Utilité de l’échographie pulmonaire dans l’évaluation des pressions de remplissage ventriculaire gauche dans un pays à ressources limitées : une étude échocardiographique transversale à Yaoundé-Cameroun.

 

 

CN NGANOU-GNINDJIO^1,2,*, AP MENANGA^1,3, A NGOUO TCHIFFO¹, AJ AHINAGA¹, DL TIWA¹, S KINGUE^1,3.

 

 

 

RESUME

 

Contexte et objectif : L'échographie pulmonaire représente un outil relativement nouveau et non invasif pour évaluer la congestion pulmonaire. L'identification des lignes B a été établie pour le diagnostic de l'insuffisance cardiaque; cependant, sa corrélation avec les pressions intracardiaques n'est pas déterminée. Cette étude visait à évaluer la relation entre le nombre de lignes B sur l'échographie pulmonaire et les pressions de remplissage ventriculaire gauche (PRVG) mesurées par l’échocardiographie transthoracique couplée au Doppler.

 

Matériels et méthodes : Il s'agissait d'une étude analytique et observationnelle entre novembre 2019 et juin 2020 dans le service de cardiologie de l'hôpital central de Yaoundé au Cameroun. Nous avons inclus des patients présentant une insuffisance cardiaque avec une classe inférieure à NYHA III. Nous avons exclu les participants souffrant d'affections pulmonaires interférant avec les lignes B. Le profil B a été considéré comme la présence d'au moins 8 lignes B dans les champs pulmonaires à l’echographie pulmonaire.

Résultats : Nous avons retenus 87 sujets dont  55 % étaient des hommes. L'âge moyen de notre population d’étude était de 62 ans. Au cours de cette étude, l'utilisation de l'échographie pulmonaire s’est avérée être un test fiable pour indiquer des PRVG élevées avec une sensibilité de 84 % et une spécificité de 99,4 %.

Conclusion : L'échographie pulmonaire est un outil simple qui présente un réel intérêt pour l'évaluation rapide et fiable des PRVG par l'identification d'un profil B dans notre contexte.

 

 

MOTS CLES

 

Insuffisance cardiaque, échographie pulmonaire, pressions de remplissage ventriculaire gauche, échocardiographie 2D, Yaoundé-Cameroun.

 

 

SUMMARY

 

 

Background and Objective: Pulmonary Ultrasound represents a relatively new, non-invasive tool for assessing pulmonary congestion. Identification of B-lines has been established for the diagnosis of Heart Failure (HF); however, its correlation with intracardiac pressures is not determined. This study aimed to evaluate the relationship between the number of B lines on lung ultrasound and the Left Ventricular Filling Pressures (LVFP) as determined by transthoracic cardiac ultrasound.

Materials and Methods: This was a cross-sectional analytic study between November 2019 and June 2020 in the Cardiology department of Yaoundé Central hospital in Cameroon. We included patients diagnosed with Heart Failure and a functional class less than NYHA III. We excluded participants with pulmonary conditions interfering with B lines. B profile was considered as the presence of at least 8 B lines in the pulmonary fields.

Results: 87 participants were enrolled. 55% were men, and the mean age was 62 years. The use of lung ultrasound was found in our study as a reliable test for diagnosing raised LVFP with a sensitivity of 84% and specificity of 99.4%.

Conclusion: Lung ultrasound is a simple tool that has a genuine interest in the rapid and reliable assessment of left ventricular filling pressures through the identification of a B profile in our context.

 

 

 

KEY WORDS

 

Heart failure, lung ultrasounds, left ventricular filling pressures, 2D-echocardiography, Yaoundé-Cameroon

 

   

 

                                                                                                                       

1.Internal Medicine and specialities department, Faculty of Medicine and Biomedical Sciences, University of Yaoundé I, Yaoundé, Cameroon.

2.Cardiology Department, Yaoundé Central Hospital, Yaoundé, Cameroon.

3.Internal medicine department, Yaoundé General Hospital, Yaoundé, Cameroon.

Adresse pour correspondance 

Dr Nganou-Gnindjio CN, Senior lecturer,

Faculty of Medicine and Biomedical Sciences,

University of Yaoundé 1;

 PO. Box: 1364 Yaoundé-Cameroon;

Email: This email address is being protected from spambots. You need JavaScript enabled to view it.

 

 

INTRODUCTION

 

The study of diastolic function and Left Ventricular Filling Pressures (LVFP) assessment are strongly recommended during the follow-up of patients with heart failure (HF)(1). The gold standard for measurement of LVFP is cardiac catheterization(2). Doppler echocardiography has been proposed as an appropriate non-invasive equivalent assay to estimate LVEDP, though unavailable in all settings. Lung ultrasound, long underused, has experienced substantial development in recent past years. It is a promising, non-invasive means of assessing pulmonary congestion. This is done through the identification of pulmonary B lines, with outstanding reliability (3). It has also been established that the number of B lines on pulmonary ultrasound is positively correlated to interstitial pulmonary congestion confirmed by chest X-ray and thoracic CT scan(4).

      However, if B lines' association with pulmonary congestion now seems obvious, the relationship between sonographic B-lines and intracardiac pressures in heart failure patients is unclear. We sought to assess the association of sonographic B-lines, as a marker of extravascular lung water, with cardiac left ventricular filling pressures in a group of patients with relatively clinically stable HF, undergoing TransThoracic Echocardiography (TTE) and Lung UltraSound (LUS) imaging.

 

 

METHODOLOGY

 

 

Study design and Subjects

 

We carried on a cross-sectional analytical study over eight months from November 2019 to June 2020 in the cardiology department of Yaoundé Central Hospital, a referral Center. During the recruitment, we included patients of all genders, aged between 18-80 years old. The participants were diagnosed with Heart Failure with a functional class NYHA less than III. We excluded from our study patients with pneumothorax, a recent history of chest trauma, pneumonia, active lung cancer and pulmonary fibrosis. These exclusion criteria were chosen based on known interactions between these conditions and pulmonary B lines (5). Subjects with non-optimal images on lung ultrasound not allowing an adequate analysis of B lines or diastolic function were also excluded.

 

Survey method and data collection

 

Data were collected in two phases. First, during face-to-face interviews where the patients were administered a pretested standardized questionnaire. Second, during LUS and TTE. All investigators received training in the study's objective, measurement method, and the reporting of the data collected.

 

Clinical data

 

We recorded the age and gender of participants, the aetiology of HF, the type of HF (preserved or reduced ejection fraction), the symptoms and signs of HF.

 

Transthoracic Echocardiography

 

Cardiac and lung ultrasound studies were performed using standard ultrasound equipment by a Sonoscape disposal with standard 2–5 MHz phased array transducers and were analyzed crossectional. Digital B-mode, tissular Doppler mode, TTE cine loops were analyzed to assess cardiac function and determine LVFP by a single investigator (NA) following current joint guidelines by the American Society of Echocardiography (ASE) and the European Society of Cardiology (ESC) of 2016 (6). Both LV mass index and left atrial (LA) volume index was calculated based on the DuBois formula for body surface area (7). LV and LA volumes and Left ventricular ejection fraction (LVEF) were measured using Simpsons' modified biplane method (8). LA volumes were measured at end-systole. Mitral inflow velocity (E), measured as peak velocity [m/s], and septal (e' septal) and lateral (e' lateral) tissue Doppler measurements were averaged over 2–4 beats. The right atrial pressure was estimated based on the diameter and inspiratory collapse of the inferior vena cava (9). The estimated systolic pulmonary artery systolic pressure (PASP) was derived from the maximal tricuspid regurgitation (TR) velocity by adding the right atrial pressure.

 

Lung Ultrasound

 

Lung ultrasound measurements were performed by a cardiologist junior and a senior cardiologist. The cardiologist junior performed echocardiography for three years (8hours/5days on 7) and pulmonary echography three months ago (8hours/5days on 7) before starting the study under the supervision of a senior cardiologist. The ultrasounds realization was not blinded. Eight LUS zones were analyzed for each patient, i.e. four on each hemithorax (10). The maximum number of vertical reverberation eartefacts (B-lines) was counted in a single intercostal space for each zone, and the sum of all eight zones was considered as the total number of B-lines. Measurements were then averaged for each LUS zone.

 

Statistical Analysis

 

Data were collected using a pretested datasheet, entered, and analyzed using Epi-info TM software version 7. We carried out univariate and multivariate analyzes and correlations between the main variables. The differences in means observed were considered significant for a value of p <0.05. The diagnostic value of B-lines in identifying subjects with raised LVFP was assessed using the ROC curves. After determining the LVFP with the maximum area under the curve (AUC) for the sum of B lines by the eight-zone method, the number of 8 B-lines in total was used as a cutoff value to determine a B profile. The results were expressed as area under the curve (AUC) with a 95% confidence interval (CI) for this area. The best threshold was obtained by selecting the point on the ROC curve, which maximized both sensitivity and specificity. A significance level of 0.05 was used for all analyzes. The results were presented in the form of tables and figures.

 

 

Ethical Considerations

 

Informed consent was obtained from all subjects, and the study conformed to the ethical guidelines on human research of the 1975 Declaration of Helsinki. Ethic clearances were obtained from the institutional ethics committee on human analysis of the Hospital and the Faculty of Medicine and Biomedical Sciences of Yaoundé.

 

 

RESULTATS

 

 

Baseline characteristics of the study population

 

Of 93 initially eligible patients based on our selection criteria, we excluded 2 for active pneumonia, 1 with pulmonary fibrosis and three for inadequate images of lung zones and impossibility of assessing LVFP. In total, 87 patients were included in the analysis. Our Flowchart is presented in Figure 1.

Baseline characteristics of our study population stratified by B-line percentiles are presented in Table 1. The median age of study subjects was 63 years (range: 41–88), 55, 2% (48) were men. The most common aetiology of HF was dilated cardiomyopathy (36.78%), followed by hypertensive cardiomyopathy (34.4%). A pulmonary B profile mainly was found in patients with dilated cardiomyopathy (78%). Fifty-seven per cent of participants were complaining of at least stage 3 dyspnea classified following New York Heart Association (NYHA) classification, and 80% had a B lung profile. Thirty-six patients (41,3%) had crackles on lung auscultation, and 86% had a B profile.

Forty-eight (55.17%) patients had HF with preserved ejection fraction (EF), while 39 (44.8%) had reduced EF. Among the 39 participants with reduced EF, 35 (90%) had a B lung profile. A total of 60 (69%) of the 87 participants had a pulmonary ultrasound B profile, and 55 (91.6%) had comparatively raised estimated LVFP on TTE (See Tables 2 and 3).

 

 

Assessment of the sensitivity and specificity of detection of raised LVFP in the presence of diffuse pulmonary B lines

 

Using a threshold determined by the ROC curve ≥ 8 B lines (considered as a B profile lung ultrasound) in the eight anterior and lateral lung fields, it was determined (on the essential basis of a significantly high threshold level of E/e and using the diagnostic algorithm of LVFP assessment guidelines of ESC 2016) an increase in LV filling pressures with a sensitivity of 84% and specificity by 99.4%. The area under the curve (AUC) was 95.8% for a 95% CI between 92.3–99.4% (see Figure 2)

The positive predictive value of a B lung profile in predicting LVFP was 100%, with a confidence interval between 87 and 100%. The negative predictive value was calculated at 92%, with a confidence interval between 82 and 97%. Table 4 summarizes these findings.

 

 

DISCUSSION

 

 

Assessment of LVFP in patients with a known history or suspected HF is essential with prognostic and therapeutic implications(11). LUS has been utilized to evaluate extravascular lung water in patients with suspected acute HF and has been found to be accurate and superior to chest radiography (3). Our study aimed to assess the presence and quantity of B-lines in patients with either a history of HF or current dyspnea and compare the B profile to the fact or not of raised LVFP based on current guidelines ESC and ASE. We considered B-profile with the cutoff values of ≥8 B-lines in an 8 zone model as proposed by current guidelines for identifying pulmonary congestion in acute decompensated HF(10).

Most patients with dilated cardiomyopathy had a B profile on LUS, and this may be explained by the fact that most of these patients presented concomitantly with altered LVEF. Among patients with a pulmonary B profile, 20 did not show dyspnea, and among them, 16 still had raised LVFP. Likewise, 29 participants did not have crackling groans on pulmonary auscultation, but 26 still had increased filling pressures estimated by TTE. These results show the more excellent reliability of pulmonary ultrasound in determining signs of pulmonary congestion than functional signs and even identifying physical signs on auscultation of patients. These findings are corroborated by many studies in a recent systematic review reporting accuracy of 90% when the lung ultrasound was compared to the clinical examination (67%, p = 0.001), as well as compared to the clinical examination combination, with NT-proBNP and chest x-ray (81%, p = 0,04)(3).

Our study shows that 32% of patients had an E/e' ratio on Doppler echocardiography > 14, and all had a pulmonary B profile. It was found that the sensitivity and specificity to detect the elevation of LVFP by the presence of a B profile by ultrasound are high when E/e' > 14 (84% and 99.4% respectively). This led to the conclusion that there is a strong correlation between the search for B profile and increased LVFP in patients with signs suggestive of HF.

The presence of B profile as a sign of pulmonary interstitial oedema is related to increased LVFP, which imbalance the Starling forces at the alveolar-capillary barrier, leading to pulmonary congestion(12). Therefore, the overall good agreement and significant correlation between B lines and the raised LVFP found in this study are not surprising.

 

Limitations

 

Several limitations of this study should be noted. The small sample size limited our analysis for an observational study performed at a single centre. The unavailability of laboratory tests, such as the dosage of NT-proBNP levels, is a flaw to our study since it could better associate clinical and sonographic findings in our population. As an ultrasound assessment, lung ultrasound shares all the limitations linked to an operator-dependent technique. However, since the realization of the exam is a lot simpler than other ultrasounds (that is to say, echocardiography), inter-operator variability has been assessed as very being low (13).

 

 

CONCLUSION

 

 

Sonographic pulmonary B lines are directly related to pulmonary congestion. They can be associated with a B lung profile to a rise in LVFP (assessed with TTE) in patients with known or suspected HF. More multicenter’ studies, and with larger samples, need to be carried out to precise this association. This can have a particular interest in our setting for rapid assessment of LVFP when TTE is not available or in complement of it.

 

Table 1

 Baseline clinical and sonographic characteristics of our study population stratified by B-line percentiles

HFpEF: Heart failure with preserved ejection fraction; HFrEF: Heart failure with reduced ejection fraction

 

Table 2

 Lung ultrasound and echocardiographic measures by B-line profile group

 

Table 3

 Lung ultrasound profiles based on the estimation of Left ventricular filling

pressure by echocardiogram

 

Table 4

Predictive value of Lung ultrasound profiles based

on the estimation of Left ventricular filling pressure by echocardiogram

 

 

 

 

 

 

 

 

 

 

 

 

 

LR+: positive likelihood, LR-: Negative likelihood

 

 

Figure 1 : Patients flowchart

 

 

Figure 2: Receiver operating characteristic curves for identification of pulmonary B lines in assessing raised left ventricular filling pressures. AUC: area under the curve.

 

 

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