This article covers the description of the ECG Analysis Attributes settings.  

QRS Tab

QRS Detection Threshold

Derivative values from previous cycles are used to calculate and aids in the identifying R waves

The QRS detection threshold is used to calculate the threshold for identifying potential R waves from the rectified derivative signal.  The % entered is applied to the largest derivative peak in a QRS segment that results in potential Rs that satisfy Minimum Heart rate criteria.

• Attribute Dialog
  • Two signals are displayed, the ECG signal and the rectified derivative of the smoothed ECG.
  • The derivative peak that is used to calculate the height of the pink region is marked in green. There will be one green cycle per QRS segment
  • When adjusting the pink region, the attribute is set relative to the height of the green derivative peak
  • The goal is to place the top of the pink box such that it only intersects valid derivative peaks.
• Too Low – analysis will be inefficient, investigating more derivative peaks than necessary. It is likely that some erroneous peaks will be identified.
• Too high – Some QRSs will be missed especially in the case of higher heart rate data (i.e. HR > Min HR)

Min R Deflection

The QRS amplitude change in the smoothed ECG must exceed the min R deflection value for the complex to be recognized.  This is based on max/min signal value, and does not depend on the iso-electric level.

• Attribute Dialog
  • The displayed signal is the smoothed ECG signal
  • The pink adjustment boxes will be anchored to the lowest point for positive complexes and vice versa
  • This attribute should be set above the noise level but lower than the smallest anticipated QRS
• Too Low – The analysis may mark noise
• Too high – The analysis may miss valid Rs

Maximum Heart Rate

The Maximum Heart Rate attribute should be set higher than the maximum expected heart rate.  Note that if premature arrhythmic beats (e.g. premature ventricular complex, premature atrial complexes, etc.) should be marked, the maximum heart rate should reflect the higher heart rate of the arrhythmic beats as the analysis will disregard Rs that result in a heart rate higher than the Max Heart Rate attribute

• Attribute Dialog
  • The displayed signal is the ECG signal
  • The pink region represents the time interval corresponding to the max heart rate
• Too Low – Noisy cycles have a greater chance of getting marked
• Too high – QRSs will be missed.

Minimum Heart Rate

This Minimum Heart Rate attribute should be set close to the lowest anticipated heart rate.  This attribute is used by the analysis to determine when it should search for missing QRS complexes.  The Minimum Heart Rate attribute does not represent a hard cutoff like the Maximum Heart Rate attribute and there may be situations where it should be set higher than the lowest heart rate.

• Too Low – Rs may be missed in noisy areas or be placed on P and T waves.
• Too high – Analysis efficiency will decrease due to unnecessary searches for QRS.

Peak Bias

The Peak Bias attribute is used to influence marking positive or negative Rs.  A positive Peak Bias favors positive Rs, a negative Peak Bias favors negative Rs.

Hidden Attributes

Display of these attributes is controlled through ShowEcgHiddenAtbsFlag=1 in the PPP3.INI file [ECG] section.  See How to enable ECG 5.3x and 6.x hidden attributes and graph presentation signals.

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QRS Smoothing Filter

The QRS Smoothing Filter attribute is used to decrease the influence of noise when searching for ECG complexes.  The attribute value corresponds to the length of a Savitzky-Golay filter.  The resultant smoothed signal is used internally for QRS identification, not for reporting of derived data.

• Increase to reduce the impact of noise or notches in the signal
• Decrease to prevent loss of fidelity of portions of the QRS complex
• Too Low – Greater influence from noise
• Too high – QRS fidelity will be lost

QRS Segment Length

The QRS Segment Length attribute defines the number of milliseconds of data that are analyzed at one time.  A longer segment length provides the analysis with more perspective through the inclusion of a larger number of complexes.  A shorter segment length limits the negative influence of noisy data. 

• Limits
  • Must be greater than or equal to 100 ms
  • Must be less than or equal to 20000 at sample rates up to 1000, above 1000 Max drops off proportionate to sample rate
• Too Low – False triggering may occur
• Too high – Impact of a noise spike may be spread over a larger number of cycles

QRS Width

The QRS width attribute defines the time span associated with a QRS complex.  The attribute is used to ensure that a QRS complex is treated as a single unit.  

• Too Low – may affect R identification
• Too high – reduces analysis efficiency

QRS Baseline Deriv Threshold

The QRS Baseline Derivative Threshold along with the Peak Baseline Window define the criteria for identifying the end of each segment that makes up a QRS complex.  The QRS Baseline Derivative Threshold is expressed as a percentage of the maximum derivative of the smoothed signal in the QRS complex

• This attribute plays a role when a QRS shows a slow return to baseline
• Too Low – R widths may be identified as wider than they should
• Too high – R widths may be identified as narrower than they should
• NOTE – When dealing with VTach, if the top of the cycle has a gradual slope, this attribute may need to be reduced to prevent the QRS from being marked too early, resulting in invalid right and left amplitudes (See Univ of Freiburg LQT2 data: required a setting of 5%)

Peak Baseline Window

The Peak Baseline Window along with the QRS Baseline Derivative Threshold define the criteria for identifying the end of each segment that makes up a QRS complex.  The Peak Baseline Window defines the number of ms over which the smoothed derivative must stay within the level defined by the QRS Baseline Derivative Threshold in order to identify the end of a section of a QRS complex

• This attribute plays a role when a QRS shows a slow return to baseline
• Too Low – R widths may be identified as narrower than they should
• Too high – R widths may be identified as wider than they should

Peak Width Similarity

The Peak Width Similarity attribute is used to reduce changes in polarity within a QRS Segment

This attribute comes into play when dealing with an ECG signal that is transitioning from a predominantly positive peak to a predominantly negative peak or vice versa.  When a QRS segment contains complexes that have viable alternate peaks, the orientation of similar peaks are considered when marking a complex. The Peak Width Similarity attribute defines how similarity is determined.

• Too Low – similar peaks may not be treated as similar resulting in flipping of polarity within a segment
• Too high – dissimilar peaks may be identified as being similar, resulting in inappropriate marking

Valid Peak Threshold

The Valid Peak Threshold attribute controls the identification of potential alternate peaks.  This attribute is used to ensure that only peaks above a certain size will be considered as alternates.

• Determines the peak value at which an peak is considered as a potential R
• This does not affect identification of the primary peak  (i.e. the QRS peak that contains the max derivative)
• Can be estimated for the adjacent peaks from the ratio of an unshared legs height to the sum of the unshared legs heights
• Clearing Valid Peak Threshold requirements does not imply a peak will be marked, next the Alternate Peak Threshold and Peak Bias come into play
• Too Low – insignificant peaks will be considered as alternates
• Too high – the primary peak will be marked – alternates will not be considered

Alternate Peak Threshold

The Alternate Peak Threshold attribute is used to introduce hysteresis into the peak identification process and defines the span over which a positive or negative peak may be marked as the R.  When R peaks transition from positive to negative, Alternate Peak Threshold may be used to reduce flipping.

• This does not affect identification of the primary peak

• This attribute should be decreased used when a single direction is desired across the analysis range

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Wide Q Wave

When enabled, the Q mark location will be calculated based on the current species selection. When disabled, the Q mark will be calculated based on species independent identification criteria

Intra Cardiac

When enabled, potential QRSs that are followed by potential QRSs within the interval specified by the P window from R attribute, will not be marked as a QRS, instead the following QRS will be marked

R Width Max

• The R Width Max Attribute is used to define an upper limit for the width of an R wave, measured on the smoothed ECG signal
• Too Low – Valid Rs may be rejected
• Too high – Signal artifact or T waves may be identified as Rs

R Width Min

The R Width Min Attribute is used to define a lower limit for the width of an R wave, measured on the smoothed ECG signal

• Too Low –Signal artifact or noise spikes may be identified as Rs
• Too high – Valid Rs may be rejected