These tools will no longer be maintained as of December 31, 2024. Archived website can be found here. PubMed4Hh GitHub repository can be found here. Contact NLM Customer Service if you have questions.


Pubmed for Handhelds

PUBMED FOR HANDHELDS

Search MEDLINE/PubMed

  • Title: Parasympathetic control of cycle length dependence of endocardial ventricular repolarisation in the intact feline heart during steady state conditions.
    Author: Malfatto G, Zaza A, Schwartz PJ.
    Journal: Cardiovasc Res; 1993 May; 27(5):823-7. PubMed ID: 8348581.
    Abstract:
    OBJECTIVE: Parasympathetic modulation of the rate dependence of ventricular repolarisation in vivo during steady state conditions was investigated by analysing the effects of removing vagal activity in three groups of anaesthetised cats. METHODS: Bilateral vagotomy was performed while different levels of background sympathetic tone were present in the control periods of each group: in group 1 (n = 6), cardiac sympathetic nerves were intact; in group 2 (n = 7), bilateral stellate ganglionectomy was performed; and in group 3 (n = 7), beta adrenergic blockade (propranolol, 0.5 mg.kg-1) was performed after stellate ganglionectomy. The duration of a left ventricular endocardial monophasic action potential (APD) was measured during atrial pacing at 7-10 cycle lengths (CL). The APD/CL relation was fitted to a hyperbolic function: APD = CL/[(axCL)+b]. Two parameters were considered: APDmax (1/a, ie, APD extrapolated at infinite cycle length, a rate-independent measure of APD) and CL50 (bxAPDmax, ie, the cycle length at which 50% of APDmax is reached). RESULTS: In control conditions, APDmax and CL50 were longer in groups 2 and 3, when cardiac sympathetic effects were reduced or absent. Vagotomy reduced APDmax and CL50 similarly in groups 1 and 2 (APDmax, -24% and -18%; CL50, -36% and -27%) (p < 0.05 v control). In group 3, vagotomy did not affect APDmax and CL50. CONCLUSIONS: No direct parasympathetic influence on the rate dependence of endocardial ventricular repolarisation was observed. The vagal modulation of sympathetic effects may take place either through vago-sympathetic reflexes or via the antagonism of circulating catecholamines distal to the beta receptor.
    [Abstract] [Full Text] [Related] [New Search]