TIMI Risk Index Calculator

About

The TIMI Risk Index was developed by Morrow et al. and published in the Journal of the American College of Cardiology in 2000 using data from 84,287 patients in the National Registry of Myocardial Infarction (NRMI) databases. The TRI is calculated using the formula: (age/10)² × (heart rate / systolic blood pressure) × 1.4. The index reflects the physiological principle that mortality risk increases exponentially with age and is directly proportional to heart rate while inversely proportional to systolic blood pressure — capturing both the patient's physiological reserve and acute hemodynamic compromise. The TRI demonstrated excellent predictive accuracy with a c-statistic of 0.78 for in-hospital mortality, comparable to the more complex 9-variable TIMI STEMI score. The score is stratified into three risk tiers: <25 indicates low risk (~1.5% 30-day mortality), 25-40 indicates moderate risk (~3.5% mortality), and >40 indicates high risk (~8% mortality). The TRI was externally validated in multiple independent STEMI cohorts and remains a useful tool for rapid risk stratification in emergency settings, particularly when complete clinical information for the full TIMI score is not immediately available.

Formula

TRI = (Age / 10)² × (Heart Rate / Systolic BP) × 1.4

The TIMI Risk Index is calculated from three physiologically essential variables. Age is squared in the formula (divided by 10 first), reflecting the exponential increase in cardiovascular mortality with advancing age — older patients have reduced physiological reserve and higher comorbidity burden. Heart rate in the numerator captures the hemodynamic stress response: tachycardia indicates sympathetic activation, reduced stroke volume, or pump failure. Systolic blood pressure in the denominator reflects myocardial perfusion pressure — hypotension directly correlates with worse outcomes. The multiplicative constant 1.4 calibrates the index. The TRI produces a continuous score: values below 25 indicate low risk (~1.5% mortality), 25-40 indicate moderate risk (~3.5% mortality), and values above 40 indicate high risk (~8% mortality). The advantage of the TRI over the full TIMI score is its simplicity — it can be calculated immediately on presentation with only the vital signs and age, without requiring history, ECG interpretation, or Killip classification.

Score Interpretation

The TIMI Risk Index provides a rapid, objective risk stratification tool that can be applied immediately on patient presentation using only vital signs and age, without requiring detailed history, ECG interpretation, or Killip classification. This makes it particularly valuable in busy emergency departments, mass casualty scenarios, and pre-hospital settings where the full TIMI STEMI score may not be immediately calculable. The TRI has been validated across diverse STEMI populations including patients undergoing primary PCI, those treated with fibrinolysis, and in multinational registries. Its discrimination (c-statistic 0.78) is comparable to the more complex TIMI STEMI score, demonstrating that the three core physiological variables capture most of the prognostic information. The TRI also correlates with in-hospital complications including cardiogenic shock, heart failure, and major adverse cardiac events. When used alongside the full TIMI STEMI score or GRACE score, the TRI provides complementary rapid risk assessment that enhances clinical decision-making. It is particularly helpful in identifying high-risk patients (TRI > 40) who may benefit from early transfer to tertiary care centers for primary PCI, and low-risk patients (TRI < 25) who may be candidates for streamlined care pathways.

Reference Ranges