Medicine is Not an Exact Science
Ramon F. Abarquez, Jr., MD, EFACC, FAsCC, FPCP, FPCC, CSPSH
Academician Project, National Academy of Science and Technology Professor Emeritus, College of Medicine, UP Manila
Dr. Ramon F. Abarquez, Jr. has been one of the most prolific consultant writers of H&L and its sister publication, Vital Signs. Highly esteemed in the medical community, he is the founding president of Philippine Society of Hypertension and a past president of the Philippine College of Physicians
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Intra-coronary plaque growth extraluminal expansion intends to preserve epicardial coronary lumen diameter. Plaque characteristics can identify acute coronary syndrome (ACS) culprit coronary vessels. But ‘silent’ ischemic/ACS that may precede a de-novo clinical first ACS since non-culprit lesion with/without plaque rupture have fibroatheroma. Post-ACS coronary microcirculation recovery and fractional flow reserve (FFR)- ischemia are relevant scenario to ‘silent ACS’. More importantly, BP lowering therapy may result in ‘collateral steal’.
Stable non-thrombotic ischemia
Patients with signs and symptoms of stable ischemic heart disease have non-obstructive coronary artery disease (NoCAD in 50 percent). And about 2/3 of patients with NoCAD have demonstrable coronary endothelial dysfunction with microvascular or diffuse epicardial spasm following acetylcholine challenge. Patients with coronary endothelial dysfunction have significant clinical concerns, morbidity and increased risk of developing flow-limiting coronary artery disease and myocardial events, including death. (Shaw, Vasc Med. 2015 Dec 15. pii: 1358863X15618268) (Huo, J Biomech. 2016 Feb 12. pii: S0021-9290(16)30127-0)
Non- and partially calcified CAD
“Several plaque characteristics detectable by coronary computed tomographic angiography (coronary CTA) are thought to be indicative of vulnerable plaques and subsequent cardiac events, particularly low attenuation plaque volume (LAPV), positive remodeling and the napkin-ring sign which is high density vascular adhesion with a small center of low density”.
Quantitative plaque assessment predicting MACE in relation to established CT risk scores such as the calcium score or Segment Stenosis Score (SSS) is unknown. In 1168 CAD-suspects, calcium score measurement and coronary plaque characterization was performed. In all non-calcified or partially calcified plaques, semi-automated plaque analysis was performed to quantify low attenuation plaque volume (density <30HU), total non-calcified plaque volume (<150HU, TNCPV) and remodeling index. The presence of the napkin-ring sign was assessed visually.
During a clinical follow up of 5.7 years, MACE was observed in 46 patients (3.9 percent) with strongest association for LAPV (HR 1.12, p < 0.0001). LAPV, TPV, PR and presence of the napkin-ring sign are predictors of MACE independently of clinical risk presentation and beyond the calcium score and conventional coronary CTA analysis. (Nadjiri, J Cardiovasc Comput Tomogr. 2016 Jan 13. pii: S1934-5925(16)30005-3)
HbA1c and plaque assessment
Retrospectively examined 1079 coronary computed tomography (CT) angiography scans and the HbA1c results: non-diabetic, =6.0; borderline, 6.1-6.4; diabetic low, 6.5-7.1; diabetic high, >7.1 and segment involvement score >4 as extensive disease. High risk plaque: features include positive (FP) plaque with positive remodeling (remodeling index >1.1) and low attenuation (<30 HU). Although the relationship of borderline patients and 2FP plaque was marginal in multivariate analysis [OR= 1.53, 0.95-2.40, p = 0.07], the elevation of HbA1c was strongly associated with 2FP plaque (diabetic low, OR 2.19, .37-3.45, p < 0.005; diabetic high, OR 4.14, 2.57-6.67, p < 0.0005).
The association of HbA1c elevation and extensive disease was quite similar between borderline and diabetic patients. Patients with elevated HbA1c of >6.0 are potentially at risk for future cardiovascular events due to increased high risk plaque and extensive disease, even below the diabetic level of 6.5. (Tomizawa, Int J Cardiovasc Imaging. 2016 Mar;32(3):493- 500) Being diabetic is a CAD equivalent?
ACS and DM review
Review included 9 case-control and 10 cohort studies (10 856 279 individuals) with at least 106,703 fatal and nonfatal ACS events showed pooled maximum-adjusted RR of ACS associated with diabetes was 2.46 (1.92-3.17) in women and 1.68 (95% CI, 1.39-2.04) in men. And, risk of ACS: the pooled women-to-men RR and the ratio of relative risks was 1.38,1.25-1.52; P < .001). [Dong, Diabetes Metab Res Rev. 2017 Jan 19] Are women really the weaker or stronger gender?
Silent CAD in DM
Prevalence of silent myocardial ischemia in DM-2 patients is 37.3 percent with significant correlation between risk factors of CVD and evidence of treadmill test ischemia (TMT) in diabetic patients. Duration of diabetic state has a strong correlation for inducible ischemia on TMT as a non-invasive screening tool for earlier detection of CAD in diabetic patients. [Sharda, J Assoc Physicians India. 2016 Nov;64(11):32-37]
Other diagnostic basis for ‘silent CAD ischemia’ among DM cases: sensitivity of PET (94.7 percent), SPECT (85.1 percent) and of stress echocardiography (77.6 percent) and specificity of PET (68.8 percent), SPECT (62.1 percent) and of stress echocardiography (69.6 percent). All currently used diagnostic strategies were cost-effective. [Cambell, Health Technol Assess. 2014 Sep;18(59):1-120] T MT is more cost-effective for silent CAD.
July 2017 Health and Lifestyle