Welch Allyn Holter System - User Manual - Manual (Page 46)

42 Directions for Use Welch Allyn Holter System
QRS Detection and Feature Extraction
The analysis program detects each QRS for each channel. Each detected QRS has several
locations identified including Isoelectric, Q, R, S and ST points. From these locations,
additional measurements are made for the width, height, morphology, ST Level, and noise
assessment.
Clustering
The analysis program groups beats based on morphology related information.
The clusters created are based on which channels are active. For instance, a single
channel event in Ch 1 would only be grouped with other single channel events.
Beat Classification
The beat classification is performed by evaluating QRS detections, features, R-R intervals,
clustering information and noise assessment. The outcome of the classification results in
the following beat types:
• Normal
• Ventricular
• Supraventricular
• Artifact
Heart Rate Calculation
The analysis program assigns an R-R interval to each detected QRS based on the time
interval to the last labeled QRS. A QRS can be assigned with an unknown R-R interval if
the region between the last detected QRS and current QRS contains artifact
classifications. Artifact regions can be automatically classified by the analysis program or
labeled through clinician editing.
The heart rate calculation is reported on each beat. The heart rate for a specific beat is
based on the average of 9 R-R intervals centered on the specific beat. This would require
the 4 previous R-R intervals, the current beat R-R interval and the next 4 R-R intervals.
A valid heart rate will require at least 5 out of 9 valid R-R intervals. If the heart rate cannot
be calculated, it will be assigned as an unknown heart rate.
The heart rate errors associated with one false positive detection (interpolated noise)
would be a +12.5% increase in reported heart rate. A false negative detection (missed
beat) would result in a -10% error in reported heart rate. The duration of time required to
correct the heart rate calculation would be 9 beats.
The HR is displayed for each strip and it represents the HR for the beat closest to the
center of the strip. If the clinician selects another beat in the strip, its HR values will be
displayed. If the HR cannot be calculated, it will be displayed as a --- value.
The HR displayed in Full Disclosure refers to the HR value found for the highlighted strip.
This HR value is based on the HR of the beat closest to the center of the strip. Refer to
Strip HR above.
ST Measurement
The ST Level is measured on normal beats with a width less than 110 msec. The ST level
is measured on each channel based on the delta between the isoelectric point and ST
Level point. The Isoelectric point is defined as an average of points between P and Q.
The ST Level point is a rate sensitive offset relative to the R-wave.