Background

Hypoplastic left heart syndrome (HLHS) is a birth defect that affects the development of the left side of the heart. Hypoplastic left heart syndrome affects many components of the heart resulting in the underdevelopment of the left ventricle, mitral valve, aortic valve, and the aorta. Additionally, it is common for newborns with HLHS have a hole between the left and right atria of the heart called an atrial septal defect. These defects reduce the hearts ability to pump oxygen-rich blood to the rest of the body. [1] Hypoplastic left heart syndrome is often diagnosed before birth via ultrasound or within hours after by pulse oximetry and echocardiogram; however, diagnoses may also require X-Ray, cardiac catherization, MRI, or electrocardiogram. [2] Hypoplastic left heart syndrome is treated through surgical procedures or sometimes a heart transplant. The cause of HLHS is not clear and is likely the result of many factors. Some patients belong to families that appear to have a genetic predisposition or tendency towards developing HLHS, but most families have no prior history of congenital heart disease. [3] Patients usually need several surgical procedures done in stages to create a pathway to get oxygen-rich blood to the body. [4] After HLHS has been repaired, patients still need lifelong follow-up care with a cardiologist. Medications may be required to maintain normal heart function. Complications can occur later in life and might require additional care. However, recent advances in surgical intervention early in life has allowed patients with HLHS to live into adulthood. [4]


Epidemiology

Alaska Birth Defects Registry (ABDR) registers birth defects as reported from health care providers using International Classification of Disease (ICD) billing codes. The use of these ICD codes can lead to misclassification of diagnosed conditions. Prior to this report, all prevalence estimates were based on the number of unique children reported to ABDR with an ICD code representing a specified condition regardless of case confirmation status.

The estimates in this report were derived by conducting medical record review and case confirmation of all reported cases between 2007 and 2018. The confirmation probability calculated from this time period is used to develop informed estimates of the defect prevalence beyond 2018. See Defect prevalence calculation.

For explanations of table columns see Column descriptions.

Prevalence

Hypoplastic left heart syndrome occurs in about 2.6 in every 10,000 live births in the United States. [5]

In Alaska, during 2007-2017, the prevalence of Hypoplastic left heart syndrome was 1.3 per 10,000 live births.
Reports Defects Births Prevalence (95% CI)
Total 22 16.2 123630 1.3 (0.8, 2.1)
Notes: 95% CI = 95% Confidence Interval

Trend

Prevalence per 10,000 births of Hypoplastic left heart syndrome during 2007-2017 by five-year moving averages, with 95% confidence interval band and Poisson estimated fitted line.
Reports Defects Births Prevalence (95% CI) Predicted Prevalence†
2007-2011 2.0 1.5 11404.7 1.3 (0.2, 4.8) 1.1
2008-2012 1.3 1.0 11354.0 0.9 (0.2, 4.3) 1.2
2009-2013 1.3 1.0 11349.0 0.9 (0.2, 4.3) 1.2
2010-2014 2.0 1.5 11334.7 1.3 (0.3, 5.3) 1.2
2011-2015 2.7 1.9 11377.3 1.7 (0.4, 5.8) 1.2
2012-2016 2.0 1.5 11295.0 1.3 (0.2, 4.8) 1.2
2013-2017 1.3 1.0 10979.7 0.9 (0.1, 3.9) 1.2
Notes: Each row is based on five-year moving averages; Prevalence reported per 10,000 live births; 95% CI=95% Confidence Interval

† Estimated rate based on Poisson model
The p-value test for trend did not detect a significant change in number of live births with Hypoplastic left heart syndrome during 2007-2017. See p-value estimate
Estimate Std. Error t value Pr(>|t|)
0.01592 0.04880 0.32627 0.75743

Regional Distribution

Distribution of Hypoplastic left heart syndrome in Alaska by Public Health Region of maternal residence at the time of birth. A description of regional breakdowns can be found here. Data suppressed for # of reports < 6.
Reports Defects Births Prevalence (95% CI)
Anchorage 8 6.0 50455 1.2 (0.4, 2.3)
Gulf Coast - - 7725 -
Interior - - 22487 -
Mat-Su - - 14937 -
Northern - - 8520 -
Southeast - - 7625 -
Southwest - - 11881 -
Notes:Prevalence reported per 10,000 live births; Data suppressed for # of reports < 6; 95% CI = 95% Confidence Interval

Demographics

Some subgroups may be more at risk for having a baby with Hypoplastic left heart syndrome. This section provides the descriptive epidemiology of specified maternal, birth, and child characteristics identified from the birth certificate.

Reports Defects Births Prevalence (95% CI)
Sex
  Female 11 8.1 59998 1.4 (0.7, 2.6)
  Male 11 8.1 63632 1.3 (0.7, 2.5)
Birth weight (grams)
  <2500 - - 7231 -
  2500+ - - 116215 1.3 (0.7, 2.0)
Maternal age
  12-19 - - 9156 -
  20-24 6 4.4 32872 1.3 (0.5, 3.1)
  25-29 7 5.1 37743 1.4 (0.6, 3.1)
  30-34 - - 28152 -
  35-39 - - 12614 -
  40+ - - 3064 -
Maternal race
  Alaska Native/American Indian - - 31560 -
  Asian/Pacific Islander - - 11810 -
  Black - - 5081 -
  White 15 10.9 73595 1.5 (0.8, 2.5)
Maternal education (years)
  <12 - - 11929 -
  12 - - 43162 1.4 (0.5, 2.7)
  12+ - - 65105 1.4 (0.6, 2.4)
Marital status
  Married 15 11 78396 1.4 (0.7, 2.4)
  Unmarried 7 5.2 44625 1.2 (0.5, 2.6)
Maternal smoking use
  Reported smoking - - 16817 -
  Reported not smoking - - 104707 1.3 (0.7, 2.1)
Medicaid (mother or child)
  Medicaid - - 62666 2.1 (1.2, 3.5)
  non-Medicaid - - 60839 -
Father on birth certificate
  None - - 6328 -
  Present - - 117302 1.3 (0.8, 2.1)
Notes: Prevalence reported per 10,000 live births; Data suppressed for # of reports < 6; 95% CI = 95% Confidence Interval

Technical notes

Column descriptions

# Reports: Unless otherwise noted, the number of unique reports of the defect received by ABDR during the specified birth year(s). Each report represents a unique child with the specified defect.

# Defects: The estimated true number of reports that are diagnosed defects based on medical record review and case confirmation.

# Births: The number of live births among Alaskan residents that occurred in Alaska during the specified birth year(s).

Prevalence (95% CI): The estimated diagnosed prevalence of the condition and corresponding 95% Confidence Interval. (For information on how the defect prevalence was estimated see below).

Defect prevalence calculation

The estimated defect prevalence was calculated using a Bayesian approach based on the reported prevalence, PPV and 1-NPV (see formula below).

Through medical records review and case confirmation of a random sample of reported cases, the defect prevalence is calculated as:

\[PPV (Positive Predictive Value) = p(defect|report)\] \[NPV (Negative Predictive Value) = p(\overline{defect}|\overline{report})\]

\[p(defect) \approx [p(report)\cdot PPV]+[p(\overline{report})\cdot (1-NPV)]\]

Defect prevalence estimates are a more accurate estimation of the actual diagnosed prevalance of birth defects compared to the reported prevalance estimates in Alaska. ABDR obtains reports from medical providers using International Classification of Disease (ICD) codes that are extracted from individual systems which when aggregated may not reflect true diagnostics. Caution should be used when interpreting and comparing the reported prevalence estimates with national estimates.

See Data analysis methods for more information.

P-value estimate

To evaluate the trend over time and account for under/over-dispersion we constructed a quasi-Poisson regression model. This model assumes the variance is a linear function of the mean and models the estimated number of annual defects by year with a natural log (ln) offset of the annual births. P-values < 0.05 are considered significant, which indicates that the predicted slope is significantly different from a slope of zero.

Data suppression

For region and demographic data tables, values are suppressed based on the number of reports received during the observation period. Counts less than 6 are suppressed (as indicated by ‘-’ in the table). For regions or demographics with only one cell count suppressed a second is suppressed to eliminate the ability to back-calculate the estimate.

References

[1] Ebstein’s Anomaly of the Tricuspid Valve | Children’s Hospital of Philadelphia. (2021). Retrieved 1 April 2021, from https://www.chop.edu/conditions-diseases/hypoplastic-left-heart-syndrome-hlhs

[2] Ebstein anomaly - Symptoms and causes. (2021). Retrieved 1 April 2021, from https://www.mayoclinic.org/diseases-conditions/hypoplastic-left-heart-syndrome/symptoms-causes/syc-20350599

[3] Ebstein’s Anomaly | Boston Children’s Hospital. (2021). Retrieved 31 March 2021, from https://www.childrenshospital.org/conditions-and-treatments/conditions/h/hypoplastic-left-heart-syndrome

Authorship

Maternal and Child Health (MCH) senior epidemiologist Dr. Jared Parrish, PhD conceived of the presented analysis. Alaska Birth Defects Registry program manager and epidemiologist Chris Barnett, MS MPH and Dr. Jared Parrish, PhD developed the theory and performed the computations. Research analysts Monica Mills and Jordyn Lord managed the project and data storage. Pediatric cardiologist Dr. James Christiansen, MD performed defect confirmations and provided medical consultation. All authors discussed the results and contributed to the final report.

Suggested Citation

State of Alaska Department of Health and Social Services, Division of Public Health, Section of Women’s, Children’s, and Family Health. Alaska Birth Defects Registry Condition Report: Hypoplastic left heart syndrome, Alaska, 2007-2017. Updated June 22, 2021. Available at: http://rpubs.com/AK_ABDR/HLHS07_17.

Contact

Alaska Birth Defects Registry (ABDR)
3601 C Street, Suite 358
Anchorage, AK 99503
(907) 269-3400 phone
(907) 754-3529 fax

Updated: June 22, 2021
Code source: R:\ABDR\Analysis_New\ABDR_CASECONF\cond_reports\Published_reports\HLHS07_17.Rmd