Um heilalóðfall á Íslandi 2007-2008

Brief Reports

Incidence of First Stroke

A Population Study in Iceland

Agust Hilmarsson, MD; Olafur Kjartansson, MD; Elias Olafsson, MD, PhD

Background and Purpose—Iceland is an island in the North Atlantic with «319000 inhabitants. The study determines the incidence of first stroke in the adult population of Iceland during 12 months, which has not been previously reported in the entire Icelandic population.

Methods—The study population consisted of all residents of Iceland, aged >18 years, during the 12-month study period. Cases were identified by multiple overlapping approaches. Medical records were reviewed to verify diagnosis, to determine stroke subtype and to determine selected risk factors.

Results—A total of 343 individuals, aged >18 years, had a first stroke during the study period. Incidence was 144 per 100000 person years; 81% ischemic infarction; 9% intracerebral hemorrhage; 7% subarachnoid hemorrhage; and 3% unknown. Fifty percent of the individuals were men. Mean age for ischemic infarction and intracerebral hemorrhage was 71 years for men and 73 years for women. Atrial fibrillation was previously known in 18% with first ischemic stroke or intracerebral hemorrhage and another 6% were diagnosed on routine admission ECG. Long-term ECG study (24 hours) found that 12% (18/154) of the remaining individuals had paroxysmal atrial fibrillation.

Conclusions—Incidence of first stroke in Iceland is similar to other Western countries. The high number of paroxysmal atrial fibrillation found during the 24-hour ECG suggests that atrial fibrillation may be underdiagnosed in patients with stroke.   (Stroke. 2013;44:1714-1716.)

Key Words: atrial fibrillation ■ Iceland ■ incidence ■ population study ■ stroke

Stroke is a major cause of long-term disability and the sec-ond leading cause of death worldwide.1 The incidence of first stroke has been reported from several well-defined populations, including 144 per 100000 individuals in south-ern Sweden,2 145 in Rochester, MN,3 and 145 in Oxfordshire, England.4 The purpose of this study is to determine the inci-dence of stroke in the adult population of Iceland, frequency of stroke subtypes, and selected risk factors.

Materials and Methods

Inclusion Criteria

The index cases are registered inhabitants of Iceland, aged > 18 years, diagnosed with a first stroke during a 12-month period from October 1, 2007, through September 30, 2008. Stroke is defined based on clinical criteria (World Health Organization definition).5 We excluded (1) recurrent stroke, (2) transient ischemic attack (clinical symptoms, compatible with stroke but lasting

Study Population

The Icelandic population in mid-2008 was 319355 individuals, 238984 who were >18 years of age and 5.6% were >75 years of age.6 There is 1 university hospital (Landspitali University Hospital [LUH]), located in Reykjavik, which has the only  specialized

neurology department in the country and is the primary hospital for acute stroke in two thirds of the population and a referral hospital for the rest. The healthcare system provides ready, and affordable, access to hospitals for individuals with symptoms of acute stroke.

Case Finding

We monitored regularly stroke admissions to all hospitals in Iceland, and admissions to the LUH were monitored daily. Primary care phy-sicians, nursing home physicians, and staff were contacted at regular intervals. We reviewed records of all radiology departments to iden-tify individuals with first stroke. The great majority of all suspected stroke cases were discovered and reviewed during the initial admis-sion for stroke.

We reviewed medical records of all suspected stroke cases to (1) verify diagnosis, (2) determine if this was the first stroke, (3) determine the stroke type, (4) determine the pathogenic category of stroke according to the Trial of Org 10172 in Acute Stroke Treatment (TOAST) classification7, and (5) determine selected risk factors, including atrial fibrillation (AF).

Calculations were performed using Excel (Microsoft, Redmond, WA). Standardization was done by the direct method. The study was approved by the Icelandic Data Protection Authority and the National Bioethics Committee.

Results

We identified 410 individuals who presented with first or recurrent stroke during the study period. We excluded the 16% with recurrent stroke, including 4 individuals, who had

Received November 26, 2012; accepted March 7, 2013.

From the Department of Neurology (A.H., E.O.), and Department of Radiology (O.K.), Landspitali University Hospital, Reykjavik, Iceland; and University of Iceland, School of Medicine, Reykjavik, Iceland (E.O.).

Correspondence to Elias Olafsson, MD, PhD, Department of Neurology, Landspitali University Hospital, 108 Reykjavik, Iceland. E-mail eliasol@lsh.is © 2013 American Heart Association, Inc.

Stroke is available at http://stroke.ahajournals.org

DOI: 10.H61/STROKEAHA.1H.000222 1714 Hilmarsson et al Incidence of First Stroke in Iceland

1715

Table 1.   Annual Incidence Rates of First Ever Stroke (Per 100000 Population)

 

Population Men Women All
Age Group, y Men Women n Incidence n Incidence n Incidence
18-39 54329 49311 2 4 5 10 7 7
40-44 11881 11086 2 17 5 45 7 30
45-49 11853 10867 9 76 7 64 16 70
50-54 10916 10043 11 101 7 70 18 86
55-59 9149 8562 12 131 12 140 24 136
60-64 7248 7006 10 138 17 243 27 189
65-69 5019 5172 17 339 13 251 30 294
70-74 4123 4514 34 825 19 421 53 614
75-79 3649 4225 28 767 29 686 57 724
80-84 2353 3198 27 1147 29 907 56 1009
>85 1601 2879 17 1062 31 1077 48 1071
All 122121 116863 169 138 174 149 343 144*

177 per 100 000 when adjusted to 2001 England and Wales population, compared with 162 per 100 000 for the The Oxford Vascular (0XVASC) study. 142 per 100 000 when adjusted to the 1970 US white population, compared with 145 per 100 000 for the Rochester study.

a history of prior stroke symptoms, for which they had not sought medical attention.

The 84% (n=343) who had their first stroke ever during the study period are the index cases of this study Cause of the stroke was ischemic infarction 81%, intracerebral hemorrhage (ICH) 9%, subarachnoid hemorrhage 7%, and unknown 3%.

Crude incidence for first ever stroke per 100000 person years of observation, for those aged >18 years, was 144 for all; 117 for ischemic infarction, 13 for ICH, 10 for subarach-noid hemorrhage, and 4 for unknown (Tables 1 and 2).

Age-Specific Incidence and Stroke by Subtypes

Imaging Studies

A total of 97% (334/343) had a computed tomography or MRI at the time of diagnosis. MRI was normal in 4% (8/201) of all studied with MRI or 2% (8/343) of all with first stroke.

Pathogenic Classification for Ischemic Stroke (TOAST)

Large artery disease was diagnosed in 7% (20/279), cardio-embolic stroke in 36%, lacunar stroke in 12%, other known

causes in 2%, and undetermined in 42%.7 The undetermined were fully investigated in 59% (70/118), that is, brain imag-ing, 24-hour ECG, and carotid imaging; 41% were not fully investigated (all had brain imaging but only some had 24-hour ECG or carotid imaging). Individuals with very large infarcts or with lacunar infarcts were less likely to be fully studied.

Age and Sex

For Ischemic infarction, ICH, and unknown stroke men were 50% (161/320) and women 50%. Mean age at presentation was 71 years for men and 73 years for the women. For sub-arachnoid hemorrhage, men were 35% (8/23), women 65%, and mean age at presentation was 51 years for all.

Atrial Fibrillation

AF was known before the stroke in 18% and was discovered in another 6% (19/320) on a routine admission ECG. Twenty-four-hour ECG was performed in 63% (154/245) of the remain-der (n=245), with ischemic infarction, ICH, or unknown.

Table 2.   Age-Specific Incidence of Stroke by Subtypes (Per 100000 Population)

 

Intracerebral Subarachnoid
Population n Cerebral Infarction Hemorrhage Hemorrhage Unknown All
Age Group, y
n Incidence n Incidence n Incidence n Incidence n Incidence
18-39 103640 3 3 0 0 4 4 0 0 7 7
40-44 22967 4 17 0 0 3 13 0 0 7 30
45-49 22720 13 57 0 0 3 13 0 0 16 70
50-54 20959 11 52 3 14 4 19 0 0 18 86
55-59 17711 18 102 1 6 5 28 0 0 24 136
60-64 14254 22 154 3 21 2 14 0 0 27 189
65-69 10191 27 265 2 20 0 0 1 10 30 294
70-74 8637 49 567 4 46 0 0 0 0 53 614
75-79 7874 45 572 8 102 1 13 3 38 57 724
80-84 5551 44 793 8 144 1 18 3 54 56 1009
>85 4480 43 960 3 67 0 0 2 65 48 1071
Total 238984 279 117 32 13 23 10 9 4 343 144

1716       Stroke        June 2013

Twelve percent (18/154) of the individuals had paroxys-mal AF. Thus, AF was present in 29% (94/320) of all with ischemic infarction (31% [87/279]), ICH (18% [6/32]), and unknowncause (11% [1/9]).

LargeArtery Disease

Carotid arteries were examined in 62% (172/279) of all with ischemic infarction, including ultrasound (58%), com-puted tomography or MRI angiography (50%). A total of 6% (10/172) of those studiedhad significant (>70%) symptomatic carotid stenosis.

Studies of intracerebral arteries were performed in 57% (160/279) of those with ischemic infarction; transcranial Doppler 27%; computed tomography or MR angiography 31%. Three percent (4/160) had severe symptomatic stenosis (>50%) of a major intracranial artery.

Discussion

We think that we have identified the great majority of strokes in Iceland occurring during the study period, possibly all. We used multiple approaches for identification and most were found by multiple methods. Brain imaging is readily avail-able, and the majority of older infirm people live in nursing homes, which facilitate case ascertainment.

The incidence in our study was similar to the Rochester and The Oxford Vascular OXVASC studies,34 after standardizing the incidence (Table 1).

AF is a major risk factor for stroke, and 18% of our patients had a known AF at the time of the first stroke, compared with 17% (ischemic infarction) in Rochester8 and 17% in Ireland (all strokes).9 Another 12% were found to have AF on routine admission ECG (6%) or 24-hour ECG (6%). Thus, nearly one third of all with ischemic infarction and ICH had AF and half of them were discovered during the admission for the stroke.

This is comparable to 29% with AF in a population sample of first ever stroke in a study from Ireland.9

AF is an important potentially treatable risk factor for stroke. Our study suggests that a 24-hour ECG identifies a high number of previously unknown AF, in individuals with first stroke.

Disclosures

None.

References

Mathers CD, Boerma T, Ma Fat D. Global and regional causes of death. BrUedBull. 2009;92:7-32.

Hallström B, Jönsson AC, Nerbrand C, Norrving B, Lindgren A. Stroke incidence and survival in the beginning of the 21st century in southern Sweden: comparisons with the late 20* century and projections into the future. Stroke. 2008;39:10-15.

Brown RD, Whisnant JP, Sicks JD, O’Fallon WM, Wiebers DO. Stroke incidence, prevalence, and survival: secular trends in Rochester, Minnesota, through 1989. Stroke. 1996;27:373-380.

Rothwell PM, Coull AJ, Giles MF, Howard SC, Silver LE, Bull LM, et al; Oxford Vascular Study. Change in stroke incidence, mortality, case-fatality, severity, and risk factors in Oxfordshire, TJK from 1981 to 2004 (Oxford Vascular Study). Lancet. 2004;363:1925-1933.

The World Health Organization Monica Project (monitoring trends and determinants in cardiovascular disease): A Major International Collaboration. Who Monica Project Principal Investigators. J Clin Epidemiol. 1988;41:105-114.

Statistics Iceland. http://statice.is. Accessed September 22, 2010.

Adams HP Jr, Bendixen BH, Kappelle LJ, Biller J, Love BB, Gordon DL, et al. Classification of subtype of acute ischemic stroke. Definitions for use in a multicenter clinical trial. TOAST. Trial of Org 10172 in Acute Stroke Treatment. Stroke. 1993;24:35^U.

Tsang TS, Petty GW, Barnes ME, O’Fallon WM, Bailey KR, Wiebers DO, et al. The prevalence of atrial fibrillation in incident stroke cases and matched population controls in Rochester, Minnesota: changes over three decades. JAm Coll Cardiol. 2003;42:93-100.

Hannon N, Sheehan O, Kelly L, Marnane M, Merwick A, Moore A, et al. Stroke associated with atrial fibrillation-incidence and early out-comes in the north Dublin population stroke study. Cerebrovasc Dis. 2010;29:43^19.