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Stable vs. Unstable Tachycardia

Rules for Sinus Tachycardia

                              Figure 37

Regularity R-R intervals are regular, overall rhythm is regular.
Rate The rate is over 100 bpm but usually less than 150 bpm.
P Wave There is one P wave in front of every QRS. The P waves appear uniform.
PR Interval Measures between 0.12 and 0.20 seconds in duration. PR interval is consistent.
QRS Complex Measures less than 0.12 seconds.

Table 15

Rules for Atrial Flutter

Figure 38

Regularity The atrial rate is regular. The ventricular rate will usually be regular, but only if the AV node conducts the impulses in a consistent manner. Otherwise, the ventricular rate will be irregular.
Rate The atrial rate is normally between 250 to 350. Ventricular rate depends on conduction through the AV node to the ventricles.
P Wave The P waves will be well defined and have a “sawtooth” pattern to them.
PR Interval Due to the unusual configuration of P waves, the interval is not measured with atrial flutter.
QRS Complex QRS measures less than 0.12 seconds.

Table 16

Rules for Atrial Fibrillation (A-Fib) Irregular Narrow Complex Tachycardia

Figure 39

Regularity The R-R intervals are irregular; therefore, overall rhythm is irregularly irregular. The ventricles conduct from different atrial foci causing the irregularity.
Rate Atrial rate usually exceeds 350. If the ventricular rate is between 60 and 100 bpm, this is known as “controlled” A-Fib. If the ventricular rate is more than 100, it is considered A-Fib with Rapid Ventricular Response (RVR), also known as uncontrolled A-Fib.
P Wave Due to the atria firing so rapidly from multiple foci, there are no obvious P waves in the rhythm. The baseline appears chaotic because the atria are fibrillating, therefore no P waves are produced.
PR Interval Because there are no P waves, PR interval cannot be measured.
QRS Complex QRS measures less than 0.12 seconds.

Table 17

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