Electrocardiogram (ECG) – Instrument Based Diagnostic Techniques

00:01 Let’s talk about another very simple and commonly performed test: the electrocardiogram.

00:07 This is really a heart test but it gives us important information about the heart that is relevant to the peripheral vascular system. This is an enlarged version of one complex from the electrocardiogram. In blue, you see the P wave. That is the depolarisation – the electrical activity running through the atrium. Then in grey the QRS. That is the ventricular depolarisation – or electrical activity – running through the ventricle. And then in brown the T wave. That is the ventricle resetting itself for the next beat.

00:46 The electrocardiogram shows the flow of electrical depolarisation current as it passes through the heart. It’s one of the first tests done. It’s a simple test that’s often done in the doctor’s office. It’s the cheapest test. It’s the most easily obtained cardiovascular test. And it has reasonable accuracy for a variety of heart conditions. For example, arrhythmias – electrical short circuits - or myocardial infarction – heart attack.

01:18 But there are many non-specific and non-diagnostic patterns so you need to interpret it in light of the patient’s history, the patient’s physical exam and any other pieces of information you might have about the patient.

01:34 Here are two examples. The one at the top is normal. This slide shows a normal electrocardiogram with a normal triphasic up and down and up again wave form for the ventricular depolarisation as I showed you previously. The small hump in the front is atrial depolarisation and the large hump after the triphasic depolarisation is the ventricle resetting itself.

02:00 Let’s look at one very simple example of an arrhythmia – of an abnormality. This is atrial fibrillation in which the little P wave has gone and, instead, you can see lots of bouncing-around activity because the atrium is fibrillating – that is it’s in a chaotic electrical and mechanical state. And you can see that the rhythm is very, very irregular. So this is one thing that’s very easily identified. And, as we’ll see in later lectures, sometimes this entity can result in a blood clot forming in the heart that can get out and cause a stroke or other damage.