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Exercise Testing in Firefighters: Work Capacity and Cardiovascular Risk Assessment in a Low-Risk Population
Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för kardiovaskulär medicin. Linköpings universitet, Medicinska fakulteten.ORCID-id: 0000-0001-9196-7820
2019 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

Background. Firefighting is one of the most physically demanding occupations and it requires a high cardiorespiratory fitness level.

Pre-duty medical evaluation of firefighters includes fitness testing and assessment of cardiac health to ensure that firefighters meet the minimum physical fitness standard and to ensure that they are not at increased risk of cardiac events. The medical evaluation methods for Swedish firefighters are regulated by the Swedish Work Environment Authority and include a 6 min constant workload treadmill (TM) test for fitness evaluation in which the firefighter wears full smoke diving equipment and a maximal effort exercise electrocardiography test (ExECG) at cycle ergometer (CE) for assessment of cardiac health. Previously, fitness was also evaluated by cycle ergometry.

The standard parameter for evaluation of ischaemic heart disease (IHD) is exercise-induced ST depression. In general, exercise testing of asymptomatic low-risk individuals is discouraged due to low sensitivity and specificity for IHD, generating both false-positive and false-negative test results. Heart rate (HR) adjustment of the ST-segment response has been shown to be superior to simple ST depression to evaluate cardiac ischaemia in some populations, but has not been extensively evaluated in an occupational setting.

Methods. We retrospectively analysed a cohort of 774 firefighters who were asymptomatic at the time of the testing.

In paper I, test approval, HR response, and calculated oxygen uptake from TM tests and CE tests for 424 firefighters (44±10 years) were compared.

Paper II methodologically described the process for data extraction, processing, and calculation of ExECG data from a clinical database. Procedures for noise assessment, error checking, and computerized calculation of ST/HR parameters were described.

In paper III, ExECG and medical records of 521 male firefighters (44±10 years) were studied. During 8.4 ± 2.1 years of follow-up, IHD was verified angiographically in 12 subjects. The predictive value of HR-adjusted ST variables (ST/HR index, ST/HR slope, and ST/HR loop) for IHD was evaluated.

In paper IV, subjects with objectively verified IHD were excluded and factors associated with exercise-induced nonischaemic ST depression were studied in the remaining 509 males (46±11 years).

 

Results. The firefighters had an average maximal exercise capacity of 281 ± 36 W (range 186-467 W) achieved by incremental CE exercise. To enable comparison, the maximal workload was converted to the workload sustainable for 6 min. It was more common to pass the 6 min TM fitness test but to fail the supposedly equivalent CE test rather than vice versa.

Twenty percent of the firefighters developed an ST depression of ≥o.1 mV in at least one lead during exercise and half of the firefighters had a horizontal or downsloping ST depression. While an abnormal ST response associated with an increased risk for IHD only in V4, both an abnormal ST/HR index and an abnormal ST/HR slope associated with IHD in three leads each. Clockwise rotation of the ST/HR loop was infrequent in all precordial leads (1%), but it associated with an increased risk for IHD.

In the subgroup without evidence of coronary artery disease, age and the HR response associated with ST depression, whereas hypertension, hyperlipidaemia, diabetes, blood pressure response, and exercise capacity did not.

 

Conclusions. Even though the calculated oxygen uptake was higher for the TM test than for the supposedly equivalent CE test, the higher treadmill approval rate may indicate that the fitness requirement for Swedish firefighters has been lowered by changing the test modality.

Exercise-induced ST depression was common in asymptomatic physically active men, although there were only a few cases of IHD during follow-up. If performing ExECG in asymptomatic, low-risk populations, ST/HR analysis could be given more importance. However, the limited clinical value of ExECG in low-risk populations was emphasised and needs to be reconsidered.

In asymptomatic, physically active men without coronary artery disease, false-positive ST depressions can be partially explained by HR variables rather than by common cardiovascular risk factors and blood pressure response to exercise.

Ort, förlag, år, upplaga, sidor
Linköping: Linköping University Electronic Press, 2019. , s. 88
Serie
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1688
Nationell ämneskategori
Kardiologi
Identifikatorer
URN: urn:nbn:se:liu:diva-159757DOI: 10.3384/diss.diva-159757ISBN: 9789176850466 (tryckt)OAI: oai:DiVA.org:liu-159757DiVA, id: diva2:1344451
Disputation
2019-09-20, Berzeliussalen, Hus 463, Universitetssjukhuset, Linköping, 09:00 (Svenska)
Opponent
Handledare
Tillgänglig från: 2019-08-21 Skapad: 2019-08-21 Senast uppdaterad: 2019-08-21Bibliografiskt granskad
Delarbeten
1. Loaded treadmill walking and cycle ergometry to assess work capacity: a retrospective comparison in 424 firefighters.
Öppna denna publikation i ny flik eller fönster >>Loaded treadmill walking and cycle ergometry to assess work capacity: a retrospective comparison in 424 firefighters.
2017 (Engelska)Ingår i: Clinical Physiology and Functional Imaging, ISSN 1475-0961, E-ISSN 1475-097X, Vol. 37, nr 1, s. 37-44Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The fitness of firefighters is regularly evaluated using exercise tests. We aimed to compare, with respect to age and body composition, two test modalities for the assessment work capacity. A total of 424 Swedish firefighters with cycle ergometer (CE) and treadmill (TM) tests available from Jan 2004 to Dec 2010 were included. We compared results from CE (6 min at 200 W, 250 W or incremental ramp exercise) with TM (6 min at 8° inclination, 4·5 km h(-1) or faster, wearing 24-kg protective equipment). Oxygen requirements were estimated by prediction equations. It was more common to pass the TM test and fail the supposedly equivalent CE test (20%), than vice versa (0·5%), P<0·001. Low age and tall stature were significant predictors of passing both CE and TM tests (P<0·05), while low body mass predicted accomplishment of TM test only (P = 0·006). Firefighters who passed the TM but failed the supposedly equivalent CE test within 12 months had significantly lower body mass, lower BMI, lower BSA and shorter stature than did those who passed both tests. Calculated oxygen uptake was higher in TM tests compared with corresponding CE tests (P<0·001). Body constitution affected approval differently depending on the test modality. A higher approval rate in TM testing suggests lower cardiorespiratory requirements compared with CE testing, even though estimated oxygen uptake was higher during TM testing. The relevance of our findings in relation to the occupational demands needs reconsidering.

Nationell ämneskategori
Idrottsvetenskap
Identifikatorer
urn:nbn:se:liu:diva-120004 (URN)10.1111/cpf.12265 (DOI)000390688200006 ()26096157 (PubMedID)
Anmärkning

Funding agencies: ALF grants; County Council of Ostergotland, Sweden; Olav Axelssons memorial fund

Tillgänglig från: 2015-07-02 Skapad: 2015-07-02 Senast uppdaterad: 2019-08-21
2. ST/HR variables in firefighter exercise ECG: relation to ischemic heart disease
Öppna denna publikation i ny flik eller fönster >>ST/HR variables in firefighter exercise ECG: relation to ischemic heart disease
2019 (Engelska)Ingår i: Physiological Reports, E-ISSN 2051-817X, Vol. 7, nr 2, artikel-id e13968Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Exercise electrocardiography (ExECG) is regularly performed by Swedish firefighters by law. Heart rate-corrected analysis of ST segment variables (ST/HR) has shown improved prediction of ischemic heart disease (IHD) compared to ST depression alone. This has not previously been extensively studied in asymptomatic persons with a low probability of IHD. We therefore evaluated the predictive performance of ST/HR analysis in firefighter ExECG. ExECG was studied in 521 male firefighters. During 8.4 ± 2.1 years, 2.3% (n = 12) were verified with IHD by catheterization or myocardial scintigraphy (age 51.5 ± 5.5 years) and were compared with firefighters without imaging proof of IHD (44.2 ± 10.1 years). The predictive value of ST depression, ST/HR index, ST/HR slope, and area and rotation of the ST/HR loop was calculated as age-adjusted odds ratios (OR), in 10 ECG leads. Predictive accuracy was analyzed with receiver operating characteristics (ROC) analysis. ST/HR index ≤-1.6 μV/bpm and ST/HR slope ≤-2.4 μV/bpm were associated with increased IHD risk in three individual leads (all OR > 1.0, P < 0.05). ST/HR loop area lower than the fifth percentile of non-IHD subjects indicated IHD risk in V4, V5, aVF, II, and -aVR (P < 0.05). ST depression ≤-0.1 mV was associated with IHD only in V4 (OR, 9.6, CI, 2.3-40.0). ROC analysis of each of these variables yielded areas under the curve of 0.72 or lower for all variables and leads. Clockwise-rotated ST/HR loops was associated with increased risk in most leads compared to counterclockwise rotation. The limited clinical value of ExECG in low-risk populations was emphasized, but if performed, ST/HR analysis should probably be given more importance.

Ort, förlag, år, upplaga, sidor
John Wiley & Sons, 2019
Nyckelord
Electrocardiography, ST depression, ST/HR variables, low risk
Nationell ämneskategori
Kardiologi
Identifikatorer
urn:nbn:se:liu:diva-159752 (URN)10.14814/phy2.13968 (DOI)000457188800007 ()30688031 (PubMedID)2-s2.0-85060598157 (Scopus ID)
Tillgänglig från: 2019-08-20 Skapad: 2019-08-20 Senast uppdaterad: 2019-08-26Bibliografiskt granskad
3. Exercise-induced ST depression in an asymptomatic population without coronary artery disease
Öppna denna publikation i ny flik eller fönster >>Exercise-induced ST depression in an asymptomatic population without coronary artery disease
2019 (Engelska)Ingår i: Scandinavian Cardiovascular Journal, ISSN 1401-7431, E-ISSN 1651-2006, Vol. 53, nr 4, s. 206-212Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Objectives. Exercise electrocardiogram (ExECG) in low risk populations frequently generates false positive ST depression. We aimed to characterize factors that are associated with exercise-induced ST depression in asymptomatic men without coronary artery disease. Design. Cycle ergometer exercise tests from 509 male firefighters without imaging proof of significant coronary artery disease were analysed. Analysed test data included heart rate at rest before exercise, and workload, blood pressure, heart rate, ST depression and ST segment slope at peak exercise. ST depression of amp;gt;0.1 mV was considered significant (STdep). With a mean follow-up of 6.1 +/- 1.7 years, medical records were reviewed for cardiovascular diagnoses, hyperlipidemia and diabetes. Logistic regression analysis was used for risk assessment. Results. In total, 22% had STdep in amp;gt;= 1 lead. Subjects with STdep were older than those with normal ExECG (p amp;lt; .001). Downsloping STdep was more common in extremity leads (9%) than in precordial leads (2%). STdep was categorized according to location (precordial/extremity) and slope direction into eight categories. Larger age-adjusted heart rate increase predicted STdep in seven categories (p amp;lt; .05). Age-adjusted peak heart rate correlated with STdep in five categories, predominantly where the ST slope was positive. Peak blood pressure and exercise capacity were both associated with STdep in few categories. We found no association between STdep and hypertension, hyperlipidemia or diabetes (all p amp;gt; .05). Conclusions. In asymptomatic men with a physically demanding occupation and no coronary artery disease, both age and heart rate response were associated with ST depression, whereas common cardiovascular risk factors, blood pressure response and exercise capacity were not.

Ort, förlag, år, upplaga, sidor
Taylor & Francis, 2019
Nyckelord
Stress test; false positive; electrocardiography; heart rate; ST segment deviation; firefighters; low risk
Nationell ämneskategori
Kardiologi
Identifikatorer
urn:nbn:se:liu:diva-158872 (URN)10.1080/14017431.2019.1626021 (DOI)000472278700001 ()31144537 (PubMedID)
Anmärkning

Funding Agencies|County Council of Ostergotland, Sweden [LIO-711261]; ALF grant [700731]

Tillgänglig från: 2019-07-15 Skapad: 2019-07-15 Senast uppdaterad: 2019-11-07

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