Feeling the Portuguese pulse: unveiling the hospitalisation-leading cardiac arrhythmias.

ALBERTO, M.1; ANDRADE, T;1 CARDOSO, S.1; CORREIA, C.1; MAGALHÃES, D.1; MEDEIROS,

N.1; NEVES, A.1; SANTOS, J.1; TELES, A.1; VIEIRA, B.1; SANTOS, J.V.2; FREITAS, J.2

1Class 22, Introdução à Medicina II, Faculdade de Medicina da Universidade do Porto

2 Advisers, Introdução à Medicina II, Faculdade de Medicina da Universidade do Porto

ABSTRACT

This article intends to find out whether there is or not an asymmetrical distribution in

hospitalisations due to cardiac arrhythmias in Portugal, and to provide a possible explanation for

those findings.

Methods: 113 631 mainland Portuguese individuals, hospitalised from 2000 to 2008 in

mainland Portuguese health facilities, whose principal diagnoses were “426” or “427” ICD9-CM

codes, were divided according to NUT II region classification. Total population and ageing index data

was obtained from external sources. Hospitalisation frequencies per a hundred thousand inhabitants

were crossed with established arrhythmia-leading factors (age, hypertension, diabetes mellitus - DM,

hyperthyroidism, obesity, chronic kidney disease - CKD and hyperlipidemia), and conclusions were

withdrawn from there.

Results: Gender and age distribution were very similar across all NUT II regions; North

constantly showed lower hospitalisation frequencies than the other four regions; North is the

youngest region; When adjusting the number of hospitalisations (NOH) for age groups, significant

differences are still found for North and Lisbon from the age of 40 onwards; North presents higher

values of NOH with Obesity, Hyperlipidemia, CKD and DM per a 100 000 hospitalisations due to

arrhythmias than Lisbon; Obesity and Hyperlipidemia increase the odds of being hospitalised due to

arrhythmias (AOR = 1,17 and AOR = 1,14) and are higher in North; Hypertension (AOR = 1,30) and

Hyperthyroidism (AOR = 3,45) are both more frequent in Lisbon and are more relevant (higher AOR)

than Obesity and Hyperlipidemia.

Conclusions: Age is a risk factor in the emergence of cardiac arrhythmias; Hypertension’s and

hyperthyroidism’s prevalence are the most relevant influencers in the number of hospitalisations;

CKD as a protective effect in the appearance of cardiac arrhythmias; North population has a lower

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risk of being hospitalised than Lisbon population; Centre, Algarve and Alentejo were similar in terms

of number of hospitalisations.

Key words: Cardiac arrhythmias; Portugal; Hospitalisation; Aging; Hypertension; Diabetes Mellitus;

Hyperthyroidism; Obesity; Chronic Kidney Disease; Hyperlipidemia; Epidemiologic studies

BACKGROUND

Cardiac arrhythmias are a large group of conditions in which there is not a normal sinus

rhythm and normal atrioventricular (AV) conduction. [1] Quan H et al (2005) updated the definition

(originally by Elixhauser et al (1998)) of a selection of ICD-9-CM codes for several comorbidities,

including “cardiac arrhythmia”.[2] Atrioventricular (AV) block, atrial (APB) or ventricular premature

beats (VPB), sinus bradycardia and atrial fibrillation (AF) stand amongst the most common

arrhythmias.[1]

Age is a decisive influencer in the appearance of arrhythmias. Atrial fibrillation (AF), which

affects approximately 0,4% of the global population,[3] doubles its prevalence every ten years beyond

the 50 year benchmark.[4] In the USA, roughly 70% of individuals with AF are between 65 and 85

years of age.[5] Various other studies support this relation.[6]

Several studies have demonstrated that changes of the thyroid function are associated to

greater levels of cardiovascular morbidity, including angina, myocardial infarction and arrhythmias. [7]

The thyroid hormones play a key role in controlling lipid metabolism. If the condition called

hyperthyroidism is present, there is an increase of cholesterol synthesis, possibly leading to the

aforementioned pathologies.[7]

Fatal arrhythmias are pointed as the most frequent cause of death among obese patients, [8]

which means that obesity is a significant cause of cardiac arrhythmias. Obesity is a status in which

body weight is grossly above the acceptable or desirable weight, and whose standards may vary with

age, sex, genetic or cultural background. An individual with BMI (Body Mass Index) greater than 30,0

kg/m2 is considered obese, and with a BMI greater than 40,0 kg/m2 is considered morbidly obese.[9] In

Portugal, a study developed in 2006 for the 10th Portuguese Congress of Obesity in Oporto found

some differences in the prevalence of obesity by NUT II regions: North (13,1%) is the least obese

region, in contrast with Alentejo (16,4%), the most obese. Algarve (13,2%), Centre (14,2%) and

Lisbon (15,8%) are in the midterm.[10]

Hypertension is one of the most important risk factors for cardiovascular disease. [11]

Hypertension facilitates development and progression of cardiac diseases such as left ventricular

hypertrophy (LVH), coronary artery disease (CAD), arrhythmia and heart failure. [12] A 2007

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Portuguese study (subjects aged 18 to 90 years old) pointed North as the region with the lowest

prevalence of hypertension (33,4%), and Alentejo with the highest (49,5%). [13]

Chronic kidney disease (CKD) affects up to 10% of adults [14] and carries a high risk for

cardiovascular disease, including atrial fibrillation (AF).[15]

Diabetes Mellitus (DM) increases the incidence of cardiac arrhythmias. [16] Individuals with DM

had one third greater risk of incident AF compared with those without diabetes after adjustment with

no evidence of interactions with race or gender.[17]

Dyslipidemia, an important risk factor for cardiovascular disease, may be associated with atrial

fibrillation (AF).[18]

There has been an increase in the prevalence of arrhythmias in industrialised countries for

more than 50 years now.[19-21] AF followed this general trend.[6] Concerning Portugal, Bonhorst D et al.

(2010) concluded that the prevalence of AF is higher than in other countries where similar data is

available, when focusing on the population aged 40 and onwards. [22]

With a growing number of patients with cardiac arrhythmias, swiftly managing them is

becoming more of a challenge. The first step towards a solution is to study and understand their

common background. However, answers might have to be regionally tailor-made rather than global.

Hence, our main goal is to find out whether there is or not an asymmetrical distribution in

hospitalisations due to cardiac arrhythmias in Portugal, and to provide a possible explanation for

those findings. Specifically, we will:

Analyse Portuguese arrhythmia-caused hospitalisations from 2000 to 2008, dividing it

by NUT II regions and age groups;

Recourse to population age, Hypertension, Diabetes Mellitus, Hyperthyroidism, Obesity,

Chronic Kidney Disease and Hyperlipidemia to try and explain our findings;

Study the evolution of the arrhythmias and associated factors.

PARTICIPANTS AND METHODS

ParticipantsThis study focuses on hospitalisations in mainland Portuguese public acute care hospitals with

discharges, between 2000 and 2008. All patients with a principal diagnosis codified in ICD-9-CM as

“426 - Conduction disorders”, “427 - Cardiac dysrhythmias”, or a subheading of these classifications,

and resident in mainland Portugal, were included.

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113 631 impatient episodes were taken into account. 58 839 (51,8%) of the episodes referred

to male individuals, and 54 792 (48,2%) to female individuals. Patients’ age ranged from 0 to 108

years (Mean = 69,7; SD = 15,6).

Study designThis is an epidemiologic, cross-sectional study[23] that covers a nine-year period, 2000 to 2008.

Each episode was analysed only once (there is no follow-up period), and readmissions were

considered independent episodes.

Data collection methodsHospitalisations’ data was provided by Department of Health Information and Decision

Sciences, Faculty of Medicine, University of Porto. Supporting evidence was withdrawn from studies

relating cardiac arrhythmias with individual factors such as age, gender, demographic or geographic

data, hyperthyroidism, obesity, hypertension, chronic kidney disease, diabetes mellitus and

hyperlipidemia. The main data collection method was on-line research on Pubmed.

ICD-9-CM arrhythmia diagnoses codes were first selected according to Quan H. et al (2005). [2]

Of those, this article only considers diagnoses which fall on the categories “426 - Conduction

disorders” or “427 - Cardiac dysrhythmias” of ICD-9-CM.

Variables descriptionPrincipal diagnosis: ICD-9-CM 426.xx or 427.xx codes.

Secondary diagnoses were chosen based on frequency (ten most frequent): Congestive Heart

Failure (428.0, 398.91), Syncope and Collapse (780.2), Atrial Fibrillation (427.31) and Chronic

Isquemic Heart Disease (414.x) are heart-related diseases, and therefore were excluded from the

analysis; Hypertension (401.xx) appeared twice, but frequencies were merged; Obesity (278.0x),

Hyperlipidemia (272.0, 272.1, 272.2, 272.3, 272.4), Chronic Kidney Disease (CKD; 585.x) and

Diabetes Mellitus (DM; 250.00, 648.8x) completed top ten. Hyperthyroidism (242.xx, 775.3) was also

included.

Demographic variables used were patients’ age group, gender, patients’ residence by NUT II

regions (mainland Portugal is currently divided in five NUT II regions: North, Central Region - from

here onwards referred as “Centre” -, Lisbon, Alentejo and Algarve) [24], Portuguese population data

(INE estimates yearly the population of each NUT II region; in 2001 the national Census took place,

determining more accurate figures for that specific year) and Ageing Index, whose data was obtained

from INE. Ageing Index: quotient between the number of people of 65 years-old or more and the

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number of those of 14 or less years-old; It is expressed in number of elders by 100 youths. Discharge

date (years) was also analysed.

Statistical analysisStatistics were performed using IBM SPSS Statistics v20® and Microsoft Office Excel 2010®.

Table 1: Characteristics of the patients, taken from database.

Supplementary table I: Population by NUT II region is available on INE (National Institute of

Statistics) website[24]. Number of hospitalisations (NOH) was withdrawn from our database.

Table 2 and Chart 1: Built based on Supplementary table I by dividing the NOH of each region

for its total population, times a hundred thousand.

Table 3: Unpaired, two-tail t-tests were performed to compare each region with the other four,

concerning NOH per a hundred thousand inhabitants. Significance level set at p < 0,05.

Table 4: Ageing Index by NUT II region is available on INE website. [24] A Welch test was ran to

compare all regions. Significance level set at p < 0,05.

Chart 2: Chart 1 was corrected for age group, i.e., age influence was eliminated by dividing the

NOH of each region for its total population by age group. An average was used for NOH and

population figures.

Supplementary table II: shows all chart 2 values and 95% CI (confidence intervals). CI’s were

calculated using the formula CI 95% ( p )=[ p−2 √ p (1−p )√n

, p+2 √ p(1−p)√n

], where p is the NOH (per

capita) and n is the absolute population within that age group in a certain region. Values for 95% CI

were adjusted to 100 000 inhabitants.

Chart 3: frequencies were obtained through the SPSS Frequencies tool applied to all

secondary diagnoses in the provided database.

Table 5: NOH with Hypertension, Obesity, Hyperlipidemia, CKD, Hyperthyroidism or DM as

secondary diagnoses, per a hundred thousand hospitalisations due to cardiac arrhythmias and per

NUT II region, were withdrawn from the provided database.

Table 6: Logistic regression including all hospitalisations in mainland Portugal from 2000 to

2008. Dependent variable - principal diagnosis for hospitalisation: cardiac arrhythmia or other.

Independent factors: secondary diagnoses (hypertension, diabetes mellitus, hyperlipidemia, obesity,

hyperthyroidism, CKD, congestive heart failure, syncope and collapse, atrial fibrillation, chronic

isquemic heart disease) and demographic variables (patients’ residence by NUT II region, age). It

was made using the Forward Stepwise Method through SPSS v20.

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RESULTS

CHARACTERISTICS NORTH CENTRE LISBON ALENTEJO ALGARVEN 28545 29606 38944 11287 5249Sex - % Male 50,9 54,5 49,3 53,9 55,8 Female 49,1 45,6 50,7 46,1 44,2Age – yearMean±SD 69,25±15,82 70,20±15,42 69,54±15,64 70,37±15,16 69,27±16,10

Table 1 – Characteristics of the patients hospitalised due to cardiac arrhythmias, from 2000 to 2008, in mainland Portugal.Note: Readmissions were considered independent episodes.

Gender and age distribution were very similar across all NUT II regions, as expected. In

particular, all five regions registered their greatest number of hospitalisations in patients within the 75-

79 years old range.

YEAR NORTH CENTRE LISBON ALENTEJO ALGARVE2000 71,0 109,1 143,7 131,8 126,52001 74,3 118,3 151,1 141,5 105,52002 74,2 122,2 153,2 143,9 129,02003 79,1 130,0 161,5 142,3 121,62004 88,8 145,3 165,7 169,0 156,82005 91,0 143,4 171,1 181,3 149,52006 97,7 157,4 160,1 182,5 146,92007 93,5 151,6 155,5 192,5 175,92008 98,0 172,0 156,8 189,7 163,5

Table 2 – Number of Hospitalisations (NOH) per a hundred thousand inhabitants, by year and NUT II region. Note: Results were obtained by dividing the NOH of each region for its total population, times a hundred thousand.

Chart 1 provides an easier overview of the values described above.

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2000 2001 2002 2003 2004 2005 2006 2007 20085060708090

100110120130140150160170180190200

NORTHCENTRELISBONALENTEJOALGARVE

Year

Num

ber o

f hos

pita

lisati

ons p

er a

hu

ndre

d th

ousa

nd in

habi

tant

s

Chart 1 – Number of Hospitalisations (NOH) per a hundred thousand inhabitants, by year and NUT II region.Note: Results were obtained by dividing the NOH of each region for its total population, times a hundred thousand.

Table 3 – p-values* for comparisons between the NOH per a hundred thousand inhabitants, by year and NUT II region (see table 2).Note: *Obtained through t-tests.

There was a general trend of increasing hospitalisations per year. Lisbon is the sole exception,

showing an inversion to negative evolution between 2005 and 2006. Reasons for this are proposed in

the discussion part.

Regarding NOH per a hundred thousand inhabitants, North stands clearly apart from all other

regions. Moreover, significant differences (p<0,001) were found between North and Centre, Lisbon,

Alentejo and Algarve, in contrast with those found between these four last regions (see table 3).

YEAR NORTH CENTRE LISBON ALENTEJO ALGARVE p*2000 80,0 130,9 110,0 173,4 127,32001 82,2 132,3 110,5 166,6 128,42002 84,2 135,3 110,7 179,8 128,22003 86,2 135,8 106,6 169,1 127,42004 88,6 138,2 105,6 170,4 127,4 < 0,0012005 90,9 140,1 105,9 170,8 126,22006 93,3 142,3 106,3 171,6 125,2

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NORTH CENTRE LISBON ALENTEJO ALGARVENORTH --- < 0,001 < 0,001 < 0,001 < 0,001CENTRE < 0,001 --- 0,349 0,060 1,000LISBON < 0,001 0,349 --- 1,000 0,717

ALENTEJO < 0,001 0,060 1,000 --- 0,141ALGARVE < 0,001 1,000 0,717 0,141 ---

2007 96,4 144,8 107,0 172,7 124,12008 99,3 147,2 108,1 172,9 123,5

Table 4 – Ageing Index (AgIdx) by NUT II regions, from 2000 to 2008.Notes: Ageing Index: quotient between the number of people of 65 years-old or more and the number of those of 14 or

less years-old. It is expressed in number of elders by 100 youngsters; *Obtained through Welch test.

Over these nine years the Ageing Index rose steadily in North and Centre, while it hovered

around the same values in the remaining regions. North is, concerning general population, by far the

youngest region, in contrast with Alentejo. This fact (North and Lisbon, the second youngest region,

are on average separated by 18,84 points) might explain the shape of chart 1.

0 to 4

5 to 9

10 to 1415 to 1920 to 2425 to 2930 to 3435 to 3940 to 4445 to 4950 to 5455 to 5960 to 6465 to 6970 to 7475 to 7980 to 8485 +

0

200

400

600

800

1000

1200

1400

NORTHCENTRELISBONALENTEJOALGARVE

Age group

Num

ber o

f hos

pita

lisati

ons p

er a

hun

dred

th

ousa

nd in

habi

tant

s

Chart 2 – Number of Hospitalisations (NOH) per a hundred thousand inhabitants, by age group and NUT II region.Notes: Results were obtained by dividing the NOH of each region for its total population by age group, times a hundred

thousand. A nine year average was used for values of NOH and population by age group; see Supplementary Table I for

all these values and all 95% C.I.

However, when adjusting the NOH for age groups (see chart 2), significant differences (see

Supplementary table II) are still found for North and Lisbon from the age of 40 onwards. Centre,

Alentejo and Algarve present close curves, while North continues to have the lowest ratios and

Lisbon stands out with the worst scenario. In the most relevant age group, 75 to 79, there is a

difference of 406,81 NOH per 100 000 inhabitants between Lisbon and North (1010,06 – 603,25; see

Supplementary Table I). Therefore, other factors must be taken into account to explain chart 1, co-

morbidities being an obvious one. Co-morbidities where studied with basis on the registered

secondary diagnoses at time of admission.

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Hypertension

Diabetes mellitus

Hyperlipidemia

Congestive heart failure

Syncope and colapse

Chronic kidney disease

Atrial fibrillation

Chronic ischemic heart disease

Obesity

0 5 10 15 20 25 30 35

Frequency (%)

Chart 3 – Most frequent secondary diagnoses registered on patients at time of admission.

Congestive Heart Failure, Syncope and Collapse, Atrial Fibrillation and Chronic Isquemic

Heart Disease are heart-related diseases, and therefore were excluded from the analysis. However,

they were included in the logistic regression (table 6) for adjustment purposes. Hypertension was the

most recorded disease, having being diagnosed to 29,1% of patients. Hyperthyroidism, despite not

appearing in this chart, is a well-known arrhythmia-potentiating factor, so was included for analysis.

HYPERTENSION OBESITY HYPERLIPIDEMIA

CKD HYPERTHYROIDISM DMNORTH 28667 4505 10618 3139 438 8937CENTRE 22664 2391 4344 2226 399 7424LISBON 33035 2956 7395 2945 704 8497

ALENTEJO 34624 3907 4988 3172 842 9817ALGARVE 26500 5430 7316 3163 972 10192

Table 5 – Number of hospitalisations with Hypertension, Obesity, Hyperlipidemia, Chronic Kidney Disease (CKD), Hyperthyroidism or Diabetes Mellitus (DM) as secondary diagnoses, per a hundred thousand hospitalisations due to cardiac arrhythmias and per NUT II region.

FACTORS N (%)*†(= 8 634 005)

UNADJUSTED ODDSRATIO (95% CI)

ADJUSTED ODDSRATIO (95% CI)

Secondary DiagnosesHypertension 1 133 475 (13,1) 2,77 (2,73-2,80) 1,30 (1,29-1,32)Diabetes Mellitus 411 762 (4,8) 1,89 (1,85-1,93) 0,97 (0,95-0,99)Atrial Fibrillation 322 997 (3,7) 1,61 (1,57-1,65) 0,53 (0,51-0,54)Hyperlipidemia 299 103 (3,5) 2,18 (2,13-2,23) 1,14 (1,12-1,17)Chronic Isquemic Heart Disease 238 259 (2,8) 3,75 (3,67-3,82) 1,57 (1,54-1,61)

Congestive Heart Failure 212 731 (2,5) 4,95 (4,86-5,05) 2,43 (2,38-2,48)Obesity 172 980 (2,0) 1,74 (1,69-1,80) 1,17 (1,13-1,21)

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Chronic Kidney Disease 133 459 (1,5) 1,88 (1,82-1,95) 0,87 (0,84-0,90)Syncope and Collapse 22 408 (0,3) 39,69 (38,57-40,83) 24,73 (23,99-25,49)Hyperthyroidism 10 310 (0,1) 5,18 (4,79-5,60) 3,45 (3,18-3,74)

Demographic VariablesNorth 3 042 889 (35,2) 1 ** 1 **Centre 2 268 053 (26,3) 1,40 (1,37-1,42) 1,19 (1,17-1,21)Lisbon 2 319 759 (26,9) 1,80 (1,78-1,83) 1,56 (1,54-1,59)Alentejo 655 611 (7,6) 1,85 (1,81-1,89) 1,49 (1,46-1,52)Algarve 347 693 (4,0) 1,62 (1,57-1,67) 1,60 (1,55-1,65)Age - 1,04 (1,04-1,04) 1,04 (1,04-1,04)

Table 6 – Odds ratio for secondary diagnoses and demographic variables on the hospitalisations motivated by cardiac arrhythmias.Notes: All hospitalisations in mainland Portugal from 2000 to 2008 were included in this logistic regression. The

dependent variable was the principal diagnosis leading to the hospitalisation: 1 – cardiac arrhythmia; 0 – other.

* For secondary diagnoses: number of hospitalisations featuring that disease as secondary diagnosis.

† For demographic variables: number of hospitalisations in that region.

** Base category for odds ratio determination.

DISCUSSION

Age is a risk factor in the emergence of cardiac arrhythmias (AOR = 1,04), which is consistent

with studies on this subject, which state that beyond the 45-50 years benchmark the prevalence rises

dramatically.

All co-morbidities (secondary diagnoses excluding heart-related diseases), bar CKD and DM,

obtained significant adjusted odds ratio (AOR) values above 1 for hospitalisations due to arrhythmias.

These roles of arrhythmia-potentiating factors go along with the scientific literature. DM is largely

irrelevant when looking to the 95% CI. CKD turned out being a protective factor, in contrast with what

is described. Hyperthyroidism deserves a special attention, since it is the most important factor for

the emergence of cardiac arrhythmias: individuals with hyperthyroidism are 3,45 times likelier to

develop arrhythmias than those without this condition.

There is no significant difference between Centre, Alentejo and Algarve regarding NOH per a

100 000 inhabitants (chart 1), nor when eliminating the factor age (chart 2). This proved to be

strange, because Centre features a lower NOH with any associated co-morbidities (table 5) than

Alentejo or Algarve and a lower AOR (table 6). A counterbalance between co-morbidities and age

influence could explain chart 1, but age was shown to be irrelevant for comparing these three regions

(chart 2).

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Chart 1 brings all attention to North, which registered the lowest NOH per a 100 000

inhabitants. Lisbon does not stand apart from Centre, Alentejo and Algarve. Lisbon’s negative

evolution between 2005 and 2006 can be explained by some changes on the classification of NUT II

Portuguese regions: in 2002 the NUT II “Lisbon e Vale do Tejo” (which consisted in 5 Nut III) was

abolished and its territory was distributed by several other Nut II regions: one of those Nut III regions

was delivered to Alentejo, two were delivered to Centre and the other two went on to form the new

Nut II region: Lisbon. This revamp only took practical effect in 2005.

However, when the age groups are included, age’s influence is eliminated and significant

differences are found for both North and Lisbon in comparison with the other three regions and

between themselves (chart 2), but while North still has the lowest ratios, Lisbon holds the worst

scenario. Since North and Lisbon are the youngest regions, some conclusions can be withdrawn:

regarding North, a young population means more protection, but other factors also contribute to a low

NOH per a 100 000 inhabitants; concerning Lisbon, age influence is offsetting co-morbidities,

resulting in an outcome (NOH/100 000 inhab; chart 1) on the level of Centre, Alentejo and Algarve.

Without age’s protective effect, hospitalisations in Lisbon rose sharply (see chart 2 and

supplementary table II). In fact, when accounting all the factors, Lisbon has a AOR of 1,56 in

comparison with North.

North presents higher values of NOH with Obesity, Hyperlipidemia, CKD and DM per a 100

000 hospitalisations due to arrhythmias (table 5) than Lisbon. CKD as a protective effect and DM is

mostly irrelevant. Obesity and Hyperlipidemia increase the odds of being hospitalised due to

arrhythmias (AOR = 1,17 and AOR = 1,14) and are higher in North, which seems to be a

contradiction. However, Hypertension (AOR = 1,30) and Hyperthyroidism (AOR = 3,45) are both

more frequent in Lisbon and are more relevant (higher AOR) than obesity and hyperlipidemia. As

such, we suppose that hypertension and hyperthyroidism are at the root of the differences found in

chart 2. Nonetheless, we believe they are not the unique reasons for such glaring disparities

displayed in chart 2 between North and Lisbon.

ConclusionsAge distribution is a major contributor in assessing the susceptibility of a population to

hospitalisation-leading cardiac arrhythmias. With this factor eliminated, hypertension’s and

hyperthyroidism’s prevalence are the most relevant influencers in the number of hospitalisations.

11

North population has a lower risk of being hospitalised than Lisbon population. This may be

due to the North’ relative youth and to a greater prevalence of hyperthyroidism and hypertension in

Lisbon. Nonetheless, we suspect there are other underlying reasons contributing to these results.

Centre, Algarve and Alentejo were similar in terms of number of hospitalisations. However, this

was an unpredictable result, revealing the high degree of complexity on the epidemiology of cardiac

arrhythmias. Therefore, further studies on this issue are encouraged.

LimitationsAs in all studies we were confronted with several limitations. Some important information is not

routinely collected, for example information related to secondary diagnoses. The high prevalence of

cardiac arrhythmias as principal diagnosis might be explained in part by the increase in repeated

hospitalisations, since readmissions were considered as independent events. This could also

introduce some bias on the results regarding co-morbidities.

ACKNOWLEDGEMENTS

We would like to express thanks to Prof. Dr. Altamiro da Costa Pereira, for his constructive

criticisms and sharp suggestions to improve our work and to Dr. Fernando Lopes, for his decisive

orientation on a critical step of our work.

12

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anticoagulation and predictors of such treatment in UK primary care. Heart. 2006; pp. 1064–1070

[21] Majeed A, et al. Trends in the prevalence and management of atrial fibrillation in general practice

in England and Wales, 1994-1998: analysis of data from the general practice research database.

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[22] Bonhorst D, et al. Prevalence of atrial fibrillation in the Portuguese population aged 40 and over:

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[24] INE – Instituto Nacional de Estatística. Available from: http://www.ine.pt/xportal/xmain?

xpid=INE&xpgid=ine_princindic

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APPENDIX

Population and number of hospitalisations by NUT II regions

YEAR NORTH CENTRE LISBON ALENTEJO ALGARVEPOP[24] NOH POP[24] NOH POP[24] NOH POP[24] NOH POP[24] NOH

2000 3 643 795 2588 2 325 186 2536 2 608 117 3749 765 742 1009 383 399 4852001 3 687 293 2741 2 348 397 2778 2 661 850 4021 776 585 1099 395 218 4172002 3 691 922 2741 2 354 552 2877 2 714 614 4159 767 983 1105 398 370 5142003 3 711 797 2935 2 366 691 3076 2 740 237 4425 767 549 1092 405 380 4932004 3 727 310 3308 2 376 609 3452 2 760 697 4574 767 679 1297 411 468 6452005 3 737 791 3402 2 382 448 3417 2 779 097 4755 765 971 1389 416 847 6232006 3 744 341 3658 2 385 891 3756 2 794 226 4472 764 285 1395 421 528 6192007 3 745 236 3502 2 385 911 3616 2 808 414 4368 760 933 1465 426 386 7502008 3 745 439 3670 2 383 284 4098 2 819 433 4421 757 069 1436 430 084 703

Supplementary Table I - Population (POP) and Number of Hospitalisations (NOH) from 2000 to 2008, by NUT II regions.Note: Only the values of the population referring to the year of 2001 are real values. All the others are official estimates

provided by INE.[24]

Chart 2 figures and 95% Confidence Intervals

AGE GROUP NORTH CENTRE LISBONNOH 95% CI NOH 95% CI NOH 95% CI

0-4 8,2 4,1 - 12,3 15,4 8,0 - 2,3 9,1 4,3 - 14,05-9 2,5 0,3 - 4,6 4,4 0,5 - 8,4 5,8 1,7 - 9,9

10-14 4,2 1,4 - 7,0 10,1 4,3 - 16,0 10,4 4,9 - 16,015-19 6,1 2,8 - 9,3 10,6 5,0 - 16,3 14,7 8,3 - 21,220-24 8,6 5,0 - 12,2 13,4 7,5 - 19,2 18,2 11,7 - 24,625-29 11,3 7,4 - 15,3 14,9 9,1 - 20,8 20,1 14,0 - 26,130-34 12,1 8,1 - 16,1 20,0 13,2 - 26,8 21,5 15,3 - 27,735-39 15,8 11,2 - 20,5 25,0 17,3 - 32,7 26,3 19,2 - 33,540-44 25,3 19,3 - 31,2 33,6 24,7 - 42,4 43,6 34,1 - 53,045-49 35,0 27,7 - 42,2 50,6 39,5 - 61,8 63,4 51,7 - 75,050-54 54,6 45,0 - 64,1 79,5 65,0 - 94,0 90,9 76,9 - 104,855-59 82,3 69,8 - 94,8 126,8 107,7 - 145,8 143,1 125,4 - 160,860-64 141,9 124,0 - 159,8 192,8 168,5 - 217,0 225,6 201,9 - 249,365-69 226,9 203,6 - 250,3 291,5 261,8 - 321,2 354,3 322,7 - 385,970-74 311,3 282,5 - 340,1 430,2 393,2 - 467,1 568,1 524,9 - 611,375-79 603,3 557,7 - 648,8 743,3 689,7 - 797,0 1010,1 943,9 - 1076,380-84 602,0 545,2 - 658,7 702,9 639,5 - 766,3 1059,5 973,7 - 1145,285 + 651,5 577,9 - 725,2 750,8 671,1 - 830,4 1203,1 1090,7 - 1315,4

AGE GROUP ALENTEJO ALGARVE

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NOH 95% CI NOH 95% CI0-4 8,8 -1,4 - 18,9 4,0 -4,5 - 12,55-9 6,0 -2,5 - 14,4 3,9 -5,1 - 12,9

10-14 8,5 -1,3 - 18,3 30,4 5,6 - 55,115-19 22,0 7,3 - 36,7 10,2 -3,4 - 23,820-24 18,5 6,2 - 30,7 10,9 -2,1 - 23,825-29 16,7 5,6 - 27,8 15,0 0,9 - 29,130-34 24,7 11,0 - 38,4 22,2 5,3 - 39,135-39 27,1 12,6 - 41,6 23,4 5,9 - 41,040-44 51,0 31,4 - 70,7 38,0 15,6 - 60,545-49 64,6 42,1 - 87,1 55,6 27,8 - 83,450-54 98,1 69,5 - 126,7 102,5 63,5 - 141,555-59 133,1 98,8 - 167,5 159,3 108,7 - 209,860-64 192,2 150,5 - 233,8 188,3 131,0 - 245,565-69 299,4 249,4 - 349,4 303,7 229,7 - 377,770-74 460,2 397,6 - 522,8 465,2 369,5 - 561,075-79 784,9 694,5 - 875,3 746,7 611,5 - 881,980-84 809,8 692,1 - 927,4 710,1 550,1 - 870,085 + 762,5 628,2 - 896,7 850,2 639,2 - 1061,2

Supplementary table II – NOH per a hundred thousand inhabitants, by age group and NUT II region (Chart 2) and 95% confidence intervals (adjusted to 100 000 inhabitants).

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