European Journal of Cardiovascular Medicine

Congenital heart disease represents the most common congenital malformation worldwide, accounting for approximately one-third of all birth defects. [1] Over the past several decades, the reported global birth prevalence of CHD has risen markedly, from approximately 0.6 per 1,000 live births in the early 20 th century  to 9.41 per 1,000 live births in 2010–2017,largely attributable to advances in diagnostic modalities and improved detection of of milder lesions such as atrial septal defect (ASD), ventricular septal defect (VSD), and patent ductus arteriosus (PDA). [2,3] In India, the burden of CHD remains substantial, with an estimated birth prevalence of 8–10 per 1,000 live births, translating to over 240,000 affected children annually, and posing a substantial public health challenge. [1,4]

Sikkim, a high-altitude Himalayan state in Northeast India, presents a unique geographic, ethnic, and socioeconomic context with limited access to specialized cardiac services. However, systematic echocardiography-based data on CHD burden and pattern in this region are unavailable. In this context, STNM Hospital, Sochakgang, the state’s primary government tertiary-care centre, serves as the principal referral hub for cardiac evaluation. Its echocardiography database therefore offers a valuable opportunity to characterize the regional profile of CHD in a high-altitude population.

This study aimed to describe the echocardiographic spectrum and proportion of CHD among patients undergoing transthoracic echocardiography at STNM Hospital over a five-year period.

Study Design and Population

This retrospective, hospital-based descriptive echocardiography study was conducted in the Department of Cardiology at STNM Hospital, Sochakgang, Gangtok, Sikkim, India. The institution is a government tertiary-care centre serving as the state-level referral hub for both pediatric and adult cardiology services. All transthoracic echocardiography (TTE) records performed between 1 January 2021 and 31 December 2025 were screened. Echocardiograms demonstrated any structural CHD in individuals of all age groups were included. Patients with isolated functional abnormalities without structural CHD, trivial lesions not classified as CHD (example isolated physiologic patent foramen ovale <5mm or clinically insignificant patent ductus arteriosus as per the reporting cardiologist), and records with incomplete data were excluded.

The study was conducted using de-identified echocardiographic records without direct patient interaction. Institutional ethics committee approval was obtained, along with a waiver of individual informed consent, in accordance with local regulatory requirements and the retrospective nature of the study.

Data Sources and Variables

Data were extracted from the echocardiography laboratory databases. The following variables were collected: year and total number of echocardiograms performed; CHD status (present/absent) and annual count of CHD cases; demographic details including age (categorized as < 1 year, 1-12 years, 13-17 years, and ≥18 years) and sex; ethnicity/community as recorded at hospital registration; and patient type (outpatient or inpatient). Clinical variables included specific CHD diagnoses ASD, VSD, PDA, tetralogy of Fallot (TOF), transposition of the great arteries (TGA), endocardial cushion defect (ECD), Ebstein anomaly, tricuspid atresia, situs inversus with dextrocardia, persistent pulmonary hypertension of the newborn, pulmonary stenosis, aortic stenosis, double outlet right ventricle, and total/partial anomalous pulmonary venous return—as well as shunt direction categorized as left-to-right, right-to-left, or bidirectional.

All transthoracic echocardiographic examinations were performed using a Vivid S70N cardiovascular ultrasound system (GE HealthCare, Chicago, IL, USA), with standard phased-array transducers and routine adult and pediatric echocardiography protocols.

Outcomes and Definitions

The primary outcome was the proportion of echocardiograms demonstrating CHD calculated annually as the number of CHD cases divided by the total number of echocardiographic studies performed. Secondary outcomes included distribution of CHD cases according to age group, sex, ethnicity, patient type, lesion type, and shunt direction. CHD lesions were categorized as acyanotic (including ASD, VSD, PDA, ECD, pulmonary stenosis, aortic stenosis) or cyanotic/complex (TOF, TGA, Ebstein anomaly, tricuspid atresia, situs inversus with dextrocardia, double outlet RV, PAPVR/TAPVR). Persistent pulmonary hypertension of the newborn was classified separately as a functional/developmental condition.

Statistical Analysis

Data were summarized as counts and percentages. The annual CHD yield was calculated as a simple proportion. Ethnicity-specific representation within the cohort was compared with 2011 Census of India data for Sikkim to assess over or under-representation relative to the general population. Fold difference was calculated as the ratio of cohort percentage to census percentage for each community.

Overall, Burden of CHD Among Echocardiograms

From 2021 to 2025, a total of 45,275 echocardiograms were performed at STNM Hospital, of which 675 studies demonstrated at least one structural CHD, corresponding to an overall proportion of 1.49% among echocardiographic evaluations. The annual proportion of CHD remained relatively stable across the study period despite a near threefold increase in total echocardiographic volume (from 4,989 to 12,828 studies), indicating a consistent detection rate within the referral population.

Adults (≥18 years) accounted for 43.4% of CHD cases. Females constituted 63.4% of the cohort. The majority of cases were identified in the outpatient setting (76.6%), while the remainder were detected among inpatients undergoing echocardiography for other clinical indications. (Table 1)

Echocardiographic Pattern of CHD

In Table 2 echocardiographic patterns are described. Among the patients with CHD, acyanotic lesions predominate, accounting for the majority of cases. Atrial septal defect was the most common lesion, observed in 369 patients (54.6%), followed by ventricular septal defect in 215 (31.9%) and patent ductus arteriosus in 54 (8.0%). Cyanotic and complex lesions were comparatively less common, with Tetralogy of Fallot identified in 31 patients (4.6%) and transposition of great arteries in 9 patients (1.3%). Shunt direction was available in 638 patients, among whom left-to-right shunting predominated (603 [94.5%]), followed by right-to-left shunts (21 [3.3%]) and bidirectional shunting (14 [2.2%]). Figure 1 illustrated percentage distribution of CHD lesions diagnosed at STNM Hospital, Sikkim

Ethnicity and Community Distribution

The ethnic/community distribution of CHD cases demonstrated variation when compared with population proportions from the Sikkim Census 2011 in Table 3. The largest representation was observed among the Chettri/Bahun community (166 [24.6%]), followed by Rai (106 [15.7%]), Limboo (85 [12.9%]), and Tamang (63 [9.2%]). Other communities included Lepcha (57 [8.6%]), Scheduled Castes (48 [7.2%]), Bhutia (45 [6.9%]), Gurung (50 [7.5%]), and Newar (35 [5.1%]), while Sherpa (14 [2.2%]) and Thapa/Mangar (6 [0.9%]) constituted smaller proportions. When compared with census-based population distribution, certain communities showed relatively higher representation among CHD cases, including Newar (5.1% vs. 2.7%; fold difference 1.9), Scheduled Castes (7.2% vs. 4.5%; fold difference 1.6), and Tamang (9.2% vs. 6.8%; fold difference 1.4). In contrast, lower representation was observed among Sherpa (2.2% vs. 4.5%; fold difference 0.5), Thapa/Mangar (0.9% vs. 2.7%; fold difference 0.3), and Bhutia (6.9% vs. 8.6%; fold difference 0.8).

Table 1: Baseline characteristics of patients with congenital heart disease at STNM Hospital, Sikkim (2021–2025)

Table 2: Echocardiographic pattern of congenital heart disease and shunt direction (2021–2025)

Table 3: Ethnic/community distribution of CHD patients compared with Sikkim Census 2011 proportions and fold difference

Figure 1: Percentage distribution of CHD lesions diagnosed at STNM Hospital, Sikkim

Table 1: Baseline characteristics of patients with congenital heart disease at STNM Hospital, Sikkim (2021–2025)

Values are represented as numbers and percentages.

CHD: Congenital heart disease

Table 2: Echocardiographic pattern of congenital heart disease and shunt direction (2021–2025)

Values are represented as numbers and percentages. CHD: congenital heart disease; PAPVR: partial anomalous pulmonary venous return; TAPVR: total anomalous pulmonary venous return. Lesion categories are not mutually exclusive; one patient may have 1 diagnosis.  ‡Shunt direction documented in 638 patients; 37 cases without documented shunt direction.

Table 3: Ethnic/community distribution of CHD patients compared with Sikkim Census 2011 proportions and fold difference

Values are represented as numbers and percentages. *2011 Census of India, State of Sikkim. Fold Difference = (Patients %) / (Census %); values 1.0 indicate over-representation.

ASD: Atrial Septal Defect; ECD: Endocardial Cushion Defect; EA: Ebstein Anomaly;
PDA: Patent Ductus Arteriosus; PPHN: Persistent Pulmonary Hypertension of the Newborn;
PS: Pulmonary Stenosis; TGA: Transposition of the Great Arteries; TOF: Tetralogy of Fallot;
VSD: Ventricular Septal Defect

Overall, Burden of CHD Among Echocardiograms

From 2021 to 2025, a total of 45,275 echocardiograms were performed at STNM Hospital, of which 675 studies demonstrated at least one structural CHD, corresponding to an overall proportion of 1.49% among echocardiographic evaluations. The annual proportion of CHD remained relatively stable across the study period despite a near threefold increase in total echocardiographic volume (from 4,989 to 12,828 studies), indicating a consistent detection rate within the referral population.

Adults (≥18 years) accounted for 43.4% of CHD cases. Females constituted 63.4% of the cohort. The majority of cases were identified in the outpatient setting (76.6%), while the remainder were detected among inpatients undergoing echocardiography for other clinical indications. (Table 1)

Echocardiographic Pattern of CHD

In Table 2 echocardiographic patterns are described. Among the patients with CHD, acyanotic lesions predominate, accounting for the majority of cases. Atrial septal defect was the most common lesion, observed in 369 patients (54.6%), followed by ventricular septal defect in 215 (31.9%) and patent ductus arteriosus in 54 (8.0%). Cyanotic and complex lesions were comparatively less common, with Tetralogy of Fallot identified in 31 patients (4.6%) and transposition of great arteries in 9 patients (1.3%). Shunt direction was available in 638 patients, among whom left-to-right shunting predominated (603 [94.5%]), followed by right-to-left shunts (21 [3.3%]) and bidirectional shunting (14 [2.2%]). Figure 1 illustrated percentage distribution of CHD lesions diagnosed at STNM Hospital, Sikkim

Ethnicity and Community Distribution

The ethnic/community distribution of CHD cases demonstrated variation when compared with population proportions from the Sikkim Census 2011 in Table 3. The largest representation was observed among the Chettri/Bahun community (166 [24.6%]), followed by Rai (106 [15.7%]), Limboo (85 [12.9%]), and Tamang (63 [9.2%]). Other communities included Lepcha (57 [8.6%]), Scheduled Castes (48 [7.2%]), Bhutia (45 [6.9%]), Gurung (50 [7.5%]), and Newar (35 [5.1%]), while Sherpa (14 [2.2%]) and Thapa/Mangar (6 [0.9%]) constituted smaller proportions. When compared with census-based population distribution, certain communities showed relatively higher representation among CHD cases, including Newar (5.1% vs. 2.7%; fold difference 1.9), Scheduled Castes (7.2% vs. 4.5%; fold difference 1.6), and Tamang (9.2% vs. 6.8%; fold difference 1.4). In contrast, lower representation was observed among Sherpa (2.2% vs. 4.5%; fold difference 0.5), Thapa/Mangar (0.9% vs. 2.7%; fold difference 0.3), and Bhutia (6.9% vs. 8.6%; fold difference 0.8).

Table 1: Baseline characteristics of patients with congenital heart disease at STNM Hospital, Sikkim (2021–2025)

Table 2: Echocardiographic pattern of congenital heart disease and shunt direction (2021–2025)

Table 3: Ethnic/community distribution of CHD patients compared with Sikkim Census 2011 proportions and fold difference

Figure 1: Percentage distribution of CHD lesions diagnosed at STNM Hospital, Sikkim

Table 1: Baseline characteristics of patients with congenital heart disease at STNM Hospital, Sikkim (2021–2025)

Values are represented as numbers and percentages.

CHD: Congenital heart disease

Table 2: Echocardiographic pattern of congenital heart disease and shunt direction (2021–2025)

Values are represented as numbers and percentages. CHD: congenital heart disease; PAPVR: partial anomalous pulmonary venous return; TAPVR: total anomalous pulmonary venous return. Lesion categories are not mutually exclusive; one patient may have 1 diagnosis.  ‡Shunt direction documented in 638 patients; 37 cases without documented shunt direction.

Table 3: Ethnic/community distribution of CHD patients compared with Sikkim Census 2011 proportions and fold difference

Values are represented as numbers and percentages. *2011 Census of India, State of Sikkim. Fold Difference = (Patients %) / (Census %); values 1.0 indicate over-representation.

ASD: Atrial Septal Defect; ECD: Endocardial Cushion Defect; EA: Ebstein Anomaly;
PDA: Patent Ductus Arteriosus; PPHN: Persistent Pulmonary Hypertension of the Newborn;
PS: Pulmonary Stenosis; TGA: Transposition of the Great Arteries; TOF: Tetralogy of Fallot;
VSD: Ventricular Septal Defect

In this five-year echocardiography-based study from a high-altitude tertiary care centre in Sikkim, CHD was identified in 1.49% of all echocardiographic evaluations (14.9 per 1,000 studies), with a stable detection rate despite a near threefold increase in echocardiographic volume.

Importantly, this echocardiographic yield is not directly comparable to birth prevalence estimates, which are typically reported per 1,000 live births.  For context, population-based Indian data report CHD prevalence ranging from 4.55 to 8.07 per 1,000 live births, while hospital-based series report wide variation from 2.25 to 27.7 per 1,000 echocardiography studies, depending on patient population selection and diagnostic inclusion criteria. [3,5-7]

The predominance of acyanotic CHD,  particularly ASD (54.6%) and VSD (31.9%), together accounting for 86.5% of cases, is consistent with established Indian and global patterns. [4,5] In the North India birth cohort, VSD comprised 43.9% and ASD 7.3% of significant CHDs; however, that study included only newborns. [4] This contrast with our study as the present cohort spans all ages and predominantly outpatients, which explains the higher proportion of ASD, reflecting the natural history wherein ASD often presents later in life or is incidentally discovered.

Cyanotic lesions accounted for 8.4% of diagnoses. TOF (4.6%) as the most common lesion, followed by Ebstein anomaly (1.8%), TGA (1.3%), and other complex lesions (1.7% combined), This distribution aligns with prior Indian pediatric CHD studies where TOF remains the dominant cyanotic lesion. [5,6,8]  The overwhelming predominance of left-to-right shunts (94.5%) further indicates that most lesions were hemodynamically tolerated and detached prior to advanced pulmonary vascular disease, suggesting a window for timely intervention.

A key finding of this study is that 43.4% of CHD diagnoses occurred in adults (≥18 years), underscoring a substantial burden of previously undiagnosed CHD presenting beyond childhood.  This aligns with emerging literature on adult congenital cardiac disease in India, where historical underdiagnosis, limited pediatric cardiac services, and lack of transition pathways result in significant numbers of adults presenting with previously undiagnosed CHD. [9,10]

In the present study, the combination of adult presentations 43.4% adult presentations, predominance of outpatient referral (76.6%), and the overwhelming presence of left-to-right shunts (94.5% among documented cases) collectively suggests that many hemodynamically stable acyanotic lesions such as ASD and small VSD may remain undetected during childhood and are often identified incidentally during echocardiography evaluation performed for other clinical indications.

Females comprised 63.4% of the CHD cohort, a finding compatible with ASD-predominant studies where female preponderance is well-established, particularly among adults. [5] This female excess diverges slightly from pediatric CHD series, which often report slight male predominance overall; however, the age-inclusive nature and ASD-heavy pattern of the present study explain this observation.

The observed variation in ethnic/community representation, including over-representation of Newar (1.9x), Scheduled castes (1.6x), and Tamang (1.4x) and under-representation of Sherpa (0.5x) and Thapa/Mangar (0.3x), is unlikely to reflect true biological differences in CHD incidence. Instead, these findings likely represent the combined effects of geographic accessibility to the tertiary center, socioeconomic factors, healthcare-seeking behaviour and referral pathways within the state. Given Sikkim’s mountainous terrain and variable healthcare access, these disparities highlight the need for decentralized screening strategies and equitable healthcare delivery. However, population-based studies with defined denominators are required to confirm these observations

This hospital-based echocardiographic profile aligns with Indian and global CHD literature while highlighting region-specific issues of delayed detection, adult CHD burden, and ethnic heterogeneity in a high-altitude state. The lower yield at STNM Hospital likely reflects the outpatient-predominant population in which milder, asymptomatic lesions such as small ASD may not be systematically screened. In contrast, neonatal screening or inpatient-only cohorts would yield higher rates due to inclusion of critically ill patients. Strengthening early childhood screening, pediatric cardiology capacity, and structured transition-of-care pathways with attention to community-specific barriers to access is essential to improve outcomes for patients with CHD in Sikkim.

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