1. Heart & It’s Rhythmical Contractions
Dr. Wasif Haq

2. General Anatomy of Heart
Myogenic organ, involved in blood circulation.
Pericardial sac encloses the heart.
Three layers; Epicardium, Myocardium & Endocardium.
4 chambers; 2 receiving & 2 discharging chambers.
Right side- Pulmonary blood flow.
Left side- Systemic blood flow.

3. Chamber & Valvular Anatomy
Right atrium collects deoxygenated blood from Vena Cavas.
Tricuspid valve= Right atrium & right ventricle, pushes blood towards ventricle.
Pulmonary valves= Right ventricle & pulmonary arteries.
Left atrium receives oxygenated blood from lungs.
Bicuspid valves/ Mitral= Left atrium & ventricle.
Aortic valve= Left ventricle & aorta.

5. Aspects of Cardiac Muscles
Involuntary, striated muscle fibers.
1. Sarcomere: Contractile unit, thick (Myosin) & thin (Actin, Troponin & Tropomyosin) filaments.
2. Intercalated disk: Junctions occurring at end of cardiac cells, contraction as single unit.
3. Gap junctions: Present at intercalated disk, rapid electrical impulse transmission.
4. Mitochondria: Abundant quantity.
5. T-tubules: Carry action potential to inside of cell, well developed in ventricles.
6. Sarcoplasmic reticulum: Storage of Ca++ ions.

6. Syncytium
Syncytium= Multi-nucleate cells resulting from multiple cell fusion into an aggregate mass.
Cardiac cells are interconnected, rapid excitation.
Two types: a. Atrial syncytium, b. Ventricular syncytium.
No transmission between two syncytiums because of separation by fibrous tissue except at A.V. bundle.

9. Rhythmical Contraction
S.A. Node
Internodal Pathways
A.V. Node
A.V. bundle (Bundle of His)
Bundle branches (2 left & 1 right)
Purkinjee fibers.

11. Sinoatrial Node Pacemaker. Normal, rhythmical impulse generation.
Location: Superior, posterolateral wall of right atrium, lateral to superior vena cava opening.
Directly connected to atrial muscle fibers.

12. Internodal pathway Anterior, middle & posterior internodal pathways.
Impulse reaches A.V. node through internodal pathway.

13. A.V. Node Delay of impulse conduction from atria to ventricles.
Allowing for ventricular filling before ventricular contraction.
Delay occurs due to lesser gap junctions causing greater resistance to conduction.

14. A.V. Bundle/ Bundle of His
Fibrous insulation all over atria & ventricles except at A.V. bundle.
Very rapid conduction.
Impulse unidirectional only.

15. Bundle Branches
The bundle of His branches into the three bundle branches: the right, left anterior and left posterior bundle branches .
The bundles give rise to thin filaments known as Purkinje fibers.

16. Purkinjee Fibers
Rapid transmission of action potential by Purkinjee fibers.
Few myofibrils, little tendency to contract.
Impulse from Purkinjee fibers travels to ventricular muscle mass by ventricular muscle fibers themselves.

17. Take Home Message
If having wisdom makes human proud, arrogant and ignorant towards his Creator then such wisdom is certainly and surely foolishness.