Interpreting T Wave Alternans Tests

1. 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

2. 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

3. 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?

4. Definition of Significant Alternans • Valt 1.9 V • K score  3 • Leads • single orthogonal leads • two adjacent precordial leads • Duration •  10 seconds

5. 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

6. 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)

7. 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

8. 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

9. 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

10. 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

11. Interpreting TWA in the Presence of Artifacts • Artifacts which can cause alternans (false alternans) • Artifacts which can obscure (or mask) true alternans

12. Artifacts Causing Alternans • RR interval alternans • Ectopic beats • Rapid changes in heart rate • Excessive noise • Motion artifact • Respiration

13. 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

14. 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

15. Maximum Negative Heart Rate • Highest interval heart rate at which sustained alternans is definitively not present

16. “Clean interval”  1 minute • without significant alternans • without artifacts that could potentially obscure alternans • < 10 % ectopic or bad beats • noise levels < 1.8 V

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

18. 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

19. 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

20. 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

21. 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

22. 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

23. 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”

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

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