Question about ECG?

Question

Why are all the deflections in the same directions, both depolarizations and repolarizations?

No, What could cause this, besides placement of leads

Answer 1

Hi there,
ECG is actually a recording of the "direction" of flow of electrical impulse thru the heart. The deflections it show is not a direct indication of the depolarisation or repolarisation of the heart, even though the waves in the graph can be an indirect representation of which all areas of the heart get stimulated by the impulse and at what time.
To know the reading , we should have an idea of the arrangement of the leads (or "the receivers"). The various leads are "receivers" of electric current that are strategically placed on the chest wall and the hands as well as the legs. The first 3 leads, L1,2,&3 " see the heart from the left arm-pit , left foot and the right foot respectively.The next three leads,viz.the aVL, aVR and aVF look at the heart from the left shoulder, from the mid point between the two legs and the right shoulder respectively. The last 6 leads V1 to V6 are placed over the chest starting from a position just below the right collar bone in the midline , and ending on a diagonally opposite point on the left chest wall just off the left nipple.
If you have noticed it, an ECG tracing of the aVR lead the deflections are all negative. In a routine lead kind of ECG this tracing comes as the 4th reading, after the leads L1,2 and 3.
This downward deflection of waves are bcoz while recording this lead, the impulse is going from the right upper side of the body, towards the left lower side.This direction is as if a straight line is drawn from the right shoulder of the patient to the left foot. The aVR lead is supposed to record the current as it is "looking " at the heart from over your right shoulder, and it "sees' the current flowing away from it.
The aVF or the V1 leads may show similar downward deflections. Meanwhile those leads (like the V5 or V6 or the aVF) that "look" at the heart from a lower level, "see" the current flowing towards them.The V6 ,for example, is a lead fixed on the extreme left of your chest - almost left of the left nipple. Thats how it sees the flow of current as "coming towards it".
In conditions that alter the size of the heart as a whole or partly affects the various chambers of heart, the lead readings can show the changes too. For example, in a chronic smoker, due to the condition called, Pulmonary hypertension, the left Ventricle(lower left chamber) is enlarged. That can lead to a high upward deflection in the V6 and V5 leads, and a low downward deflection in the V1, V2 or V4 leads.

So thats about deflections of an ECG in short!

Hope it was informative enough for you.
bye.

Answer 2

they arent. there are deflections below and above baseline, depending on the lead.