Performing TWA Tests:Performing TWA Tests:

Tips for Reducing Indeterminate Tips for Reducing Indeterminate Test Results Test Results (Dan Bloomfield MD)(Dan Bloomfield MD)Importance of gradual increase in heart rate

between 90 - 110 bpmAim for heart rates of 120 bpmMaximal effort needed for patient with

maximal heart rates < 105 bpmRole of immediate re-testingTrain physicians and staff to interpret tests

Importance of Gradual Importance of Gradual Increase in Heart Rate from Increase in Heart Rate from

90 - 110 bpm90 - 110 bpmInterpretation 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

Tips to Achieve Gradual Tips to Achieve Gradual Increase in Heart Rate from Increase in Heart Rate from

90 - 11090 - 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.

Tips to Achieve Gradual Tips to Achieve Gradual Increase in Heart Rate from Increase in Heart Rate from

90 - 11090 - 110 When running a treadmill stress test with

alternans, it is important that the patient’s 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

Tips to Achieve Gradual Tips to Achieve Gradual Increase in Heart Rate from Increase in Heart Rate from

90 - 11090 - 110 If the increase in the patient’s 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 patient’s heart rate to decrease to below 100 BPM, and then restart the test.

Target Heart Rate of 120 bpmTarget 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

Maximal effort required for Maximal effort required for patient with maximal heart patient with maximal heart

rates < 105 bpmrates < 105 bpm Under current rules, patients with MaxHR < 105

bpm cannot be negative New rules ( B Rules) evaluated in The Lancet

Paper suggest that patients without alternans and with MaxHR < 105 bpm but >80 bpm are at low risk if the test was a maximal test and (MaxHR-MaxNegHR) < 5bpm

Treadmill exercise more likely to result in HR > 105 than bicycle exercise

Role of Repeat TestingRole 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%

Value in Interpreting Value in Interpreting Numerous T Wave Alternans Numerous T Wave Alternans

TestTest 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 > 150 tracings to interpret– Collect and re-interpret your own tracings