SCAI: Where and how angio falls short in the cath lab

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During left ventriculography in a 46-year-old man with hypertrophic cardiomyopathy was injected with 20 ml of contrast material, using a power injector at a rate of 10 ml per second through a multipurpose catheter
Source: N Engl J Med 2008;359:e8.

LAS VEGAS—Coronary angiography has a variety of limitations in the cardiac cath lab due to both operator and technological causes, according to a May 9 presentation by J. Dawn Abbott, MD, of Rhode Island Hospital in Providence, at the 35th annual meeting of the Society for Cardiovascular Angiography and Interventions (SCAI).

The causes of non-diagnostic angiograms, according to Abbott, are broken down into two categories:

  1. The fault of the operator because angiography can only be as good as the quality of the images taken; and
  2. Limitation of the technology of angiography because even experienced operators cannot always get a diagnosis from the angiogram alone.

“You need to be aware of its limitations to obtain proper images for certain patients, and employ different modalities,” said Abbott, who added that you need to consider the needs of the individual patient as well. For instance, better images will be obtained from thinner patients, as opposed to obese patients.

The operator’s technique should depend on a variety of factors, including:

  • Patient factors, size, movement and hardware (such as implantable devices).
  • Appropriate catheter selection and manipulation: “Selective engagement is necessary for appropriate contrast filling,” said Abbott. “If you can’t fill a coronary due to severe aortic insufficiency or severe left ventricular hypertrophy, then you may need to employ a slightly different technique.”
  • Injection technique: She said that complete opacification is required, for which she said an automatic system can sometimes work well.
  • Imaging: Breath holds, collimators and frame rate/panning can be used to optimize imaging. “People shouldn’t rush through the imaging procedure,” she said.
  • Equipment quality.

Comprehensive imaging is a “no brainer,” said Abbott, and recommended taking multiple views to avoid missing lesions through foreshortening or overlap. Also, catheter-induced spasms can lead to misinterpretation. “Spasms do occur and not only at the catheter tip,” said Abbott, who also suggested using smaller catheter or different angle catheters to avoid misinterpretation.

She noted the “eccentric nature of plaque,” which is difficult to overcome with angiography, but the goal is to account for all vascular territories, including anomalous coronaries and bypass grafts. Also, due to plaque’s histopathology, it is important to obtain multiple views because arteries can appear more or less occluded based on the angiographic angle—ranging from 20 or 30 percent to 90 percent.

Incomplete angiographies are not uncommon, as there are many challenges of anomalous coronaries, according to Abbott. Thus, she often recommends to her fellows to review the left ventricular gram to see where the coronaries are coming off before catheter selection to engage the coronary. Despite these efforts, she acknowledged that it is “very different to selectively engage anomalous coronaries, so try to recognize the signs and review the left ventricular gram.” In the most extreme cases, alternative imaging techniques, such as CT angiography or MR angiography, may need to be used to help define a portion of the coronaries.

In addition to the operator issues, the technological limitations of coronary angiography include its inability:

  • To detect the presence and extent of plaque, requiring physiologic remodeling;
  • To detect plaque content, such as calcium, vulnerable plaque and thrombus;
  • To detect the functional significance of the disease, or the severity of intermediate lesions; and
  • To assess stent deployment and PCI-related dissection.

Due to all these considerations, operators need to be careful not to designate an angiography as normal when it’s not, warned Abbott. "Physicians need to follow their instincts and training in assessing angiograms, and use adjunctive tools, when necessary."