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Cardiac Overview (ECG = graph of e- currents in heart (CO = SV x HR (i.e.:…
Cardiac Overview
ECG = graph of e- currents in heart
Afterload ≈ SVR, resistance to ventricular pushing
preload = volume entering ventricles before contraction
Contractility = muscular contraction force
Stroke volume = amount ejected w/ each beat
CO = SV x HR
i.e.: CO= volume of blood expelled by ventricles
Cardiac Tissue Basics
Drugs act on:
Myocardium
Conduction System
Coronary vessels
Types of myocardial contraction
Systole = contraction
Diastole = relaxation
Electrophysiology
Automaticity
SA Node = 72 BPM
AV node = 40 BPM
His-Purkinje System = 15-40 BPM
Rhythmicity
Conductivity
SA node → internodal pathways → AV node → bundle of His → R and L bundle branches → Purkinje fibers
Refractoriness
cardiac tissue cannot be stimulated for a short period during systole
Prevents overstimulation
ANS effects on Cardiac Tissue
Parasympathetic NS
Vagal nerve innervates:
SA Node
Myocardium of atrium
AV junction
Releases ACh
-chronotrope
↓ HR
-dromotrope
↑ refractory period
Sympathetic NS
Sympathetic Ganglion (multiple):
SA Node
Myocardium of atrium and ventricles
AV junction
Releases NEPI
acts on beta1 adrenergic receptors
+inotrope
↑ contraction force
+chronotrope
↑ HR
+dromotrope
↓ refractory period at AV junction
↑ conduction velocity
Releases EPI