+ Answer R-0017A
The QRS complexes in the rhythm strip have been numbered. Atrial activity is seen before each QRS complex except for complex 16. Abnormal P waves are identified by a blue asterisk.
The complexes can be grouped according to P wave shape and QRS shape:
- Complexes 3, 4, 6, 8, 10, 12, 14 have normal P waves with normal ventricular conduction i.e. they represent normal sinus rhythm.
- Complexes 1, 2, 5, have inverted or biphasic P waves but the morphology of the QRS complexes is normal i.e. they are atrial ectopic beats with normal ventricular conduction
- Complexes 7 and 11 have an inverted or biphasic P wave and a widened S wave in the QRS complex i.e. they are atrial ectopic beats with possible bundle branch block
- Complexes 9, 13 and 15 have P waves that differ in shape from the normal P waves. They are followed by widened and QRS complexes that are predominately negative (rS shape), widened and notched i.e. they are atrial ectopic beats with aberrant conduction
+ Answer R-0017B
The rhythm strip and a laddergram with a tier (A) for atrial activity are shown. The position of visible P waves is shown by the black circles. The P-P interval between visible P waves is used to identify the location of P waves that are obscured by the T waves. These hidden P waves are shown by the blue lines and the blue circles.
The rhythm strip and the complete laddergram are shown. Every third P wave is not conducted to the ventricle. The numbers in the AVN tier are the PR interval of conducted P waves. The PR intervals of (most of) the conducted P waves increase progressively from a base interval of 240 msec until a P wave is not conducted
The rhythm strip shows 3:2 Wenckebach block
+ Answer R-0017C
Descriptive Analysis There are nine P - QRS complexes in the rhythm strip; the third P wave and the eighth P wave occur earlier than the preceding P waves and have a different shape compared to the dominant P waves. The third and eighth P waves are atrial ectopic beats.
Analysis with Measurement of Intervals (See also Ectopic Beats, Intervals & Pauses)
Another approach to the analysis of this rhythm involves measuring intervals. The R-R interval are shown along the bottom of the rhythm strip, and consist of:
- A basic interval of 880 - 920 sec, which correspond to a ventricular rate of 65 and 68 beats per minute
- An interval of 640 msec between the first atrial ectopic beat (P'1) and the normal complex that immediately precedes the ectopic beat. This interval is called the coupling interval. The coupling interval (CI1P) between the P waves and the coupling interval between the R waves (CI1R) is the same.
- A coupling interval of 560 msec between the second atrial ectopic beat (P'2) and the preceding normal complex. Multiple extrasystoles can have the same coupling interval (also called a fixed or constant coupling interval) or a varying coupling interval. Extrasystoles that have a variation in their coupling interval that is 80 msec or less are regarded as having a constant coupling interval.
- A R-R interval of 1040 msec after the first atrial ectopic beat and a R-R interval of 1080 after the second atrial ectopic beat. The delay after each atrial ectopic beat produces a compensatory pause, which is defined as the sum of the compensatory interval and the post extrasystolic R-R interval. In this case the compensatory pause due to the first atrial ectopic beat (CP 1) is 1680 msec, and that due to the second atrial ectopic beat (CP 2) is (the same at) 1680 msec. The duration of the compensatory pause can be compared to the interval that is the sum of two normal R-R intervals. In this case the compensatory pause of 1660 - 1680 msec is less than the 2 x R-R interval of 1760 msec. This is called a incomplete compensatory pause.
Final diagnosis: Sinus rhythm with two atrial ectopic beats that have a constant coupling interval and are associated with a incomplete compensatory pause
Comment: Identification of ectopic beats involves noting a premature (early) impulse that is followed by a pause. Further analysis is usually not needed. Measuring coupling intervals or compensatory pauses may be of value in:
- The diagnosis of parasystole, where the coupling interval is variable (the coupling interval in atrial extrasystoles or ventricular extrasystoles is usually constant).
- Distinguishing between atrial ectopic beats (where the coupling interval is usually incomplete) and ventricular ectopic beats (where the coupling interval is usually complete)