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Lab 2 Intrinsic Cardiac Conduction System Spring 2016 V10.Pdf Lab 2 The Intrinsic Cardiac Conduction System 1/23/2016 MDufilho 1 Figure 18.13 Intrinsic cardiac conduction system and action potential succession during one heartbeat. Superior vena cava Right atrium 1 The sinoatrial (SA) node (pacemaker) generates impulses. Pacemaker potential Internodal pathway 2 The impulses Left atrium SA node pause (0.1 s) at the atrioventricular (AV) node. Atrial muscle 3 The Subendocardial atrioventricular conducting (AV) bundle network connects the atria (Purkinje fibers) AV node to the ventricles. 4 The bundle branches Pacemaker Ventricular conduct the impulses Inter- potential muscle through the ventricular interventricular septum. septum Plateau 5 The subendocardial conducting network depolarizes the contractile 0 100 200 300 400 cells of both ventricles. Milliseconds Anatomy of the intrinsic conduction system showing the sequence of Comparison of action potential shape at electrical excitation various locations 1/23/2016 MDufilho 2 Video • Conducting System Of The Heart 1/23/2016 MDufilho 3 Figure 18.12 Pacemaker and action potentials of pacemaker cells in the heart. 1 Pacemaker potential This slow depolarization is due to both opening of Na+ channels and closing of K+ channels. Notice that the membrane potential is Action Threshold never a flat line. +10 potential 0 2 Depolarization The action –10 potential begins when the 2 2 pacemaker potential reaches –20 threshold. Depolarization is due –30 3 3 to Ca2+ influx through Ca2+ –40 channels. –50 3 Repolarization is due to 1 1 2+ –60 Pacemaker Ca channels inactivating and potential K+ channels opening. This allows –70 + Membrane potential(mV) K efflux, which brings the membrane potential back to its most negative voltage. Time (ms) 1/23/2016 MDufilho 4 SA node R Depolarization Repolarization R P T Q P T S 1 Atrial depolarization, initiated Q by the SA node, causes the S P wave. 4 Ventricular depolarization AV node R is complete. R P T P T Q S Q 2 With atrial depolarization S complete, the impulse is 5 Ventricular repolarization delayed at the AV node. begins at apex, causing the R T wave. R P T P T Q S Q 3 Ventricular depolarization S begins at apex, causing the 6 Ventricular repolarization QRS complex. Atrial is complete. 1/23/2016 repolarization occurs. MDufilho 5 QRS complex Sinoatrial node Ventricular depolarization Atrial Ventricular depolarization repolarization Atrioventricular node P-Q S-T Interval Segment Q-T Interval 1/23/2016 MDufilho 6 Figure 18.18 Normal and abnormal ECG tracings. Infant undergoing an electrocardiogram (ECG) ECG Cardiac Arrest Normal sinus rhythm Junctional rhythm Normal ECG trace (sinus rhythm) The SA node is nonfunctional. As a result: • P waves are absent. • The AV node paces the heart at 40–60 beats per minute. Second-degree heart block Ventricular fibrillation The AV node fails to conduct some SA node impulses. Electrical activity is disorganized. Action potentials occur • As a result, there are more P waves than QRS waves. randomly throughout the ventricles. • In this tracing, there are usually two P waves for each • Results in chaotic, grossly abnormal ECG deflections. QRS wave. • Seen in acute heart attack and after an electrical shock. MDufilho Figure 18.15 Intrinsic cardiac conduction system and action potential succession during one heartbeat. Superior vena cava Right atrium 1 The sinoatrial (SA) node (pacemaker) generates impulses. Pacemaker potential Internodal pathway 2 The impulses Left atrium SA node pause (0.1 s) at the atrioventricular (AV) node. Atrial muscle 3 The Subendocardial atrioventricular conducting (AV) bundle network connects the atria (Purkinje fibers) AV node to the ventricles. 4 The bundle branches Pacemaker Ventricular conduct the impulses Inter- potential muscle through the ventricular interventricular septum. septum Plateau 5 The subendocardial conducting network depolarizes the contractile 0 100 200 300 400 cells of both ventricles. Milliseconds Anatomy of the intrinsic conduction system showing the sequence of Comparison of action potential shape at electrical excitation various locations 1/23/2016 MDufilho 8 Pacemaker 1/23/2016 http://www.youtube.com/watch?v=8Mz36HnMsYYMDufilho 9 Pacemaker Inplantation • Pacemaker 1/23/2016 MDufilho 10 Surgery for Pacemaker • Getting a Pacemaker 1/23/2016 MDufilho 11 .
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