interpreting t wave alternans tests
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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: - PowerPoint PPT PresentationTRANSCRIPT
Interpreting T Wave Alternans Tests
Daniel M. Bloomfield, MDHerbert Irving Assistant Professor of Medicine
Director, Syncope Center
Columbia Presbyterian Medical Center
Columbia University College of Physicians & Surgeons
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
• 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
• Valt 1.9 V
• K score 3
• Leads» single orthogonal leads» two adjacent precordial leads
• Duration 10 seconds
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
• 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?
• 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?• Sustained alternans
1.9V» 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
• 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
Is Sustained Alternans present?
Present at Rest?MaxNeg HR?
105< 105
Rest Positive OnsetHR?
MaxNegHR?
IndeterminateTracing
Negative Tracing
110 > 110
Positive Tracing
105< 105
IndeterminateTracing
Negative Tracing
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
• RR interval alternans
• Ectopic beats
• Rapid changes in heart rate
• Excessive noise
• Motion artifact
• Respiration
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?
• 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
• Highest interval heart rate at which sustained alternans is definitively not present
“Clean interval”
1 minute
• without significant alternans
• without artifacts that could potentially obscure alternans» < 10 % ectopic or bad beats» noise levels < 1.8 V
60
80
100
120
140
He
art
Ra
te (
bp
m)
0
2
4
6
eV
M (
V) Sustained Alternans
Onset HR
Maximum Negative HR Without Gap:Positive Tracing
Max Neg. HR
Clean Interval
Max HR
1 min
60
80
100
120
140H
ea
rt R
ate
(b
pm
)
0
2
4
6
eV
M (
V) Sustained Alternans
Onset HR
Maximum Negative HR with Gap: Positive Tracing (Onset Gap)
Clean Interval
Max Neg. HR
Max HR
1 min
Ex 2.13
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
Is Sustained Alternans present?
Present at Rest?MaxNeg HR?
105< 105
Rest Positive OnsetHR?
MaxNegHR?
IndeterminateTracing
Negative Tracing
110 > 110
Positive Tracing
105< 105
IndeterminateTracing
Negative Tracing
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
• 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
• 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”
60
80
100
120
140H
ea
rt R
ate
(b
pm
)
0
2
4
6
eV
M (
V) Non-sustained
Alternans
Maximum Negative HR with Gap:Negative Tracing
Clean Interval
Max Neg. HR
Max HR
1 min
60
80
100
120
140H
ea
rt R
ate
(b
pm
)
0
2
4
6
eV
M (
V)
Maximum Negative HR Without Gap:Negative Tracing
Clean Interval
Max Neg. HR
Max HR
1 min