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European Journal of Heart Failure 2003 5(6):767-774; doi:10.1016/S1388-9842(03)00155-7
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© 2003 European Society of Cardiology

Screening for left ventricular dysfunction using a hand-carried cardiac ultrasound device

Eleni C. Vourvouria, Arend F.L. Schinkela, Jos R.T.C. Roelandta, Frans Boomsmab, Georgios Sianosc, Manolis Bountioukosa, Fabiola B. Sozzia, Vittoria Rizzelloa, Jeroen J. Baxa,d, Haralambos I. Karvounisa and Don Poldermansa,*

a Department of Cardiology, Erasmus Medical Centre Rotterdam, The Netherlands
b Department of Interventional Cardiology, Erasmus Medical Centre Rotterdam, The Netherlands
c Thoraxcentre and Department of Internal Medicine, Erasmus Medical Centre Rotterdam, The Netherlands
d Department of Cardiology, Leiden Medical Centre Leiden, The Netherlands

* Corresponding author. Thoraxcentre, Room Ba 300, Erasmus Medical Centre, Rotterdam, Dr. Molewaterplein 40, 3015 GD Rotterdam, The Netherlands. Tel.: +31-10-463-9222; fax: +31-10-436-2995 E-mail address: d.poldermans{at}erasmusmc.nl


   Abstract
Top
 Abstract
1. Introduction
 2. Methods
 3. Results
 4. Discussion
 5. Conclusion
 References
 
Background: The hand-carried cardiac ultrasound (HCU) device is a recently introduced imaging device, which may be potentially useful in the primary care setting.

Aim: To test the screening potential of a HCU for the detection of left ventricular (LV) dysfunction by evaluating LV ejection fraction (LVEF) and inferior vena cava (IVC) collapse. Standard echocardiographic system (SE) and plasma brain natriuretic peptide (BNP) measurements were used as a reference.

Methods: Eighty-eight consecutive patients (56 male, aged 59±12 years) with suspected LV dysfunction were enrolled in the study. The HCU-LVEF was visually estimated and the SE-LVEF was derived by the Simpson's biplane method. A LVEF <40% represented LV dysfunction. An IVC collapse of <50% and BNP levels ≥15 pmol/l were considered abnormal. The correlation of HCU-LVEF, HCU-IVC and BNP to the SE-LVEF and SE-IVC was analysed independently using 2x2 tables.

Results: Six patients were excluded because of poor echo images. 19/82 patients had LV dysfunction. The HCU and BNP could identify 17 and 18 out of these 19 patients, respectively. The agreement for LVEF and IVC collapse between SE and HCU was 96% for both parameters. The sensitivity of IVC collapse, HCU-LVEF and BNP in identifying patients with LV dysfunction was 26, 89 and 94%, respectively.

Conclusion: A HCU device can reliably be used as a screening tool for LV dysfunction.

Key Words: SE, standard echocardiographic device • BNP, brain natriuretic peptide • IVC, inferior vena cava • IVC-CI, inferior vena cava collapse index • LV, left ventricular • EF, ejection fraction • 2D, two-dimensional

Received October 8, 2002; Revised March 15, 2003; Accepted May 1, 2003


   1. Introduction
Top
 Abstract
 1. Introduction
2. Methods
 3. Results
 4. Discussion
 5. Conclusion
 References
 
Congestive heart failure is a disease associated with high morbidity, mortality and cost [1–3]. One of the main precursor forms of heart failure is left ventricular (LV) dysfunction, which in the early stages is asymptomatic. Appropriate and early treatment can delay if not prevent the development of chronic heart failure [4,5] which makes screening for this disorder worthwhile [6]. However, clinical diagnosis of LV dysfunction with the existing conventional criteria is often difficult and inaccurate [7,8].

Brain natriuretic peptide (BNP) is a cardiac neurohormone secreted in the ventricles as a response to volume and pressure overload [9,10] and may be elevated in patients with LV dysfunction [11,12]. Studies have suggested measurement of plasma BNP levels as a potential new screening method for the diagnosis of patients with impaired LV function [11–14].

Echocardiography on the other hand, is known to be the screening method of choice for LV dysfunction [2,15,16] but is considered to be impractical and costly [12,13,17]. Furthermore, the inspiratory changes in diameter of the inferior vena cava (IVC) collapse as an indicator of right-sided filling pressure can be measured by echocardiography [18,19]. However, the value of this parameter as a marker of LV dysfunction has not previously been studied.

Hand-carried cardiac ultrasound (HCU) devices aim to bring echocardiography into the community setting, allowing screening programmes for various cardiac pathologies [20–22].

The purpose of the current study was to test the diagnostic potential of a HCU device (SonoHeartTM, SonoSite Inc. and OptiGoTM, Philips Medical Systems) in screening for LV dysfunction, by evaluating LV ejection fraction (LVEF) and the IVC collapse. A standard echocardiographic system (SE) to evaluate LV function and IVC collapse, and measurement of BNP concentration were used as a reference.

1.1. The HCU device
Two HCU devices were used: the OptiGoTM (Philips Medical Systems) and the SonoHeartTM Plus (SonoSite Inc.) (Fig. 1).


Figure 1
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  		Fig. 1 Photograph of the HCU devices used in this study. To the left, the OptiGoTM and to the right, the SonoHeartTM Plus.

 
Both devices operate on a rechargeable battery or AC current and have measurement packages including linear measurement callipers. SonoHeartTM has a storage memory of 50 images, which can be downloaded into a Personal Computer and can also be connected to a video-recorder, a printer or an external monitor. The OptiGoTM uses a CompactFlash card to archive images, which can also be downloaded into a Personal Computer. Colour flow Power Doppler and Colour flow Doppler are integrated into the SonoHeartTM and OptiGoTM, respectively. SonoHeartTM Plus has in addition M-Mode and pulsed Doppler.


   2. Methods
Top
 Abstract
 1. Introduction
 2. Methods
3. Results
 4. Discussion
 5. Conclusion
 References
 
2.1. Study patients
The study was approved by the Institutional Medical Ethical Committee and informed consent for the study was obtained from all patients.

Eighty-eight consecutive patients referred from the outpatient cardiology clinic to the echo lab with suspected LV dysfunction were included in the study. All patients were clinically stable and cardiac medication was unchanged during the study period.

Patients’ characteristics are listed in Table 1.


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  		Table 1 Baseline characteristics of the 88 patients with suspected LV dysfunction

 
2.2. Study protocol
2.2.1. Echocardiographic data
The study protocol consisted of two consecutive echocardiographic examinations: one examination using a SE (Sonos 5500, Andover, Mass) and the other using a HCU device (SonoHeartTM, SonoSite Inc. or OptiGoTM, Philips Medical Systems). All images were stored in the memory of the portable devices and as digital loops onto optical discs for the SE. Both studies were performed on the same day by two independent cardiologists, blinded to each other's results and to the medical history or clinical status of the patient.

2.3. LVEF evaluation using SE
Images were acquired with the SE at standard cardiac views [23]. We used LVEF, derived by the previously validated modified Simpson's biplane discs method [24], as our gold standard for classification of LV function. The analysis was performed on a computerised off-line station by an independent third observer blinded to the HCU device and BNP results. The cinematic frames corresponding to end-diastole and end-systole were selected from two-chamber and four-chamber views. Normal/mildly reduced LV systolic function was defined by an EF >=40%, whereas a LVEF <40% represented a severely abnormal LV systolic function [25].

2.4. LVEF evaluation using a HCU device
Global LV systolic function was estimated visually from images acquired at the same cardiac views with the SE. Normal/mildly reduced LV systolic function was defined by an estimated EF >=40%, whereas a LVEF <40% represented a severely abnormal LV systolic function [25].

2.5. IVC measurements
The expiratory and inspiratory IVC diameter and percent collapse were measured with the SE and the HCU device from the subcostal view with the patient in supine position. The diameter was measured within 2 cm of the right atrium (RA) origin of IVC. In case of quiet respiration and minimal IVC variation, the patient was asked to suddenly inhale (‘sniff’) and the subsequent IVC was measured (Fig. 2). The collapse index (IVC-CI) was calculated by taking the difference of the two dimensions and dividing it by the end-expiratory IVC dimensions. An IVC-CI <50% represented an elevated RA pressure (>10 mmHg) [19].


Figure 2
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  		Fig. 2 Imaging of the IVC during expiration (left) and inspiration (right). A collapse of less than 50% is present, indicating an elevated right-sided filling pressure (OptiGoTM).

 
2.5.1. Measurement of plasma BNP
Before the echocardiographic assessments, blood samples were obtained from the antecubital vein of all patients after they had rested for at least 15 min. Blood was collected into chilled tubes containing edetic acid (EDTA) and aprotinin (1.9 mg and 100 kl U/ml blood, respectively). Plasma samples were centrifuged promptly (1111xg for 10 min) and stored at –80 °C until final analysis. BNP was measured using a standard, commercially available, immunoradiometric assay kit (Shionoria BNP kit, Shionogi, Osaka, Japan). Results of the BNP test were obtained within 1 month of the echocardiographic examination. A BNP level of >=15 pmol/l was considered to represent severely abnormal LV function [26].

2.5.2. Invasive hemodynamic data
Right-sided heart catheterisation was performed in a subgroup of 20 patients to compare invasively obtained RA pressure measurements to the RA pressure estimated echocardiographically by the IVC collapse. An IVC-CI <50% represented an elevated RA pressure (>10 mmHg).

The hemodynamic data were acquired with fluid-filled Swan-Ganz catheters (Baxter Healthcare Corp., Edwards Critical Care Division, Irvine, CA) immediately after the echocardiographic study with the HCU device and before any invasive interventions. Normal RA pressure was considered as <=10 mmHg. Medication remained unchanged during the study period. Blood samples for BNP were obtained from all the patients prior to invasive interventions and results were compared to invasive data.

2.6. Statistical analysis
Descriptive statistics were reported as mean±S.D. for continuous variables and as percentages for categorical variables. The agreement for the two examination techniques in evaluating LVEF and IVC-CI measurements was assessed from 2x2 tables using weighted {kappa} statistics. The same statistical method was used for the agreement between BNP measurements vs. LVEF and between RA pressure measured invasively vs. the echocardiographically estimated RA pressure. {kappa} values <0.4, between 0.4 and 0.75, and >0.75 were considered to represent poor, fair to good and excellent agreement, respectively, based on Fleiss's classification [27]. Differences between proportions were compared using the Chi-square test. The Student's t-test was used to compare continuous variables. A value of P<0.05 was considered statistically significant.


   3. Results
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
4. Discussion
 5. Conclusion
 References
 
3.1. Patients characteristics
Eighty-eight patients (56 male, aged 59±12 years) referred for echocardiography with suspected LV dysfunction were included in the study. Out of the initial 88 patients, 6 were excluded from the study due to either poor visualisation of the LV (2 patients) or IVC (4 patients) leaving 82 patients included in the analysis. Sixty-four of the 82 patients were classified as New York Heart Association functional class I or II, 14 were class III and 4 patients were class IV. An investigator, blinded to the results of the echocardiographic examinations, performed this classification. Of 18 patients with congestive heart failure, 15 had ischemic cardiomyopathy (LVEF <40% due to chronic coronary artery disease) and 3 patients had non-ischemic cardiomyopathy.

3.2. Echocardiographic data
Of the 82 patients included in the analysis, 19 had an EF <40% as assessed by the SE Simpson's biplane discs method. The HCU examination detected 17/19 patients, showing a sensitivity of 89% and specificity of 98% in the diagnosis of LV dysfunction (Table 2A). Table 3 shows the agreement between the NYHA functional classification and the echocardiographic results.


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  		Table 2 Agreement between (A) a HCU device and (B) BNP measurements and a standard echo (SE) in the assessment of LVEF

 


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  		Table 3 Agreement between the NYHA functional classification and echocardiographic results

 
The agreement between the two imaging techniques for the IVC-CI was very good (96%, {kappa}=0.87) (Table 4A). However, there was no correlation between IVC-CI and LVEF assessed by SE (agreement: 73%, {kappa}=0.15) (Table 4B). Eleven out of the 14 patients with abnormal (SE) IVC collapse had depressed RV systolic function.


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  		Table 4 (A) Agreement between a HCU device and a standard echo (SE) in the assessment of IVC collapse and (B) correlation between IVC collapse and LVEF

 
3.3. BNP data
Results of BNP testing were available for all 82 patients. BNP levels were elevated in 18 out of the 19 patients with LV dysfunction. However, in six patients with normal LVEF the BNP levels were elevated resulting in a sensitivity of BNP in diagnosing patients with LV dysfunction of 95% and a specificity of 90% (Table 2B).

3.4. Subgroup analysis
Twenty patients underwent right-sided heart catheterisation as part of the diagnostic procedure. The characteristics of these patients are shown in Table 5. The mean RA pressure measured invasively was 8±9 mmHg. The agreement for the detection of elevated RA pressure between the two techniques was 95%, {kappa}=0.9 (Table 6). The agreement between BNP and invasively measured RA pressure was poor (60%, {kappa}=0.29).


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  		Table 5 Baseline characteristics of the 20 patients that underwent right-sided heart catheterisation

 


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  		Table 6 Agreement between echocardiographically vs. invasively assessed right atrium pressure (RAP)

 

   4. Discussion
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
 4. Discussion
5. Conclusion
 References
 
Heart failure and LV systolic dysfunction occur frequently, especially in the elderly and are related to poor prognosis and considerable health-care cost [2]. Early recognition and initiation of appropriate treatment can improve survival [4]. However, diagnosis of LV dysfunction, especially in asymptomatic patients, may be difficult to assess by physical examination alone, even when routine laboratory values, electrocardiograms and chest X-rays are added [28].

BNP is a 32-amino acid polypeptide containing a 17-amino acid ring structure common to all natriuretic peptides. The source of BNP is the cardiac ventricles and its release is directly proportional to ventricular volume expansion and pressure overload [9,10]. BNP levels are elevated in patients with heart failure and LV dysfunction. Also the effect of treatment in these patients can be monitored with repeated BNP measurements, as suggested by Troughton et al. [29]. Furthermore, BNP levels seem to be an independent predictor of long-term survival after myocardial infarction [30] and all cause mortality for patients with LV dysfunction [31,32]. BNP measurements have therefore been proposed as a new, simple and inexpensive screening tool for LV dysfunction [11–14,33,34]. Furthermore, the European Society of Cardiology has recently incorporated BNP measurement into the guidelines for diagnosis of heart failure [15]. BNP levels are useful in ‘ruling out’ this disorder, due to very high negative predictive values, especially in untreated patients. In accordance with previous studies we demonstrated that BNP measurements show high sensitivity in detecting patients with LV dysfunction.

However, we have to take into account that BNP, as an indicator of raised intra-cardiac pressure, can be elevated in various forms of heart disease besides LV systolic dysfunction including atrial fibrillation, LV diastolic dysfunction, LV hypertrophy and significant valve disease [26,35]. This may explain our results for the BNP measurements.

4.1. Echocardiography as a screening tool for LV dysfunction
According to the guidelines of the European Society of Cardiology, objective evidence of LV dysfunction must be added to clinical symptoms to establish the diagnosis of heart failure. Echocardiography has been proposed to be the screening method of choice to demonstrate cardiac dysfunction [15,16].

However, echocardiography is not considered to be cost-effective as a screening tool, especially for patients with a low probability of cardiac dysfunction, and its availability is often limited in different clinical settings. Newly developed HCU devices offer high image quality, ultra-portability and significantly lower capital cost (1/10th of the cost of a SE). The value of such devices for screening for various cardiac pathologies has been shown in previous studies [20,21,23,36,37]. The main finding of the current study was that a HCU device, estimating LVEF, is a sensitive tool for screening for LV dysfunction as assessed by SE.

Kimura et al. recently demonstrated that the combination of physical examination with HCU echocardiography improved the diagnostic evaluation of LV systolic function [38]. Bruce et al., on the other hand, found a discordance rate of 10% for HCU vs. SE LV function evaluation. This discrepancy can be explained by the broader range of LV function classification that is used in this study (EF <40%, 40–54%, 55–70%) leading to a misclassification of borderline EFs even by experienced echocardiographers [39].

In addition, we tested the hypothesis of diagnosing LV dysfunction by the assessment of the percentage collapse of IVC. We based this hypothesis on the fact that there is a relationship between right and left ventricular function due to the presence of the so-called ventricular interdependence. This is defined as the forces that are transmitted from one ventricle to the other ventricle through the myocardium and pericardium [40,41]. Due to the ventricular interdependence, it has been suggested that in the absence of pressure or volume abnormalities of the right heart or lungs, an increase of RA pressure may reflect LV dysfunction [40]. To our knowledge this is the first study to evaluate IVC collapse as a potential screening marker for LV dysfunction. However, this parameter appeared to be of low sensitivity (26%) and positive predictive value (38%) for the detection of LV dysfunction with both devices (SE and HCU echocardiography).

The echocardiographically estimated RA pressure correlated well with the invasively assessed RA pressure (agreement: 95%). These results are in concordance with previous studies [19,42].

Echocardiography can provide non-invasively additional valuable information about other significant abnormalities beyond LV function. Thus, LV hypertrophy, valvular abnormalities or mass lesions can be diagnosed instantly with echocardiography but could be missed by physical examination or a blood test. Furthermore, the addition of the Doppler feature in some of these devices enables the differentiation between systolic and diastolic dysfunction.

4.2. Use of ultrasound stethoscopes
The American Society of Cardiology recommends Level I training as the absolute minimum level required for the use of HCU devices [43]. Studies have shown that minimal echo training may enable physicians to use HCU for interpreting simple abnormalities with high efficacy and accuracy [38,44,45].

Physical examination undoubtedly remains the cornerstone of cardiovascular assessment and its use should be encouraged. However, the addition of a bedside echocardiographic examination helps us to instantly visualise the heart and to differentiate normal from abnormal patients. Furthermore, in case of doubt or whenever hemodynamic and quantitative information is needed for further management, an examination with a fully featured SE should follow.

4.3. Limitations
The HCU devices used in this study were SonoHeart PlusTM (in 42 patients) and OptiGoTM (in 46 patients). Although the former has two additional modalities (pulsed Doppler and M-Mode), we used only the two-dimensional (2D) feature for the LVEF and the IVC collapse evaluation to avoid bias between the two devices. There are therefore no data about the diastolic LV function of the heart or flow data. No analysis of consistency of results between the two HCU devices was performed. This may form the basis of a future study.

Furthermore, no additional data about other cardiac abnormalities were reported since the purpose of the study was to test the potential of a HCU device as a screening tool for LV dysfunction.


   5. Conclusion
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
 4. Discussion
 5. Conclusion
References
 
A HCU device is a reliable screening tool for the identification of LV dysfunction and is comparable to SE and to BNP measurements. IVC collapse is not a sensitive marker of this disorder. This study suggests that HCU echocardiography could result in cost-effective screening programmes for LV dysfunction in primary care.


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

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