Comorbidity of heart, stroke and vascular disease

What is multimorbidity and comorbidity?

Many people with chronic conditions do not have a single, predominant condition, but rather they experience multimorbidity—the presence of 2 or more chronic conditions in a person at the same time (AIHW 2021).

The health effect of multimorbidity can be greater than the combined effect of individual conditions, leading to more severe illness, poorer prognosis and premature death. People with multimorbidity generally use more health services, including increased contact with primary health care services, with more complex hospitalisations and poorer outcomes.

People with cardiovascular disease (CVD) often live with other chronic conditions besides CVD. The additional conditions experienced by a person who has CVD is known as comorbidity. In this report, the focus is on the comorbidity of CVD (noting that a person may have more than 1 cardiovascular disease) in combination with diabetes and/or chronic kidney disease (CKD). These 3 diseases are closely associated, with shared underlying causes and risk factors, along with common prevention, management and treatment strategies. The interrelationship between their effects means that diabetes and CKD also act as risk factors for coronary heart disease, stroke and other cardiovascular diseases (AIHW 2016).

An ageing population, along with unfavourable risk factor trends and a high prevalence of chronic disease in the community are expected to result in a rise in the prevalence of CVD comorbidity, and higher rates of CVD among among people with other chronic conditions.

In 2017–18, based on self-reported data, of the estimated 1.2 million Australians who had heart, stroke and vascular disease, 950,000 (82%) also had at least 1 of 9 other selected chronic conditions, including:

  • arthritis, 572,000 (49%)
  • back problems (dorsopathies), 401,000 (35%)
  •  mental and behavioural conditions, 342,000 (30%)
  • diabetes mellitus, 261,000 (23%)
  • asthma, 195,000 (17%)
  • osteoporosis, 166,000 (14%)
  • chronic obstructive pulmonary disease, 119,000 (10%)
  • cancer, 82,400 (7.1%)
  • kidney disease, 76,900 (6.6%) (ABS 2018).

Heart, stroke and vascular disease was reported as a comorbidity by 32% of people with kidney disease, 22% of people with diabetes mellitus, 20% of people with chronic obstructive pulmonary disease and 19% of people with cancer (ABS 2018).

Note that these data are based on self-report, and rely on respondents providing accurate information—some conditions, such as chronic kidney disease, are under-reported.

Prevalence of CVD, diabetes and CKD

Reliable estimates of the comorbidity of CVD, diabetes and CKD in the Australian population can be derived from large-scale biomedical health surveys. The most recent of these was the National Health Measures Survey, the biomedical component of the 2011–13 Australian Health Survey (ABS 2013).

In 2011–12, an estimated 4.9 million Australian adults (29%) had CVD or diabetes or CKD (AIHW 2014). Of these, over three-quarters (3.7 million or 22% of adults) had only 1 of CVD, diabetes or CKD, however 1.2 million (7.2% of adults) had at least 2 of CVD, diabetes or CKD:

  • 601,000 (3.5%) had CVD and CKD
  • 342,000 (2.0%) had CVD and diabetes
  • 96,000 (0.6%) had diabetes and CKD
  • 182,000 (1.1%) had all 3 conditions (Figure 1).

Men were more likely than women to have all 3 conditions (1.5% compared with 0.6%).

Among adults with CVD, 30% also had diabetes and/or CKD.

The prevalence of comorbidity of CVD, diabetes and/or CKD increased with age, more than tripling between the ages of 18–44 and 65 and over (from 12% to 44%) (AIHW 2014).

Figure 1: Prevalence of CVD, diabetes, CKD and their comorbidity, persons aged 18 and over, 2011–12

The Venn diagram shows the overlapping proportion of adults who had CVD, diabetes or CKD in 2011–12. An estimated 15.1% had CVD only and 1.1% had all 3 conditions.

Prevalence of CVD, diabetes and CKD in the Aboriginal and Torres Strait Islander population

In 2012–13, an estimated 117,000 Indigenous adults (35%) had CVD, diabetes or CKD. This proportion was higher than in the non-Indigenous population (30%) (AIHW 2015).

Of all Indigenous adults with CVD, diabetes or CKD, 38% had 2 or more conditions together, compared with an equivalent figure of 26% for the non-Indigenous population—11% had all 3 conditions together, compared with 3.9% of the non-Indigenous population.

In the Indigenous population, 33% had CVD only without diabetes or CKD comorbidities—a lower proportion than in the non-Indigenous population (51%).

Hospitalisations with CVD, diabetes and CKD

Hospital comorbidity

Where a person has 2 or more of CVD, diabetes or CKD recorded in their episode of hospitalisation, this is referred to as hospital comorbidity.

Dialysis hospitalisations have been excluded because they are often performed as routine treatments on a same-day basis and have no other comorbid diagnoses recorded.

Note also the coding rule for diabetes—if present, diabetes is universally coded on a patient’s hospital record. This is unlike CVD and CKD, which are coded only if they affected the care and treatment provided during the hospitalisation. This may under-report hospital comorbidity of these diseases.

In 2018–19, there were around 2.2 million hospitalisations in people aged 18 or over in which CVD, diabetes or CKD was present as the principal and/or an additional diagnosis. This equates to 21% of all non-dialysis hospitalisations for people 18 and older.

The majority of hospitalisations (1.2 million, or 55%) included CVD, either alone (853,000, or 39%) or in combination with diabetes and/or CKD (354,000, or 16%) (Figure 2).

The most common comorbidity was CVD and diabetes (185,000, or 8.4%), with CVD and CKD present in 55,100 hospitalisations (2.5%). There were a further 114,000 hospitalisations (5.2%) where all 3 diseases were present.

Figure 2: Hospitalisations (excluding dialysis) with CVD, diabetes or CKD, persons aged 18 and over, 2018–19

The Venn diagram shows the overlapping proportion of hospitalisations among adults in 2018–19 with CVD, diabetes or CKD as the principal and/or additional diagnosis. 38.8% of hospitalisations were for CVD only, but 5.2% of hospitalisations had all 3 conditions.

Age and sex

The rate of hospitalisations with comorbidity of CVD, diabetes and/or CKD increases with age.

In 2018–19, for example, people aged 45–64 were 8.6 times as likely to have a combination of CVD and diabetes recorded on their hospital record as people aged 18–44 (730 and 85 per 100,000 population). For those aged 65 and over, this difference increased to more than 40 times the rate of those aged 18–44 (3,600 and 85 per 100,000 population.

Men were more likely to be hospitalised with comorbidity than women. After adjusting for age, the rate of hospitalisation where all 3 diseases were recorded was 1.6 times as high for men as for women (625 and 379 per 100,000 population).

Hospital comorbidity in the Aboriginal and Torres Strait Islander population

In 2018–19, there were 89,100 non-dialysis hospitalisations of Indigenous people aged 18 and over where CVD, diabetes or CKD was present as a principal diagnosis and/or additional diagnoses.

Of these hospitalisations, 33,100 (37%) recorded 2 or 3 of the diseases—8,200 (9.2%) recorded diabetes and CVD together, 1,900 (2.1%) recorded CVD and CKD, 13,600 (15%) recorded CKD and diabetes, and 9,300 (10%) recorded all 3 diseases.

A higher proportion of Indigenous adults had CVD, diabetes and CKD hospital comorbidity, compared with non-Indigenous adults (37% and 22%). The proportion of Indigenous hospitalisations with all 3 diseases (10.5%) was also higher than that in the non-Indigenous population (5.0%).

After adjusting for age differences in the populations, the rate of hospitalisation of Indigenous people recording all 3 diseases was 2.3 times as high as the rate of non-Indigenous people (22,000 and 9,400 per 100,000 population).

Deaths from CVD, diabetes and CKD

Often, more than 1 disease contributes to a death. Along with the underlying cause of death, a medical practitioner or coroner will also record associated causes on a death certificate. The most complete representation of cause-of-death will consider the contribution of both underlying and associated causes (Harding et al. 2014).

Whereas CVD is a common underlying cause of death, diabetes and CKD are more likely to be recorded as associated causes of death. Both diabetes and CKD are known to be under-reported in national mortality statistics, and can be omitted from death certificates as contributory causes of death (Sypek et al. 2018, McEwen et al. 2011).

Association of CVD, diabetes and CKD deaths

Of the 165,000 deaths registered among persons aged 18 and over in Australia in 2019, CVD, diabetes and CKD were listed as underlying or associated causes in 93,300 of these.

CVD was listed as either an underlying or associated cause of death in 85,800 (52% of adult deaths), while diabetes (17,100) and CKD (17,600) were each associated with about 10%. In total, 57% of adult deaths had at least 1 of these diseases recorded.

At least 2 of CVD, diabetes and CKD were recorded as causes of death in 24,000 death certificates, representing 14% of all adult deaths. CVD and diabetes occur together in half of these, contributing to 10,100 (6.1%), while CVD and CKD was associated with 9,400 deaths (5.7%). Diabetes and CKD (800 deaths) accounted for less than 1% of adult deaths. About 2% of adult deaths (3,500) in 2019 had all 3 diseases recorded (Figure 3).

Figure 3: Deaths with CVD, diabetes and CKD listed as any cause of death, persons aged 18 and over, 2019

The Venn diagram shows the proportion of deaths among adults in 2019 with CVD, diabetes or CKD as any cause of death. CVD was recorded as the only cause in 38.1% of deaths, and all 3 diseases were recorded as the underlying or associated cause in 2.1% of deaths.

Diseases commonly associated with CVD deaths

When the underlying cause of death is a cardiovascular disease, another cardiovascular disease is often listed as an associated cause of death (Table 1). Associated causes commonly listed with coronary heart disease deaths, for example, include heart failure, hypertensive diseases and cardiac arrhythmias.

Non-CVD causes that were commonly associated with CVD deaths in 2019 included dementia, diabetes and diseases of the urinary system (largely CKD).

Table 1: Common associated causes where a cardiovascular disease is the underlying cause of death, 2019

Coronary heart disease (I20–I25)

N=17,731

Cerebrovascular diseases (I60–I69)

N=9,783

Heart failure (I50–I51)

N=3,580

Heart failure (I50–I51)

5,183 (29%)

Hypertensive diseases (I10–I15)

2,627 (27%)

Diseases of urinary system (N00–N39)

797 (22%)

Hypertensive diseases (I10–I15)

4,103 (23%)

Dementia, incl. Alzheimer's disease (F01, F03, G30)

1,644 (17%)

Symptoms, signs and abnormal clinical and laboratory findings (R00–R99)

551 (15%)

Cardiac arrhythmias (I47–I49)

2,955 (17%)

Symptoms, signs and abnormal clinical and laboratory findings (R00–R99)

1,279 (13%)

Influenza, pneumonia (J09–J18)

442 (12%)

Diabetes mellitus (E10–E14)

2,469 (14%)

Cardiac arrhythmias (I47–I49)

1,210 (12%)

Cardiac arrest (I46)

313 (8.7%)

Diseases of urinary system (N00–N39)

2,517 (14%)

Coronary heart diseases (I20–I25)

1,036 (11%)

Dementia, incl. Alzheimer's disease (F01, F03, G30)

297 (8.3%)

Source: AIHW National Mortality Database.

Cardiovascular diseases commonly associated with other causes of death

CVD was listed as an associated cause of death for 44% of all deaths registered in 2019. When a type of CVD was listed as an associated cause in 2019, the most common underlying causes of death include:

  • Heart failure as associated cause: common underlying causes included coronary heart disease (25%), malignant neoplasms (cancer) (9.8%), chronic lower respiratory diseases (8.6%)
  • Hypertensive disease as associated cause: common underlying causes include coronary heart disease (22%), malignant neoplasms (cancer) (15%), cerebrovascular diseases (mostly stroke) (14%)
  • Coronary heart disease as associated cause: common underlying causes include malignant neoplasms (cancer) (21%), diabetes mellitus (13%), dementia, including Alzheimer’s disease (9.6%)
  • Cardiac arrhythmias as associated cause: common underlying causes include coronary heart disease (22%), malignant neoplasms (cancer) (15%), cerebrovascular diseases (mostly stroke) (8.9%).