Cardiac Cycle: Diastole and Systole

• Diastole and systole are the two main phases of the cardiac cycle.
• The cardiac cycle refers to the complete sequence of events in one heartbeat.
• A heartbeat consists of diastole (relaxation and filling) and systole (contraction and pumping).

Diastole

• Diastole is the phase of the cardiac cycle when the heart muscle relaxes.
• Ventricular diastole specifically refers to the period when the ventricles are relaxed.
• During diastole, the ventricles fill with blood coming from the atria.
• Diastole involves a pressure decrease within the ventricles, allowing them to expand.
• The relaxation of the myocardium enables the ventricles to passively receive blood.
• Atrial contraction occurs during the late phase of diastole to ensure complete ventricular filling.
• The duration of diastole is typically longer than systole, allowing for sufficient ventricular filling.
• Impaired diastolic function can lead to heart failure with preserved ejection fraction (HFpEF).
• Diastolic dysfunction can arise from conditions that stiffen the ventricular walls.
• Conditions like hypertension and hypertrophic cardiomyopathy can impair diastolic function.
• The assessment of diastolic function involves echocardiography and Doppler techniques.
• Diastolic blood pressure is the minimum arterial pressure during ventricular relaxation and filling.
• Medications such as calcium channel blockers and beta-blockers can affect diastolic function.
• Diastolic filling is crucial for maintaining adequate cardiac output.

Systole

• Systole is the phase of the cardiac cycle when the heart muscle contracts.
• Ventricular systole refers to the period when the ventricles contract to eject blood.
• During systole, the ventricles pump blood into the pulmonary artery and the aorta.
• Systole involves a pressure increase within the ventricles, which forces blood outwards.
• The contraction of the myocardium generates the force needed to eject blood.
• Systole is divided into two main phases: isovolumetric contraction and ventricular ejection.
• Isovolumetric contraction is the initial phase when the ventricles contract without volume change.
• Ventricular ejection is the phase when blood is pumped out of the ventricles into circulation.
• The duration of systole is typically shorter than diastole.
• Systolic blood pressure is the maximum arterial pressure during ventricular contraction and ejection.
• Ejection fraction (EF) is a measure of systolic function, representing the percentage of blood ejected with each contraction.
• Systolic dysfunction can result from conditions that weaken the ventricular myocardium.
• Myocardial infarction and dilated cardiomyopathy can impair systolic function.
• Assessment of systolic function often involves echocardiography and cardiac MRI.
• Heart failure with reduced ejection fraction (HFrEF) is characterized by systolic dysfunction.
• Medications such as ACE inhibitors and ARBs can improve systolic function.
• Adequate systolic function ensures effective blood circulation to meet the body's demands.