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RHYTHM STATEMENTS

Rhythm Statements and Modifiers

VERITAS rhythm statements describe the predominant rhythm in the 10 seconds of analyzed data. A modifier, listed after the rhythm statements, may also be added to more accurately describe the type of rhythm. The main rhythm statements and their criteria follow.

Rhythm Statements

Sinus RhythmEctopic Atrial RhythmJunctional RhythmSupraventricular Rhythm

Idioventricular Rhythm

Uncertain Regular RhythmUncertain Irregular Rhythm

Atrial Fibrillation Atrial Flutter/Tachycardia

Electronic Atrial Pacemaker Electronic Ventricular Pacemaker

Qualifications of the above rhythm statements based on rate are also generated. For example: “Sinus” may be Sinus Bradycardia, Sinus Rhythm, or Sinus Tachycardia. These rate qualifications are made for Sinus, Ectopic Atrial, Junctional and Supraventricular rhythm statements. Criteria for limits of Bradycardia and Tachycardia based on age are included in the Reference Summary.

Rhythm Statement Criteria

The rationale behind generation of the rhythm statements is described in the following sections. It is important to note that these descriptions are intended to provide a general overview of the VERITAS algorithm logic in a compact reference form. As such, some details and dependencies have been intentionally omitted to improve readability and understanding.

Electronic Atrial or Ventricular Pacemaker

In interpreting resting ECGs where a pacemaker is present, it is important to note that the VERITAS programdoes not attempt to assess pacemaker performance criteria such as failure to capture or failure to sense. The 10-second ECG is not adequate in duration for an algorithm to make this determination. All pacemaker generated statements are based upon pacing impulses that have been captured and hence resulted in stimulation of atrial or ventricular activity.

There are two independent tests for pacemaker detection: hardware-driven detection (hard pace detection) and software-driven detection (soft pace detection). Hard pace detection is based upon triggering hardware flags and the repeated presence of these flags in a minimum number of beats. These hardware flags are based upondetection of “spikes” in the high resolution front-end data stream (10,000 – 40,000 samples/second depending upon ECG front-end) preceding either atrial activity, ventricular activity, or both. If the hard pace criteria aremet, then the appropriate pacemaker statement is set and the subsequent soft pace detection step is skipped.

RHYTHM STATEMENTS

Soft pace detection utilizes the acquisition data stream (1,000 samples/second) and inspects high frequency, “spike” activity, before atrial and ventricular complexes. This secondary test is used to detect impulses that did not pass the hard pace detection due to low amplitude and/or temporally wide pulses.

The distinction between atrial and ventricular pacing is made on the basis of the latency between the spike and the QRS complex.

The combined results of applying these two tests are presented in the VERITAS Resting ECG Interpretation Evaluation section.

If both electronically paced and intrinsic QRS complexes are found, the phrase “-- contour analysis based on intrinsic rhythm” is added to the statement. Most statements based on contour analysis are suppressed for paced complexes, with the exception of the most severe level of ST-elevation statements. Although this canlead to false positive “Acute MI” statements, this was deemed acceptable given the relatively low percentage of artificially paced ECGs in most hospital populations.

Atrial Flutter/Tachycardia

The Atrial Flutter/Tachycardia statement is generated if flutter waves (P-P) are detected with a rate above 200 and less than 350 beats per minute. Additionally, in the presence of a ventricular rate above 140 beats per minute, a statement of “Possible Atrial Flutter” will be generated.

Note that the P-wave axis and PR interval are not defined in the presence of atrial flutter and hence will not be determined by VERITAS.

Atrial Fibrillation

The Atrial Fibrillation statement is triggered based on the presence of low amplitude or undetected P waves in combination with a disorganized rhythm. A disorganized rhythm is characterized by the lack of “clustering” of RR intervals, while highly clustered RR intervals are indicative of an organized rhythm. The clustering criteriaare utilized to distinguish premature atrial contractions, from atrial fibrillation as illustrated in the following RR histograms.

 

 

 

Sample RR histogram of normal conduction. Note single cluster of RR intervalscharacteristic of normal conduction at steady sinus rate.