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European Journal of Heart Failure 2007 9(1):55-61; doi:10.1016/j.ejheart.2006.04.003
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© 2007 European Society of Cardiology

A critical re-appraisal of different ways of selecting ambulatory patients with suspected heart failure for echocardiography

Sanjay Jeyaseelana,*, Barclay M. Goudieb, Stuart D. Pringlec, Peter T. Donnand, Frank M. Sullivand and Allan D. Strutherse

a Department of Cardiology, Charing Cross Hospital Fulham Palace Road, London, W6 8RF, UK
b Westgate Health Centre Dundee, UK
c Department of Cardiology, Ninewells Hospital Dundee, UK
d Division of Community Health Sciences, University of Dundee UK
e Division of Medicine and Therapeutics, University of Dundee, Ninewells Hospital and Medical School Dundee, UK

* Corresponding author. Tel.: +44 2088461234. E-mail address: sjeyaseelan{at}doctors.org.uk


   Abstract
Top
 Abstract
1. Introduction
 2. Methods
 3. Results
 4. Discussion
 References
 
Background: ECG and BNP have been assessed as screening tests for LVSD and heart failure. However, echocardiography also provides information about valvular disease and LVH. We assessed how good these screening tests are in identifying whether the subsequent echocardiogram will have any significant abnormality.

Aims: To re-appraise the ECG and BNP as screening tests for echocardiography since there are important practical deficiencies in our current knowledge in this area.

Methods: General practitioners referred suspected heart failure patients for clinical assessment, echocardiography, electrocardiography, and BNP measurement. The accuracy of each screening test and combinations of screening tests were calculated for LVSD, heart failure, valvular disease, and LVH.

Results: The sensitivities of the ECG for LVSD, heart failure, LVH and valvular disease were 97%, 95%, 76%, and 69%, respectively. The corresponding figures for BNP were 86%, 82%, 59%, and 48%, respectively. When patients with atrial fibrillation and murmurs were excluded, the values for ECG were 94%, 87%, 53%, and 55%, while for BNP they were 83%, 73%, 50%, and 32%.

Conclusions: ECG interpretation and BNP are adequate screening tests to detect LVSD or heart failure but fail to screen for other echocardiographic abnormalities, like valvular disease and LVH. This remains the case even if patients with atrial fibrillation or heart murmurs are excluded on the basis that they require echocardiography anyway.

Key Words: Echocardiography • Heart failure • β-type natriuretic peptide • Electrocardiography

Received August 11, 2005; Revised February 19, 2006; Accepted April 10, 2006


   1. Introduction
Top
 Abstract
 1. Introduction
2. Methods
 3. Results
 4. Discussion
 References
 
Heart failure due to left ventricular systolic dysfunction (LVSD) is a disabling, deadly and costly condition [1-5]. It is vital to make an accurate diagnosis as ACE inhibitors and β-blockers can markedly improve morbidity and mortality [6-9]. However, diagnosis can be difficult as the clinical symptoms and signs of heart failure vary which means that a high proportion of patients suspected to have heart failure by general practitioners/family medicine physicians do not actually have the condition [10-14]. Echocardiography is the key investigation [15], but access to echocardiography is limited in many countries and patchy in many developed countries such that diuretics are often prescribed without echocardiographic confirmation [16,17]. Another problem with performing echocardiography on all suspected heart failure patients in the community is that it can be costly because a high proportion of such patients turn out not to have heart failure. Therefore screening tests, such as 12-lead electrocardiography and brain natriuretic peptide [BNP], have been recommended in guidelines, such as the UK NICE guidelines, in order to help select those patients who should proceed to echocardiography [18].

The 12-lead electrocardiogram (ECG) has been suggested as a screening test as a normal ECG excludes the presence of LVSD [19,20]. BNP, a hormone released by the left ventricle, has been suggested as another screening test [12,21,22].

The many papers that have already assessed the value of these screening tests have had three weaknesses. Firstly, they have usually limited their analysis to whether these tests identify LVSD or heart failure only. This is understandable, but such an analysis ignores other structural abnormalities seen on echocardiography that might lead to a change in treatment. In other words, LVSD is not the only important finding from an echocardiogram (ECHO), even in this group of patients since an ECHO might pick up, for example, valve disease that is not causing symptoms, but does warrant antibiotic prophylaxis and surveillance. Secondly, patients with atrial fibrillation or cardiac murmurs deserve echocardiography in their own right and should really be excluded when considering the value of these two screening tests. Thirdly, many non-specialists rely on the ECG machine interpretation rather than their own ECG interpreting skills and yet no previous work has assessed the ECG machine interpretation itself. We therefore have set out to correct these three deficiencies. We here assess the ability of BNP and of the ECG to pre-screen patients for any important echocardiographic abnormality and not just for LVSD, as previous work has done. The important echocardiographic abnormalities were LVSD, clinical heart failure, valvular disease needing surveillance or antibiotic prophylaxis and finally left ventricular hypertrophy needing better blood pressure control. We also did an analysis where patients with atrial fibrillation or cardiac murmurs were excluded because they deserve echocardiography anyway. We also assessed the accuracy or otherwise of ECG machine interpretation itself.


   2. Methods
Top
 Abstract
 1. Introduction
 2. Methods
3. Results
 4. Discussion
 References
 
2.1. Practices and participants
A total of 26 general practitioner surgeries in the community in the Dundee, Tayside and North East Fife areas of Scotland, UK were asked to participate. Recruitment of patients occurred from June 2002 to September 2003. Patients who had symptoms or signs of dyspnoea, ankle oedema and lethargy and were suspected of having heart failure by their general practitioner and not been previously diagnosed with an ECHO were recruited into the study. No general practitioners were trained specifically for the identification of such patients prior to the study as we wished to assess the performance of these tests in the real world. The simplicity of the criteria for recruitment into the study ensured consistency in the referral pattern throughout the study. Informed written consent was obtained from patients. The Tayside Research Ethics Committee and North East Fife Research Committee approved the ethics of this study. The investigation conforms with principles outlined in the Declaration of Helsinki (Br Med J 1964;ii:177).

2.2. Data collection
A structured history and examination was performed and documented by S.J. for each patient. S.J. performed echocardiography in the community using a Siemens Cypress® system with a 2.5 MHz probe. Echocardiography was performed in the standard way, with the patients placed in the left lateral decubitus position and 2D, M mode and colour Doppler techniques were used. Fractional shortening using M Mode echocardiography and ejection fraction using Simpson's method of discs, or visual assessment were performed to assess left ventricular function. The ECHOs were reported at the end of examination. S.J. used the E-lite 6.34® system for 12-lead electrocardiography and interpreted the ECGs immediately in the community. The E-lite 6.34® system has an ECG interpretation package that uses the Minnesota criteria. The report of the E-lite 6.34® system was recorded also. The Biosite Triage® fluorescence immunoassay was used by S.J. for BNP measurement in the community.

2.3. Data definition
LVSD was defined as a fractional shortening, using M mode echocardiography, of less than 25% or ejection fraction, using Simpson's method of discs, of less than 50% was used as the cut-off for the presence of LVSD. Visual assessment of left ventricular systolic function was done when fractional shortening or ejection fraction calculations could not be done [23].

Clinical heart failure was defined using the European Society of Cardiology (ESC) guidelines: "The symptoms or signs of heart failure and the presence of a cardiac abnormality" [24]. This definition includes patients with LVSD, cor pulmonale, and valvular disease causing heart failure. A panel, A Struthers, S Jeyaseelan and a cardiology research fellow, by consensus, decided which patients had clinical heart failure using all the available clinical and echocardiographic data except the ECG and the BNP result. As the definitions and parameters for diagnosing diastolic dysfunction heart failure had not been established at the time of recruitment, we did not investigate for this.

Left ventricular hypertrophy was defined as the interventricular septal wall and posterior wall thickness greater than 12 mm in diastole as measured in the M mode parasternal log axis view at the level of the mitral valve leaflet tips.

Valvular disease of note was defined as any valve disease that required action whether it was surveillance, antibiotic prophylaxis or valve replacement as recommended by the American College of Cardiology guidelines [25]. This categorisation was performed by S.J.

The electrocardiogram was considered normal if it was sinus rhythm 60-100/min with an axis –30° to +90°, and the PR interval <0.2 s, QRS duration <0.12 s, QTc interval <0.42 s. The morphology of the P wave, QRS complex, ST segment, and T wave had to be normal also. Any electrocardiogram having any feature different from the stated definition of a normal electrocardiogram was considered abnormal. Atrial fibrillation, left bundle branch block, left ventricular hypertrophy, pathological Q waves, left axis deviation, and T wave inversion on electrocardiography were consider major abnormalities.

BNP analysis was considered normal if the level was less than or equal to 100 pg/ml as recommended by Biosite®.

2.4. Data analysis
Calculations for the sensitivity, specificity, positive predictive value, and negative predictive value was done for individual screening tests and combination of screening tests for the detection of LVSD, clinical heart failure, left ventricular hypertrophy, and valvular disease. For individual screening tests, an abnormal test indicated referral for echocardiography and a normal test indicated that echocardiography was not needed. For a combination of screening tests, when one or more test was abnormal it was considered as an indication for echocardiography. Only when both tests in a screening combination were normal, was it considered that echocardiography was not indicated. Data was entered into Microsoft Excel® and Microsoft SPSS® 11.0.

A preliminary economic analysis is presented to put the results into context. The costs of an ECG, BNP and echocardiography were £32, £40 and £250, respectively, and were obtained from the Finance Department of Ninewells Hospital. The calculations of the costs for each screening was done with all patients having a test/combination of tests e.g. for ECG (458 ECGx£32=£14656) plus the cost of an ECHO (£250) for each ECG determined as abnormal. The analysis was repeated with patients noted to have atrial fibrillation and/or patients with murmurs upon cardiac auscultation removed from the calculations as these patients should have an ECHO irrespective of the screening tests results. Likewise, patients with murmurs upon cardiac auscultation were also removed from the calculations as these patients should have an ECHO too. Removing those with atrial fibrillation or murmurs enabled us to focus on a group of patients where general practitioners have genuine clinical uncertainty over whether an ECHO should be done or not.


   3. Results
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
4. Discussion
 References
 
458 symptomatic patients suspected by their general practitioner of having heart failure were referred for assessment and echocardiography. The characteristics of the 458 patients are shown in Table 1. Sixty percent of patients referred were female and the majority was over 65 years of age. As recruitment specified symptomatic patients, all patients complained of dyspnoea, lethargy and/or ankle swelling. The prevalence of left ventricular systolic dysfunction in this cohort was 8.1%. Atrial fibrillation was noted in 42 (9%) patients and an audible murmur in 95 (21%) patients. There were 37 (8%), 58 (13%), 44 (10%), and 209 (46%) cases of LVSD, clinical heart failure, left ventricular hypertrophy and valvular disease, respectively.


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  		Table 1 Characteristics of the 458 patients referred

 
The sensitivities, specificities, positive predictive values, and negative predictive values of individual and of combination screening tests for LVSD, clinical heart failure, echocardiographic left ventricular hypertrophy, and valvular disease are shown in Table 2.


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  		Table 2 Results, costs, and cases missed using different screening tests in all suspected heart failure patients

 
The sensitivity and specificity of ECG were: 97% and 50% for LVSD, 95% and 52% for clinical heart failure, 76% and 48% for left ventricular hypertrophy, and 69% and 59% for valvular disease. The sensitivity and specificity of machine ECG were: 91% and 21% for LVSD, 94% and 22% for clinical heart failure, 90% and 21% for left ventricular hypertrophy, and 86% and 25% for valvular disease. The sensitivity and specificity of BNP were: 86% and 74% for LVSD, 82% and 76% for clinical heart failure, 59% and 73% for left ventricular hypertrophy, and 48% and 84% for valvular disease. Table 2 also shows the costs per 100 patients investigated, costs per abnormal case detected, and the percentage of cases missed using individual and combination screening tests for LVSD, clinical heart failure, echocardiographic left ventricular hypertrophy, and valvular disease.

Table 3 shows the adjustment to the results, costs, and cases missed after those patients with atrial fibrillation and/or a cardiac murmur on examination were removed from analysis. The sensitivity and specificity of ECG were: 94% and 60% for LVSD, 87% and 61% for clinical heart failure, 53% and 58% for left ventricular hypertrophy, and 55% and 62% for valvular disease. The sensitivity and specificity of machine ECG were: 82% and 25% for LVSD, 87% and 26% for clinical heart failure, 89% and 26% for left ventricular hypertrophy, and 81% and 27% for valvular disease. The sensitivity and specificity of BNP were: 83% and 85% for LVSD, 73% and 85% for clinical heart failure, 50% and 83% for left ventricular hypertrophy, and 32% and 89% for valvular disease.


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  		Table 3 Results, costs, and cases missed using different screening tests in all suspected heart failure patients except those with atrial fibrillation and/or a cardiac murmur

 

   4. Discussion
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
 4. Discussion
References
 
This study demonstrates that open access echocardiography detects both significant valvular disease and LVH more frequently than LVSD in patients referred from the community with symptoms suggestive of heart failure. ECG and BNP are effective pre-echo screening tests for LVSD and clinical heart failure but are of no value in identifying patients with other cardiac pathologies.

In order to decide whether suspected heart failure patients should have echocardiography, we focused on the wider remit of how these screening tests performed in picking up any echocardiographic abnormality. Obviously, if all patients had echocardiography, there would be no missed cases of LVSD, clinical heart failure, left ventricular hypertrophy, or valvular disease. The total cost of echocardiography for all patients would be £25000. For screening tests to be useful, a tradeoff is to be expected whereby total costs can be reduced but at the price of missing a certain number of cases.

Our results, for detecting LVSD, are in line with previous work. An ECG is excellent for screening for LVSD, with only 2.9% of cases being missed and saving £8268/100 cases investigated. Similarly good results were obtained, even when patients with atrial fibrillation and murmurs were excluded. Restricting the ECG cut-off to major abnormalities only led to a larger percentage (15%) of cases of LVSD being missed.

The E-lite 6.34® ECG machine interpretation package was not useful for screening for LVSD as it saved only a tiny amount (£1737/100 patients) and yet still missed 8.9% of cases. BNP, when screening for LVSD, did lead to a saving of £13460/100 patients investigated, but this was at the expense of 14.3% of cases of LVSD being missed. As 67.5% of the patients were on diuretics already, this may have reduced the effectiveness of BNP as a screening test [22]. However a sensitivity of 80% for BNP is stated in the Triage® BNP test booklet, so our results are as expected. Combinations of screening tests, such as an ECG and BNP, did not miss any cases of LVSD. However, the costs of combination screening tests nearly approached and in one case exceeded that of performing echocardiography on all patients. The results for clinical heart failure were essentially similar to those for LVSD.

However, the screening tests both did badly in detecting cases of clinically important valvular disease and echocardiographic left ventricular hypertrophy. Presumably valvular disease and left ventricular hypertrophy did not cause enough of an increase in the intracardiac pressure to cause a diagnostically clear rise in BNP level. Mild to moderate valvular disease judged by S.J. to require antibiotic prophylaxis or surveillance was not adequately detected by either the ECG or BNP. The ECG also missed over 30% cases of echocardiographic left ventricular hypertrophy. It could be argued that detecting left ventricular hypertrophy is worthwhile as risk returns to normal if it regresses fully and this appears to be very cost-effective [25]. Therefore, if we wanted to detect valvular disease and left ventricular hypertrophy as well as clinical heart failure, it would be necessary to perform echocardiography on all patients, since the screening tests do not perform well enough for this purpose. Table 3 illustrates the bottom line for policymakers. If we exclude patients with atrial fibrillation or heart murmurs who deserve an ECHO anyway, the choice is either to spend £25000 by performing echocardiography on everyone and missing no abnormalities or to use an ECG screening test, whereby the total cost will be reduced to £13927 at the price of missing 6% of left ventricular systolic dysfunction cases, 13% of heart failure cases, 45% of valvular disease and 45% of left ventricular hypertrophy. Similar figures were found for BNP, i.e. BNP pre-screening would cost only £11564, but miss 14% of LVSD cases, 18% of heart failure cases, 52% of valvular disease and 41% of left ventricular hypertrophy. Hopefully, this kind of information will help health planners to make decisions on how best to spend available resources. This information should also help inform future analyses designed to assess the cost-effectiveness of detecting and treating valvular disease and left ventricular hypertrophy in these patients. One analysis suggests that detecting left ventricular hypertrophy could be cost-effective but no cost-effectiveness analysis is available for valve disease in this population [26]. The limitations of our study are that S.J. interpreted ECG after performing the echocardiography and this may have affected its interpretation. Our results do reflect the ideal situation where an independent cardiologist interpreted the ECG.

In conclusion, the ECG and, to a lesser extent, BNP are adequate screening tests to detect LVSD or heart failure but they fail to detect other echocardiographic abnormalities, like valvular disease and left ventricular hypertrophy, which might influence the patient's wider treatment. This failure of the screening tests was still present even when patients with murmurs or atrial fibrillation were excluded. Screening tests are therefore not useful at detecting these extra echocardiographic abnormalities. This infers that all suspected patients should have echocardiography, but this would generally double the total cost requirements. Future analyses should examine whether doubling the investigation costs and picking up these extra abnormalities would cost-effectively alter future cardiovascular events.


   Acknowledgements
 
We thank the British Heart Foundation for financial support.


   References
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
 4. Discussion
 References
 

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