INTERACTIONS BETWEEN DILTIAZEM AND INHALATION ANAESTHETICS IN THE ISOLATED HEART

Transcription

1 Br. J. Anaesth. (1989), 63, INTERACTIONS BETWEEN DILTIAZEM AND INHALATION ANAESTHETICS IN THE ISOLATED HEART M. D. CARCELES, F. S. MIRALLES, M. L. LAORDEN AND J. HERNANDEZ Although the mechanisms underlying the cardiac effects of inhalation anaesthetics are not understood completely, they appear to be related to changes in ionic fluxes, principally those involving calcium [1]. There is also evidence for a similarity between the pharmacological effects of anaesthetics and calcium channel blockers. Indeed, depressant effects on sino-atrial node conduction produced by halothane, enflurane and isoflurane have been shown to be similar to those of the cardioactive calcium blockers [2]. The aim of the present study was to examine the interaction between different doses of diltiazem and the inhalation anaesthetics halothane and isoflurane on sinus automaticity in isolated right atria (SAIRA), in which the actions of extracardiac systems are eliminated. MATERIALS AND METHODS Experiments were carried out on isolated right atria preparations. Sixty-six male Sprague- Dawley rats (weights g) were humanely killed. The chest was opened by midsternal incision and the right atrium was isolated by a technique similar to that described previously [3, 4]. The right atrium was suspended in a 30-ml organ bath (Allihn tube) with 0.5 g of resting tension. Tyrode solution was used (composition (mmol litre" 1 ): NaCl 136.9; KC15.0; MgCl ; CaCl 2 1.8; NaH 2 PO 4 0.4; NaHCO ; dextrose 5). The bathing solution was maintained at 37 C, ph 7.4 and bubbled with 5 % carbon M. D. CARCELES, M.D.; F. S. MIRALLES, M.D.; Department of Anesthesiology, Virgen Arrixaca Hospital, Murcia, Spain. M. L. LAORDEN, M.D.; J.HERNANDEZ, M.D.; Department of Physiology and Pharmacology, School of Medicine, Murcia, Spain. Accepted for Publication: February 10, Correspondence to F.S.M. SUMMARY It has been postulated that inhalation anaesthetics may interfere with calcium movement across cell membranes. We have evaluated the interaction between diltiazem and the inhalation anaesthetics halothane and isoflurane on sinus automaticity in the isolated right atrium (SAIRA). Isoflurane significantly reduced atria/ rate at all concentrations tested. However, halothane produced only a small but significant decrease at the higher concentrations used (1-2 v/v%). Diltiazem modified the maximal negative chronotropic response to inhalation anaesthetics. Maximum depression of SAIRA was significantly greater in the presence of two different doses of diltiazem compared with exposure to halothane and isoflurane alone. These results suggest that inhalation anaesthetics may block the influx of extracellular calcium through voltage-dependent calcium channels inhibited by diltiazem. dioxide in oxygen. The frequency of spontaneous contraction of the right atrium was measured using a force-displacement transducer (Grass FT 03) and recorded on a Dynograph Beckman polygraph. After a 30-min stabilization period, cumulative concentration-response curves to halothane (I.C.I.) and isoflurane (Abbott) (concentration range v/v%) were obtained. Both volatile anaesthetics were delivered from standard vaporizers (Ohmeda) which were calibrated with the EMMA multigas analyser (Engstrom), itself previously calibrated against certified gas mixtures. Similar dose-response curves for halothane and isoflurane were obtained in the presence of

2 322 BRITISH JOURNAL OF ANAESTHESIA of control) ' oo co 01 O Z J ' J > '"? '"1 i ~~ Halothane concn (%) FIG. 1. Effect of halothane on atrial automaticity in the absence (A, n= 10) and in the presence of diltiazem (5xlO-'mol litre" 1 D, n = 6 and Ixl0-6 mol litre" 1, n = 6) (mean, SEM). diltiazem (Esteve Laboratories) 5 x 10" 7 and 1 x 10~ 6 mol litre" 1 added to the organ bath in normal saline 0.1 ml 5 min before halothane or isoflurane. Results for inhalation anaesthetics alone are expressed as percent changes from baseline values without diltiazem. Results with inhalation anaesthetics in the presence of diltiazem are expressed as percent changes from the baseline values after diltiazem. In order to compare the inhibitory effect of the agent used in absence and in presence of two different doses of diltiazem, we measured the corresponding IC 50 (the dose of which produced a 50 % decrease of atrial rate) for each set of experiments [5]. Data were analysed by Student's t test and analysis of variance. An analysis of linear regression with the log of response was used for the estimation of IC 50. P < 0.05 was considered to indicate statistical significance. RESULTS Effects of halothane The concentration-response curves for halothane in the absence and presence of two different concentrations of diltiazem are illustrated in figure 1. The smaller concentration of diltiazem (5 x 10~ 7 mol litre" 1 ) was devoid of any effect on the atrial rate. However, diltiazem 1 x 10" 6 mol litre" 1 produced a small (13%) but significant decrease of SAIRA. Halothane alone did not change SAIRA at low concentrations ( v/v%), but it produced a small (4% maximal), significant decrease at the higher concentrations (l-2v/v%). Diltiazem modified the maximal negative chronotropic response to halothane. The maximal decrease in SAIRA induced by halothane (2v/v%) alone was to 96 (SEM 2.2)% of control. In the presence of diltiazem 5 x 10~ 7 and 1 x 10" 6 mol litre" 1, the maximal decrease of atrial rate was to 91 (2.3)% and 70 (8.5) %, respectively. The difference between each of these two values and the maximal decrease in SAIRA induced by halothane was significant (table I). Effects of isoflurane The concentration-response curve for isoflurane in the absence and presence of two different concentrations of diltiazem is shown in figure 2. The results obtained with diltiazem alone were similar to those described previously. SAIRA was significantly depressed from control values by all concentrations of isoflurane. The TABLE I. Effects of diltiazem on the maximal negative chronotropic response to halothane and isoflurane (mean (SEM)). IA = Inhalation anaesthetic, n = 6 for each group except for halothane and isoflurane alone (n = 10) Halothane Isoflurane Maximal effect (%) Change (%) P Maximal effect (%) Change (%) P IA alone With diltiazem 5 x 10"? mol 1 x 10" 6 mol litre"1 litre" 1 91 (2.2) 91 (2.3) 70 (8.5) (1.8) 84 (2.4) 84(2.1) 7 7

3 DILTIAZEM AND INHALATION ANAESTHETICS I I 82 I~.X-.-I.. K,, is DC U..J i i i! * * t-t-t--. * -.. 0* Isoflurane concn (/0 FIG. 2. Effect of isoflurane on atrial automaticity in the absence (A> " = 10) and in the presence of diltiazem (5 x 10"' mol litre" 1 D, " = 6 and 1 x lo" 6 mol litre" 1, n = 6) (mean, SEM). maximal decrease (to 91 (1.8)% of control) was obtained at the higher concentration (2v/v%) (table I). When diltiazem was present in the organ bath, isoflurane (2v/v%) produced a maximal decrease of control SAIRA of approximately 16%, significantly greater than that produced by isoflurane alone (9%). The IC 50 values of halothane and isoflurane with and without the two doses of diltiazem are summarized in table II. The difference in IC 50 between halothane alone and in the presence of diltiazem was significant (P < 0.02). Similarly, the IC 50 of isoflurane alone was significantly greater than that in the presence of the two doses of diltiazem (P ). Calcium Concentration-response curves to halothane and isoflurane were also obtained in the presence Halogenated anaesthetics (/o) FIG. 3. Effect of halothane (, n = 10) and isoflurane (A, n = 10) on atrial automaticity in normal calcium solution compared with the effect of halothane (. n = 6) and isoflurane (A, n = 6) in an increased concentration of calcium (mean, SEM). of a high concentration of calcium (5.4 mol litre *) (fig. 3). The calcium concentration attenuated the inhibitory effects of high concentrations of halothane and isoflurane, but the attenuation was not statistically significant. DISCUSSION This study was designed to examine the interaction between inhalation anaesthetics and diltiazem on isolated right atria which were free from the compensating mechanisms present in intact animals or man. This method has been used widely to evaluate the actions and interactions between different drugs on chronotropic automaticity [3,4,6]. Our results confirmed the findings of other investigators [2]: halothane and isoflurane alone showed depressant effects on atrial automaticity TABLE II. /C 50 of the inhalation anaesthetics halothane and isoflurane in the absence and presence of diltiazem upon sinus automaticity of isolated right atria (mean (SEAf)). IA = Inhalation anaesthetic. n = 6 for each group except for halothane and isoflurane alone (n = 10) Halothane Isoflurane IA alone With diltiazem 5 x 10"' mol litre- 1 1 x 1Q-' mol litre" (0.14) 1.00(0.1) 1.00(0.13) <0.02 < (0.16) 0.83(0.11) 0.87(0.11)

4 324 BRITISH JOURNAL OF ANAESTHESIA similar to those of the cardioactive calcium blockers. It had been suggested from in vivo experiments that the depression of cardiac muscle function by halothane appeared to be antagonized by calcium [7,8]. In the present in vitro model, the negative chronotropic effects induced by halothane and isoflurane were sensitive to changes in the concentration of calcium in the medium. It has been established that the myocardial depression produced by inhalation anaesthetics is related, at least in part, to alterations in calcium ion flux [1,9]. The importance of calcium as a carrier of the inward current of the sinus node is shown by the observation that an increase in Ca 2+ concentration increases the sinus rate [2]. In addition, calcium antagonists suppress sinus node activity by decreasing the rate of phase 4 and phase 0 depolarization and the amplitude of the action potential [10]. The pharmacological interactions between inhalation anaesthetics and calcium channel blocking drugs in vitro [11,12], in vivo [13-15] and in humans [16,17] have been described previously. The data obtained from in vitro experiments showed that calcium channel blockers modified the negative inotropic effects induced by inhalation anaesthetics, but the effects on cardiac chronotropism have not been reported. Our results using isolated right atria showed that halothane dose-response curves obtained in the presence of the two different concentrations of diltiazem were significantly more inhibitory. Similar results were obtained with isoflurane, but the chronotropic effects it induced in the presence of diltiazem were less than those seen with halothane. These data are in agreement with those of Lynch [18], who demonstrated that halothane appeared to have calcium channel blocking activity, while isoflurane appeared to affect intracellular calcium kinetics [19]. Although diltiazem and halothane or isoflurane are considered to have minimal adverse effects on heart rate, our results demonstrated that halothane and isoflurane exerted a direct negative chronotropic effect on SAIRA. These inhibitory effects induced by both agents were blocked in the presence of increased calcium concentration in the organ bath, but not significantly. The maximal decrease in SAIRA induced by inhalation anaesthetics was significantly greater in the presence of increasing concentrations of diltiazem. At present, there is no evidence that the patient receiving calcium channel blocking drugs, without other complicating factors, presents a significantly increased risk for anaesthesia and surgery. However, these observations may have some clinical relevance to patients concurrently receiving the calcium antagonist, diltiazem, and submitted to general anaesthesia. ACKNOWLEDGEMENT The authors are grateful to Matilde Campos (Department of Statistics, School of Medicine, Murcia, Spain) for statistical advice. REFERENCES 1. Broadbent MP, Swan PC, Jones RM. Interactions between diltiazem and isoflurane. An in vitro investigation in isolated guinea pig atria. British Journal of Anaesthesia 1985; 57: Bosnjak ZJ, Kampine JP. Effects of halothane, enflurane and isoflurane on the SA node. Anesthesiology 1983; 58: Serrano JS, Moratinos J, Garcia de Jalon PD. Efecto del ph sobre el estimulo inotropico y cronotropico del isoproterenol en auricula aislada de rata. Adas de la Sociedad Espanola de Ciencias Fisioldgicas 1970; 12: Furchgott RF, Kierpekar SM, Rieker M. Actions and interactions of norepinephrine, tyramine and cocaine on aortic strip of rabbit and left atria of guinea-pig and cat. Journal of Pharmacology and Experimental Therapeutics 1963; 142: Van Rossum JM. Cumulative dose response curves. II. 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5 DILTIAZEM AND INHALATION ANAESTHETICS Kates RA, Laggy AP, Norfleet EA, Heath KR. Comparative cardiovascular effects of verapamil, nifedipine and diltiazem during halothane anesthesia in swine. Anesthesiology 1984; 61: Priebe HJ, Skarvan K. Cardiovascular and electrophysiologic interactions between diltiazem and isoflurane in the dog. Anesthesiology 1987; 66: Merin RS, Chelly JE, Hymig ES, Rogers K, Plewati A, Hartley ZJ, Abernethy DR, Doursout MF. Cardiovascular effects of and interaction between calcium blocking drugs and anesthetics in chronically instrumented dogs. IV. Chronically administered oral verapamil and halothane, enflurane and isoflurane. Anesthesiology 1987; 66: Kates RA, Kaplan JA. Cardiovascular responses to verapamil during coronary artery bypass graft surgery. Anesthesia and Analgesia 1983; 62: Kapur PA, Norel EJ, Dajee H, Cohen G, Flacke W. Haemodynamic effects of verapamil administration after large doses of fentanyl in man. Canadian Anaesthetist's Society Journal 1986; 33: Lynch C, Vogel M, Sperelakis N. Halothane depression of myocardial slow action potentials. Anesthesiology 1981; 55: Lynch C. Differential depression of myocardial contractility by halothane and isoflurane in vitro. Anesthesiology 1986; 64: