The rising incidence and ethnic disparities in aortic dissection in Aotearoa New Zealand

Acute aortic dissection (AD) is a lethal medical diagnosis, associated with a high morbidity and mortality if not recognised and treated promptly. In recent years there has been increasing awareness of this diagnosis, with both national and international studies demonstrating a rising incidence of AD worldwide.^1–3

In Aotearoa New Zealand, our previous paper looked at all cases of AD and found that over the last two decades there has been a rising incidence of AD, with a current median incidence rate of 4.99 per 100,000 per annum.² This was further explored in a collaborative study carried out nationally, which demonstrated this rising incidence was mainly driven by increasing cases of acute type A AD with a calculated average of 3% increase per year after adjusting for age and gender.³

Ethnic-specific disparities have been documented in vascular disease in Aotearoa New Zealand, including in aortic conditions. This was explored in the Midland Region of Aotearoa New Zealand, looking at patients with a diagnosis of acute aortic syndromes (AAS) including AD.⁴ The study demonstrated a statistically significant difference in age-standardised rates of AAS in Māori patients (6.9 per 100,000 person-years) compared with non-Māori patients (2.0 per 100,000 person-years).⁴ The data show the significant ethnic disparity that exists in cases of AD, and following a further study that was performed on a national level a concordant result was found. The age-standardised incidence rates by ethnicity demonstrate that Māori and Pacific peoples have a significantly higher rate, almost three to six times more, respectively compared with their European counterparts.³

Methods

Patients diagnosed with AD based on the International Classification of Diseases (ICD-10) version 2 code were identified from the Aotearoa New Zealand Ministry of Health National Minimum Dataset (NMDS).² Data were analysed further by performing an age-adjusted incidence rate according to gender and prioritised ethnicity using census population data (estimated resident population) obtained from Statistics New Zealand. This was then grouped into four blocks based on the closest census year, and person-years were obtained from that census year. The age standardisation was performed using the World Health Organization standard population.⁵ Case numbers and person-years were derived for the periods 2001–2003, 2004–2009, 2010–2015 and 2016–2020. Comparisons of age-standardised incidence rates were made using z-tests, where differences between rates were divided by Euclidean distance of their standard errors. “European and Other” was used as the reference group for comparisons between ethnicities within each time period, while 2001–2003 served as the reference period for comparisons of temporal trends within each ethnicity. A p-value of <0.05 (two-tailed) was considered statistically significant.

Results

There was a significant difference in age-standardised incidence rate of AD in patients who identify as Māori and Pacific peoples compared with their European counterparts (p<0.001) (Table 1). The findings were similar when stratified by both gender groups. However, the age-standardised incidence rate in female Māori and Pacific peoples was almost four to five times higher over the four census years compared with patients who identify as European and Other (p<0.001) (Figure 1 and 2).

Based on the 2018 census data, age-standardised incidence rates of AD in both male and female Māori patients were three times higher, with males being 11.3 per 100,000 person-years and females being 7.2 per 100,000 person-years compared with their European and Other counterparts (p<0.001). The age-standardised incidence rates of AD in male and female Pacific peoples were substantially higher, with males being four times higher at 13.9 per 100,000 person-years and females being five times higher at 10.1 per 100,000 person-years compared with their European and Other counterparts (p<0.001) (Table 1).

View Table 1, Figure 1–2.

Discussion

The findings demonstrate an ongoing and significant disparity affecting the Māori and Pacific peoples in Aotearoa New Zealand. This was also addressed in a previous study that demonstrated that Māori patients are at a higher risk of AAS, showing that prompt identification and diagnosis is crucial to ensure optimal implementation of appropriate treatment.⁶ From what has been shown in our study, this should also apply for patients who identify as Pacific peoples.

Outcomes following intervention for type A AD based on ethnicity also demonstrate a similar disparity in outcomes, with Pacific peoples having a higher rate of operative mortality compared with other ethnic groups.⁷ This was also observed in other population-based studies looking at the outcome following AD—in the United States of America, Black and African Americans were shown to have a higher mortality rate from AD compared with non-Hispanic white Americans.⁸ The cause of this disparity remains unknown, and it is likely to be multifactorial. It is well published that Māori and Pacific peoples have a higher prevalence of cardiovascular risk factors (i.e., hypertension, hyperlipidaemia and smoking), which would predispose them to developing AD.^3,4 Other factors include socio-economic barriers to accessing healthcare and inequalities that exist within the current healthcare system.^3,4

With the ongoing rising incidence of AD affecting Māori and Pacific peoples as demonstrated, it is prudent to have a call for better awareness. Disparities affecting these ethnic groups need to be research priorities in reducing morbidity and mortality. A tailored approach needs to be devised to engage with the Māori community to improve patient awareness to seek prompt medical treatment in honour of Te Tiriti O Waitangi and how partnership and protection leads to improved outcomes for all.