Acute myocardial infarction with high Killip class: do geographic differences matter?

Graphical Abstract

Impact of evidence-based interventions on geographic variations and on differences in outcomes between ST-segment elevation myocardial infarction and non-ST-segment elevation myocardial infarction. Quality indicators might have a role to reduce these differences by assessing healthcare delivery.

This editorial refers to ‘Difference in the in-hospital prognosis between ST-segment elevation myocardial infarction and non-ST-segment elevation myocardial infarction with high Killip class: Data from the Japan Acute Myocardial Infarction Registry’, by Motoki Fukutomi et al. pp. 503–512.

Coronary artery disease (CAD), including myocardial infarction (MI), is the most common cause of heart failure (HF). Conversely, HF is a frequent complication of MI and significantly worsens the prognosis of patients with CAD. Although the impact of HF on outcomes in patients hospitalized with MI have been evaluated in the past,¹ little is known about outcome differences between ST-segment elevation MI (STEMI) and non-STEMI (NSTEMI) in the setting of acute HF (AHF). Although STEMI and NSTEMI share some common underlying pathophysiological mechanisms,² they have some major biological and clinical differences. In STEMI, an acute thrombotic coronary occlusion is generally observed, whereas in NSTEMI, the coronary artery is usually affected by non-occlusive stenosis. This fact has pathophysiological, diagnostic, and therapeutic implications: (i) because of the wavefront phenomenon (myocardial necrosis progressing with increasing duration of ischaemia as a transmural wavefront from the subendocardium towards the subepicardium), myocardial infarct size in STEMI was larger and transmural, whereas infarct size in NSTEMI was smaller and subendocardial³; (ii) STEMI and NSTEMI are different in the electrocardiogram with respect to the reflection of acute myocardial ischaemia and necrosis; (iii) although coronary angiography is recommended in both entities, according to current clinical practice guidelines, most STEMIs are managed with a preferential invasive strategy as soon as possible, whereas in NSTEMI, an early invasive strategy is generally recommended with coronary angiography within the first few 24 h, if possible. However, in patients with AHF and NSTEMI, current European Society of Cardiology (ESC) guidelines recommend an emergent revascularization within the first 2 h.⁴ For both MI types, timely reperfusion limits myocardial infarct size and improves long-term left ventricular systolic function, entailing better prognosis in terms of clinical outcomes.²

Before the broad implementation of primary percutaneous coronary intervention (PPCI) programmes,⁵ several studies showed that STEMI was associated with poorer in-hospital prognosis than NSTEMI. Using an American cohort, Chan et al.⁶ described that STEMI was associated with a higher risk of short-term mortality in comparison to NSTEMI, but the latter was associated with a higher risk of long-term mortality. Similar findings were reported in a Korean registry (KAMIR),⁷ where in-hospital rates of all-cause and cardiac death were significantly higher in STEMI patients than in NSTEMI patients and were still higher within the first month, but changed after 30 days mortality (mortality rates higher in NSTEMI patients).⁷ In Europe, the SCAAR registry (2006–2010) showed a higher mortality for the entire first year in patients with STEMI compared to NSTEMI, and a comparable adjusted mortality risk between 1 and 6 years after percutaneous coronary intervention.⁸ In the current PPCI era, less differences are observed between STEMI and NSTEMI patients in terms of myocardial infarct size, transmural necrosis and clinical outcomes.⁹ Other acute complications aside (i.e. ventricular arrhythmias), it would be expected for PPCI programmes to close the historical gap of the higher short-term outcome rate of in-hospital mortality in STEMI patients compared to NSTEMI patients. Nevertheless, the risk-based invasive approach in NSTEMI patients¹⁰ would also be expected to translate into better outcomes, though less is known in this regard.

In this issue of European Heart Journal—Acute Cardiovascular Care, Fukutomi et al.¹¹ focused on patients presenting with AHF (Killip class II, III, or IV) and evaluated differences in a very short-term outcome (in-hospital prognosis) between STEMI and NSTEMI. Using data from the Japan Acute Myocardial Infarction Registry (JAMIR), they claimed a non-significant difference in all-cause in-hospital mortality (20.0% for STEMI vs. 17.1% for NSTEMI), though their data showed a statistical trend (P = 0.065). Whereas there were no differences in in-hospital death among those below 80 years (15.7% for STEMI vs. 15.2% for NSTEMI, P = 0.807), there were large differences among those ≥80 years of age (29.3% for STEMI vs. 19.8% for NSTEMI, P < 0.001). Importantly, these differences between STEMI and NSTEMI in elderly patients were also significant for in-hospital cardiac mortality (23.3% vs. 15.0%, P = 0.002). Unlike young people, older patients presenting with acute MI (AMI) and AHF were at higher risk of in-hospital mortality if they had STEMI (the adjusted was odds ratio 2.12, relative to NSTEMI). Beyond these valuable findings, this article brings some other interesting issues to light, such as the need to make a historical remark about the Killip classification and to assess geographic differences in short-term outcomes between STEMI and NSTEMI patients.

In 1967, Killip and Kimball¹² published a landmark study establishing a method for early risk stratification of AMI patients admitted to Coronary Care Units, worldwide known as the Killip classification. Among the 250 patients included in this seminal study, 33% had no AHF (6% in-hospital mortality), 38% was Killip II (17% in-hospital mortality), 10% was in Killip III (38% in-hospital mortality), and 19% was in Killip IV (81% in-hospital mortality). Although the implementation of PCI has changed the incidence of AHF and their associated in-hospital outcome, this bedside tool has stood the test of time and is yet a very reliable tool to stratify prognosis based on AHF severity. In a very recent cohort of STEMI patients including patients from 83 Spanish centres, Killip class at catheterization laboratory arrival was ∼82% Killip I, ∼9% Killip II and ∼9% Killip III–IV,¹³ a very similar figures to those reported by Fukutomi et al.¹¹ in this issue. Data from the USA¹⁴ and other European countries¹ show a consistence incidence in concomitant AHF (Killip class >I in ∼20%), which is a similar rate to the data reported from Japan by Fukutomi et al.¹¹ As predicted by Killip and Kimball more than 60 years ago, the higher the Killip class, the higher the mortality regardless of the geographic origin of the patient.^1,11,14 Besides its prognostic value in the hospital care setting, Killip class has shown to predict all-cause mortality in AMI survivors who have survived the index episode (post-discharge setting).¹⁵

Previous studies have shown wide regional variations in patient features, hospital care, coronary reperfusion (or revascularization) rates and post-discharge mortality among patients hospitalized for either STEMI¹⁶ or NSTEMI.¹⁷ Although regional differences in short-term outcomes between STEMI and NSTEMI seem to attenuate over time, there is yet an urgent need to keep improving cardiovascular outcomes. The use of the 2020 Quality Indicators (QIs) for AMI¹⁸ might help to address differences in AMI management (from pre-hospital to post-discharge care), and homogenize mortality across regions (Graphical abstract).¹⁹ Quality indicators (QIs) are a useful tool for measuring opportunities to improve cardiovascular care and outcomes in AMI patients, regardless of their Killip class.

Conflict of interest: none declared.

Data availability

There is no original data in this editorial.

 

The opinions expressed in this article are not necessarily those of the Editors of the European Heart Journal: Acute Cardiovascular Care or of the European Society of Cardiology.