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Myocardial viability

In patients with impaired left ventricular (LV) function, the accurate assessment of viable and non-viable tissue has important prognostic implications in terms of clinical planning for revascularization procedures such as angioplasty or coronary artery bypass grafts. It is known that patients with dysfunctional but viable myocardium usually benefit from revascularization.

Cine image demonstrating absent wall motion (akinesis) along the inferior wall Corresponding viability image showing hyperenhancement along the inferior wall

Although there are various noninvasive methods of determining myocardial viability, such as positron emission tomography (PET) and dobutamine echocardiography, magnetic resonance imaging with gadolinium has demonstrated several advantages over conventional modalities, including higher spatial resolution and larger field of view.

Key Points

  • Viability studies require the IV injection of the contrast agent gadolinium. Using a “delayed enhancement” technique, where five to 20 minutes elapse between injection time and scan acquisition, a high-resolution cardiac-gated inversion recovery (IR) turbo FLASH or TrueFISP (true fast imaging with steady-state precessional) sequence identifies irreversibly damaged myocardium from reversibly damaged tissue which may benefit from revascularization.
  • Viable tissue appears dark on delayed images, whereas non-viable, fibrotic or scar tissue has increased contrast retention, resulting in “hyperenhancement” when compared with normal myocardium. This hyperenhancement typically indicates that the patient’s LV function will not improve following revascularization of these areas of myocardium.
  • Magnetic resonance imaging (MRI) has higher spatial resolution than nuclear medicine studies, allowing it to determine the transmural extent of infarction rather than simply determining whether tissue is either viable or non-viable. This is a significant indicator of patient prognosis for revascularization, as there is an inverse relation between the transmural extent of infarct and recovery of function.
  • The detection of an epicardial rim of viable tissue by enhanced MRI represents diagnostic information that is not available with the use of other noninvasive imaging techniques (see Kim RH et. al. below).
  • Viability studies can identify myocardial infarcts in both acute and chronic situations, and when combined with cine wall motion studies, can depict viable myocardium which may benefit from revascularization.
  • Cine imaging for wall motion can distinguish between stunned and hybernating myocardium.

Case in Point

MRI of the human heart (2 chamber view) showing left ventricular aneurysm MRI of the human heart (4 chamber view) showing left ventricular aneurysm

65 year old male status post myocardial infarct. In addition to viability imaging, the two figures below demonstrate additional complications of myocardial infarcts, in particular the development of a left ventricular true aneurysm.

For Further Reading