Origin and Conduction of the Signal to Contract

Timing adequate rate adequate rate time to fill time to fill adjustable adjustableTiming adequate rate adequate rate time to fill time to fill adjustable adjustable Coordination atrial syncytium pause ventricular syncytium

P The Pacemaker

AV Sinoatrial Node Septum RA LA Fibrous skeleton Right Ventricle Left Ventricle His Bundle SA Atrioventricular Node

Maximum Diastolic Potential Time (ms) Membrane Potential (mV) Spontaneous Depolarization Ca ++ Refractory Period g Ca Ca ++ K+K+ g K (K open) K+K+ gKgK g Ca, T ? g Na in i f, K+K+ K close K+K+ g K K close g Na in i f, hyperpolarization-activated current Threshold for Ca,L Ca ++ g Ca, L

Origin and Conduction of the Signal to Contract Timing adequate rate adequate rate time to fill time to fill adjustable adjustableTiming adequate rate adequate rate time to fill time to fill adjustable adjustable Coordination atrial syncytium pause ventricular syncytium

Septum RA LA Fibrous skeleton Right Ventricle Left Ventricle AV Atrial Depolarization His Bundle SA

RA LA RVLV Septum SA AV Left bundle branch of Purkinje network Right bundle branch of Purkinje network His Bundle AV Connective Tissue Right Atrium Right Ventricle

Slow conduction Slow conduction small cells small cells slow depolarization slow depolarization few gap junctions few gap junctions Low pass filter Low pass filter Reserve Pacemaker Reserve Pacemaker Slow conduction Slow conduction small cells small cells slow depolarization slow depolarization few gap junctions few gap junctions Low pass filter Low pass filter Reserve Pacemaker Reserve Pacemaker Atrioventricular Node Nodal fibers Bundle of His fibers Nodal fibers

Fibrous skeleton of the Heart

Connective Tissue Insulation Atrium Ventricle Ventricular Septum

His Bundle Bundle of His

RA LA RVLV Septum SA AV Left bundle branch of Purkinje network Right bundle branch of Purkinje network Left bundle branch of Purkinje network AV Connective Tissue Right Atrium Right Ventricle His Bundle Bundle of His

RA LA Fibrous skeleton Right Ventricle Left Ventricle SA AV His Bundle Septum Purkinje Network Left bundle branch of Purkinje network Right bundle branch of Purkinje network

Purkinje Fibers Normal Myocardium Nerves

Purkinje Fibers Large fiber diameter Rapid depolarization Many gap junctions High speed conduction of the signal to contract

Ventricular Depolarization RA LA Fibrous skeleton Right Ventricle Left Ventricle SA AV His Bundle Septum Left bundle branch of Purkinje network Right bundle branch of Purkinje network

Impulse Conduction Time Costanzo Fig 4-13

Terminology Epicardium and Endocardium are connective tissue & endothelium or mesothelium. Only the myocardium contains cardiac muscle.

Ventricular Action Potential Duration Epicardium Endocardium

Ventricular Repolarization Epicardium Endocardium Subepicardial Myocardium Subendocardial Myocardium depolarization Predominant path of repolarization

AV Autonomic Influence on Pacemaker Septum RA LA Fibrous skeleton Right Ventricle Left Ventricle His Bundle SA

Parasympathetic Effect on Pacemaker Cells Membrane Potential (mV) Time (ms) 1000 No autonomic influence Heart period = 600 ms Parasympathetic influence Heart period = 1000 ms Slower rise to peak More negative maximum diastolic potential Slower spontaneous depolarization

K+K+ Ach ATP c-AMP opening of Ca ++ channelsc-AMP out in GiGi GiGi AC M2

Vagal Influence at Rest Heart Rate (beats/min) Dose of Atropine (Acetylcholine receptor antagonist)

Sympathetic Effect on Pacemaker Cells Membrane Potential (mV) Time (ms) 1000 No autonomic influence Heart period = 600 ms Sympathetic influence Heart period = 400 ms Faster spontaneous depolarization dV/dt during depolarization Faster repolarization

NE C-AMP ATP AC GSGS ß1 outin Na + I f opens at less negative membrane potential Ca ++ PO 4 PKA active PKA inactive Ks (more rapid repolarization) dV/dt during depolarization

Heart Rate (beats/min) Atropine Atropine (Ach receptor antagonist) Propranolol (ß-receptor antagonist) Propranolol

Autonomic Innervation of the AV node Parasympathetic Ganglion Cells Parasympathetic Parasympathetic slower conduction slower conduction more filtering more filtering slower pacemaker slower pacemaker Sympathetic Sympathetic faster conduction faster conduction less filtering less filtering faster pacemaker faster pacemaker Parasympathetic Parasympathetic slower conduction slower conduction more filtering more filtering slower pacemaker slower pacemaker Sympathetic Sympathetic faster conduction faster conduction less filtering less filtering faster pacemaker faster pacemaker

The Electrocardiogram (ECG) or is it EKG?

Completely Polarized RefExp muscle Potential Difference (voltage) Time Potential Difference (voltage) Reference Electrode Exploring Electrode voltmeter

Depolarizing RefExp depolarization

Depolarized +-0 RefExp

Repolarizing +-0 RefExp repolarized

Repolarized +-0 RefExp repolarized

Wave of depolarization

Septum LV LV free wall RV LA Lead I Generation of Lead I ECG Reference Electrode Right Arm Exploring Electrode Left Arm depolarized normally polarized dipole vector