Untitled Quiz

Electrocardiogram Overview

• Electrocardiogram (ECG) records heart-generated voltage from the body surface, representing each heartbeat.
• P wave indicates atrial depolarization, leading to atrial contraction.
• QRS complex results from ventricular depolarization, occurring approximately 0.16 seconds after P wave onset, initiating ventricular contraction.
• T wave reflects ventricular repolarization.

Atrial and Ventricular Interaction

• Approximately 80% of ventricular filling occurs during diastole before atrial contraction.
• Atrial contraction contributes the remaining 20% to the ventricles' filling, enhancing pumping effectiveness by 20%.
• Atria dysfunction may lead to significant symptoms like shortness of breath during exercise but usually remain asymptomatic at rest.

Diastole Phases

• At the start of diastole, A-V (atrioventricular) valves are closed; atria fill with blood during systole.
• Isovolumic relaxation occurs as ventricles relax, leading to decreased pressure.
• A-V valves open when ventricular pressure falls below atrial pressure, allowing blood flow into the ventricles.
• Rapid ventricular filling occurs in the first third of diastole, providing most volume, followed by continuous filling.
• Atrial contraction, termed “atrial kick,” happens in the last third of diastole, contributing 20% of ventricular filling.

Systole Mechanism

• Systole begins with ventricular contraction, closing A-V valves and increasing ventricular pressure.
• Isovolumic contraction occurs when no blood is ejected, and fetal volume remains constant while pressure builds.
• Aortic and pulmonary valves open when left ventricular pressure exceeds 80 mm Hg and right ventricular pressure surpasses 8 mm Hg, allowing blood ejection.
• 70% of the total blood ejected from the ventricles occurs during the rapid ejection phase, while 30% happens in the slow ejection phase.

Ventricular Volumes and Ejection Fraction

• End-diastolic volume, the volume in each ventricle at the end of diastole, ranges from 110 to 120 milliliters.
• Stroke volume, the amount of blood ejected per beat, is approximately 70 milliliters.
• End-systolic volume, remaining blood post-ejection, measures around 40 to 50 milliliters.
• Ejection fraction is calculated by the formula: Ejection Fraction = Stroke Volume / End-Diastolic Volume, typically around 60%.
• Stroke volume may be increased by elevating end-diastolic volume and reducing end-systolic volume.