Question

If a signal took longer to transmit through the ventricles such as in the cases of a bundle branch block or RV paced rhythm how would this change the QRS complex? If a signal experienced a significant time delay in the AV node before being transmitted to the ventricles how would this manifest in a PR interval?

If a signal had more tissue to travel through in the heart such as in the case of left ventricular hypertrophy how would this change the QRS complex? If we had to record through more tissue outside the heart such as in posterior leads or in very obese patients how would this change QRS voltages on the ECG?

Answer 1

Answer

In bundle branch block or RV paced rhythm

QRS Complex gets widened (Prolonged) due to slower muscle to muscle spread of ventricular depolarization (duration more than 120 ms).

Conduction through the Atrioventricular node

It is slower than normal which causes a prolongation of the PR interval. In certain condition can reduce the ability AV node to conduct the atrial impulse to the ventricles. As the conductivity reduces, PR interval becomes longer. Normal PR interval duration 220Msec (0.22 Sec) if the PR interval prolong more than 220msec it would be due to First degree AV block.

Left ventricular hypertrophy (LVH)

LVH in which the myocardium is hypertrophied, there is a larger mass of myocardium for electrical impulses to pass through. In this condition the duration of the QRS complex may be widened. This is known as LVH with QRS widening.

Very obese patients

In very obese patients there is more tissue present for the electrical impulse hence the QRS voltage for the obese group was slightly lower than the voltage of the normal population