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Every pulse in the heart triggers a series of electrical and mechanical actions known as the cardiac cycle. A cardiac cycle is a rhythmic pattern in the beating of the heart. A cardiac cycle process duration is usually 0.8 seconds with a heart rate of 75 beats per minute. 

Diastole and systole are the two stages of the heart cycle. During systole, the heart muscle contracts, and while diastole, it relaxes. Each step of the cardiac cycle process comprises critical actions that ensure healthy blood flow to the body. 

These stages include retracting heart chambers and appropriate opening and shutting of certain cardiac valves. Both the atria and the ventricles experience systole and diastole. Both parts must be in sync for blood to be circulated efficiently throughout the body.

Cardiac cycle process

  • The cardiac cycle process is a sequence of heart contractions that direct the blood flow in the chambers of the heart in a specific direction. This is the cardiac cycle process definition. 
  • A cardiac cycle is one heartbeat or one cycle of contraction and relaxation by the cardiac muscles. During a heartbeat, the atria and ventricles contract and relax in sync. The contraction stage is referred to as systole, whereas the relaxation stage is referred to as diastole.
  • The atria and ventricles contract alternately during a cardiac cycle, which also considerably changes the pressure in the chambers. Blood flows from the left atrium (LA) and right atrium (RA) into the left ventricle (LV) and right ventricle (RV), respectively.
  • Atrioventricular valves (mitral and tricuspid) divide the atria from the ventricles, and blood flows through them. Through the superior vena cava (SVC) and inferior vena cava (IVC), the RA receives venous blood from the body (IVC).
  • Oxygenated blood is delivered from the lungs to the LA via four pulmonary veins that enter the LA. Both atria contract after diastole, propelling an additional volume of blood into the ventricles.
  • The systole of the atrial and ventricular chambers will never overlap. Based on intraventricular pressure changes, the subsequent events of the cardiac cycle process in the ventricular chambers are described. With cardiac catheterisation, changes in the pressure and volume in the ventricular chambers can be determined.

Phases of cardiac cycle 

  • All physiological events; such as – electrical events, mechanical events (i.e., pressure and volume), sound of heart, associated with a single heartbeat are composed by the cardiac cycle process. 
  • The cardiac cycle process mainly has two phases – the systole, and the diastole. These two are then split into their atrial and ventricular components. Thus, a total of four categories – atrial systole, atrial diastole, ventricular systole, and ventricular diastole are there in the phases of cardiac cycle process.

Atrial Systole

  • During this phase, both atria in the heart contract forcing the blood into the ventricles from the atria.
  • At the point where the atrial systole ends, the ventricular systole starts.

Ventricular Systole

  • During this phase, both ventricles contract during this cardiac cycle, and blood is propelled to the lungs via the pulmonary trunk and the rest of the body via the aorta.
  • Isovolumetric contraction is the period of ventricular systole when both the SL and AV valves are closed, causing a rapid increase in intraventricular pressure.
  • The SL valves are pushed open when the intraventricular pressure exceeds 80 mm Hg, causing the following sub-phase of the ventricular systole, known as the maximal ejection phase.

Atrial Diastole

  • The atria relax during this phase and it is filled with blood from the vena cava (i.e., the large veins).

Ventricular Diastole

  • This phase starts before the atrial systole, allowing blood from the atria to enter the ventricles passively in a cardiac cycle process.

Cardiac cycle process duration 

  • The cardiac cycle process duration is the time taken to complete one cycle or heartbeat.
  • The length of a cardiac cycle i.e., the cardiac cycle process duration is calculated by the heart rate per minute. If the heart rate is 60 beats/minute, the cardiac cycle will last one second. 
  • The heart rate and the cardiac cycle process duration have an inverse connection. For example, if the heart rate increases to 120 beats per minute, the cardiac cycle will take around 0.5 seconds to complete. 
  • The duration of atrial systole is roughly 0.1 seconds. Both atria contract during the cardiac cycle, forcing blood from the atria into the ventricles.
  • The duration of the ventricular systole is roughly 0.3 seconds. Both ventricles contract during this cardiac cycle, and blood is propelled to the lungs via the pulmonary trunk and the rest of the body via the aorta.
  • The duration of an atrial diastole is around 0.7 seconds. The atria relax during this procedure, and the atria fill with blood from the big veins (the vena cava).
  • The diastole of the ventricles lasts roughly 0.5 seconds. It starts before atrial systole, allowing blood from the atria to enter the ventricles passively in a cardiac cycle process.

Conclusion

The cardiac cycle process is divided into main two phases: diastolic and systolic. Diastole is the process of the heart chambers filling with blood and the heart muscles relaxing. Systole refers to the period during which the heart ventricles contract and pump pure blood to various body parts through the blood vessels. It’s crucial to know the difference between diastolic and systolic dysfunctions when diagnosing and treating people with heart failure. In echocardiography, ultrasonic waves show the heart and its surrounding arteries. The cardiac cycle process duration is the time taken to complete one cycle or heartbeat and is calculated by the heart rate per minute.