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: »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 V alt  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 »  1.9  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 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? Indeterminate Tracing Negative Tracing  110 > 110 Positive Tracing  105 < 105 Indeterminate Tracing 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

Sustained Alternans Onset HR Maximum Negative HR Without Gap: Positive Tracing Max Neg. HR Clean Interval Max HR 1 min

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? Indeterminate Tracing Negative Tracing  110 > 110 Positive Tracing  105 < 105 Indeterminate Tracing 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”

Non-sustained Alternans Maximum Negative HR with Gap: Negative Tracing Clean Interval Max Neg. HR Max HR 1 min

Maximum Negative HR Without Gap: Negative Tracing Clean Interval Max Neg. HR Max HR 1 min