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# Why is sinus rhythm important for maintaining a normal blood pressure?

In order to understand the relationship between sinus rhythm and blood pressure, we first need to focus on the concept of blood pressure.

Simply put, blood pressure is the outwards force which blood exerts on the walls of arteries. We need to keep this pressure within certain limits, so that nutrients, oxygen and waste products can be transported effectively around the body, between the various cells and organs.

Diagram depicting blood pressure in an artery
© St George’s, University of London

Blood pressure is determined by two factors: the volume of blood being pumped out of the heart within a given timeframe and the resistance to the flow of this blood within the blood vessels (referred to as peripheral vascular resistance).

When we record a blood pressure, we get two values. The top value is called the systolic pressure and this relates to the contraction of the ventricles and ejection of blood from the heart, causing a pressure wave through the arterial system. We can detect this pressure wave when we feel a person’s pulse. The bottom value within the blood pressure recording is called the diastolic pressure, which is the background pressure within the arteries when the heart is resting between beats.

The volume of blood pumped out of a ventricle (usually referring to the left ventricle) in one beat is called the stroke volume and the volume ejected from the ventricle in one minute is called the cardiac output.

© St George’s, University of London

Cardiac output can be represented by the following equation:

Cardiac output = stroke volume x heart rate (the number of stroke volumes in one minute).

Cardiac output is related to blood pressure as follows:

Blood pressure = cardiac output x peripheral vascular resistance

The above illustrates why the effective ejection of blood from the heart is crucial for maintaining blood pressure. Sinus rhythm co-ordinates the order and timing of atrial and ventricular contraction, ensuring that the atria have contracted and emptied their contents into the ventricles, before the ventricles then contract. This helps to optimise stroke volume and cardiac output.

© St George’s, University of London