🫀 [#2] CICLO CARDÍACO: DIAGRAMA DE WIGGERS | MK Fisiologia

Summary

This video breaks down the cardiac cycle through the Wiggers diagram, a powerful tool that links electrical and mechanical events in the heart. It explains how ECG waves correspond to changes in pressure, volume, and heart sounds throughout a single heartbeat, focusing on the left side of the heart. Key phases such as atrial systole, ventricular contraction, ejection, and relaxation are explored step by step, including valve movements and sounds like S1 and S2. By connecting these events visually and conceptually, the video helps simplify a complex topic and guides viewers on how to study and internalize the cardiac cycle effectively.

Takeaways

• 😀 The Wiggers diagram illustrates the temporal relationship between electrical and mechanical events in the cardiac cycle, including ECG and changes in blood pressure and volume.
• 😀 The script explains the difference between the left and right heart pressures, emphasizing that the left heart works under higher pressures for systemic circulation, while the right heart deals with the pulmonary circulation.
• 😀 The electrical event that begins the cardiac cycle is the action potential generated in the sinoatrial node, which triggers atrial depolarization (represented by the P wave on an ECG).
• 😀 Atrial contraction (atrial systole) fills the ventricle to its maximum volume, known as the end-diastolic volume (EDV). This phase is crucial before ventricular systole begins.
• 😀 During ventricular depolarization (QRS complex), the ventricles contract, and this causes the closure of the atrioventricular valve (mitral valve), creating the first heart sound (S1).
• 😀 The ventricular pressure increases during isovolumetric contraction, and no blood is ejected from the ventricles yet because all valves are closed.
• 😀 When the ventricular pressure exceeds the aortic pressure, the aortic valve opens, and blood is ejected from the left ventricle into the aorta during ventricular ejection.
• 😀 After ventricular ejection, the T wave represents ventricular repolarization, which marks the beginning of ventricular diastole.
• 😀 The closure of the aortic valve produces the second heart sound (S2), and the phenomenon of aortic valve closure leads to a brief backflow of blood, creating the dicrotic notch in the aortic pressure curve.
• 😀 During ventricular relaxation (isovolumetric relaxation), the volume of the ventricles doesn’t change, and the ventricle prepares for the next filling phase.
• 😀 The cycle ends as the atria fill with blood from the pulmonary veins, increasing atrial pressure until it surpasses the ventricular pressure, leading to the opening of the mitral valve and starting the next cycle.
• 😀 The script emphasizes that if the diagram is confusing, it’s okay to take time to review, draw the diagram, and slowly internalize the sequence of events.

Q & A

What is the Wiggers diagram used to represent?

The Wiggers diagram represents the temporal relationship between electrical and mechanical events during a cardiac cycle, including changes in arterial pressure, atrial and ventricular pressure, and ventricular blood volume. It also shows heart sounds through a phonocardiogram.

What are the primary components of the Wiggers diagram?

The primary components of the Wiggers diagram are: the electrical events shown by the electrocardiogram (ECG), mechanical events such as changes in atrial and ventricular pressure, changes in blood volume in the ventricles, and heart sounds as represented by the phonocardiogram.

How does the diagram of the left heart differ from the right heart in the Wiggers diagram?

In the Wiggers diagram, the values of pressure and volume typically represent the left heart, as this is more commonly used to explain the cardiac cycle. The left heart has higher pressure values because it pumps blood to the entire systemic circulation, while the right heart only pumps blood to the pulmonary circulation, resulting in lower pressure values.

What electrical event starts the cardiac cycle and how is it represented?

The cardiac cycle starts with the generation of an action potential in the sinoatrial node, which causes depolarization of the atria. This electrical event is represented by the P wave on the electrocardiogram (ECG).

What is the significance of the first heart sound (S1)?

The first heart sound (S1) is generated by the closure of the left atrioventricular valve (mitral valve) during ventricular systole. This sound is low-pitched and is often described as 'lub' in the 'lub-dub' sound pattern of the heartbeat.

What does the term 'isovolumetric contraction' refer to in the Wiggers diagram?

Isovolumetric contraction refers to the phase of the cardiac cycle during which all heart valves are closed and the ventricles contract, increasing pressure without changing the volume of blood in the ventricles. This occurs after the closure of the mitral valve and before the opening of the aortic valve.

What causes the second heart sound (S2)?

The second heart sound (S2) is caused by the closure of the aortic valve at the end of ventricular systole, as the ventricular pressure falls below the arterial pressure in the aorta. This sound is high-pitched and is described as 'dub' in the 'lub-dub' sound pattern.

What is the significance of the dicrotic notch (incisura dicrótica)?

The dicrotic notch is a brief dip in arterial pressure that occurs immediately after the closure of the aortic valve. It is caused by a small backflow of blood into the ventricle, which results in a temporary decrease in arterial pressure.

What is the difference between systolic volume and diastolic volume?

Systolic volume refers to the amount of blood left in the ventricles after contraction (end-systolic volume), while diastolic volume refers to the volume of blood in the ventricles at the end of diastole, right before ventricular contraction (end-diastolic volume).

How can the Wiggers diagram help in understanding the cardiac cycle?

The Wiggers diagram helps visualize the relationship between electrical and mechanical events in the heart, making it easier to understand the sequence of heartbeats, pressure changes, heart sounds, and blood flow throughout the cardiac cycle. It provides a clear representation of how the heart functions in a time-dependent manner.