ROME, ITALY. Although lone atrial fibrillation (LAF) as such is not a risk factor for ischemic stroke, the likelihood of suffering a stroke or transient ischemic attack (TIA) increases if the LAF is accompanied by heart disease, presence of prosthetic heart valves, hypertension (blood pressure greater than 160/90 mm Hg), diabetes, low left ventricular ejection fraction (< 45%) or a history of stroke, TIA, heart attack or peripheral vascular embolism.
A group of Italian medical researchers now report that an elevated level of the inflammation marker C-reactive protein (CRP) and a reduced blood flow through the left atrial appendage (LAA) are associated with an increased risk of forming blood clots (thrombi) in the left atrium. Their study included 150 patients (46% men, age ranging between 53 and 77 years) with persistent, non-valvular atrial fibrillation (AF). Prior to their scheduled electrical cardioversion, all patients underwent transesophageal echocardiography (TEE) and had blood samples drawn for later analysis. Examination of the echocardiograms revealed the existence of dense spontaneous echo contrast (SEC) in 52 patients. SEC is considered to be the origin of thrombi and is seen as a swirling pattern (fog) on the TEE; the denser the pattern the more likely it is that a clot will eventually develop. Nine patients were found to have a thrombus in the LAA and were excluded from further evaluation. The remaining 98 patients had no dense SEC. It is interesting that 85% of study participants were on warfarin, which is supposed to prevent clot formation.
Analysis of blood samples drawn prior to cardioversion showed that the presence of dense SEC was directly associated with elevated levels of C-reactive protein, D-dimer and fibrinogen. Examination of the echocardiogram revealed that the presence of dense SEC was strongly associated with a low velocity of blood flow in the LAA and significantly related with an enlarged left atrium. Somewhat surprisingly, left ventricular ejection fraction did not seem to affect LAA flow velocity. After correcting for possible confounders, a multivariate analysis showed that only LAA flow velocity and CRP level were associated with the presence of dense SEC at a level achieving statistical significance.
The researchers conclude that patients with low LAA velocity (less than 0.25 m/sec) have a 19-fold increased risk of harboring dense SEC as compared to those with normal flow velocity. Similarly, a CRP level above 3 mg/L (0.3 mg/dL) was associated with a 3.4-fold increased risk of dense SEC.
Cianfrocca, C, Santini, M, et al. C-reactive protein and left atrial appendage velocity are independent determinants of the risk of thrombogenesis in patients with atrial fibrillation. International Journal of Cardiology, Vol. 142, 2010, pp. 22-28
Editor's comment: The finding that a low LAA flow velocity is associated with a greater risk of forming dense SEC and blood clots is not surprising. Blood stasis, such as also found in deep vein thrombosis, is an obvious incubator of thrombi. What is somewhat surprising is the finding that left ventricular ejection fraction is not associated with SEC formation. Seeing that the left ventricle abuts the LAA, one would expect that a more forceful left ventricular ejection would result in a greater LAA emptying velocity. The finding that a high CRP level (inflammation) is associated with an increased risk of dense SEC once again emphasizes the importance of knowing one's CRP level and, if necessary, reduce it through the use of natural anti-inflammatories such as Zyflamend, ginger, curcumin, vitamin C, beta-sitosterol, boswellia or Moducare.