How to Measure Basic Intervals

Basic Intervals

The measurement of vital signs is a part of basic patient assessment. In Electrophysiology, Basic Intervals (BI’s) is the basic assessment of the cardiac conduction system. Sort of the "vital signs" of the conduction system.

Basic Intervals measure the amount of time it takes an impulse to travel thru the conduction system.  Ideally this is performed when the patient is in Sinus Rhythm. 

Basic Intervals are usually taken during an EP study and at the end of an ablation procedure.

How to Measure Basic Intervals

**Note**    Learning to measure Basic Intervals takes lots of time,  practice and patience.

An easy way to learn how measure BI’s is, during a procedure,  have a Fellow or Attending measure and record  basic interval measurements and then reproduce their measurements yourself. 

P-A)  Measured between the earliest activation recorded atrial activity in any channel (either the   P- wave onset, or that of the earliest arterial electrogram) and the rapid deflection of the atrial electrogram (not earliest) on the HIS Bundle catheter.                                                                            Normal P-A interval is; 25-55 mS.

A-H)  Measured between the rapid deflection (not the point where the A signal leaves the baseline) atrial electrogram recorded by the HIS catheter and earliest deflection of the HIS electrogram itself.    Normal A-H interval is; 55-125 mS.

H-V) Measured from the earliest deflection of the HIS electrogram and the earliest recorded ventricular activation.  Normal H-V is; 35-60mS

P-R)  Measured from the earliest activation recorded atrial activity and the earliest recorded ventricular activation. Normal P-R interval is; 120mS to 200mS.

QRS)  Measured from the earliest recorded ventricular activation to the point that the ventricular electrogram returns to baseline.  Normal QRS is; ≤ 100mS.

QT) Measured from the earliest ventricular activation to the point the T-Wave returns back to baseline.  Normal QT is; Men-≤ 450/Women-≤ 470

R-R)   Measured from the earliest ventricular activation to the earliest ventricular activation of the next Sinus Beat.   Normal R-R is; 1000mS to 600mS (60bpm to 100bpm).

Measured Basic Intervals

Again, it takes time and practice and patience to learn to measure Basic Intervals. Don’t get discouraged…….keep trying!