Search results for "Chronotropic"
showing 2 items of 22 documents
On the mechanism of action of phenylephrine in rat atrial heart muscle
1994
Both in rat left atrial heart and in aortic smooth muscle preparations, phenylephrine (PE) caused a concentration-dependent increase in force of contraction (FC) in the presence of atenolol (10 mumol/l), which was antagonized by phentolamine, prazosin and WB 4101 in a competitive manner. The pA2 values of the antagonists in the cardiac tissue were 10-20fold lower than those in the rat thoracic aorta. In the spontaneously beating right atrium, PE exerted a positive chronotropic action, which was not significantly antagonized by phentolamine or prazosin. It is therefore assumed that the effects of phenylephrine in the left atrium and in the aorta are mediated by different subtypes of alpha 1-…
Effect of β-Blocker Withdrawal on Functional Capacity in Heart Failure and Preserved Ejection Fraction
2021
BACKGROUND Chronotropic incompetence has shown to be associated with a decrease in exercise capacity in heart failure with preserved ejection fraction (HFpEF), yet b-blockers are commonly used in HFpEF despite the lack of robust evidence. OBJECTIVES This study aimed to evaluate the effect of b-blocker withdrawal on peak oxygen consumption (peak VO2) in patients with HFpEF and chronotropic incompetence. METHODS This is a multicenter, randomized, investigator-blinded, crossover clinical trial consisting of 2 treatment periods of 2 weeks separated by a washout period of 2 weeks. Patients with stable HFpEF, New York Heart Association functional classes II and III, previous treatment with b-bloc…