SummaryClassically haemodilution is regarded as causing coagulopathy. However, haemodilution with saline seems to cause a hypercoagulable state both in vivo and in vitro. The aim of the present study was to measure the effect of mild to severe haemodilution using thrombelastography. Blood samples were taken in 12 healthy volunteers and divided into seven aliquots. One aliquot was undiluted and acted as control. The other six were diluted with normal saline, Ringer Acetate, 4% albumin, Dextran 70, 6% and 10% hydroxyethylstarch to 10%, 20%, 40%, 50% and 60% dilution. The dilution was checked by measuring the haemoglobin concentration. Each aliquot was placed in a temperature-controlled thrombelastography channel. Increased coagulation activity, as measured by thrombelastography changes, was detected at low and medium levels of dilution with all the tested solutions. At more than 40% dilution, coagulation returned to normal while in the case of dextran and hydroxyethylstarch coagulopathy developed. For crystalloids and albumin, dilution had to exceed 50% before coagulation was impaired. If these findings can be reproduced in vivo, they may have implications for transfusion practice and prophylaxis against thrombosis.Keywords Coagulation: haemodilution; thrombelastography. Correspondence to: Dr K. Ekseth E-mail: kare.ekseth@rikshospitalet.no Accepted: 14 May 2002 Haemodilution is common following blood loss. Traditionally the focus during haemodilution has been on the oxygen carrying capacity of blood [1], and haemodilution has generally been regarded as a cause of hypocoagulation. However, in 1950 Tocantins et al. reported that moderate blood dilution with normal saline caused accelerated coagulation. Numerous reports describing alterations of coagulation during haemodilution followed [2][3][4][5][6]. During normovolaemic haemodilution in patients under anaesthesia, abnormal haemostasis develops before impaired global tissue oxygenation [7].Thrombelastography was developed as a research tool [8] but has been developed into a clinically useful coagulation monitor [9]. Thrombelastography can be used at the bedside and can detect impaired coagulation as well as hypercoagulable states. By using thrombelastography, Tuman et al. found increased coagulability with progressive blood loss, even when losses were replaced by crystalloids and packed red cells [3].Therefore the aim of the present investigation was to use thrombelastography in vitro to find the level of dilution required to cause hypercoagulation with commonly used crystalloids and colloids. We also wanted to determine whether the degree of dilution influenced coagulation. MethodsThe thrombelastograph (Haemoscope Corp., 5693 West Howard Street ⁄ Niles, IL 60714, USA) consists of a heated (37°C) cuvette containing 0.36 ml of whole blood. A pin suspended by a torsion wire is lowered into the blood. The cuvette oscillates on its vertical axis through 4.0-4.5 degrees. While the blood remains liquid, Anaesthesia, 2002Anaesthesia, , 57, pages 1102Anaesthesia, -1...

Aims: To describe the effects of the K Ca 2 channel inhibitor AP30663 in pigs regarding tolerability, cardiac electrophysiology, pharmacokinetics, atrial functional selectivity, effectiveness in cardioversion of tachy-pacing induced vernakalant-resistant atrial fibrillation (AF), and prevention of reinduction of AF. Methods and Results: Six healthy pigs with implanted pacemakers and equipped with a Holter monitor were used to compare the effects of increasing doses (0, 5, 10, 15, 20, and 25 mg/kg) of AP30663 on the right atrial effective refractory period (AERP) and on various ECG parameters, including the QT interval. Ten pigs with implanted neurostimulators were long-term atrially tachypaced (A-TP) until sustained vernakalant-resistant AF was present. 20 mg/kg AP30663 was tested to discover if it could successfully convert vernakalantresistant AF to sinus rhythm (SR) and protect against reinduction of AF. Seven anesthetized pigs were used for pharmacokinetic experiments. Two pigs received an infusion of 20 mg/kg AP30663 over 60 min while five pigs received 5 mg/kg AP30663 over 30 min. Blood samples were collected before, during, and after infusion on AP30663. AP30663 was well-tolerated and prominently increased the AERP in pigs with little effect on ventricular repolarization. Furthermore, it converted A-TP induced AF that had become unresponsive to vernakalant, and it prevented reinduction of AF in pigs. Both a >30 ms increase of the AERP and conversion of AF occurred in different pigs at a free plasma concentration level of around 1.0-1.4 µM of AP30663, which was achieved at a dose level of 5 mg/kg. Conclusion: AP30663 has shown properties in animals that would be of clinical interest in man.

Aims: Small conductance Ca 2+ -activated K + channels (SK channels, K Ca 2) are a new target for treatment of atrial fibrillation (AF). AP30663 is a small molecule inhibitor of K Ca 2 channels that is currently in clinical development for treatment of AF. The aim of this study is to present the electrophysiological profile and mechanism of action of AP30663 and its efficacy in prolonging atrial refractoriness in rodents, and by bioinformatic analysis investigate if genetic variants in KCNN2 or KCNN3 influence the expression level of these in human heart tissue.Methods and Results: Whole-cell and inside-out patch-clamp recordings of heterologously expressed K Ca 2 channels revealed that AP30663 inhibits K Ca 2 channels with minor effects on other relevant cardiac ion channels. AP30663 modulates the K Ca 2.3 channel by right-shifting the Ca 2+ -activation curve. In isolated guinea pig hearts AP30663 significantly prolonged the atrial effective refractory period (AERP) with minor effects on the QT-interval corrected for heart rate. Similarly, in anaesthetized rats 5 and 10 mg/kg of AP30663 changed the AERP to 130.7±5.4% and 189.9±18.6 of baseline values. The expression quantitative trait loci analyses revealed that the genome wide association studies for AF SNP rs13376333 in KCNN3 is associated with increased mRNA expression of KCNN3 in human atrial appendage tissue.Conclusions: AP30663 is a novel negative allosteric modulator of K Ca 2 channels that concentration-dependently prolonged rodent atrial refractoriness with minor effects on the QT-interval. Moreover, AF associated SNPs in KCNN3 influence KCNN3 mRNA expression in human atrial tissue. These properties support continued development of AP30663 for treatment of AF in man.

In isolated human atrial cardiomyocytes, inhibition of K2P3.1 K(+) channels results in action potential (action potential duration (APD)) prolongation. It has therefore been postulated that K2P3.1 (KCNK3), together with K2P9.1 (KCNK9), could represent novel drug targets for the treatment of atrial fibrillation (AF). However, it is unknown whether these findings in isolated cells translate to the whole heart. The purposes of this study were to investigate the expression levels of KCNK3 and KCNK9 in human hearts and two relevant rodent models and determine the antiarrhythmic potential of K2P3.1 inhibition in isolated whole-heart preparations. By quantitative PCR, we found that KCNK3 is predominantly expressed in human atria whereas KCNK9 was not detectable in heart human tissue. No differences were found between patients in AF or sinus rhythm. The expression in guinea pig heart resembled humans whereas rats displayed a more uniform expression of KCNK3 between atria and ventricle. In voltage-clamp experiments, ML365 and A293 were found to be potent and selective inhibitors of K2P3.1, but at pH 7.4, they failed to prolong atrial APD and refractory period (effective refractory period (ERP)) in isolated perfused rat and guinea pig hearts. At pH 7.8, which augments K2P3.1 currents, pharmacological channel inhibition produced a significant prolongation of atrial ERP (11.6 %, p = 0.004) without prolonging ventricular APD but did not display a significant antiarrhythmic effect in our guinea pig AF model (3/8 hearts converted on A293 vs 0/7 hearts in time-matched controls). These results suggest that when K2P3.1 current is augmented, K2P3.1 inhibition leads to atrial-specific prolongation of ERP; however, this ERP prolongation did not translate into significant antiarrhythmic effects in our AF model.

AP14145 is a negative allosteric modulator of K 2.2 and K 2.3 channels that shifted the calcium dependence of channel activation, an effect strongly dependent on two identified amino acids. AP14145 prolonged AERP in rats and did not trigger any acute CNS effects in mice. The understanding of how K 2 channels are inhibited, at the molecular level, will help further development of drugs targeting K 2 channels.