Performing TWA Tests: Tips for Reducing Indeterminate Test Results Dan Bloomfield MD

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Performing TWA Tests Tips for Reducing
Indeterminate Test Results (Dan Bloomfield MD)

• Importance of gradual increase in heart rate
  between 90 - 110 bpm
• Aim for heart rates of 120 bpm
• Maximal effort needed for patient with maximal
  heart rates lt 105 bpm
• Role of immediate re-testing
• Train physicians and staff to interpret tests

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Importance of Gradual Increase in Heart Rate
from 90 - 110 bpm

• Interpretation of TWA often depends heavily on
  whether alternans is present between heart rates
  of 90 - 110
• Goals during exercise testing
• low noise levels
• gradual increase in heart rate from 90 - 110 over
  2 - 4 minutes

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Tips to Achieve Gradual Increase in Heart Rate
from 90 - 110

• Press Start Treadmill key prior to pressing
  Start Exercise
• While in the standing stage, have the patient
  practice walking on the treadmill for 15-30
  seconds at its minimum speed and at a 0 grade
• Ensure that the patient is calm and comfortable
  walking on the treadmill before starting exercise
• Once the patient is comfortable, press the Start
  Exercise key.

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Tips to Achieve Gradual Increase in Heart Rate
from 90 - 110

• When running a treadmill stress test with
  alternans, it is important that the patients
  heart rate does not increase too rapidly from 90
  - 110 BPM
• Patients who have limitations in exercise
  tolerance are ill not fit.
• Treadmill testing use a Naughton or Modified
  Bruce protocol
• Bicycle Ergometer testing use a ramp protocol
  (or manually increase worload

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Tips to Achieve Gradual Increase in Heart Rate
from 90 - 110

• If the increase in the patients heart rate from
  90-110 BPM is too rapid for accurate alternans
  determination, a message will be displayed.
• If this message is displayed, it is advisable to
  stop the test, allow the patients heart rate to
  decrease to below 100 BPM, and then restart the
  test.

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Target Heart Rate of 120 bpm

• Goal is to have a test with a 3-4 minutes of
  alternans over range of heart rates
• allows interpretation of alternans in presence of
  artifacts
• appreciate relationship between the increasing in
  heart rate and the increase in alternans
  magnitude
• Alternans starting at 104 bpm may be hard to
  interpret if test is stopped after 1 minute at
  105 bpm

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Maximal effort required for patient with maximal
heart rates lt 105 bpm

• Under current rules, patients with MaxHR lt 105
  bpm cannot be negative
• New rules ( B Rules) evaluated in The Lancet
  Paper suggest that patients without alternans and
  with MaxHR lt 105 bpm but gt80 bpm are at low risk
  if the test was a maximal test and
  (MaxHR-MaxNegHR) lt 5bpm
• Treadmill exercise more likely to result in HR gt
  105 than bicycle exercise

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Role of Repeat Testing

• Exercise Protocol Failure
• Rapid rise in heart rate
• Some T wave alternans test results are ambiguous,
  repeat testing may be helpful
• Immediate repeat testing reduces indeterminate
  test results by 50

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Value in Interpreting Numerous T Wave Alternans
Test

• Interpreting tests provides valuable feedback
  about the exercise protocol and the importance of
  rate of change of heart rate during testing
• Train staff to interpret tests
• CD Training Course suitable for physicians,
  nurses, technicians
• Course includes gt 150 tracings to interpret
• Collect and re-interpret your own tracings