Balanced myocardial ischaemia

Balanced myocardial ischaemia

If all three major coronary branches have similar degree of stenosis, the radionuclide used for perfusion study will have equal uptake in all regions of the myocardium. Thus a balanced three vessel coronary artery disease can produce a false negative myocardial perfusion scan. This situation is called balanced myocardial ischemia. In most cases this is picked up by the treadmill ECG usually done along with stress myocardial perfusion imaging. Since the ECG findings of myocardial ischemia does not depend on the relative perfusion in the coronary tree, ischemic changes will be noted in treadmill ECG even when nuclear perfusion study shows false negative due to balanced myocardial ischemia.

In a case reported in Heart [1], adenosine technetium (Tc99) setamibi scan showed no resting or stress induced perfusion defects in an elderly person with stable exertional chest pain. But ST segment depression was noted on the ECG. Coronary computed tomography (CT) angiogram showed severe calcified ostial left main lesion, which was further confirmed by invasive coronary angiography. The patient underwent successful coronary artery bypass surgery.

In another case report published in Heart International, there was triple vessel coronary artery disease including 95% distal left main stenosis, with markedly positive stress ECG and a negative SPECT 99m-sestamibi scintigram [2]. This patient also underwent successful coronary artery bypass surgery.

Other potential causes of false negative nuclear perfusion studies are lesions in the left circumflex coronary artery, use of antianginal agents prior to the test and low levels of exercise leading to low myocardial oxygen demand. Caffeine use can interfere with dipyridamole stress nuclear perfusion imaging due to drug interaction.

As a corollary, balancing of electrical vectors in opposite directions have been invoked to explain false negative exercise treadmill ECGs in patients with multi vessel coronary artery disease [3].

References

  1. Lesser JR et al. Balanced myocardial ischaemia: a case of “normal” stress Tc99 sestamibi scan and diagnosis. Heart. 2005 Jul; 91(7): e53.
  2. Aziz EF et al. Triple vessel coronary artery disease presenting as a markedly positive stress electrocardiographic test and a negative SPECT-TL scintigram: a case of balanced ischemia. Heart Int. 2011 Sep 29; 6(2): e22.
  3. Madias JE et al. The paradox of negative exercise stress ECG/positive thallium scintigram. Ischemic ST-segment counterpoise as the underlying mechanism. J Electrocardiol. 1996 Jul;29(3):243-8.