Posts Tagged ‘tread mill testing’

In this politically and scientifically  uncertain world nothing is  in black and white. How can you  expect  EST to behave differently ?

Even as  we  are fully  aware of the  limitations  of EST  ,  it  does not make sense   to categorize  EST result into either positive or negative .

In fact , our  estimate suggests  a significant bulk of the patient would fall in the grey zone  .

It is referred  in various terms by  the reporters of EST .

  • Borderline positive
  • Mildly positive
  • Equivocal
  • Inconclusive

What does all these terms mean to the patient ?

It mans only one thing . . .

Physician  who reports  the  EST    is unable to  conclude whether  his patient has  significant  CAD  or not . It is a dignified way of  expressing  the  limitations .

Many factors may play a role. (See the illustration above )

  • Patient factors : Poor exercise stress levels and conditioning
  • Lesion factors:  Collateralised CAD, treated CAD  can result in partial or mild  changes.
  • Machine factors :Caliberation errors.
  • Interpreter : (Physician ) factors

Error in measurement of ST segment . What is borderline  for  one doctor may indeed be true positive  for the other and vice versa .

How will be the  EST in  a  revascularised  or  medically treated CAD ?

If revascularization is a complete success ,  stress test  would  revert back to normal or it can be a borderline as we have just mentioned.

To our  surprise ,  it may  remain  positive in spite of apparently successful procedure.(Residual wall motion defects , scar mediated  ?)

How to proceed  after this borderline EST/TMT ?

Few options are available for the physician/patient

Talk  with the patient again  , assess the  baseline risk  of CAD   if it is low ignore the TMT result and reassure.

  • Repeat  stress test after  a month.
  • Stress thallium
  • Doubutamine  stress
  • CT angiogram
  • Regular Cath  angiogram* (May be the best , of course it also carries a  risk of labeling  the condition as  mild  CAD / non critical CAD etc )

For the  patient  the  easiest  option  may be ,   self  referral to a different cardiologist .   (Also called second opinion )

Final message

There is indeed an entity called   borderline  EST  . Do not dare to  ignore it  or else  face the consequences .

Read  related articles in this site .

1.Can medical management convert EST positive to negative ?

2. Should every one with positive EST should undergo CAG ?

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The quantum of electrical energy reaching the surface of the chest wall varies widely .It depends upon myocardial mass, proximity to the chest wall  and the thickness of chest wall.

Apart from this ,  the amount of blood within the left ventricle also determine the QRS voltage of ECG.

In dilated LV due to a regurgitant lesion , the LVEDV is increased . Since  blood is a very good conductor of  electricity , it amplifies the transmural  activation front and results  in high voltage QRS complex.This is referred to as Brody’s effect.

Where else , we  can  visualise the Brody effect  ?

During excercise stress testing , when  the heart rate and   the  LV diastolic volume increases .There is  a significant increase in QRS  voltage in leads facing LV, especially V5 and V6.

This is  usually a benign response in healthy individuals. However in patients  with preexisting CAD and LV dysfunction an  increase in R wave amplitude may  be a marker of  exercise induced LV dilatation  which  could  predict an adverse outcome .

Is there  a reversed Brody effect , where Q waves get deepened on exercise ?

This has not been described in literature , but it is seen often in patients with post MI stress testing .Q gets deepened .If the q gets minimised* it could indicate presence of significant viable tissue  , as it gets recruited during the excercise induced positive inotrpism mediated by   catecholamine .Lengthening or deepening of Q indicate less viable tissue.

*Study in progress : Will  be referenced shortly .

Brody effect is a complex phenomenon.

Advanced readers follow the link for illustration on Brody effect


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