Sinus rhythm means that the electrical impulses which regulate the heart rhythm are being produced in the pacemaker that god gives us all when we are born. This ‘pacemaker’ is otherwise called the Sino-atrial node and this is why this rhythm that is generated from the sinus node is called sinus rhythm.
A nice analogy is to think of the sinus node as a drummer who beats the drum at regular intervals. The drummer is receptive to what the body tells it and therefore increase the speed with which it beats the drum in response to adrenaline and slows the speed does in response to activation of the vagus nerve. When we are young and healthy, our drummer is extremely receptive and therefore our heart rate can go up quickly when it is needed to and slows down equally quickly when it is no longer needed to.
This responsiveness of our drummer is measured in terms of heart rate variability and a good heart rate variability is considered a sign (but by no means the only sign) of very good health. As we get older or sicker, the drummer becomes less receptive and our heart rate variability gets less.
Usually the drummer beats very regularly and if you measure the time difference between beats, it does not vary by more than 120 ms and therefore on the ECG, the intervals between successive beats look identical. Each beat looks normal and identical with a normal P wave (which tells us that the rhythm is being generated in the sino-atrial node) followed by a QRS complex.
Sometimes we can see that the time difference between successive beat intervals can vary by more than 120ms and because of this the intervals between successive beats look different on the ECG. Each beat still starts off with a normal P wave and is followed by a QRS but the time interval between 2 P waves can vary by more than 120ms. This appearance is termed sinus arrhythmia.
The reason this happens most commonly is because of breathing. When we breathe in, our vagus nerve is inhibited and therefore our heart rate increases and we breathe out the opposite happens and because in young, very healthy people, our pacemaker is so receptive, we see this phasic change in the time intervals between each heart beat by more than 120 seconds which may then show up as a slightly irregular rhythm on the ECG. Often it you repeat the ECG during breath-holding this pattern will disappear. Sometimes sinus arrhythmia pattern on the ECG may not necessarily be linked to breathing but nevertheless it does not signify anything to cause concern in the overwhelming majority of patients. In my 30 years as a cardiologist i have never come across a single case where the sinus arrhythmia was telling me that there was something sinister going on in the patient.
Sinus arrhythmia is simply an ECG pattern. It will cause no symptoms and does not have any bearing on a person’s quality of life or length of life. Moreover, it is a sign of good heart health and a healthy pacemaker. As we get older it is common for sinus arrhythmia to become less prevalent on our ECGs.
It does not require any further investigations and does not require any treatment.
I hope you found this blog useful and would love to hear your thoughts.
Here is a video that i have done on this subject
Tags: Sinus rhythm; Sinus arrhythmia; sick sinus node disease; vagus nerve; heart rate
variability; autonomic function