Mini-dose CTA?

15. October 2007 William Davis (11)
I caught this little news report in the online edition of Canyon News , an LA paper, under the title Cedars-Sinai Develops Test to Prevent Heart Attacks .

They report that Dr. Daniel S. Berman M.D., chief of Cardiac Imaging and Nuclear Cardiology at Cedars-Sinai, reports that a new method of performing CT coronary angiography, "mini-dose CTA," has been developed that allows both coronary calcium scoring as well as CT coronary angiography (CTA) at a dose as low as 10% of standard dose. No technical details were provided.

Now, that may be worth knowing more about. If this is true, then CTA may indeed be useful as a "screening" procedure. However, we are going to need to know more: What devices are capable of doing this, what settings on the devices were used, etc. It does indeed come from a reputable source in Dr. Dan Berman, who is well known in nuclear cardiology circles.

We will try and dig for info. Stay tuned.
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Comments (11) -

  • wccaguy

    10/15/2007 5:57:00 PM |

    Very interesting.

    The article also contains this potential nugget:

    Dr. Daniel S. Berman M.D., chief of Cardiac Imaging and Nuclear Cardiology at Cedars-Sinai reports that the danger in not testing for non-calcified blockages is great. These plaques, he says, are “more prone to rupture than calcified plaques. The new procedure, which does test for these, provides “better risk assessment.”

    Any thought about these "non-calcified blockages"?  This is somewhat related to a question I asked a while back about "reducing plaque as measured by calcium score" and reducing risk by reducing risk of rupture in the artery.  You had a good answer to the question but it seems like there is more to explore here.

    Thanks for the info.

  • Anonymous

    10/15/2007 8:54:00 PM |

    Here is a similar study using ct to diagnose degree of stenosis:

    Dual-source CT non-invasively detects coronary stenoses

    15 October 2007

    MedWire News: Dual-source multi-slice computed tomography (DSCT) angiography can accurately detect coronary stenoses in patients with an intermediate likelihood of coronary artery disease (CAD), even in the presence of arrhythmias and raised heart rates (HRs), researchers say.

    Alexander Leber (University of Munich, Germany) and team explain in the European Heart Journal that using multi-slice CT to detect coronary stenoses can be limited by the appearance of motion artefacts.

    The researchers tested the newly-developed DSCT technique in 90 patients with an intermediate pretest likelihood of CAD referred for invasive coronary angiography. They obtained data sets providing image quality sufficient for analysis in 88 patients.

    The image quality was diagnostic in six of seven patients with atrial fibrillation, and in 46 out of 48 patients with HR >65 beats per minute (bpm).

    In 1165 of 1174 segments, significant (>50% stenosis) disease was correctly ruled out using DSCT.

    All patients (n=9) with at least one stenosis >75% (sensitivity 100%) and 11 of 12 (sensitivity 88%) patients with at least one stenosis ranging from 50-75% were correctly identified by DSCT.

    Meanwhile DSCT-angiography correctly excluded a lesion >50% in 60 of 67 patients (specificity 90%, positive predictive value 74%).

    The accuracy to detect coronary stenoses >50% was similar in patients with HR >65 bpm and those with HR =65 bpm (sensitivity 92 and 100%, specificity 88 and 91%, respectively).

    The researchers conclude: "DSCT is a non-invasive tool that allows to accurately rule out coronary stenoses in patients with an intermediate pretet likelihood for CAD, independent of the HR."

    Eur Heart J 2007; 28: 2354-2360

  • wccaguy

    10/16/2007 4:10:00 AM |

    I thought I'd take another shot at stating the question I have about the relationship of a declining calcium score and plaque rupture risk.

    If the calcium within plaque is reduced at greater rate than the plaque it had calcified, hence leaving that plaque non-calcified, then, does that recently non-calcified plaque qualify as being a type of plaque that, as Berman puts it, is "more prone to rupture than calcified plaques"?

    There are a lot of different ways to state the question I guess.  Here's another try.

    Does the process of calcium/plaque reduction per se result a type of instability that is "more prone to rupture"?

    Perhaps it does not.  But if it does, then, it seems as if it would be important to understand how to increase stability per se.

    In that case, aren't BOTH plaque reduction and plaque stability important?

    How is plaque stability promoted?

    Hope all this make sense.

    Thanks.

  • Dr. Davis

    10/16/2007 11:44:00 AM |

    Great questions. Not all answers are available.

    However, there are several things we do know, mostly from intracoronary ultrasound studies, autopsy studies, and extrapolations from animal studies. (Real, live human data is not generally available, since few people would allow us to remove plaque.)

    We know that:

    --The lipid components of atherosclerotic plaque are fairly readily regressible, e.g., LDL cholesterol reduction. Lipid resorption precedes calcium extraction.

    --Plaque instability is determined less than calcium presence or absence than by the presence of high-rupture risk markers, like collections of lipid near the surface, so called "lipid pools" and think fibrous "caps" at the surface-to-lumen interface, as well as inflammatory cell collections and enzymatic activity, e.g., matrix metalloproteinase.

    --Calcium is probably the least resorbable factor in plaque. If you resorb calcium by x percent, you've probably resorbed the lipid and inflammatory elements hugely. However, given the rarity of profound regression in studies, these observations are scant.

    --The trend towards substantial reductions in cardiovascular events in people who have not progressed heart scan score (or other measures of coronary atherosclerotic burden) vs. those who progress confirm that progressively increasing scores are accompanied by increasing risk of events, "plaque rupture."

    --There are not enough data on event rates in people who drop their score substantially because: 1) Nobody except our program has achieved this, and 2) Events in people who reduce their score are, for all practical purpose, non-existent. We are collecting our data for publication in the coming year, as well as assembling the pieces for subsequent studies for full validation of these concepts.

  • wccaguy

    10/16/2007 12:16:00 PM |

    Dr. Davis,

    Thanks for an answer right on point.

    You continue to amaze with your knowledge that speaks to an issue and makes common sense while at the same time you acknowledge that sometimes "we just don't know".

  • wccaguy

    10/16/2007 1:16:00 PM |

    I know I've already said thanks for the answer but I thought I'd make one last point here.

    There is a clear distinction between plaque reduction and plaque rupture risk reduction.

    I think your last comment contained solid evidence, to the extent we now have it, that plaque reduction doesn't increase plaque rupture risk but in fact decreases it.

    This has settled my mind on the issue (until there is more evidence to evaluate).

    I understand that this is a needling kind of point but it seems to me an important one and I think the answer you gave is a great start on a new TYP Program Special Report.

    You probably have a long list of these kinds of reports to write.  I'd recommend adding this topic to that queue.

    Thanks again for everything you do.

  • Dr. Davis

    10/16/2007 4:47:00 PM |

    Eventually, I'd like to see a two armed study comparing the Track Your Plaque appraoch to a control group using statins and an American Heart Association diet. My prediction is that there will be no comparison. However, I doubt a drug company would sponsor such a study that likely would cost several million dollars, given the large numbers of people required for conclusive outcome (i.e., cardiovascular events) data.

    A more practical approach would be to do side-by-side serial heart scans with intracoronary ultrasound. I think this may be more achievable in the foreseeable future, but will require a great deal of planning. Believe it or not, I tried such a study nearly 12 years ago but encountered tremendous resistance, since such a study needs to be performed in a hospital setting.

    Another thought: With the tremendous experience we are developing on line, this could be construed as a "virtual clinical trial" that allows us to quantify events among a growing number of people. Not as "clean" but still persuasive.

  • Anonymous

    10/16/2007 8:26:00 PM |

    A pdf file with a more detailed description of how they do the mini-dose CCTA is at the cedars-sinai website here.

    They reduce the radiation dose by using x-rays produced during only 1/10th of the cardiac cycle.

  • Dr. Davis

    10/16/2007 10:43:00 PM |

    Thanks for the lead.

    I looked at the press release but it leaves me puzzled. Many scan centers "gate" to the EKG. I'm not sure what they are doing differently. I'll do some digging.

  • G

    11/13/2007 2:49:00 AM |

    No smart drug company will do a drug trial versus the TYP plan. (if they're smart!!) In the PROVE-IT trial, Bristol Myers conclusively demonstrated that their drug (pravastatin) sucked...  maybe you can use your favorite colleague's patients for the control-arm? *wink wink*

    You definitely need to publish a 'metabolic' arm, including any T2DM patients. I think by distinguishing the difference, you may demonstrate even more accelerated plaque regression compared with non-metabolic.  Perhaps most pts are 'metabolic?'.  

    remember if you have Asians or Indo-Asian patients, the BMI >= 27.5 is considered 'obese' and waist circumference > 35.5 inches for men is 'metabolic'...  hope that helps!

  • Dr. Davis

    11/13/2007 2:56:00 AM |

    I agree.

    Our first release of the data this coming spring will lump together people with metabolic syndrome and diabetes along with everybody else. As the experience grows, I believe that a subset analysis will be possible.

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