Discussion
Our findings indicate that in African American patients with cryptogenic
stroke detection of AF occurs earlier and yet at similar rate that in
other populations1,7-9. Brachmann et al, specifically
found near identical detection rates in the ILR monitoring arm at 36
months (30% vs 29%), but detection occurred later after implantation
compared to our population (median time to detection = 8.4 months vs
37.5 days. Furthermore, the detection rate after 1 month was 3.7% in
this study compared to around 14% in our population.9 In the CRYSTAL-AF trial at 1 month out from
implantation the detection rate was also lower that in our population
with only about 4%. 1
Given the retrospective nature and lack of control group we are not able
to conclude with certainty that the detection of AF would occur earlier
after implantation that in other ethnic groups. Our patients had more
comorbidities as indicated by a higher CHADS2VASc than
those in the CRYSTAL-AF trial (4.4 vs 3.0) and Brachmann et al. yet
similar rates of AF detection suggesting a “protective effect”.1,9 African Americans appear to have an increased risk
of developing stroke in the setting of AF independent of the relative
higher prevalence of comorbidities in this population.10
Those with detected AF had a numerical older age, greater prevalence of
prior stroke, and incidence of CAD but none of these results were
statistically significant. This is likely related to insufficient power
to detect a difference as multiple other studies have demonstrated a
correlation between these variables and an increased detection rate of
AF. 8,11 No electrocardiographic or echocardiographic
parameters were associated with an increased detection rate in this
group despite some parameters like PR interval prolongation, LA size and
frequent premature atrial beats have been reported as predictors of AF
detection in other studies. 8, 11, 12
When a multivariate regression analysis was performed including
variables that approached significance the presence of CAD,
hyperlipidemia, age, and nonuse of calcium channel blockers demonstrated
predictive capacity. It is uncertain though what mechanism may be
involved but CCB are known to decrease aldosterone synthesis and that in
turn might decrease the odds of developing AF. 13 The
combination of these factors demonstrating significance might have been
driven mainly by the combination of age and CAD which are well
documented predictors of development of atrial fibrillation.14
In conclusion, it appears that extended electrocardiographic monitoring
with an implantable loop recorder it as effective for the detection of
AF in African Americans as in the general population, time to detection
is shorter and baseline characteristics were unable to predict the
detection of AF.