Dr David Begley Papworth Hospital, Cambridge HRUK Certificate of Accreditation Course: Core Heart Rhythm Congress 2011

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1 Dr David Begley Papworth Hospital, Cambridge HRUK Certificate of Accreditation Course: Core Heart Rhythm Congress 2011

2 The AV node is the soul of the heart, and whoever understands its anatomy and electrophysiology will unlock the key to understanding the anatomic and electrical working of the heart itself A riddle wrapped in mystery inside and enigma

3 Overview Structural anatomy Orientation Action potentials

4 Overview Electrical anatomy Sinoatrial node Intra-atrial connections Atrio-ventricvular node His-purkinje system Autonomic system

5 Orientation

6 Orientation Superior Border Atrial Triangle Base of Ventricular Mass Ventricular Triangle Inferior Border (Diaphragmatic) Apex

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12 Ventricular Anatomy Inflow Tricuspid valve Mitral valve Outflow tracts Pulmonary valve Aortic valve Tricuspid valve Mitral valve Aortic valve Pulmonary valve

13 Action Potentials Essential for normal conduction Determined by Concentration of intracellular/extracellular ions Selective permeability Cardiac muscle cells can rapidly reverse membrane potential Generation of action potential causes muscle contraction Divided into 5 phase (0-4) Action potentials differ in different parts of the heart

14 Action Potentials: Phase 4 Resting membrane potential -85 to -95 mv Maintained by potassium equilibrium Na + -K + exchanger Na + -Ca 2+ exchanger I K1 K + I K1 (inward rect)

15 Action Potentials: Phase 0 Rapid depolarization Membrane potential becomes positive Determined by rapid conduction of sodium into the cells through sodium channels Na + (in) I Na (rapid)

16 Action Potentials: Phase 1 Early repolarization Inactivation of fast sodium channels Transient movement of K + and Cl - K +, Cl - (out) I to1,2 (transient outward)

17 Action Potentials: Phase 2 Plateau phase Balance between Inward movement of Ca 2+ Outward movement of K + K + (out), Ca 2+ (in) I Ca-L (Ca long) I KS (K slow delayed rect)

18 Action Potentials: Phase 3 Rapid repolarization L-Type Ca 2+ channels close Number of potassium channels open K + (out) I KS (K slow delayed rect) I KR (K rapid delayed rect) I K1 (inward rect)

19 Action Potentials (SA Node) Phase 0 Phase 3 Phase 4

20 Action Potentials (Atrium) Phase 1 Phase 0 Phase 2 Phase 3 Phase 4

21 Action Potentials (AV Node) Phase 0 Phase 3 Phase 4

22 Action Potentials (His Bundle) Phase 1 Phase 0 Phase 2 Phase 3 Phase 4

23 Action Potentials (Purkinje) Phase 1 Phase 0 Phase 2 Phase 3 Phase 4

24 Action Potentials (Ventricle) Phase 1 Phase 0 Phase 2 Phase 3 Phase 4

25 Action Potentials (Automaticity) Phase 4 not in equilibrium Permeability to potassium Passive permeability to calcium Gradual increase in membrane potential Threshold reached

26 Electrical Anatomy Sinoatrial node Intra-atrial connections Atrio-ventricvular node His-purkinje system

27 Sino-Atrial Node: Location Sup-epicardial Junction of CT, SVC and appendage 1-2 cm in length

28 Sinus Node: Structure Extensive connection tissue Characteristic pacemaker P cells at centre Gradual transition in cell type in all directions Perinodal transitional T cells transmit signal to surrounding right atrium

29 Sinus Node: Blood supply Multiple different routes Dual blood supply in more than 50% of cases

30 Intra-atrial Connections Impulse dissemination via atrial myocardium No insulated conduction tracts Preferential conduction provided by anisotropic arrangement of muscular fibres

31 Intra-atrial Connections

32 Atrio-Ventricular Node: Location Located at apex of Triangle of Koch Pentrates the fibrous insulating plate as the bundle of His

33 Atrio-Ventricular Node: Structure Transitional cells between compact AV node and ordinary myocardium

34 Atrio-Ventricular Node: Structure Significant areas of ordered ordinary atrial myocardium approach the AV node

35 Atrio-Ventricular Node: Blood Supply From posterior inter-ventricular artery Branch of the right coronary artery in right-dominant individuals Branch of the left circumflex artery in left-dominant individuals

36 Bundle of His First suggested by Wilhelm His the younger in 1893 First accurate descriptions by Sunao Tawara in 1906 No histological separation between compact AV node and proximal His bundle Emerges from fibrous tissue at crest of muscular septum First gives of fascicles of left bundle followed by cordlike right bundle

37 Left and Right Bundle Branches Left bundle branch is short splitting into anterior and posterior fascicles Left posterior fascicle is short with dual blood supply Left posterior fascicle transmits impulses to the papillary muscles Right bundle branch emerges in right ventricular myocardium at level of the anterior papillary muscle Subdivision of bundle branches into purkinje fibres

38 Autonomic Nervous System Autonomic control originates in medulla oblongata Parasympathetic and sympathetic innervation

39 Parasympathetic Nervous System Pre-ganglionic efferents arrive via vagus nerve Post-ganglionic efferents from ganglionic plexi Sparse innervation of ventricular mycocardium Right- Left bias Have negative chronotropic inotropic and dromotropic effects

40 Ganglionic Plexi Singh S et al. J Thoracic Cardiovasc Surg 1996;112:

41 Sympathetic Nervous System Sympathetic efferents arrive from Middle cervical ganglion Cervico-Thoracic (Stellate) ganglion First Four ganglia of thoracic sympathetic chain Ubiquitous distribution Positive chronotropic, inotropic and dromotropic effects

42 Summary Remember attitudinal correctness Normal electrical anatomy Sino-atrial node Intra-atrial connections AV node His-Purkinje system