Einthoven's Triangle Case Study

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The heart is a complex myogenic organ composed of four chambers and a thick myocardium which has the ability to contract on its own without the intervention of the nervous system. This intrinsic rhythm is generated and controlled by the firing of action potentials of myocardial autorhythmic cells in the sinoatrial node (SAN) known as the pacemaker. The electrical conduction of the heart can be represented by an electrocardiogram (ECG), where each wave corresponds to different stages of the cardiac cycle, with reference to the heart anatomy in figure 3. To understand how an ECG is produced, The Einthoven’s Triangle provides us with different perspectives of the heart which is particularly helpful in distinguishing between depolarisation and…show more content…
The SAN located in the right atrium spreads a wave of electrical excitation across the Bachmann’s bundle to the walls of the atria causing it to contract, inducing atrial systole. The pressure in both atria increases greatly causing the tricuspid valves in the right atrium and bicuspid valves in the left atrium to open. Although the majority of the blood enters the ventricles during atrial diastole, the contraction of the atria forces the remaining 20% of blood volume (Shrestha, 2011) to fill the ventricles. Contraction of the right atrium fills the right ventricles with deoxygenated blood from the systematic circulatory system, while the left atrium receives oxygenated blood from the lungs via the pulmonary vein and fills the left ventricle. During the P-R segment, the electrical impulse passes down to the atrioventricular node (AVN) via the internodal pathway. However, there is a slight delay of approximately 0.12s (Klabunde, 2008) in order to ensure that the remaining 20% of blood fills the ventricles during atrial…show more content…
As the blood leaves the ventricles, the pressure in the aorta and pulmonary artery surpasses the ventricular pressure. Consequently, the semi lunar valves shut and the chordae tendineae attached to the valves prevent them from inverting, thus preventing back-flow. The shutting of these valves can be heard as the second heart beat (S2). At this point, the ventricles are in isovolumic ventricular relaxation as both sets of AV valves and semilunar valves are closed. Both the T wave and P wave are similarly shaped but they represent different phases of the cardiac cycle, repolarisation and depolarisation
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