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