SVT

What is the ventricle doing during SVT? One book says that the AV node acts as a gate allowing only a fraction of the SVT pulses to get through. It sounds logical because causing VT would be a big problem. Any comments?

2 Comments

svt

by Tracey_E - 2013-11-26 11:11:38

The way svt was explained to me is it is tachycardia (generic name for a fast heart rate) that originates above the ventricles, so that would imply the ventricles are keeping up with the atria. In our case, they will keep up anyway because the pm will kick in if the heart doesn't stay in sync on its own. VT is tachy that originates from the ventricles. It's more serious because the ventricles are going off on their own, not beating with the atria.

I thought it was afib that only a fraction of the signals get through, not atach, but I could be mistaken,

Wenckebach point

by golden_snitch - 2013-11-27 03:11:25

Hi!

Everyone has a so called "Wenckebach point" (also called Wenckebach cycle length) defined as the heart rate at which the AV-node starts to slow the rhythm down by not allowing every signal coming from the atria to pass through. Happens in fast atrial tachycardias, too, not only atrial flutter or fibrillation. If you, for instance, have an atrial tachy that goes up to more than 200 bpm, the AV-node might start to block every second impulse. I say "might" because the Wenckebach point is different in everyone. You cannot say that this 2:1 block will always start at, for example, 240bpm in the atria. It really differs from person to person. In patients with 2nd degree heart block, this Wenckebach point is significantly lower than in healthy people. When I was first diagnosed with intermittent heart blocks, my Wenckebach point was at about 120bpm, and then I'd get this 2:1 block.

I read somewhere:
"Most normal individuals develop Wenckebach AV block at paced atrial cycle lengths of 500 to 350 ms (heart rates of 120 to 170 beats/min). AV nodal block does not usually occur during exercise when similar heart rates are achieved because catecholamines enhance conduction through the AV node."
("Paced" here refers to a test during an EP study, not a pacemaker).

So, usually the AV-node prevents the ventricles from tracking fast atrial rhythms. I know that in patients with WPW-syndrome there is a risk that the tachycardia causes a VT; happens very rarely, but there are a few known cases. Normally, VT originates in the ventricles, as Tracey said.

Best

Inga

You know you're wired when...

Your license plate reads “Pacer4Life”.

Member Quotes

The pacer systems are really very reliable. The main problem is the incompetent programming of them. If yours is working well for you, get on with life and enjoy it. You probably are more at risk of problems with a valve job than the pacer.