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  • 1
    Electronic Resource
    Electronic Resource
    Modulation of cardiac impulse generation and conduction by nifedipine and verapamil analyzed by a refined surface ECG technique in Langendorff perfused guinea pig hearts (1988)
    Springer
    Basic research in cardiology 83 (1988), S. 202-212 
    Details
    ISSN: 1435-1803
    Keywords: sinoatrial blocks ; atrioventricular blocks ; Ca-antagonists ; HV duration ; PQ duration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Using a modified Langendorff system, a special ECG recording technique and appropriate placement of two silver wire electrodes, early atrial and His bundle activity can be detected continuously from the surface of intact and spontaneously beating guinea pig hearts. This new method was applied to measure the direct and inhibitory effects of nifedipine and verapamil on impulse generation and conduction in isolated and perfused guinea pig hearts. Depression of sinoatrial conduction was the most prominent effect of nifedipine. In all concentrations applied (10−7 M, 10−6 M, 10−5 M) nifedipine predominantly led to sinoatrial blocks of different degrees. Heart rate decreased slightly in a dosedependent manner. PQ and HV duration remained essentially constant. In the highest concentration of nifedipine (10−5 M), sinus node activity was so depressed that AV dissociation or ventricular rhythm developed. Only in one out of eight experiments with cumulative increase of nifedipine concentrations to 10−5 M was the AV node affected by nifedipine and a second-degree AV block developed (10−6 M). Verapamil's inhibitory effects on the rate of impulse initiation in the sinus node were more pronounced than those of nifedipine, but the inhibition of sinoatrial conduction by verapamil was less marked. At 10−6 M verapamil, the incidence of sinoatrial blocks and of ventricular rhythm was similar to the incidence of first degree AV blocks. PQ time (+14%) but also HV time (+12%) were prolonged under the influence of this concentration of verapamil. At the highest concentration of verapamil (10−5 M) applied for 10 min, ventricular rhythm developed in five out of eight experiments, as well as one second and two third-degree AV blocks. The results confirm that the simultaneous measurement of sinus node activity of sinoatrial and atrioventricular conduction and of HV duration is feasible with this ECG technique, to evaluate the inhibitory effects of Ca-antagonists on sinus and AV node activity in the intact heart.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01907274
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  • 2
    Electronic Resource
    Electronic Resource
    Effects of adenosine on electrical activity of isolated guinea pig hearts (1993)
    Springer
    Basic research in cardiology 88 (1993), S. 23-32 
    Details
    ISSN: 1435-1803
    Keywords: Adenosine ; refractoriness ; cardiac conduction ; AV-node ; isolated heart preparation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Negative chronotropic and dromotropic effects of adenosine seem to be responsible for its antiarrhythmic action on supraventricular tachyarrhythmias. To further characterize the effects of adenosine on supraventricular arrhythmias heart rate, conduction, refractoriness, the time to steady-state of AV-nodal conduction slowing and of sinus rate reduction were evaluated. Changes of heart rate, conduction intervals and effective refractory periods were determined by the use of a high-resolution ECG recording technique in isolated guinea pig hearts perfused by the method of Langendorff. Adenosine in concentrations of 3 and 10 μM reduced sinus rate and prolonged AV-nodal conduction significantly, while intraventricular and His bundle conduction were not altered. The maximal effect of adenosine on the sinus node and AV nodal conduction occurred after 636±109 and 111±35 (mean±SE) beats, respectively. During programmed stimulation at a cycle length of 250 ms, adenosine reduced atrial ERP in a dose-dependent manner. At cycle lengths of 170 and 200 ms, adenosine increased the atrial ERP at 3 μM, and then progressively shortened the ERP at higher doses. At all adenosine concentrations used, the usual rate-dependent adaption in ERP was suppressed. These observations explain the efficacy of adenosine against supraventricular tachyarrhythmias where the AV-node forms a part of a reentrant circuit. Adenosine shortened the atrial ERP, but at high pacing rates also led to a relative prolongation of the atrial ERP as the rate-dependent adaption was suppressed. These opposite effects of adenosine may explain earlier contradictory findings of its action on atrial arrhythmias.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00788527
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
    Fulltext
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