regional blood flow was measured by radiolabeled microspheres, and infarct areas were quantitated with triphenyl tetrazolium chloride staining. Infarct sizes expressed as a percentage of the left ventricle or as a percentage of perfusion territory were significantly (p less than 0.05) smaller in animals with total reperfusion (group 2) than in dogs with partial reperfusion (group 1). Endocardial flows in the central infarct zone were significantly higher in dogs with total reperfusion than was observed with partial reperfusion; epicardial flows were not significantly different. In the peripheral region both endocardial flows and epicardial flows with total reperfusion were significantly higher than with partial reperfusion. These studies suggest that residual stenosis after thrombolysis may increase infarct size and reduce endocardial flow in the central infarct zone and transmural flow in the peripheral zone.

Neutrophils as potential participants in acute myocardial ischemia: relevance to reperfusion

An interaction among leukocytes, platelets and endothelial cells is important in atherogenesis and in maintenance of blood flow and vascular tone. These complex cell-cell interactions are mediated by release of such metabolic substances as arachidonic acid metabolites, growth factors, oxygen free radicals and endothelium-derived relaxing factor. These substances participate in the regulation of blood flow in health and disease, and perturbation in the delicate equilibrium among various cellular elements may lead to evolution and propagation of myocardial ischemia. During reperfusion of ischemic myocardium, neutrophils together with platelets cause capillary plugging in the coronary microcirculation and exert detrimental effects on endothelial function resulting in the "no reflow" phenomenon, ventricular arrythmias, loss of coronary vascular reserve and, perhaps, extension of cellular injury. This review addresses the mechanisms of cell-cell interactions with special reference to myocardial ischemia and the potential for development of improved therapy to protect and preserve ischemic myocardium.

Rate of reperfusion blood flow modulates reperfusion injury in skeletal muscle

The mechanisms of ischemia-reperfusion (I-R) injury in skeletal muscle remain controversial. We investigated the effect of the rate of reperfusion blood flow on I-R injury in an isolated in vivo canine gracilis muscle model in six anesthetized dogs. In all animals, both gracilis muscles were subjected to 6 hr of ischemia followed by 1 hr of reperfusion. During reperfusion, one gracilis artery was partially occluded to limit the rate of reperfusion blood flow to its preischemic rate (limited reperfusion, LR), while the contralateral artery was allowed to perfuse freely at a normal rate (normal reperfusion, NR). Muscle injury was quantified by histochemical staining (triphenyltetrazolium chloride, TTC) with computerized planimetry of the infarct size, and by spectrophotometric determination of technetium-99m pyrophosphate uptake. Endothelial permeability was quantified by measurement of gracilis muscle weight gain and 125I-albumin radioactivity after intravenous injection. Results are presented as the means +/- SEM, and differences are considered to be statistically significant if P less than 0.05 by Student's t test for paired data. LR resulted in significantly less blood flow (9.7 +/- 1.7 cc/min/100 g) when compared to NR (55.7 +/- 11.6 cc/min/100 g). I-R injury was significantly reduced by LR as evidenced by a decrease in TTC infarct size from 41 +/- 7% to 11 +/- 5%, and a decrease in technetium-99m pyrophosphate uptake from 512 +/- 20 to 163 +/- 44 X 10(3) counts/min/g. LR also significantly decreased the postreperfusion edema formation as evidenced by a reduction in the muscle weight gain from 27 +/- 6 to 9 +/- 1 g, and a reduction in the 125I-albumin radioactivity from 45 +/- 14 to 32 +/- 8 counts/min/g. These data suggest that the hyperemic rate of reperfusion blood flow is a significant factor in the pathophysiology of postreperfusion edema and that clinical control of reperfusion injury in skeletal muscle may be achieved by limiting the rate of reperfusion blood flow.

Increase in experimental infarct size with digoxin in a canine model of myocardial ischemia-reperfusion injury

In the present study, dogs were pretreated with intravenous digoxin, 0.0125 mg/kg/day, for 6 to 7 consecutive days to achieve clinically relevant serum concentrations; untreated animals were used as control subjects. After pretreatment, nine digoxin-pretreated dogs and nine control dogs were anesthetized and subjected to a 60-minute occlusion of the left circumflex coronary artery, followed by 6 hours of reperfusion. Anatomic myocardial infarct size, expressed as a percentage of the areas at risk of infarction and as a percentage of the total left ventricle were: 20.2 +/- 3.3% control vs 35.4 +/- 6.2% digoxin-pretreated (p less than 0.05) and 8.6 +/- 1.3% control vs 14.7 +/- 2.5% digoxin-pretreated (p less than 0.05), respectively (2.04 +/- 0.37 ng/ml serum digoxin). Regional myocardial blood flow in the nonischemic and ischemic zones tended to be lower in digoxin-pretreated than in control animals at baseline testing and were significantly reduced in the anterior subendocardial sites of digoxin-pretreated dogs during ischemia and reperfusion. These data suggest that an exacerbation or enhancement of myocardial ischemia-reperfusion injury may occur in the presence of clinically observable serum digoxin concentrations.

Factors that determine the occurrence of reperfusion arrhythmias

The determinants of reperfusion arrhythmias were investigated in 63 open-chest dogs undergoing a 25-minute coronary artery occlusion followed by reperfusion. Heart rate correlated positively with the occurrence of reperfusion ventricular tachycardia (VT) and ventricular fibrillation (VF). Collateral flow during ischemia (radioactive microspheres) exhibited a strong negative correlation with the incidence of both VT and VF upon reperfusion. Importantly, a sensitive coupling was present, whereby small differences in flow were associated with large differences in rhythm disorders. The rise in intramyocardial CO2 tension (another index of severity of ischemia) was greater in dogs exhibiting reperfusion VT (p less than 0.001) and VF (p less than 0.08); however, this variable was significantly correlated with collateral flow (r = -0.57, p less than 0.01). The size of the occluded coronary bed, determined by postmortem perfusion, was not consistently related to VT; within a given range of occluded bed sizes, the incidence of VT was inversely related to collateral flow. Thus, reperfusion-induced VT is relatively independent of the size of the occluded bed, and is determined primarily by the degree of myocardial hypoperfusion. In contrast, VF did not develop with occluded beds less than 25% of the left ventricular mass; above this critical occluded bed size, its incidence was inversely related to collateral perfusion. Reperfusion VF is therefore determined by the association of a large occluded bed with a poor collateral flow. This study identifies and systematically analyzes three major determinants of reperfusion arrhythmias: (1) the severity of antecedent ischemia, estimated either from the degree of flow reduction or the rise in intramural CO2 tension; (2) the amount of ischemic/reperfused myocardium; and (3) the heart rate. In addition to conceptual interest and clinical implications, the findings have important implications for the design of future studies aimed at evaluating antiarrhythmic interventions in experimental models.

Iloprost inhibits neutrophil function in vitro and in vivo and limits experimental infarct size in canine heart

The prostacyclin analogue iloprost (ZK 36374) inhibits neutrophil activation in vitro, reduces neutrophil accumulation in inflammatory skin lesions, and reduces ultimate infarct size in an anesthetized open-chest canine model of regional ischemia and reperfusion. Iloprost (0.1-100 microM) inhibited the in vitro production of superoxide anion by canine neutrophils in a concentration-dependent manner. Iloprost (100 ng/kg/min i.v.) inhibited C5a-induced neutrophil migration into inflammatory skin lesions as assessed by the neutrophil-specific enzyme marker, myeloperoxidase. The myeloperoxidase activity determined 2 hours after the intradermal administration of C5a in each of the groups was control 13.3 +/- 1.8 units/g tissue (n = 12) and iloprost 6.5 +/- 0.9 units/g (n = 12), p less than 0.01. Iloprost was administered to anesthetized open-chest dogs (100 ng/kg/min) 10 minutes after left circumflex coronary artery (LCCA) occlusion and continued during the 90-minute occlusion period and the first 2 hours of reperfusion. Regional myocardial blood flow was similar between treatment groups at baseline, 5 minutes and 80 minutes after LCCA occlusion, and after 1 hour of reperfusion. Infarct size, assessed 6 hours after reperfusion, was reduced by iloprost treatment: 22.4 +/- 3.1% of the area at risk (n = 15) compared with 42.4 +/- 3.3% of control (n = 13), p less than 0.01. Iloprost treatment reduced the accumulation of neutrophils (measured by myeloperoxidase activity) in the ischemic myocardium at the interface between infarcted and noninfarcted tissue: control (n = 9) 9.0 +/- 1.8 units/g tissue, iloprost (n = 6) 2.0 +/- 0.4 units/g, p less than 0.01.(ABSTRACT TRUNCATED AT 250 WORDS)

Coronary artery spasm

Coronary artery spasm is a transient reduction in lumen diameter of an epicardial coronary artery of sufficient degree to produce objective evidence of myocardial ischemia in the absence of any significant increase in heart rate or blood pressure. In this article are summarized pathophysiological observations, the coronary angiographic anatomy of patients with coronary spasm, etiologic considerations, methods to provoke coronary artery artery spasm and their clinical usefulness, the role of coronary artery spasm in patients with clinical angina pectoris and myocardial infarction, and finally, the role of coronary artery spasm in patients undergoing coronary artery surgery.

Prostacyclin protects ischemic reperfused myocardium in the dog by inhibition of neutrophil activation

Prostacyclin (PGI2) and the stable PGI2 analogue SC39902 (6,9 alpha-epoxy,5S-fluoro-11 alpha, 15S-dehydroxyprosta-6,13E-dien-1-oic acid, sodium salt) were studied in anesthetized open-chest dogs subjected to 90 minutes of left circumflex coronary artery (LCCA) occlusion and 6 hours of reperfusion. PGI2 (50 ng/kg/min, infused into the left atrium) reduced infarct mass by 59% compared to control, but SC39902 (1.5 micrograms/kg/min) failed to produce a significant reduction in infarct size. Both PGI2 and SC39902 reduced mean arterial blood pressure, heart rate, and rate-pressure product to the same extent. Regional myocardial blood flow measured with radiolabelled tracer microspheres did not demonstrate an increase in regional blood flow to the ischemic myocardium during the 90 minutes of LCCA occlusion in the PGI2 and control treatment groups. Canine neutrophils were isolated from whole blood and activated with opsonized zymosan. PGI2 produced a concentration-dependent inhibition of neutrophil activation as measured by superoxide production in vitro, whereas SC39902 failed to effectively inhibit neutrophil activation. Neutrophil migration into inflammatory skin lesions was effectively attenuated when dogs were pretreated with PGI2 (50 ng/kg/min, intravenously). Therefore, it is suggested that the cytoprotective effect of PGI2 during myocardial ischemia and reperfusion is related to an inhibition of neutrophil migration and the production of cytotoxic activated oxygen species.

Protective effects of N-2-mercaptopropionyl glycine against myocardial reperfusion injury after neutrophil depletion in the dog: evidence for the role of intracellular-derived free radicals

Reperfusion of the previously ischemic myocardium is associated with the production of oxygen free radicals and their metabolites, which contribute to the ultimate extent of irreversible myocardial injury. The relative importance of polymorphonuclear leukocytes vs intracellular-derived oxygen metabolites has remained uncertain. We evaluated the effectiveness of a free-radical scavenger, N-2-mercaptopropionyl glycine (MPG), in limiting infarct size after ischemia/reperfusion in dogs that were depleted of neutrophils with specific antisera. Twenty-four urethane-anesthetized open-chest dogs were subjected to 90 min of ischemia by occlusion of the left circumflex coronary artery followed by 6 hr of reperfusion. Dogs were randomly assigned to receive nonimmune serum, neutrophil antiserum, or neutrophil antiserum plus MPG (20 mg/kg intra-atrially 15 min before reperfusion was initiated and for 45 min after reperfusion). Infarct size, as a percent of the area at risk, was reduced by 33% in the neutrophil antiserum group as compared with the nonimmune group (30.7 +/- 2.7% vs 45.6 +/- 3.7%, p less than .01). The combined administration of neutrophil antiserum plus MPG reduced the size of infarction by 63% of the area at risk compared with that in the nonimmune group (17.0 +/- 2.7% vs 45.6 +/- 3.7%, p less than .01). The reduction in infarct size with neutrophil antiserum plus MPG was significantly greater than that with the neutrophil antiserum alone (p less than .01). The areas at risk did not differ among the groups. Myocardial protection could not be explained on the basis of hemodynamic differences. The observation that MPG enhances the protective effects of neutrophil depletion suggests that both extramyocardial- and intramyocardial-derived oxygen free radicals contribute significantly to reperfusion-induced myocardial injury.

Disparity of reperfusion arrhythmias after reversible myocardial ischemia in open chest and conscious dogs

Myocardial reperfusion after brief, reversible ischemia is frequently associated with malignant arrhythmias in experimental animals. These observations have been extrapolated to humans despite being restricted to anesthetized, open chest preparations. No data are available regarding the incidence of reperfusion arrhythmias after reversible (less than 20 minutes) ischemia in the conscious state. Thus, reperfusion arrhythmias after a 15 minute occlusion of the left anterior descending coronary artery were compared in 24 open chest dogs (17 anesthetized with pentobarbital and 7 with chloralose plus urethane) and 25 conscious, unsedated, trained dogs. The incidence of all rhythm disorders (single premature ventricular complexes, pairs, ventricular tachycardia and fibrillation) was markedly and significantly lower in conscious than in either pentobarbital- or chloralose-anesthetized dogs. The disparity was not accounted for by differences in coronary collateral flow, coronary reactive hyperemia or occluded bed size. The conscious animals, however, exhibited lower heart rates and arterial pressures during reperfusion than did the open chest dogs, suggesting a lower level of adrenergic stimulation, which might have contributed to the reduced incidence of reperfusion arrhythmias. Coronary reperfusion after 15 minutes of occlusion is unlikely to precipitate ventricular tachyarrhythmias in the conscious, trained dog, even after severe ischemia. The occurrence of these rhythm disorders in anesthetized models may reflect the influence of surgical trauma or excessive adrenergic activity, or both. Reperfusion arrhythmias after reversible ischemia may be considerably less common in the clinical setting than previously postulated on the basis of open chest animal experiments.

Reduction of the size of infarction by allopurinol in the ischemic-reperfused canine heart

This study was performed to assess the effect of allopurinol in a canine preparation of myocardial infarction. Dogs underwent occlusion of the left circumflex coronary artery for 90 min, followed by reperfusion for 6 hr. Three groups were studied: (1) control, (2) dogs receiving 25 mg/kg allopurinol 18 hr before occlusion and 50 mg/kg 5 min before occlusion, and (3) dogs receiving allopurinol as above plus 5 mg/kg superoxide dismutase over 1 hr beginning 15 min before reperfusion. Infarct size expressed as a percentage of the area at risk was 40 +/- 4 in the control group, 22 +/- 5 in the allopurinol group (p less than .05 vs control), and 17 +/- 4 in the allopurinol plus superoxide dismutase group (p less than .05 vs control). The differences in infarct size were not due to differences in myocardial oxygen supply or demand. Neutrophil superoxide anion production was not altered by allopurinol treatment. The results suggest that myocardial xanthine oxidase may generate oxygen radicals that play a role in myocardial injury due to ischemia and reperfusion.

Postinfarction sudden death: significance of inducible ventricular tachycardia and infarct size in a conscious canine model

The relationship between inducible ventricular tachycardia in the convalescent phase of myocardial infarction and subsequent spontaneous ventricular fibrillation is uncertain. Thirty conscious instrumented dogs underwent programmed ventricular stimulation 5 days after anterior infarction; 15 had inducible ventricular tachycardia and 15 were noninducible. Following programmed ventricular stimulation, the application of a 150 uA current to the intima of the proximal circumflex artery initiated intimal damage, thrombosis, and acute ischemia of the posterolateral wall. After 20 minutes of ischemia, 73% inducible and 15% noninducible animals developed ventricular fibrillation (p less than 0.005) without previous hypotension. At 24 hours, 7% inducible and 85% noninducible animals survived (p less than 0.001). Anterior infarct size (percentage of left ventricular mass) was much larger in inducible (24.7 +/- 1.7%) than in noninducible (5.3 +/- 1.1%) (p less than 0.001) animals. Inducible ventricular tachycardia following infarction was highly predictive of spontaneous ventricular fibrillation during a later ischemic episode in this model. The mass of previously injured myocardium was a critical determinant of both.

Cardiac rhythm disorders complicating coronary arterial spasm

Practically every known form of arrhythmia may complicate vasospastic ischemia. Of special importance are sinus node arrest and ventricular fibrillation. The high incidence of arrhythmia in this syndrome may be related to the usually severe profound ischemia or to the sudden massive reperfusion; both can frequently characterize transient severe segmental spasm of an artery without pre-existing stenosis. Nitrates and calcium channel blockers may be effective in the control of vasospasm-induced arrhythmia, but other traditional antiarrhythmic agents and pacemaker treatment may be required in some patients.

Beneficial effects of nafazatrom on ischemic reperfused myocardium

The effect of nafazatrom, a new antithrombotic agent, was studied in a canine model of regional myocardial ischemia. Nafazatrom was administered 1 mg/kg intravenously every 6 h for 48 h. After 24 h of drug or placebo administration, animals underwent 90 min of occlusion of the proximal left circumflex coronary artery followed by gradual reperfusion over a period of 30 min. Twenty-four hours later, the animals were sacrificed and infarct size was determined by histochemical staining with triphenyltetrazolium chloride. Nafazatrom-treated animals had a significant reduction in infarct size expressed as a percent of the anatomical area at risk for infarction: 21 +/- 5% in the treated group vs. 41 +/- 5% in the control group (X +/- S.E.M., P less than 0.05). Histological examination confirmed the gross results of postmortem histochemical staining. Salvage of ischemically jeopardized tissue appeared to be unrelated to myocardial oxygen demand as there were no hemodynamic differences between groups. The beneficial effects of nafazatrom are presumably related to a limitation of autolytic processes on the heart during and after ischemia as a result of the drug's ability to inhibit lipoxygenase and to prevent the enzymatic degradation of prostacyclin.

Canine myocardial reperfusion injury. Its reduction by the combined administration of superoxide dismutase and catalase

Therapy directed against the toxic effects of reactive oxygen species may reduce the final extent of ischemic injury in otherwise viable tissue irreversibly injured by the abrupt reoxygenation of reperfusion. In four groups of dogs, superoxide dismutase plus catalase (groups I-III) or saline (controls) (group IV) was infused into the left atrium. Group I received the infusion for 2 hours, beginning 15 minutes before occlusion of the left circumflex coronary artery (90 minutes) and ending 15 minutes after reperfusion. Group II received the infusion for 1 hour starting 15 minutes before reperfusion. Group III received the infusion for 1 hour beginning 40 minutes after reperfusion. Dogs were killed the next day, and infarct size was determined by dissection and weighing, and confirmed histologically. Infarct size expressed as percent of the anatomic area at risk was: group I, 19.4 +/- 5.0; group II, 21.8 +/- 3.3; group III, 47.6 +/- 10.3; group IV, 43.6 +/- 3.5 (mean +/- SEM). Analysis of variance followed by Duncan's multiple range test showed that ultimate infarct size as assessed in groups I and II differed significantly (P less than 0.05) from that observed in the control animals in group IV, whereas infarct size between groups III and IV did not differ significantly (P greater than 0.05). The percent of left ventricle at risk did not differ between the four groups. The beneficial effects of superoxide dismutase plus catalase could not be explained by hemodynamic differences. Similar protection of jeopardized myocardium in groups I and II suggest that potentially viable tissue is salvaged by scavenging free radicals during early reperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Ventricular arrhythmias during ergonovine-induced episodes of variant angina

Of 95 consecutive patients with active variant angina who underwent ergonovine testing in the coronary care unit while off treatment, 24 (25%) developed serious ventricular arrhythmias: ventricular tachycardia in eight, bigeminy in seven, pairs in five, and frequent ventricular extrasystoles in four. Ergonovine-induced arrhythmias were observed more often in patients with anterior than inferior ST segment elevation (p less than 0.05). ST segment elevation was significantly higher (10.3 +/- 8.1 vs 3.1 +/- 2.1 mm) in patients who developed arrhythmias. All ventricular arrhythmias began within 3 minutes after the onset of ST segment elevation. The intravenous administration of nitroglycerin eliminated arrhythmias in 22 of 24 cases; in only two patients did ventricular arrhythmias develop after the administration of nitroglycerin. Serious ventricular arrhythmias were found during spontaneous variant angina attacks in 14 of 24 patients with ergonovine-induced arrhythmias compared to 16 of 71 patients without ergonovine-induced arrhythmias (p less than 0.001). We conclude that arrhythmias during ergonovine testing are most often caused by ischemia and not reperfusion. Patients with arrhythmias during ergonovine-induced attacks are more likely to have arrhythmias during spontaneous attacks.

Effect of BW755C in an occlusion-reperfusion model of ischemic myocardial injury

BW755C is a new antiinflammatory agent which predominantly inhibits lipoxygenase over cyclooxygenase. Effects of BW755C have been examined in a canine, occlusion-reperfusion, model of ischemic myocardial injury. In pentobarbital anesthetized open-chest dogs, the proximal left circumflex coronary artery (LCX) was occluded for 90 minutes and slowly reperfused using a micrometer-driven occluder. Thirty minutes before occlusion, animals randomly received BW755C, 3 mg/kg (n = 7), or 10 mg/kg (n = 8), or saline (n = 16) by intravenous infusion. The thoracotomy was closed and the animals subsequently were killed at 24 hours. Infarct size and anatomic area dependent on the occluded LCX were determined by a dual staining technique using triphenyltetrazolium and Evan's blue. Both doses of BW755C significantly reduced the ultimate extent of irreversible myocardial ischemic injury, whether results were expressed as grams of infarcted tissue or as percent of risk region infarcted. No difference in risk region size was observed between groups. No effects of BW755C on heart rate, arterial pressure, or left circumflex flow were observed. BW755C (10 mg/kg) did not significantly inhibit ex vivo platelet aggregation in response to collagen, adenosine diphosphate, or arachidonic acid. These results suggest that inhibition of lipoxygenase may reduce the extent of ischemic damage to the heart.

Ventricular tachyarrhythmias in Prinzmetal's variant angina: clinical significance and relation to the degree and time course of S-T segment elevation

Fifty-six patients with active Prinzmetal's variant angina were studied to determine the incidence and clinical significance of ventricular tachyarrhythmias and the correlation between arrhythmias and degree and time course of S-T segment changes during the ischemic attacks. Twenty-nine patients (Group I) had no ventricular arrhythmias in any of the 1,083 recorded episodes, while 27 patients (Group II) developed arrhythmias in 18% of the attacks. No significant differences in clinical, electrocardiographic, angiographic, or hemodynamic findings could be found between the 2 groups. In 23 of the 27 Group II patients, ventricular arrhythmias developed during maximal S-T segment elevation (occlusion arrhythmias), while in 10 they occurred during resolution of S-T segment changes (reperfusion arrhythmias); 6 of the latter patients also had occlusion arrhythmias. Eight of the 23 patients with occlusion arrhythmias and 6 of the 10 with reperfusion arrhythmias had ventricular fibrillation or ventricular tachycardia. Maximal S-T segment elevation was significantly greater (p less than 0.001) in patients with occlusion arrhythmias than in those without arrhythmias. The episodes with reperfusion arrhythmias were significantly longer (p less than 0.001) and showed a significantly greater S-T segment elevation (p less than 0.001) than those without arrhythmias in Group I patients. This study shows that significant ventricular tachyarrhythmias develop during ischemic attacks in about 50% of patients with active variant angina; clinical and angiographic features are not useful in distinguishing patients with arrhythmias from the others. Our findings suggest that in variant angina ventricular arrhythmias may be due to the effects of both coronary artery occlusion and reperfusion; both types of arrhythmias are correlated with the severity of ischemia, as measured by the degree of S-T segment elevation. Reperfusion arrhythmias also appear to be correlated with the duration of ischemia.

Relationship between sympathetic neural activity, coronary dynamics, and vulnerability to ventricular fibrillation during myocardial ischemia and reperfusion

The relationship between neural sympathetic discharge and vulnerability to ventricular fibrillation during myocardial ischemia and reperfusion was studied in 26 chloralose-anesthetized dogs. Preganglionic cardiac sympathetic impulse activity and ventricular fibrillation thresholds were separately determined before and during a 10-minute period of left anterior descending coronary artery occlusion and during release-reperfusion. Within 2 minutes of occlusion the ventricular fibrillation threshold was significantly decreased (from 25 +/- 1.3 to 16 +/- 2.3 mA, p less than 0.05) corresponding with the period of maximal activation of cardiac sympathetic preganglionic fibers (from 4.4 +/- 0.2 to 6.3 +/- 0.5 impulses/sec). Coronary sinus blood flow and oxygen tension decreased significantly. All these changes persisted for 5 to 6 minutes, thereafter returning to control levels despite continued obstruction of the coronary artery. A transient but significant reduction in ventricular fibrillation threshold also occurred with release of the occlusion but was unaccompanied by increases in sympathetic neural discharge. Bilateral stellectomy completely prevented the ventricular fibrillation threshold changes observed during coronary artery occlusion. However, there was no change in coronary sinus oxygen tension or blood flow. During reperfusion, stellectomy increased rather than decreased vulnerability to ventricular fibrillation. Stellectomy augmented the reactive hyperemic response to release-reperfusion. These findings indicate that enhanced cardiac sympathetic neural activity contributes to ventricular vulnerability associated with coronary artery obstruction. An opposite action results during release-reperfusion. Cardiac sympathetic neural discharge, by reducing the magnitude of reactive hyperemic response through influence on coronary vascular tone, exerts an antifibrillatory effect.

Determinants of arrhythmic death during coronary artery reperfusion: effect of perfusion bed size

To further our understanding of the factors determining the consequences of transient episodes of ischemia, we studied the influence of the size of the ischemic bed on the incidence of ventricular fibrillation (VF). The circumflex coronary artery (CFX) was occluded at various locations in 19 dogs. After 20 minutes of occlusion followed by 10 minutes of reperfusion the dogs were killed. The portion of the left ventricle (LV) at risk of infarcting (R/LV) was defined as the region supplied by the occluded CFX and determined by simultaneous perfusion of the CFX with saline solution, just beyond the occlusion site, and of the aorta with Evan's blue. Bread loaf slices of the heart were photographed and projected, and the normal (blue) and risk regions (unstained) traced. The product of area and slice weight yielded mass of normal and risk regions. The R/LV of dogs that died of reperfusion VF (n = 6) was 42.3 +/- 5.0%, larger (p less than 0.001) than R/LV in all surviving dogs (n = 13), 24.2 +/- 9.4%. Twelve of the 13 survivors had R/LV less than 35%, whereas all dogs that died had R/LV greater than 35% (p = 0.0005). As is true for VF occurring during coronary artery occlusion, the incidence of reperfusion VF is related to the size of the ischemic insult.

Diurnal distribution of ST-segment elevation and related arrhythmias in patients with variant angina: a study by ambulatory ECG monitoring

Twenty-four-hour ambulatory ECG recording was performed in 26 patients with variant angina to evaluate the diurnal distribution of ST-segment elevation in relation to chest pain and the incidence of arrhythmias during the episodes. During a recording period of 52 days, 364 ST-segment elevations of 1 mm or greater were observed and 79% were asymptomatic. ST-segment elevation frequently occurred between 0:00 and 9:00 hours (72%) and most frequently between 5:00 and 6:00 hours (13%). Only a few episodes occurred between 10:00 and 18:00 hours. Premature atrial contractions, premature ventricular contractions (PVCs), ventricular tachycardia (VT) and complete atrioventricular block occurred during 12% of the episodes and were more common during painful episodes (32%) than during painless ones (6%). However, VT and severe forms of PVCs (couplets and bigeminy) appeared eight times during painless episodes and nine times during painful ones. Arrhythmias occurred more frequently when the elevated ST segment started to return or was returning to the control level (n = 38) than when the ST segment was rising (n = 8). The incidence of arrhythmias was lower when the daily frequency of ischemic episodes was high. This study shows that episodes of asymptomatic coronary artery spasm predominantly occur early in the morning as symptomatic episodes; complex dysrhythmias appear during the asymptomatic episodes; arrhythmias occur predominantly during a "reperfusion period;" and more arrhythmias accompany infrequent daily episodes of ischemia than frequent ones.