Ischemic preconditioning may be defined as a rapid and adaptive response to a brief episode of ischemia that slows the cellular death in a next and longer episode of ischemia. There are different views about the advantages of this phenomenon; it is why it is interesting to evaluate non-conventional parameters to compare successive episodes of ischemia.
There are many divergent results in the studies that have been made in this subject. Nevertheless, it is interesting to study this phenomenon to better understand the myocardial activity even if there is no conclusive result on the ischemic preconditioning.
In the hope of better understanding the myocardial activity this thesis had for objectives:
- To study the Ischemic Preconditioning phenomenon in the stress test through the measurement of electrocardiographic parameters
- To document in a wide, objective and reproducible manner the Ischemic Preconditioning phenomenon
- To evaluate parameters and methodologies proposed in previous works for the interpretation of the ECG stress test that allow the detection of the Ischemic Preconditioning phenomenon and a second myocardial window of protection in the 24 hours that follow an ischemic event
- To propose electrocardiographic parameters obtained from Time Series and their relation with the hemodynamic changes of the patient during a stress test
- To correlate the results obtained with the traditional clinical results in the Ischemic Preconditioning context
- To develop an ECG stress test signals database with the particular characteristics of the Ischemic Preconditioning phenomenon
The Ischemic Preconditioning study led, as a main result, to the creation of the database that is presented in this web page. Also, during the study, a great number of parameters were analyzed and the results allow establishing a close relation between the Ischemic Preconditioning.
In cooperation with the Caracas' University Hospital, ECG registries from derivations II, V5 and V6 were collected under the following conditions:
- Each patient performed two stress tests with 24 hours separation between each test
- Two groups of male individuals were formed: i) a group of 14 individuals presenting ischemic cardiopathy of 59 +/- 10.26 years old called CAD group and ii) a group of 6 asymptomatic individuals for the control group of 54 +/- 9.66 years old called Healthy group.
- There was no medication variation between both tests. No cardiac events or symptom changes happened. Each registry pair was conducted at the same time with the same equipement.
- The stress tests were conducted with a QUINTON 5000 equipment, following the Bruce protocol without modifications
For the data acquisition a prototype developped in the GBBA called SISPAS (Signal acquisition system) was used. The main characteristics of this system are:
- 3 channels of 12 bit resolution
- Variable sampling frequency: 250Hz, 360Hz, 500Hz and 1000Hz
- Serial RS-232 @ 57600 BPS communication
- Gain control (1, 2, 4, 8) to adjust the siganls to the A/D converter and thus increase the S/N ratio
The data acquired by the QUINTON was connected to the SISPAS were it was preamplified, filtered, digitalized and transmitted to the Hard Drive Disk. The sampling frequency used in this work was 250 Hz, chosen because it was a standard in databases and due to storage limitations.
Each registry of the database is stored using the D**$.dat notation where '**' is the number asigned to each patient and '$' is the reference to the sequence of each test. $ will be 'A' when the registry correspods to the initial stress test and 'B' when it corresponds to the test carried out 24 hours later.
This MATLAB function is used to read the registries acquired using the Signal Acquisition System (SISPAS). The function definition is as follows:
[D2 v5 v6 t] = read_reg(name)
The input value of this function is a string containing the full (relative) path to the registry one wishes to read. The string must also contain the .DAT extension at the end of the file, i.e.: name = 'ControlGroup/D151.DAT'.
The return values of this function are the three complete raw signals corresponding to the three derivations plus a time axis that may be used to plot the three signals with a time reference. In addition to this, the function returns a plot showing a part of the three signals that were read. An example of the return plot of the function is:
These plots are used to check that the signals were correctly read.
It's important to take into account there has been no preprocessing (other than that made by SISPAS), so the signals may need some processing before they are useful.
Make sure you have read the prior sections before using these signals. Their correct usage and results interpretation may depend on it.
To download the Ischemic Cardiopathy Database signals click here