Cardiovascular research
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Cardiovascular research · Jan 1987
Effect of autonomic nervous system modulation on retrograde atrioventricular nodal conduction in the human heart.
Although the influence of the autonomic nervous system on anterograde atrioventricular nodal conduction is well established, its effect on retrograde atrioventricular nodal conduction has not been examined systematically. Since retrograde atrioventricular nodal conduction in subjects with normal anterograde conduction may vary from intact retrograde conduction to complete retrograde block when assessed during ventricular pacing, in this study patients with (a) intact retrograde atrioventricular nodal conduction (group 1) were studied during parasympathetic (vagal) stimulation by carotid sinus pressure and during sympathetic inhibition (propranolol 0.2 mg.kg-1 intravenously) and (b) retrograde atrioventricular nodal block (group 2) were studied during vagal blockade (atropine 0.04 mg.kg-1 intravenously) and during sympathetic stimulation (isoproterenol 1-4 micrograms.min-1 infusion). In both groups changes in sinus cycle length and anterograde atrioventricular nodal conduction were measured. ⋯ In group 2 vagal blockade by atropine caused a 1:1 retrograde response during ventricular pacing up to a mean(SD) cycle length of 470(135) ms in six out of eight patients. The infusion of isoproterenol caused the retrograde atrioventricular nodal block to be abolished and 1:1 conduction to be resumed up to a ventricular pacing mean(SD) cycle length of 364(57) ms in six out of eight patients. It is concluded that (a) the autonomic nervous system modulates retrograde atrioventricular nodal conduction in a similar manner to its anterograde counterpart and (b) that since retrograde atrioventricular nodal conduction was reversible after the administration of either atropine or isoproterenol retrograde atrioventricular nodal block may be dynamic (physiological) rather than fixed (anatomical) in nature.