One diagnostic tool used to predict the potential for illness and possibly death due to cardiac issues is the treadmill test and this is mostly associated with Duke Treadmill Score. In this test, the person is connected to machines to monitor blood pressure and heart activity. The person is then required to walk on a treadmill that increases in speed and incline. The reaction to this physical stress has been found to be a good predictor of future cardiac issues.
This exercise test is beneficial in assessing symptomatic patients to determine the possibility of significant coronary disease and the likelihood of future cardiac events.
The Duke Treadmill Score is a standardized measure for interpreting the results of the exercise test that is normally administered with strict monitoring.
There is a particular, though complicated, formula for Duke Treadmill Score. The basis for determining accomplishment is an exercise scale called Bruce protocol. The formula involves the number of minutes a person is able to keep to the protocol without having to terminate the test. The test is terminated due to severe ischemia (lowered blood flow) and angina, with a corresponding change in the ECG at the ST wave, with a lowering or increasing of the blood pressure, and with heart arrhythmias.
The actual formula is as follows:
(Bruce equivalent number of minutes until test termination) – (5 x the amount of ST segment deviation in mm) – (4 x the angina index)
The angina Index is the severity of pain: 0=none, 1=non-limiting and 2=exercise-limiting.
Total score of >/ = +5 is low risk; -10 to +4 is moderate risk; < = -11 is high risk
So, for example, if a patient goes 15 minutes before interruption, but the test is stopped because of severe ischemia and angina, with a 3mm change in the ST wave, the score is thus: 15 – 5(3) – 4(2) or 15-15-8 = -8. Based on the scale above, the risk is moderate (within the range of -10 to +4.
Studies have shown that over a six year period, the above score is a good indicator of cardiac illness and/or death. Different groups of people have been tested, with the same result so far as prediction is concerned. Some of these groups have been those with prior cardiac histories, those with diabetes, and a comparison of an overweight group with a normal weight group. All groups showed similar results so far as prediction of future illness and death.
One of the major predictors of future problems in the diabetic group and the control non-diabetic group was the rate at which the heart recovered. The longer the time it took for the heart to return to the pretest level the more likelihood of future problems. This seems to hold true across other test groups.
Though the formula seems hard to interpret, it is a basic standardized measurement that can give a good prediction based on the numbers obtained. Different factors are accounted for, and weighted, according to the formula coefficients. This allows different groups of patients to be compared to the formula to predict the effect of different factors on cardiac health.
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