How long do the periods of systole and diastole last?

Question

The background to this is i'm doing some work using ECGs for an animation of the heart and i'm having trouble defining the end points of these periods, particularly diastole. Currently, the only information the animation uses is the time (in seconds) when a R peak was detected in an ECG.

So i was wondering what the normal lengths of these periods are and what could affect the lengths of these periods.

I assume that the lengths of the periods is mainly affected by pressure/blood volume and not electrical activity so an ECG won't tell you how long these periods are (unless a heart beat is interrupted by another?). Is that assumption correct?

On a side note: what would happens to the heart physically if there is a large gap between beats. Does it sit relatively still during that period?

EDIT:

My original post could have worded better, so: I want to know specifically about long it takes for the ventricles to physical contract and relax. How would i determine the length of these two periods in seconds and where could i find the "normal" lengths of these periods? in the cause of relaxation, i'm wondering about what to do when there is a substantial gap between heart beats.

Answer 1

The following image from wikipedia answer what you need. You can check corresponding page for details.

The top part shows the details of the different processes during a heart beat. Corresponding to these events the ECG reads are marked. As you can see the distance between the T wave ( the small bump after the QRS complex) and the next P wave corresponds to the diastole. As you can see the pressure changes correlate well with the electric reads from the heart. This wiki page has great descriptions of the features of the ECG and the corresponding events.

For example P to QRS corresponds to the conduction of stimulus from the sine node to AV node, or QRS depicts the rapid depolarization and repoliarization of the ventricles. This latter leads to strong muscle contraction and this causes intaventicular pressure rise, that is followed by aortic pressure change.

Edit: Sorry, for missing the key point, I totally misunderstood what you needed. I'll try to correct my mistake (I'll leave the previous info as it may be useful for others) The authors of this paper did a really nice work on modeling and measuring left ventricle contraction time and other things.

The reference: (Beyar and Sidman 1984)
Long story short: the contraction of the ventricle depends on the initial amount of blood (preload), aortic blood pressure at the end (afterload), and intial contractility. The results are summarized in three tables:

As you can see in the last columns, the ejection time varies with the parameters. The ejection time that is required for the ventricle to push the blood out to the aorta. Under normal circumstances a complete heart cycle is about 0.8s (or 800ms) this pie char shows the time ratio of main events. (Image taken from: tutorvista.com)

Note that complete cardiac diastole is when all the heart muscles are relaxed (this can be shortened if higher heart rate is required).

According to wikipedia

Isovolumic relaxation time (IVRT) is an interval in the cardiac cycle, from the aortic component of the second heart sound, that is, closure of the aortic valve, to onset of filling by opening of the mitral valve. A normal IVRT is about 70 ± 12 ms, and approximately 10 ms longer in people over forty years. In abnormal relaxation, IVRT is usually in excess of 110 ms.

Isovolumic relaxation is when the muscle relaxes, yet the volume of the ventricle remains the same, thus only the internal pressure changes (it is analogue to isovolumic contraction - when the volume is unchanged, but pressure is built up, this happens at early ventricle contraction).

Answer 2

Systole lasts about 3/8 and diastole 5/8 of a cardiac cycle.

Keep in mind though that such values vary with heart rate. The higher the heart rate, the shorter the fraction of diastolic time compared to the entire cardiac cycle.

That said, an ECG is not the best thing to look at if you wish to determine systolic and diastolic time intervals. What you would need is a heart ultrasound, so you can actually see the valves opening and closing. These events can be considered to happen in an instant. The potential you see on an ECG instead can vary with continuity and it would be a little harder to tell the exact timing. So your assumption is correct. Yes, a large gap between beats would show a heart expanding very slowly (this typically happens just before the atrial systole). With substantial gaps between heart beats, consider those time intervals to belong to diastole.