Adenosine instead of supranormal potassium in cardioplegia: it is safe, efficient, and reduces the incidence of postoperative atrial fibrillation. A randomized clinical trial

OBJECTIVE

We aimed to evaluate the efficacy and safety of a cold crystalloid cardioplegic solution with adenosine (1.2 mmol/L) instead of supranormal potassium.

METHODS

Sixty low-risk patients scheduled for elective coronary artery bypass grafting (CABG) were randomized to receive standard cold crystalloid hyperkalemic cardioplegia (hyperkalemic group) or normokalemic cardioplegia in which supranormal potassium was replaced with 1.2 mmol/L adenosine (adenosine group). End points were postoperative release of troponin T and creatine kinase MB, hemodynamics measured by PiCCO arterial thermodilution catheters, perioperative release of markers of endothelial activation and injury, and clinical course.

RESULTS

The adenosine group had a significantly shorter time to arrest than did the hyperkalemic group (mean ± standard deviation, 11 ± 5 vs 44 ± 18 seconds; P < .001). Three hearts in the adenosine group were probably not adequately drained and received additional hyperkalemic cardioplegia to maintain satisfactory cardioplegic arrest. There were no differences between groups with respect to perioperative release of markers of endothelial activation or injury and no differences between groups in postoperative release of troponin T or creatine kinase MB. Postoperative hemodynamics including cardiac index were similar between groups. The incidence of postoperative atrial fibrillation was significantly lower in the adenosine group than in the hyperkalemic group (4 vs 15; P = .01).

CONCLUSIONS

Adenosine instead of hyperkalemia in cold crystalloid cardioplegia is safe, gives more rapid cardiac arrest, and affords similar cardioprotection and maintenance of hemodynamic parameters, together with a marked reduction in the incidence of postoperative atrial fibrillation.

Pretreatment with the nitric oxide donor SNAP or nerve transection blocks humoral preconditioning by remote limb ischemia or intra-arterial adenosine

We have previously shown that remote ischemic preconditioning (rIPC) by transient limb ischemia leads to the release of a circulating factor(s) that induces potent myocardial protection. Intra-arterial injection of adenosine into a limb also leads to cardioprotection, but the mechanism of its signal transduction is poorly understood. Eleven groups of rabbits received saline control or rIPC or adenosine administration with additional pretreatment with the nitric oxide (NO) synthase blocker N(G)-nitro-l-arginine methyl ester, the NO donor S-nitroso-N-acetylpenicillamine, its non-NO-donating derivative N-acetylpenicillamine, or femoral nerve section. Blood was then drawn from each animal, and the dialysate of the plasma was used to perfuse a naïve heart from an untreated donor. Infarct size was measured after 30 min of global ischemia and 120 min reperfusion. When compared with that of the control, mean infarct size was significantly smaller in groups treated with rIPC alone (P < 0.01) and intra-arterial adenosine (P < 0.01). Pretreatment with N(G)-nitro-l-arginine methyl ester or N-acetylpenicillamine did not affect the level of protection induced by rIPC (P = not significant, compared with rIPC alone) or intra-arterial adenosine (P = not significant, compared with intra-arterial adenosine alone), but prior femoral nerve transection or pretreatment with S-nitroso-N-acetylpenicillamine abolished the cardioprotective effect of intra-arterial adenosine and rIPC. Intra-arterial adenosine, like rIPC, releases a blood-borne cardioprotective factor(s) that is dependent on an intact femoral nerve and is inhibited by pretreatment with a NO donor. These results may be important when designing or assessing the results of clinical trials of adenosine or rIPC cardioprotection, where NO donors are used as part of therapy.

Mechanical restitution curves reflect post-ischemic stunning in pigs

OBJECTIVES

The time constant of mechanical restitution (T(MRC)), proposed to reflect changes in calcium release and uptake, has been shown to increase in left ventricular (LV) failure. In this study, we tested the hypothesis that T(MRC) also can identify post-ischemic, reversible LV dysfunction (stunning).

DESIGN

Stunning was induced by a series of left main coronary artery occlusions in eight anesthetized open chest pigs. Left ventricular pressure-volume relations were assessed using a pressure-volume catheter during right atrial pacing. Mechanical restitution curves (MRCs) were constructed using two different measures of contractile response: maximal first derivative of pressure (CR(dP/dtmax)) and stroke work (CR(SW)).

RESULTS

Mean arterial pressure, stroke volume and dP/dtmax were decreased 30 min after stunning. Slopes of end-systolic pressure volume relation and preload recruitable stroke work, however, showed no significant changes after stunning. For MRCs based on CR(dP/dtmax), T(MRC) increased in all eight animals. Using CR(SW), T(MRC) increased in seven out of eight pigs.

CONCLUSIONS

Ischemia-reperfusion induce changes in MRCs based on CR(dP/dtmax), and CR(SW). The MRC concept may have potential as a clinical left ventricular performance index.

Unilateral adrenal haemorrhage following systemic thrombolysis

We report a case of unilateral adrenal bleeding, worsened or initiated by systemic thrombolytic therapy given for a suspected myocardial infarction. Initial clinical diagnosis was ruptured aortic aneurysm or aortic dissection. A preoperative contrast-enhanced computer tomography (CT) scan showed a possible bleeding from the left adrenal gland. An emergency left subcostal retroperitoneal approach revealed a ruptured and bleeding adrenal gland and its arteries were ligated.

Adenosine instead of supranormal potassium in cardioplegic solution improves cardioprotection

OBJECTIVE

To determine whether adenosine instead of supranormal potassium in cold crystalloid cardioplegia gives satisfactory cardiac arrest and improved cardioprotection. Cold crystalloid cardioplegia with adenosine, procaine and magnesium (A) was compared with standard cold crystalloid hyperkalemic cardioplegia (K).

METHODS

Sixteen pigs were randomized to receive either cold K (n=8) or A (n=8), where hyperkalemia was substituted with 1.2 mM adenosine. The cold (6 degrees C) cardioplegia was given intermittently and antegradely, with an aortic cross-clamp time of 1 h. Hemodynamic data was continuously measured and pressure-volume conductance catheters were used to determine global left ventricular systolic and diastolic function. Coronary flow and O2 content differences allowed determination of left ventricular energetics. Blood samples, and left ventricular microdialysis were used to measure parameters of ischemia. Measurements were done at 1 and 2 h after cross-clamp release.

RESULTS

Mean arterial pressure was reduced with 55 mmHg (standard deviation, SD: 19) in the K group versus 30 mmHg (SD: 14) in the A group 2 h after cross-clamp release (p=0.030). Left ventricular contractility expressed as slope of the preload recruitable stroke work index (Mw) was reduced to 53% (SD: 14) in the K group versus 78% (SD: 23) in the A group 2h after cross-clamp release (p=0.046). Reduction of maximum of first derivate of pressure with respect to time (dP/dtmax) was 804 mmHg/s (SD: 189) in the K group versus 538 mmHg/s (SD: 184) in the A group (p=0.033). The slope of the myocardial oxygen consumption-pressure volume area was at 2 h reperfusion increased from 1.37 (SD: 0.64) to 2.86 (SD: 1.27) in the K group, whereas no shift was detected in the A group (p=0.019). Cardiac troponin T measured in the coronary sinus 1 h after cross-clamp release was 1.25 microg/l (SD: 0.64) in the K group versus 0.73 microg/l (SD: 0.31) in the A group (p=0.046).

CONCLUSION

Adenosine instead of supranormal potassium in cold crystalloid cardioplegia gives satisfactory cardiac arrest, improves post cardioplegic left ventricular systolic function and efficiency, and attenuates myocardial cell damage.

Mechanical restitution curves: a possible load independent assessment of contractile function

OBJECTIVE

The time constant of mechanical restitution (T((MRC))), proposed to reflect changes in calcium release and uptake, has been shown to increase in left ventricular (LV) failure, and might have a potential as an index of contractile function. However, in vivo studies of the effect on T((MRC)) of changing loading conditions in the normal and failing heart have not been reported. Consequently, in this study, we tested the hypothesis that the increase in T((MRC)) in vivo is independent of preload and afterload.

METHODS

Left ventricular pressure-volume loops were assessed at baseline in eight open chest pigs using the combined pressure-volume conductance catheter technique during right atrial pacing at 120b/min. Mechanical restitution curves (MRC) were constructed during four different loading conditions in all eight animals: uninfluenced load, reduced preload (balloon catheter in v. cava inferior), increased afterload (balloon catheter in descending aorta), and increased preload combined with reduced afterload (aortocaval shunting). Acute LV failure was then induced by microembolization through the left main coronary artery, and the experimental protocol was repeated. Contractile response was defined as the maximal first derivative of pressure (dP/dt(max)), and T((MRC)) was calculated using a least square approximation algorithm.

RESULTS

Hemodynamic data 30min after microembolization showed decreased mean arterial pressure (98+/-14-67+/-10mmHg, (mean+/-SD) P<0.0001) and dP/dt(max) (1482+/-193-1001+/-125mmHg/s, P=0.001). Stroke volume decreased from 30+/-5 to 20+/-5ml (P<0.0001) compared to baseline, and preload recruitable stroke work decreased from 52+/-7 to 31+/-10mmHg (P=0.002). T((MRC)) increased in all eight animals after induction of LV failure at all loading conditions. There was no difference between the different loading conditions at baseline, nor at LV heart failure, but T((MRC)) increased significantly after the induction of heart failure (ANOVA, two ways).

CONCLUSIONS

We have shown that the left ventricular T((MRC)) increases after developed heart failure. The increase in T((MRC)) was independent on loading conditions and thus have a potential for a contractility index.

Contractile recovery of heart muscle after hypothermic hypoxia is improved by nicorandil via mitochondrial K(ATP) channels

BACKGROUND

The ATP-sensitive potassium channel (K(ATP)) opener nicorandil used instead of potassium in hypothermic cardioplegia significantly improves preservation of cardiac function and energetics in the in situ heart preparation. The present study, therefore, examines the effect of nicorandil at different temperatures and the role of sarcolemmal and mitochondrial K(ATP) channels under ex vivo conditions using contractile force (CF) and action potential duration (APD) as end points.

METHODS

Guinea-pig papillary muscles at 37, 27, or 22 degrees C (1Hz) were exposed to nicorandil 0.2-1.1 mM. The contributions of K(ATP) channel subtypes in cardioprotection were examined using mitochondrial (mito) (0.1 mM) or non-selective (1.0 mM) concentrations of nicorandil, mito K(ATP) blocker 5-hydroxyl decanoate (5HD, 300 microM) or sarcolemmal (sarc) K(ATP) blocker HMR1098 (30 microM) before and during 140 min of hypothermic (22 degrees C) glucose-free hypoxia.

RESULTS

Nicorandil >0.5 mM shortened the APD, and this was abolished by hypothermia and HMR1098 but not by 5HD. Nicorandil in both tested concentrations preserved contractile force after hypoxia-reoxygenation significantly better than control (73.7+/-4.4% and 75.8+/-3.9% vs 40.6+/-2.6%, n=6 in each group). Protection was blocked by 5HD but not by HMR1098. 5HD and HMR1098 alone did not change recovery of contractile force compared to control.

CONCLUSION

Shortening of APD and activation of sarc K(ATP) by nicorandil were not related to myocardial protection. Thus, the mito K(ATP) seems to play a significant role in cardioprotection compared to the sarc K(ATP) also when substrate depletion and hypoxia are combined with hypothermia.

Clinical testing of nicorandil supplemented normokalemic cardioplegic solution

Does nicorandil instead of supranormal potassium safely provide cardioplegia and cardioprotection in humans? Fifty patients eligible for coronary artery surgery were randomly divided into two groups; one group received standard St Thomas' Hospital solution (STHS) and the other group got a crystalloid solution in which supranormal potassium was replaced with 0.2 mmol/l nicorandil. We measured time to arrest, rhythm abnormalities, pre- and postoperative troponin-T, CK-MB and myoglobin release as well as hemodynamic parameters. Time to arrest was significantly shorter in the STHS group (41.0+/-16.8 s) than in the nicorandil group (120.9+/-78.8 s, P<0.001). Four patients in the nicorandil group needed additional STHS to achieve satisfactory cardiac arrest. Troponin-T was elevated in the nicorandil group at four (P=0.042) and at eight (P=0.044) hours after surgery, myoglobin levels were elevated at 0 h after surgery (P=0.014), CK-MB levels were not group different. Hemodynamic performance was similar in both groups. Potassium should probably not be replaced by nicorandil alone in the cardioplegic solution. This study of low-risk patients with short (43.2 min) aortic cross-clamp times showed similar cardioprotection as revealed by hemodynamic performance whereas early release of troponin-T and myoglobin release in the nicorandil group raised some concern.

Nitric oxide synthase inhibition impairs myocardial efficiency and ventriculo-arterial matching in acute ischemic heart failure

BACKGROUND AND AIMS

The effect of nitric oxide (NO) manipulation in acute heart failure has not been sufficiently investigated. Therefore, we assessed the impact of NO-synthase (NOS) inhibition on left ventricular (LV) function and energetics as well as overall hemodynamics, in a porcine model of acute ischemic LV failure.

METHODS

Acute heart failure was induced by left coronary artery microembolization in fourteen anesthetized pigs. LV pressure-volume relationships and mechanical work (PVA) were assessed 30 min after stable heart failure, using pressure-conductance catheters. Myocardial oxygen consumption (MVO(2)) was determined from coronary flow and coronary arteriovenous oxygen difference. Microembolization led to a significant decrease in cardiac output, arterial pressure and LV systolic and diastolic performance. Animals were then randomized to a control group (n=7) or to receive 15 mg/kg N(omega)-Nitro-L-arginine-metyl ester (n=7), an inhibitor of NO synthase (NOS).

RESULTS

Measurements 15 min later revealed that NOS inhibited animals had significantly reduced cardiac output (1.53+/-0.45 vs. 2.13+/-0.49 l/min, P=0.003) and stroke work (1054+/-461 vs. 1296+/-348 mmHg ml, P=0.03), and also displayed a significant increase in the slope of the MVO(2)-PVA relationship (2.57+/-0.53 vs. 1.92+/-0.15, P=0.008), i.e. an inefficient chemomechanical coupling. NOS inhibition did not alter contractility, diastolic function or arterial pressure, but afterload was significantly increased compared to controls (arterial elastance 6.03+/-1.48 vs. 2.74+/-0.34 mmHg/ml, P=0.009).

CONCLUSION

Inhibition of NOS in experimental acute heart failure increased afterload without altering left ventricular systolic and diastolic function. Consequently, cardiac output was reduced. Furthermore, mechanoenergetic efficiency was severely impaired. NOS inhibition in acute heart failure and cardiogenic shock warrants further investigations.

Intraaortic Balloon Pumping Improves Hemodynamics and Right Ventricular Efficiency in Acute Ischemic Right Ventricular Failure

BACKGROUND

Left ventricular unloading has a potentially deleterious effect in right ventricular failure as a result of altered septal interplay. However, a positive effect of an intraaortic balloon pump during right ventricular failure has been suggested. We investigated the impact of intraaortic balloon pumping on hemodynamics and both left and right ventricular function in an experimental model of isolated right ventricular failure.

METHODS

Sixteen anesthetized pigs (25 to 34 kg) were used in an in vivo model. Pressure-conductance catheters assessed right and left ventricular pressure-volume relationships. Acute right ventricular failure was induced by right coronary microembolization, and led to severely impaired right ventricular function, reduced cardiac output and arterial pressure, and an increased pulmonary vascular resistance and pulmonary arterial elastance. Animals were then randomized to balloon pump or control groups and evaluated with respect to hemodynamics and ventricular function after 1 hour.

RESULTS

Intraaortic balloon pumping did not alter right or left ventricular contractility. However, balloon pump-treated animals had significantly improved cardiac output (+18% +/- 18% versus -6% +/- 7%; p = 0.003) and mean arterial pressure (+36% +/- 30% versus -7% +/- 14%; p = 0.004) compared with controls. Animals in the balloon pump group had lower pulmonary vascular resistance (795 +/- 63 versus 912 +/- 259 dynes . sec . cm(-5); p < 0.01) and pulmonary arterial elastance (1.14 +/- 0.20 versus 1.69 +/- 0.65 mm Hg/mL; p < 0.01), and increased stroke volume (22.3 +/- 4.7 versus 17.9 +/- 4.7 mL; p = 0.016). Right ventricular efficiency was also improved in the balloon pump group (stroke work per pressure-volume area = 0.60 +/- 0.14 versus 0.41 +/- 0.12; p < 0.01).

CONCLUSIONS

Intraaortic balloon pump support does not alter right or left ventricular function in acute right ventricular failure. However, arterial pressure, cardiac output, and right ventricular efficiency are improved, possibly because of a balloon pump-induced reduction in pulmonary arterial resistance.

Mechanoenergetic inefficiency in the septic left ventricle is due to enhanced oxygen requirements for excitation?contraction coupling

OBJECTIVE

Myocardial oxygen consumption (MVO2) in the septic myocardium is increased despite reduced left ventricular mechanical work. We investigated the mechanism behind this energetic inefficiency in the septic myocardium.

METHODS

To clarify whether energy consumption in basal metabolism or excitation-contraction (EC) coupling is elevated in the septic myocardium, we separated MVO2 used for these two processes. We assessed hemodynamics, left ventricular pressure-volume area, left ventricular MVO2, myocardial substrate metabolism and the inflammatory response in eight control pigs and in eight septic pigs receiving E. coli endotoxin. Using cardiopulmonary bypass (CPB), unloaded MVO2 was assessed before and after arrest of electromechanical activity using KCl infusions.

RESULTS

Unloaded MVO2 was significantly higher in the septic group compared to the control group (65.7 +/- 12.9 vs. 43.3 +/- 15.1 J.min(-1).100 g LV(-1), p < 0.005), but basal MVO2 after 5 min KCl arrest was equal in the two groups. No difference in mechanical energy consumption or substrate metabolism was observed between groups.

CONCLUSION

Basal MVO2 in the septic myocardium is not elevated, but an increased MVO2 for EC coupling is responsible for the energetic inefficiency.

Replacing potassium with nicorandil in cold St. Thomas' Hospital cardioplegia improves preservation of energetics and function in pig hearts

BACKGROUND

To determine whether the adenosine triphosphate-sensitive potassium channel opener nicorandil, instead of potassium in cold crystalloid cardioplegia, may enhance cardioprotection, crystalloid cardioplegia with nicorandil, magnesium, and procaine was compared with standard crystalloid cardioplegia in terms of left ventricular performance and efficiency.

METHODS

Sixteen pigs were randomly assigned to receive cold hyperkalemic crystalloid cardioplegia (n = 8) or nicorandil in cold saline (n = 8). Cold (4 degrees C) cardioplegic solutions were given antegradely and intermittently, with a cross-clamp time of 60 minutes. The preload recruitable stroke work relationship (PRSW), pressure-volume area (PVA), and myocardial oxygen consumption (MVO(2)) were calculated at baseline and at one and two hours following cross-clamp release, using combined pressure-volume conductance catheters, coronary flow probes, and O(2)-content differences.

RESULTS

The left ventricular contractility expressed in PRSW was reduced to 58% (standard deviation [SD]: 20) of baseline in the crystalloid group and to 89% (SD: 20) in the nicorandil group two hours after cross-clamp release (p = 0.044). The slope of the MVO(2)-PVA relationship increased in the crystalloid group from 1.59 (SD: 0.22) before cardioplegia to 2.55 (SD: 0.73) afterwards, significantly more than in the nicorandil group, where the slope changed from 1.69 (SD: 0.30) to 1.95 (SD: 0.47) (p = 0.027).

CONCLUSIONS

Nicorandil in a crystalloid cardioplegic solution was easily employed and contractility was significantly better than after standard hyperkalemic cardioplegia. The smaller shift of the slope in the MVO(2)-PVA relationship in the nicorandil group shows improved efficiency in oxygen to mechanical transfer compared with the crystalloid group.

Superior myocardial protection with nicorandil cardioplegia

OBJECTIVE

The ATP-sensitive potassium channel (K(ATP)) activator nicorandil used as cardioplegic agent may protect the left ventricle during cardiac arrest. Nicorandil in cold blood was compared with standard hyperkalemic blood and crystalloid cardioplegia.

METHODS

Twenty-one pigs were randomly assigned to three groups: (1) cold hyperkalemic crystalloid (n=7); (2) cold hyperkalemic blood (n=7); and (3) nicorandil as cardioplegia in cold blood (n=7). Left ventricular mechanical performance, pressure-volume area (PVA) and myocardial oxygen consumption (MVO(2)) were measured before and at 1 and at 2 h after 60 min of cold global ischemia on cardiopulmonary bypass using intraventricular pressure-volume conductance catheters, coronary flow probes and O(2)-content difference.

RESULTS

The slope (M(w)) of the stroke work end-diastolic volume relationship, the preload recriutable stroke work relationship, was unchanged after ischemia in the nicorandil group, but was reduced to averaged 62.5% (standard deviation 14) of baseline values in both hyperkalemic perfusions (P<0.05). The slope of the MVO(2)-PVA relationship was unchanged after nicorandil cardioplegia while the slope after hyperkalemic blood and crystalloid cardioplegia increased with 33% (P<0.02) and 52% (P<0.02) of baseline values, respectively.

CONCLUSIONS

Nicorandil as sole cardioplegic agent in cold blood given intermittently preserves left ventricular contractility and myocardial energetics significantly better than traditional forms of cardioplegia after cardiac arrest.

Preserved myocardial energetics in acute ischemic left ventricular failure -- studies in an experimental pig model

OBJECTIVE

We hypothesised that acute ischemic left ventricular failure is characterised by depressed systolic and diastolic function combined with inefficiency in oxygen to mechanical work energy transfer.

METHODS

Eight anaesthetised pigs (32+/-3 kg) were employed in an in vivo open chest model. Intraventricular combined pressure and conductance catheters were used to generate continuous left ventricular pressure-volume relations. Myocardial oxygen consumption (MVO(2)) was determined from coronary flow and coronary arteriovenous oxygen difference. After baseline measurements, ischemia was induced by repeated left coronary injections of 50 microm polystyrene microspheres until stroke volume was reduced by 30%. Haemodynamic and biochemical measurements were repeated 30, 90 and 150 min after microembolisation.

RESULTS

Coronary embolisation induced a significant reduction in stroke work (2749+/-504-1473+/-449 mmHg ml, P<0.05) at 30 min compared to baseline. Post-embolic contractility was reduced measured by the slope of the preload recruitable stroke work index (66.2+/-12.8-50.0+/-5.8 mmHg, P<0.05) and the slope of the curvilinearly fitted end-systolic pressure-volume relation in V(0) (7.1+/-2.2-4.9+/-2.2 mmHg/ml, P<0.05). The dP/dt(min) decreased (2076+/-291-1468+/-266 mmHg/s, P<0.05), but there was no significant change in diastolic stiffness or Tau. Following the 30 min measurements, there were only small changes in most indices. We found no change in myocardial oxygen consumption for basal metabolic processes or excitation-contraction coupling (unloaded MVO(2)), and there were no changes in conversion of oxygen to total mechanical work (MVO(2)-PVA slope). However, decreased mechanical efficiency (SW/MVO(2)) paralleled an increased ratio of arterial elastance to ventricular elastance.

CONCLUSIONS

Coronary microembolisation in pigs induce a stable ischemic left ventricular failure characterised by reduced contractility and minimally impaired diastolic function. In this acute ischemic left ventricular failure, the main contributor to all over cardiovascular inefficiency is increased ratio of arterial- to ventricular elastance, a setting that impairs mechanical efficiency. However, efficiency of oxygen to total mechanical work transfer in the myocardium is unaltered. The mechanism behind this finding is elusive and warrants further investigation.

Vasodilation and mechanoenergetic inefficiency dominates the effect of the "Ca(2+)-sensitizer" MCI-154 in intact pigs

OBJECTIVE

Ca(2+)-sensitizing agents hold potential as ideal cardiac inotropes, but effects in intact animals are scarcely described. We evaluated a pyridazinone derivative, MCI-154, for hemodynamic, inotropic, mechanoenergetic and oxidative metabolic effects.

DESIGN

Intracavitary left ventricular (LV) pressure and conductance (volume) was assessed in open chest anesthetized pigs (n = 6). Contractile performance, pressure-volume area (PVA) and myocardial oxygen consumption (MVO(2)) were assessed. Myocardial substrate uptake and production of (14)CO(2 )(from glucose) and (3)H(2)O (from fatty acids) were monitored. MCI-154 administration: "low range": 0.1, 0.2, 0.3, 0.5 microg/kg/min and "high range": 0.75, 1.0, 2.0, 3.0 microg/kg/min. Parameters were compared with baseline and a time reference group (n = 7).

RESULTS

MCI-154 induced a progressive dose-dependent decrease in systemic vascular resistance, with a concomitant increase in heart rate and cardiac output. Contractility increased only in the high-dose range, and mechanoenergetic efficiency was significantly reduced by drug infusion in all doses.

CONCLUSION

The pyridazinone derivative MCI-154 has minimal inotropic action, induces a significant "oxygen waste", and decreases vascular resistance in intact pigs. A potent phosphodiesterase inhibitory effect may explain this, which suggests further drug refinement.

[Virtual reality in medical education]

Virtual reality technology has found new applications in industry over the last few years. Medical literature has for several years predicted a break-through in this technology for medical education. Although there is a great potential for this technology in medical education, there seems to be a wide gap between expectations and actual possibilities at present. State of the technology was explored by participation at the conference "Medicine meets virtual reality V" (San Diego Jan. 22-25 1997) and a visit to one of the leading laboratories on virtual reality in medical education. In this paper we introduce some of the basic terminology and technology, review some of the topics covered by the conference, and describe projects running in one of the leading laboratories on virtual reality technology for medical education. With this information in mind, we discuss potential applications of the current technology in medical education. Current virtual reality systems are judged to be too costly and their usefulness in education too limited for routine use in medical education.