Effect of the potassium channel opener ZM260384 on skeletal muscle function during restricted blood flow in the anaesthetized cat

The aim of the present experiment was to determine whether the potassium channel opener 2-(2,2-bis(difluoromethyl)-6-nitro-3,4-dihydro-2H-1, 4-benzoxazine-4-yl)pyridine-N-oxide (ZM260384) was capable of accelerating the decline in skeletal muscle function during restricted blood flow in vivo. Cats (3.0-4.5 kg body weight) were anaesthetized with alphaxalone-alphadalone and breathed spontaneously following tracheotomy. Isometric tension was measured in the extensor digitorum longus-anterior tibialis (EDL-TA) muscle group. Ischaemia was induced by perfusing the hindlimb with the animal's own blood at a rate of 12.5 ml min-1 using a roller pump and stimulating the common peroneal nerve to induce repetitive submaximal tetanic contractions in the EDL-TA. The number of stimulation voltage increments required each minute to maintain a constant level of submaximal mechanical output and the time to exhaustion were used as indices of the rate of tension decline. The rate of tension decline in the ischaemic EDL-TA in the presence of ZM260384 at 3 mg kg-1, a maximally hypotensive dose predicted to be within the dose range required to exert direct effects on skeletal muscle, was measured and compared with the rate of tension decline in the presence of ZM260384 at 0.03 mg kg-1, also maximally hypotensive dose but below the predicted dose range for skeletal muscle effects. The number of voltage increments per minute was 1.93 +/- 0.07 and 1.48 +/- 0.14 (P < 0.05) in the presence of 3 and 0.03 mg kg-1 ZM260384, respectively. Time to exhaustion was 17.5 +/- 4.2 and 7.2 +/- 0.8 min (P < 0.05) in the presence of 3 and 0.03 mg kg-1 ZM260384, respectively. Given that there was no difference between these two groups in any haemodynamic variable measured, the results of the present study suggest that ZM260384 (3 mg kg-1) increases the rate of isometric force loss in ischemic skeletal muscle in vivo.

EuroQol: the current state of play

The EuroQol Group first met in 1987 to test the feasibility of jointly developing a standardised non-disease-specific instrument for describing and valuing health-related quality of life. From the outset the Group has been multi-country, multi-centre, and multi-disciplinary. The EuroQol instrument is intended to complement other forms of quality of life measures, and it has been purposefully developed to generate a cardinal index of health, thus giving it considerable potential for use in economic evaluation. Considerable effort has been invested by the Group in the development and valuation aspects of health status measurement. Earlier work was reported upon in 1990; this paper is a second 'corporate' effort detailing subsequent developments. The concepts underlying the EuroQol framework are explored with particular reference to the generic nature of the instrument. The valuation task is reviewed and some evidence on the methodological requirements for measurement is presented. A number of special issues of considerable interest and concern to the Group are discussed: the modelling of data, the duration of health states and the problems surrounding the state 'dead'. An outline of some of the applications of the EuroQol instrument is presented and a brief commentary on the Group's ongoing programme of work concludes the paper.

Pharmacodynamics of ZM 241385, a potent A2a adenosine receptor antagonist, after enteric administration in rat, cat and dog

4-(2-[7-Amino-2-(2-furyl)[1,2,4]triazolo[2,3-a][1,3,5] triazin-5-ylamino]ethyl)phenol (ZM 241385) is currently the most selective for the A2a adenosine receptor antagonist. This paper describes the in-vivo activity of ZM 241385 after administration by both oral and intraduodenal routes. In conscious spontaneously hypertensive rats, ZM 241385 (1-10 mg kg-1) selectively attenuated the mean arterial blood pressure response produced by exogenous adenosine (1 mg kg-1 min-1, i.v.) by up to 45% after oral administration. Activity of ZM 241385 was maintained for at least 6 h after 3 and 10 mg kg-1 (p.o.). In conscious normotensive cats, ZM 241385 attenuated the blood pressure responses to adenosine (0.6-1.0 mg kg-1, i.v.) by 94% after 10 mg kg-1 (p.o.) and by up to 74% after 0.3 mg kg-1 (i.v.). Duration of action of ZM 241385 up to 12 h (36% inhibition) was observed after 3 mg kg-1 (p.o.). In anaesthetized dogs and cats, ZM 241385, after intraduodenal administration (1-10 mg kg-1), produced a rapid (dose ratio 100-fold 15 min after administration of 10 mg kg-1 in the cat) and prolonged (dose ratio of 14 at 6 h after administration of 10 mg kg-1) attenuation of the vasodilatation responses to adenosine receptor stimulation. When administered by this route ZM 241385 was six times more potent than theophylline in the cat and at least twice as potent as theophylline in the dog. In conclusion, ZM 241385 is a potent, selective A2a adenosine receptor antagonist which is orally active, with a good duration of action by the enteric route in cat, rat and dog. It could therefore be used to evaluate the role of adenosine A2a receptors in the action of adenosine in-vivo.

The yield of head-up tilt testing is not significantly increased by repeating the baseline test

BACKGROUND AND HYPOTHESIS

Head-up tilt is widely used in evaluating patients with syncope. Data suggest that baseline tilt without isoproterenol is associated with few (< or = 10%) positive results in normals. However, there is considerable day-to-day variability in patients with syncope, resulting in low reproducibility. We hypothesized that repeating the baseline tilt would increase the total number of positive responses.

METHODS

In all, 193 patients with syncope of unknown etiology prospectively underwent serial baseline tilt (Tilt-1 and Tilt-2) at 70 degrees for 25 min on two consecutive days.

RESULTS

Of 193 patients, 39 (20%) had a positive Tilt-1. Of these, 19 had a positive Tilt-2, (positive concordance rate: 19/39 = 49%). Of 154 patients with a negative Tilt-1, 145 had a negative Tilt-2 (negative concordance rate: 142/151 = 94%). Only 9 of 154 patients (6%) with a negative Tilt-1 had a positive Tilt-2. Thus, the yield increased from 20% (39/193) after Tilt-1, and to 25% (48/193) after Tilt-1 plus Tilt-2, p = NS.

CONCLUSIONS

(1) Reproducibility of a positive Tilt-1 is moderate. (2) Reproducibility of a negative Tilt-1 is high. (3) Repetition of tilt in patients with a negative Tilt-1 does not significantly increase the number of positive results.

In vivo characterisation of ZM 241385, a selective adenosine A2A receptor antagonist

The in vivo characterisation of ZM 241385 (4-(2-[7-amino-2-(2-furyl)[1,2,4]triazolo[2,3-a][1,3,5]triazin-5-+ ++ylamino] ethyl)phenol), a novel, non-xanthine, selective adenosine A2A antagonist is described. In anaesthetised dogs ZM 241385 (i.v.) was 140-fold more potent in attenuating vasodilator responses to exogenous adenosine in the constant flow perfused hind limb than the bradycardic effects. In pithed rats in which blood pressure was supported by angiotensin II infusion, ZM 241385 (10 mg kg-1, i.v.) did not inhibit the hypotensive or bradycardic effects of the A3/A1 receptor agonist N(6)-2-(4-amino-3-iodophenyl)ethyladenosine (APNEA). In conscious spontaneously hypertensive rats, ZM 241385 (3-10 mg kg-1, p.o.) selectively attenuated the mean arterial blood pressure response produced by exogenous adenosine. No inhibition of the bradycardic effects of adenosine was observed following these doses of ZM 241385. The results indicate that ZM 241385 can be used to evaluate the role of adenosine A2A receptors in the action of adenosine in vivo.

Malfunction of implantable cardioverter defibrillators placed by a nonthoracotomy approach: frequency of malfunction and value of chest radiography in determining cause

OBJECTIVE

The purpose of this study was to determine the frequency of system malfunction in patients with nonthoracotomy implantable cardioverter defibrillators and to assess the role of chest radiography in detecting and determining the cause of malfunction.

MATERIALS AND METHODS

The study population consisted of 300 consecutive patients in whom implantable cardioverter defibrillators were implanted using an initial nonthoracotomy approach between September 1990 and October 1994. Transvenous electrodes were placed via the subclavian or cephalic vein under local anesthetic. Intraoperative testing, pulse generator implantation, and, if necessary, subcutaneous patch or extrapericardial patch placement via thoracotomy were done in the operating room under general anesthetic. Follow-up consisted of routine device interrogation every 2-3 months and annual chest radiography. Chest radiographs were obtained more often if patients were symptomatic or if results of device interrogation were abnormal.

RESULTS

Patients were followed up for a mean +/- SD of 19 +/- 14 months following implantation. Implantable cardioverter-defibrillator malfunction occurred in 17 patients (6%) during the follow-up period. Of these, 12 (71%) had component abnormalities on chest radiographs. Patients with radiographically apparent implantable cardioverter-defibrillator abnormalities presented in two discrete time periods after device implantation, early (mean, 35 +/- 14 days) and late (mean, 18 +/- 5 months).

CONCLUSION

Malfunction of nonthoracotomy implantable cardioverter-defibrillator systems develops infrequently after device implantation. In most cases, the cause can be identified on chest radiographs.

IgH and L chain variable region gene sequence analyses of twelve synovial tissue-derived B cell lines producing IgA, IgG, and IgM rheumatoid factors structure/function comparisons of antigenic specificity, V gene sequence, and Ig isotype

In the present study, the complete sequences of the Ig H and L chain variable region genes of twelve RF+ B cell lines from two patients with RA were analyzed. Seven of the RF-producing B cells used VH3 family genes, four used VH4 genes, and one a VH1 gene. All but two of the cell lines expressing VH3 genes utilized different family members; among the VH4-expressing cells, a more restricted pattern was noted. V kappa gene use was restricted to the V kappa I and III families; V lambda gene use was more diverse, involving five different families. Computer comparisons of the expressed VH genes with their presumed germline progenitors indicated significant differences in every instance; eight of the corresponding VL genes also were significantly different. In many cases, assignment of the germline D segment(s) incorporated into the rearranged VH genes was impossible. These differences from the germline gene segments indicated the extensive changes induced by rearrangement, enzymatic activities, and somatic mutation. In hopes of defining a structural reason for the disparate antigen specificities of these cells, the CDR3 amino acid sequences of the multi- vs. the mono-reactive RF-producers were compared. Although CDR3 length was not appreciably different between these two sets of mAb, a greater than two-fold increase in charged amino acids was found in the H chain CDR3 of the multireactive RF. This relationship did not exist for the L chain CDR3. Thus, these sequence data indicate the use of a broad base of Ig V gene segments that have undergone extensive diversification. Based on the localization of R substitutions in the CDR of most of the V genes studied, the diversification appears to be antigen driven and selected. The significance of these findings for the evolution of these B cell clones into isotype-switched producers that are heterogeneous for antigen specificity (mono- vs. multi-reactivity) is discussed.

Implantation of transvenous nonthoracotomy cardioverter-defibrillator systems in patients with permanent endocardial pacemakers

Among 177 patients in whom a nonthoracotomy approach was initially used to implant a cardioverter-defibrillator system, 11 (6%) patients also received a separately implanted permanent pacemaker. The main problem encountered in these patients were previously implanted unipolar pacemakers (n = 3) and ventricular pacing leads positioned at the right ventricular apex, the latter interfering with optimal placement of the tripolar implantable cardioverter-defibrillator (ICD) lead (n = 9). The approaches used to solve these problems were individualized and included placement of the ICD sensing lead at the right ventricular outflow tract (n = 3), initial placement (n = 1) or subsequent repositioning (n = 2) of the right ventricular pacing lead at the outflow tract, upgrade from unipolar to bipolar systems (n = 2), reprogramming from the DDD to AAI mode (n = 2), inactivation of the pacemaker (n = 1), and simultaneous placement of a single-chamber atrial pacemaker with the ICD lead (n = 2). These revisions fulfilled the pacing needs in each patient and prevented unfavorable sensing interaction between the two systems.

Three-year outcome of a nonthoracotomy approach to cardioverter-defibrillator implantation in 189 consecutive patients

To date, no long-term clinical data have been published in patients undergoing a nonthoracotomy approach to cardioverter-defibrillator system implantation. In the present report, 189 consecutive patients prospectively underwent a standardized approach to cardioverter-defibrillator system implantation in which the nonthoracotomy configurations were tested first. If satisfactory defibrillation thresholds were not obtained, thoracotomy was performed during the same intraoperative session. A nonthoracotomy system was successfully implanted in 149 of 189 patients (79%), with a higher success rate (90%) observed in patients who had more recent implantations. The overall rate of complications associated with these systems was low (11%). Over a mean follow-up of 12.5 +/- 9.3 months, 17 patients (9%) died. Three-year total, cardiac, and sudden death-free actuarial survival for all patients was 83 +/- 11%, 88 +/- 7%, and 94 +/- 2%, respectively. Three-year sudden death-free actuarial survival was higher in the nonthoracotomy than in the thoracotomy patients (97 +/- 2% vs 87 +/- 6%, p = 0.047), although total survival was similar (77 +/- 11% vs 83 +/- 7%, p = 0.77). These data suggest that a majority of patients (> 80%) requiring a cardioverter-defibrillator system can undergo implantation using a nonthoracotomy approach. Patients receiving nonthoracotomy systems have 3-year outcomes comparable to those implanted via thoracotomy. If these results are maintained, a nonthoracotomy approach will supplant thoracotomy-implanted systems as the preferred method because of the simpler implant procedure and lower overall cost involved.

Plant defences against mammalian herbivores: are juvenile Acacia more heavily defended than mature trees?

Juvenile trees are expected to be more heavily defended against browsing mammals than mature plants. Juvenile and mature trees of Acacia tortilis and A. nilotica occurring at Nylsvley, Northern Transvaal, were quantitatively compared in terms of some potential chemical and physical defences. Neither species showed any significant difference between juvenile and mature trees in terms o f total polyphenol content, condensed tannin content, protein precipitating ability or protein content in leaves. Both species showed age-class differences in spinescence. In A. nilotica, thorns on branch tips were longer and more closely spaced and leaves were smaller in juveniles than in adults. Hence juveniles of this species appear to be physically more heavily defended than mature plants. In A. tortilis, curved thorns were longer, but straight thorns were shorter than in mature trees. There was no difference between age classes in overall thorn density, but juveniles had a higher curved to straight thorn ratio. It is not obvious what the effects of these differences might be on mammalian browsers.

Myocardial infarction and purine transport inhibition in anaesthetised ferrets

The potential cytoprotective effect of the purine transport inhibitor S-(p-nitrobenzyl)-6-thioinosine (NBTI) in a model of myocardial ischaemia and reperfusion was investigated in the anaesthetised ferret. The left anterior descending coronary artery (LAD) was occluded for 90 min, producing ischaemia in 53 +/- 3% of the left ventricular free wall, followed by 240 min reperfusion. NBTI (0.5 mg kg-1, i.v.) was given prior to ischaemia or prior to reperfusion. In addition the effect of purine transport inhibition was investigated in animals subjected to ischaemia without reperfusion. NBTI reduced infarct size from 84.0 +/- 1.7 to 71.4 +/- 3.7% of the area at risk (P < 0.05) when given prior to occlusion of the LAD. NBTI was ineffective however when given 15 min prior to reperfusion. NBTI had no effect upon infarct size produced by ischaemia without reperfusion. The effect of NBTI was independent of significant changes in myocardial blood flow during ischaemia and reperfusion or upon neutrophil infiltration.

Determinants of successful nonthoracotomy cardioverter-defibrillator implantation: experience in 101 patients using two different lead systems

OBJECTIVES

This study was conducted to identify the determinants of successful nonthoracotomy cardioverter-defibrillator implantation.

BACKGROUND

Until recently, either median sternotomy or thoracotomy was necessary to implant the electrodes used for internal cardioverter-defibrillator systems. A number of manufacturers have developed nonthoracotomy lead systems comprising two transvenous coil electrodes and a subcutaneous patch electrode. At present, the factors associated with the success or failure of a nonthoracotomy approach are unknown.

METHODS

A total of 101 consecutive patients requiring a cardioverter-defibrillator underwent an initial nonthoracotomy approach. Factors associated with successful nonthoracotomy implantation were prospectively determined.

RESULTS

A nonthoracotomy system was implanted in 72 (71%) of 101 patients. Twenty-nine patients (29%) required thoracotomy. Univariate predictors of successful nonthoracotomy implantation included smaller cardiac size (p < 0.0001), smaller cardiothoracic ratio (p < 0.0002), QRS duration < 120 ms (p = 0.003), female gender (p = 0.006), ventricular fibrillation as the presenting arrhythmia (p = 0.03) and smaller echocardiographic left ventricular size (p = 0.04). Multivariate predictors included smaller cardiac size (p < 0.002) and female gender (p < 0.007). Total actuarial survival over a mean (+/- SD) follow-up interval of 12 +/- 7 months was 91 +/- 0.03% and was not different in the thoracotomy and nonthoracotomy groups.

CONCLUSIONS

A nonthoracotomy cardioverter-defibrillator system can be implanted in a majority of patients. Smaller cardiac size and female gender are associated with a high probability of successful implantation.

Successful implantation of cardioverter-defibrillator systems in patients with elevated defibrillation thresholds

OBJECTIVES

. The purpose of this study was to conduct a retrospective analysis of 16 patients with high initial defibrillation thresholds in whom a three-electrode system was used to lower defibrillation thresholds and permit implantation of a cardioverter-defibrillator system.

BACKGROUND

Patients with high defibrillation thresholds (> 25 J) are uncommon but may be problematic to physicians implanting cardioverter-defibrillator systems. Most conventional systems use two defibrillating electrodes, most commonly two epicardial patches. When defibrillation thresholds remain elevated despite extensive testing of a two-electrode system, a third electrode can be incorporated and tested. However, few published data exist on the use of a three-electrode system in patients with high defibrillation thresholds.

METHODS

After failure to achieve satisfactory defibrillation thresholds < 25 J with a two-patch electrode system, a third electrode was incorporated and tested. In all cases, two electrodes were joined to form a common cathode or anode, while a single electrode was used as the opposite polarity electrode. Various three-electrode configurations were then tested.

RESULTS

In all 16 patients, satisfactory defibrillation thresholds were achieved and a cardioverter-defibrillator was implanted (95% confidence interval [CI] = 0% to 21%). The mean final defibrillation threshold using the revised three-electrode system was 19.5 +/- 3.7 J (p < 0.0001). A mean of 6 +/- 3 electrode configurations/patient were tested before the final configuration was selected. A total of nine different electrode configurations were used in the 16 study patients; the most common of these incorporated left and right ventricular patches as combined cathode and a superior vena cava coil (n = 5) or right atrial patch electrode (n = 3) as single anode.

CONCLUSION

Patients with high initial defibrillation thresholds can generally undergo successful cardioverter-defibrillator implantation with a three-electrode system if enough electrode configurations are tested after a third electrode is incorporated.

Efficacy of a tiered therapy defibrillator system used to treat recurrent ventricular arrhythmias refractory to drugs

OBJECTIVE

To evaluate an implantable tiered therapy defibrillator system that delivered antitachycardia pacing treatment for slower well tolerated ventricular tachycardias and cardioversion or defibrillation for fast tachycardias or ventricular fibrillation.

METHODS

A tiered treatment device (Ventritex Cadence V-100) was implanted in 30 patients with ventricular tachycardia that was refractory to drugs. Efficacy was evaluated by the responses of induced or spontaneous arrhythmias to the treatments delivered.

RESULTS

Antitachycardia pacing successfully terminated 80% of episodes of ventricular tachycardia induced by non-invasive programmed stimulation, but acceleration was brought about by pacing in six patients in 10% of episodes. During a follow up of two to 17 (mean seven) months, 18 patients (60%) had recurrence of ventricular arrhythmias. Antitachycardia pacing terminated ventricular tachycardia in 17 of 18 patients in 87% of episodes. Twelve patients received shocks for ventricular tachycardia or fibrillation. Failure of pacing, with subsequent cardioversion, occurred in nine patients (50%) in one or more episodes. Acceleration of tachycardia by pacing occurred in 10 patients in 5% of episodes. Only two of these patients had experienced acceleration of previously induced arrhythmia. Five patients had spontaneous fast ventricular tachycardia or fibrillation treated by cardioversion or defibrillation. Spurious treatment was delivered in nine patients (30%), during atrial fibrillation in five, sinus tachycardia in two, and because of fracture of the sensing lead system in two patients. The retrieval of stored intracardiac electrograms was of clinical value in assessing spurious treatment.

CONCLUSIONS

Tiered treatment was effective in terminating recurrent ventricular arrhythmias in these selected patients. Most episodes were treated successfully by pacing, and resistant tachycardias, pacing induced acceleration, or haemodynamically compromising arrhythmias were treated by shocks.