This document discusses the electrophysiology of the heart and how cardiovascular drugs can act on heart tissue. It outlines several key properties of cardiac electrophysiology that are important for understanding drug action, including impulse generation, conduction, excitability, and refractory period. Automatic fibers located in the sinoatrial and atrioventricular nodes generate impulses, while nonautomatic fibers cannot. The document also notes that autonomic influences like the sympathetic and parasympathetic nervous systems impact cardiac electrophysiology and contractility, and that many cardiovascular drugs have indirect autonomic effects.

1. Electrophysiology of
heart
By s.m.more

2. Introduction
Drugs having their major action on heart or blood vessels, or those used primarily for cardio-
vascular disorders are designated cardiovascular drugs. They can act directly on the
cardiovas-cular structures or through autonomic/central nervous system, kidney, autacoids or
hormones which regulate cardiovascular function

3. CARDIAC ELECTROPHYSIOLOGY
The properties which are especially important for understanding drug action on heart are
1. Impulse generation Electrophysiologi-cally, two types of myocardial fibres can be
distinguished (Fig.).
(a) Nonautomatic fibres: These are the ordinary working myocardial fibres; cannot generate an
impulse of their own.

4. (b) Automatic fibres These are present in the sinoatrial (SA) and atrioventricular (A-V) nodes,
and in the His-Purkinje system, i.c. especialized conducting tissue. In addition, patches of
auto-matic tissue are present in the interatrial septum, A-V ring and around openings of the
great veins

5. 2. Conduction : the rate of conduction through a fibre is a function of its membrane
responsiveness ,which is defined by rate of rise AP (dv/dt) as a function of membrane
potential at which activation occurs.

6. 3 Excitability : These property of fibre is defined by the strength of stimulus required to elicit to
response and produce AP.
4.Refractory period : pharmacologycally the effective refractive period (EPR) which is
minimum interval between two propogating APs.it closely related to AP duration (APD).
AUTONOMIC INFLUENCES ON CARDIAC ELECTROPHYSIOLOGY AND CONTRACTILITY
It would be profitable to recaptulate the influence of sympathetic and parasympathetic
stimulation on variables of cardiac function , because many cardiovascular drug have
indirect/secondary autonomic effects.

7. Reference
Essentials of Medical Pharmacology;Seventh Edition ;KD TRIPATHI MD