Type 2 - Myocardial injury due to imbalance between oxygen supply and demand

Clinical conditions which reduce the myocardial perfusion (e.g. severe hypotension or shock) or those which increase the myocardial oxygen demand (e.g. sustained tachycardia such as AF, or severe hypertension) can cause myocardial injury resulting in a rise in the cTn. In this situation, the clinical presentation is key to making the correct diagnosis and applying the correct treatment. As a result of implementation of hs Tn, the number of patients diagnosed with type 2 MIs has doubled.

The criteria for Type 2 MI includes detection of a rise and/or fall of cTn with at least one value above the 99th percentile and evidence of an imbalance between myocardial oxygen supply and demand, unrelated to coronary thrombosis and with at least one of the following:

•    Symptoms of acute myocardial ischaemia.
•    New ischemic ECG changes.
•    Development of pathological Q waves.
•    Imaging evidence of new loss of viable myocardium, or new RWMA in a pattern consistent with an ischemic aetiology.

It is increasingly recognised that some patients experience MI with normal or near normal coronary arteries on angiography (≤ 50% stenosis in a major coronary artery). Myocardial infarction with non-obstructive coronary arteries (MINOCA) disproportionately affects women and may account for up to 50% of MIs in women < 55 years of age. MINOCA is more commonly seen in non-Caucasian individuals, and those affected are less likely to have the typical cardiovascular risk factors such as hypertension, diabetes, smoking and hyperlipidaemia. There are several recognised causes of MINOCA including coronary artery spasm, which can occur spontaneously or following the use of illicit drugs e.g. cocaine.

This article focuses on the two main types of MI (Type 1 and Type 2) seen by Underwriters and Claims Assessors. However, there are other types of MI, particularly Type 4a and 4b, which are briefly covered below. Type 3 MI refer to MIs diagnosed at death, and Type 5 MIs are associated with coronary artery bypass grafting. Details of these can be found at Assessment and classification of patients with myocardial injury and infarction in clinical practice | Heart

Type 3 – Myocardial Infarction - diagnosed at death


Type 4 a  – Myocardial Infarction with percutaneous coronary intervention (PCI)

Type 4 a - PCI may cause a rise in cTn, and this form of cardiac procedural myocardial injury is arbitrarily defined by increases of cTn values (> 99th percentile Upper Reference Limit/URL) in patients with normal baseline values (≤ 99th percentile URL) or a rise of cTn values > 20% of the baseline value when it is above the 99th percentile, but it is stable or falling.


Type 4 b – Myocardial Infarction with stent thrombosis associated with PCI

Type 4 a & Type 4 b are both iatrogenic related MIs, and in addition to the cTn rise, they require one of the following:

•    New ischaemic ECG changes.
•    Imaging evidence of new loss of viable myocardium, or RWMA in a pattern consistent with an ischemic aetiology.
•    Angiographic findings consistent with flow limiting complications, such as coronary dissection or vessel thrombus.

 

Type 5 – Coronary artery bypass grafting (CABG) - related Myocardial Infarction


Comparing Type 1 and Type 2 MIs

Studies comparing Type 1 with Type 2 MI patients, reveal statistically different patient characteristics and outcomes, including:

•    Type 2 MI patients are older than Type 1 MI patients.
•    Type 2 MI patients have a higher prevalence of comorbidities, such as heart failure, AF, and kidney disease.
•    Rates of intervention, such as PCI and CABG are lower among Type 2 MI patients.
•    Type 2 MI patients have a significantly increased risk of all–cause death compared to Type 1 MI patients, in both the short-term and long-term. This increased risk is likely reflective of more comorbidities in the older Type 2 MI patients.


What is the relevance of these different types of MIs for Insurers?

Heart Attacks are a very common cause for claims on Critical Illness (CI) policies. The policy definitions for Heart Attack have evolved over time with successive generations of policies. These changes were developed by the ABI, CI working party, and were reflected in the Statements of Best Practice, and latterly, the Guide to Minimum Standards.

The older definition requires evidence of heart muscle death due to inadequate blood supply, as evidenced by chest pain, new ECG changes, and a rise in cardiac enzymes/Tn. Subsequent policy definitions included a “severity threshold” for Tn, reflecting the introduction of  hs Tn by clinicians, and with it the diagnosis of more MIs, many of which would formerly have been diagnosed as “unstable angina”.

Insurers frequently see claims for MI where cTn measurements are below the policy threshold. In these cases, the advice of a CMO may be required to determine if the trajectory of cTn readings would have exceeded the threshold, if measurements had been obtained at the peak time.

Claims for patients who have presented to hospital with MIs associated with ST segment elevation on ECG (STEMI) will usually not have had cTn levels measured. This is because the diagnosis of STEMI requires only symptoms suggestive of MI and confirmatory ECG evidence (ST segment elevation). The priority in these cases is for rapid reperfusion of the myocardium by primary PCI (image 4), and cTn evidence is not required.