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Interpreting T Wave Alternans Tests. Daniel M. Bloomfield, MD Herbert Irving Assistant Professor of Medicine Director, Syncope Center Columbia Presbyterian Medical Center Columbia University College of Physicians & Surgeons. Positive and Negative Tests. Positive Tests:

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interpreting t wave alternans tests

Interpreting T Wave Alternans Tests

Daniel M. Bloomfield, MD

Herbert Irving Assistant Professor of Medicine

Director, Syncope Center

Columbia Presbyterian Medical Center

Columbia University College of Physicians & Surgeons

positive and negative tests
Positive and Negative Tests
  • Positive Tests:
    • Alternans present below a heart rate of 110 bpm
  • Negative Tests:
    • Alternans not present below a heart rate of 110 bpm and
    • You are confident that there are no artifacts obscuring alternans
fundamental questions for the interpretation of twa
Fundamental Questions for the Interpretation of TWA
  • Is sustained alternans present?
    • If yes: is it real or artifactual?
    • What is the threshold (onset heart rate)?
  • If alternans is not present, are there artifact present which could be masking true alternans?
definition of significant alternans
Definition of Significant Alternans
  • Valt 1.9 V
  • K score  3
  • Leads
    • single orthogonal leads
    • two adjacent precordial leads
  • Duration
    •  10 seconds
what is sustained alternans
What is sustained alternans?
  • Duration of alternans
    •  1 minute
  • Relationship of alternans to heart rate
    • alternans must persist above a patient specific heart rate threshold
  • “Heart rate centric” view of alternans
significant vs sustained alternans
Significant vs. Sustained Alternans
  • Both require
    • Valt  1.9 V
    • K  3
  • Sustained is  1 minute and consistently present above threshold heart rate
  • Significant alternans must only be 10 seconds in duration and need not be present above a threshold heart rate (non-sustained)
what is onset heart rate
What is onset heart rate?
  • Heart rate threshold above which significant alternans is consistently present
  • Can read onset heart rate during increase in heart rate in exercise (preferable) or during decrease in heart rate in recovery
  • In precordial leads: read onset heart rate when 2 adjacent leads have significant alternans
what is a positive tracing
What is a positive tracing?
  • Sustained alternans
    •  1.9V
    • K  3,
    • for  1 minute in duration
  • Threshold heart rate
    • Onset HR must be below predetermined threshold heart rate (currently 110 bpm)
  • Artifact free interval
    • documented as dark black bar
rest alternans
Rest Alternans
  • Sustained alternans is present at lowest smoothed heart rate
    • regardless of whether this lowest smoothed heart rate occurs at the beginning of the tracing
  • Rest alternans is classified as positive regardless of the OnsetHR
  • “rest” does not refer to a stage of the exercise test
  • MaxNegHR = 0
slide10
Is Sustained Alternans present?

yes

no

MaxNeg HR?

Present at Rest?

 105

yes

< 105

no

OnsetHR?

Indeterminate

Tracing

Negative Tracing

Rest Positive

 110

> 110

Positive Tracing

MaxNegHR?

 105

< 105

Indeterminate

Tracing

Negative Tracing

interpreting twa in the presence of artifacts
Interpreting TWA in the Presence of Artifacts
  • Artifacts which can cause alternans (false alternans)
  • Artifacts which can obscure (or mask) true alternans
artifacts causing alternans
Artifacts Causing Alternans
  • RR interval alternans
  • Ectopic beats
  • Rapid changes in heart rate
  • Excessive noise
  • Motion artifact
  • Respiration
interpreting alternans during periods of potential artifacts
Interpreting Alternans During Periods of Potential Artifacts
  • Wary of considering alternans “real” if only present during periods of potential artifacts
  • Characteristics of alternans may be helpful
    • relationship to heart rate
    • alternans during artifact free intervals
what is a negative tracing
What is a negative tracing?
  • Tracing without sustained alternans
    • or with sustained alternans with an OnsetHR > 110 bpm
  • MaxNegHR  105 bpm
    • Clean interval with interval heart rate  105
maximum negative heart rate
Maximum Negative Heart Rate
  • Highest interval heart rate at which sustained alternans is definitively not present
clean interval
“Clean interval”

 1 minute

  • without significant alternans
  • without artifacts that could potentially obscure alternans
    • < 10 % ectopic or bad beats
    • noise levels < 1.8 V
maximum negative hr without gap positive tracing
Maximum Negative HR Without Gap:Positive Tracing

Onset HR

Max HR

1 min

Max Neg. HR

Sustained Alternans

Clean Interval

maximum negative hr with gap positive tracing onset gap
Maximum Negative HR with Gap: Positive Tracing (Onset Gap)

Onset HR

Max HR

Clean Interval

1 min

Max Neg. HR

Sustained Alternans

Ex 2.13

factors that may obscure alternans
Factors That May Obscure Alternans
  • Noise
    • loss of K score
    • reduce alternans voltage (complete loss of alternans uncommon)
  • Ectopic beats
    • high levels of alternans may rapidly disappear and reappear centered on an ectopic
  • Rapid changes in heart rate
    • especially immediately after exercise
    • look carefully at the instantaneous heart rate

Ex 2.5, 2.6, 2.9

slide20
Is Sustained Alternans present?

yes

no

MaxNeg HR?

Present at Rest?

 105

yes

< 105

no

OnsetHR?

Indeterminate

Tracing

Negative Tracing

Rest Positive

 110

> 110

Positive Tracing

MaxNegHR?

 105

< 105

Indeterminate

Tracing

Negative Tracing

effect of factors that may obscure alternans
Effect of Factors That May Obscure Alternans
  • Interpreting gaps in sustained alternans
  • Interpreting maximum negative heart rate in the presence of factors that may obscure alternans
gaps in sustained alternans
Gaps in Sustained Alternans
  • Duration of the gap relative to duration of sustained alternans
  • Explicable vs. inexplicable gaps
  • Characteristics of alternans
    • relationship to heart rate
    • alternans during artifact free intervals
    • confirmation in other leads
maximum negative heart rate in the presence of factors that obscure alternans
Maximum negative heart rate in the presence of factors that obscure alternans
  • Heart rate above which you are confident that alternans is not present
  • Confidence is affected by these factors that may obscure alternans
  • Maximum negative heart rate is the highest interval heart rate of all “clean” intervals”
maximum negative hr with gap negative tracing
Maximum Negative HR with Gap:Negative Tracing

Max HR

1 min

Max Neg. HR

Non-sustained

Alternans

Clean Interval

maximum negative hr without gap negative tracing
Maximum Negative HR Without Gap:Negative Tracing

Max HR

1 min

Max Neg. HR

Clean Interval

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