The Pacemaker of the Heart: Sinoatrial and Atrioventricular Nodes

The Role of the Pacemaker of the Heart

The role of the pacemaker of the heart are:

- Creates the action potential for the impulses for the contraction of the heart

- It initiates the beating of the heart.

- The cells of the SA node have an ability of self-excitation and thus the reason that beating the heart is a natural procedure (Hennis et al. 2021).

- It is situated below the epicardium and attached to the wall of the right atrium

There is a short pause in the opening when the electrical impulses pass through the AV node, it is the time when both the ventricles and atria depolarize. This delay is required as it allows ventricles to be filled with blood with full capacity before the contraction takes place.

c. Action potential is a simulation of electrical impulses which is developed by a sequence of ions across the specialised pathways in the sarcolemma membrane of the cardiomyocytes which caused the cardiac muscles to contract. The proper transmission of electronic signals throughout the conduction channel is required for a well-organized cyclic heart contraction.  At the top right corner of the atrium, the Sino-atrial node (SAN) is situated and the atrioventricular node (AVN) is situated at the bottom left corner in the ventricle. The SAN is responsible for generating the action potential. The SAN can excite them and generate maximum action potential which is around 70 to 75 per minute, therefore the reason SAN is called the natural pacemaker of the heart (Wing and Schiffman 2021). The impulse travels from Bachmann’s bundle to the left atrium (LA) and then travels through the internodal pathway towards to atrioventricular node. Therefore, this is how the action potential causes the ventricle to contract.2.

The beating of the cardiac muscles cells which uses the electrical signals is caused by the pacemaker of the heart known as the sinoatrial node (SAN) located at the walls of the right atrium. The electrical impulses begin spontaneously from the SAN which leads to the contraction of the right atria. The impulse to the left atria via the Bachmann’s bundle leads it also to contract. Then using the internodal pathway the impulse finally reaches the atrioventricular node. Here the impulse is slowed down or rather paused for a split 0.1 seconds for the blood to be completely filled in the ventricle before being transmitted to the ventricle (Grewal et al. 2018). As the SAN sends electrical impulses rapidly and simultaneously is the prime reason for completing the cardiac cycle. If the electrical impulse would not be generated it would not cause the heart to beat and the further processes would also be stooped. Therefore, this is how the pacemaker regulates the cardiac cycle and as well as ensures that correct contraction of the heart is taking place by regulating the action potential gradient.

Reference

Grewal, A., Bhatia, N., Ramachandran, G., Yadav, M., Kantor, S., Chakravarty, C., Mehta, Y., Arora, D., Kapoor, P.M., Sadera, G. and Gwinnutt, J., 2018. SeCtion 2: CARDioVASCULAR SYSteM. Monitoring in Anesthesia and Critical Care, p.27.

Hennis, K., Biel, M., Wahl-Schott, C. and Fenske, S., 2021. Beyond pacemaking: HCN channels in sinoatrial node function. Progress in Biophysics and Molecular Biology.

Lazzerini, P.E., Acampa, M., Cupelli, M., Gamberucci, A., Srivastava, U., Nanni, C., Bertolozzi, I., Vanni, F., Frosali, A., Cantore, A. and Cartocci, A., 2021. Unravelling Atrioventricular Block Risk in Inflammatory Diseases: Systemic Inflammation Acutely Delays Atrioventricular Conduction via a Cytokine‐Mediated Inhibition of Connexin43 Expression. Journal of the American Heart Association, 10(21), p.e022095.

Wing, E.J. and Schiffman, F.J. eds., 2021. Cecil Essentials of Medicine E-Book. Elsevier Health Sciences.