Stimulation Basics

In measuring the HV interval, the earliest ventricular activation is usually seen on

• CS electrode

• RV apex elecrode

• Surface QRS

• RV outflow electrode

Answer explanation

Murtgatroyd says, "The HV interval is measured between the His bundle electrogram and the earliest recorded ventricular activation. As with the AV interval, the timing of the His electrogram is taken from its onset. The earliest recorded ventricular activation is almost always the beginning of the surface QRS complex. An HV interval of 35-55 ms is considered normal."

The AH interval measures __________.

The AH interval measures AV node conduction time, and is measured from the ______ to the beginning to the beginning of the H on the his bundle catheter.

Answer explanation

The AH interval is the time taken from the cardiac impulse to travel over the AV node, and his measured from the electrograms recorded by the His bundle catheter. The AH interval is measured between the atrial electrogram recorded by the his bundle catheter and the beginning of the His electrogram itself.

Match the normal values for each EP measurement shown

• 180-290 msec (Ventricular)

• HV interval

• 180-330 msec (Atrial)

• AV Nodal ERP

• 250-400 msec (antegrade)

• VERP

• 50-120 msec

  (55-125 Murgatroyd)

• Atrial ERP

• 35-55 msec

• AH interval

Match the following measurements with the numbers that make it up on this electrogram

• BCL

• 1 + 2 + 3 + 4 + 5 + 6

• HV

• 1

• IACT

• 2 + 3

• AH

• 4

Answer explanation

BCL (Basic cycle length) is the interval between successive A waves (measured from the RA catheter); ... IACT (intra-atrial conduction time) is the interval from the SA node to the AV node and is measured from beginning of the P wave on the surface ECG to the A deflection on the His bundle electrogram ... The conduction interval from the beginning of the A deflection to the beginning of the H deflection (the HAH interval) represents the conduction time through the AV node (normally 50-120 msec) ... The interval from the beginning of the H deflection to the beginning of the V deflection (the HV interval) represents the conduction time through the His-Purkinje system (normally 35-33 msec). Disease in the AV node will often produced prolongation of the AH interval whereas disease in the distal conduction system produces a prolongation of the HV interval.

On this electrogram, measure the CL, PA, AH, and HV intervals.

d

c

b

a

Cycle length = 544 msec.

PA or IACT interval = 46 msec.

AH interval = 128 msec.

HV interval = 43 msec.

Match the following

• 128 msec.

• Cycle Length

• 46 msec.

• AH interval

• 43 msec.

• PA interval

• 544 msec.

• HV interval

On the electrogram below, measure the cycle length and coupling interval. Cycle length = ______; Coupling interval = _______.

Answer explanation

Programmed stimulation consists of two general types of pacing: incremental and extrastimulus pacing. Incremental pacing (or burst pacing) consists of introducing a train of paced impulses at a fixed cycle length. The incremental train may last for a few beats or for several minutes... The extrastimulus technique consists of introducing one or more premature impulses, each as its own specific coupling interval. The extrastimuli are introduced synchronously either from an intrinsic cardiac impulse or following a short train of incrementally paced impulses (traditionally eight beats).

In the diagram there is a pulse train of rapidly paced beats followed by the even more rapid premature extrastimulus. Measure the RR interval or each type of beat. AH the S1 pulse train beats are 450 msec. There are easiest to measure between the clear HRA S1. S1-S1=450, S1-S2 = 250 msec. These are easiest to measure between the clear HRA pacing spikes using capilers. Note the 4 spikes on the HBE recordings S1, A, H, and V.

On this ECG measure the cycle length and heart rate.

Answer explanation

There are 21.5 boxes between spikes. (21.5 boxes) x (40 msec/box) = 860 msec. which is a rate of 70 beats/min. Rate = 60,000/RR interval. Rate = 60,000/(860) = 70 bpm. This strip shows ventricular pacing since pacemaker artifacts (negative spikes) precede each QRS complex. Whether it is rate or mSec needed, always divide into sixty thousand - the number of milli-Seconds in a minute.

Convert a heart rate of 250 bmp into its cycle length in milliseconds.

Answer explanation

Here 60,000/250 = 240 msec., Formula is CL = 60,000/heart rate. Whether it is rate or mSec needed, always divide into sixty thousand - the number of milli-Seconds in a minute.