Lab 2

The Intrinsic Cardiac Conduction System

1/23/2016 MDufilho 1 Figure 18.13 Intrinsic cardiac conduction system and succession during one heartbeat.

Superior vena cava Right atrium

1 The sinoatrial (SA) node (pacemaker) generates impulses.

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 () AV node to the ventricles.

4 The bundle branches Pacemaker Ventricular conduct the impulses Inter- potential muscle through the ventricular . 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

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 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 +

Membranepotential (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 . 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

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 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

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