Programa de capacitación

3.2.1 The ECG Repeatability Study ECG methods

The ECG Repeatability Study followed the standardized protocol used in the ARIC Study for placing electrodes, room condition and data collection (4). All ECG recordings were carried out in a quiet, temperature-controlled room. Participants

reported for the visits between 7:30 and 11:30 am. After participants rested in the supine position for fifteen minutes, one of four trained and certified ECG technicians recorded ten-second, twelve-lead ECGs using Kendall Q-Trace 5400 Ag/AgCl electrodes (Ludlow Co, Chicopee, Mass). The E-V6 Halfpoint method (5) was used when recording the first of two ECGs using a MAC Personal Cardiographer (Marquette Electronics, Inc,

Milwaukee, WI). The E-V6 Halfpoint method improves the precision and the

repeatability of chest electrode positioning by placing the V4 electrode at the horizontal

level of the fifth intercostal space at the half-way point between the midsternal line and the left midaxillary line (V6 location). Without removal of the electrodes, the recording

was repeated after 1 to 2 minutes. ECGs were digitized and sent via modem after each recording session to the Epidemiological Cardiology Research (EPICARE) Center at the Wake Forest University School of Medicine. The EPICARE Center, blinded to

participant identity and previous ECG readings, processed the ECGs using the most 56

recent version of the Marquette GE program, version 12SL. Following an identical protocol, a second set of ECGs from the same participants were obtained on the second visit.

3.2.2 The ARIC Study ECG methods

The ARIC Study used standardized protocol for the acquisition of and processing of ECGs (4). All ECG recordings were carried out in a quiet, temperature-controlled room. After participants rested in the supine position for fifteen minutes, trained and certified ECG technicians recorded ten-second, twelve-lead ECGs using Kendall Q-Trace 5400 Ag/AgCl electrodes (Ludlow Co, Chicopee, Mass). The E-V6 Halfpoint method (5) was used when recording ECGs using a MAC Personal Cardiographer (Marquette Electronics, Inc, Milwaukee, WI). The E-V6 Halfpoint method improves the precision and the repeatability of chest electrode positioning by placing the V4 electrode at the

horizontal level of the fifth intercostal space at the half-way point between the midsternal line and the left midaxillary line (V6 location). ECGs were digitized and sent via modem

after each recording session to the EPICARE Center (Wake Forest University, Winston- Salem, NC). The EPICARE Center, blinded to participant identity processed the ECGs using the 12SL version of the Marquette GE program.

The ARIC Study standardized procedure for data collection of ECGs

The ARIC Study standardized procedure for data collection of ECGs and quality control are briefly described below (6).

Each participant, chest exposed, was instructed to lie on the recording bed with arms relaxed at the sides. The individual was asked to avoid movements which might cause errors in marking the electrode locations. A felt tip pin was used to mark the six chest electrode positions. In order to increase the electrode/skin interface, the electrodes were placed on the skin for at least 2 to 3 minutes before taking the ECG. The 10 electrode sites (6 chest and four limb sites) were wiped with sterile alcohol in order to remove skin oil and perspiration. The four limb leads were placed on the medial side of the left ankle, right ankle, the left wrist and the right wrist. The six chest leads were placed as follows: Electrode V2 was placed in the intercostals space immediately to the

left of the sternal border. Electrode V1 was placed in the fourth intercostal space

immediately to the right of the sternal border. The E point was defined as the space horizontally to the midsternal line and parallel with the fifth intercostal space. Electrode 6 was the same location as the E point in the midaxillary line (straight down from the center of the armpit). Electrode V4 was located using the E-V6 halfpoint method. A

measuring tape was placed over the skin between the E point and the V6 marking. V4 was

midway between the E and V6. Likewise, V3 was midway between V2 and V4. V5 was

midway between the location between V4 and V6. If technical problems were observed

due to poor electrode contact then it was necessary to do further preparation: 1) remove excess hair with a razor; or 2) brush sandpaper over the skin three times using light pressure. When placing each electrode, it was massaged in a circular motion to maximize the contact with the skin.

After placing the electrodes on the skin, the ‘record’ key was pressed. The machine read, ‘acquiring data.’ The machine automatically printed the ECG after it acquired 10 seconds of good data. The ECG was torn off the machine and filed at the field center, and read locally by clinical physicians for notification and referral. The records were then placed in participants’ local data files.

Additionally, the ECGs were transmitted to the EPICARE Center. If there was a problem transmitting to the EPICARE Center, ECGs were transmitted to the MAC 12 at the Minneapolis ECG Coding Center. Every morning, the EPICARE Center notified each ARIC field center of the identification numbers (IDs) received. After successful confirmation that EPICARE received the transmission, and it was of good quality, the ECG was deleted from the Mac PC Storage Directory. Every other week EPICARE sent these data to the Coordinating Center (CC). All resting twelve-lead ECG records with computer generated ECG findings listed below, which qualified for serial change coding at follow-up visits, and at least a 10% random sample of the remaining ECGs were visually coded at the Minnesota Coding Center by the Minnesota Code: 1) any 1-code; 2) and 4-1, 4-2, 5-1 or 5-2 code; 3) any 9-2, 6-4, 7-1-1, 7-2-1 or 7-4 code; and 4) any 6-1, 6- 8 or heart rate ≥ 140. The visual Minnesota Codes were sent to the CC for data

comparison with the computer generated codes. Adjudication of computer codes was made only on ECGs that had a discrepancy involving any Q-code, ST, or T wave changes from Visit 1 to Visit 2. The CC determined the IDs that had any of these discrepancies and sent a report form to the Minnesota Coding Center. These ECGs were examined and the adjudicated record was sent to the CC. The CC added the adjudicated codes to the database as the definitive Minnesota codes for the IDs involved.

The computer assigned codes were used in the Study Data in all cases except when adjudication resulted in a code different from the original EPICARE code. If the two centers disagreed on ‘minor’ codes (codes other than Q waves, ST depression, T waves, ST-elevation, bundle branch block, Wolf-Parkinson-White, complete atrio- ventricular block, heart rate ≥ 140), the EPICARE reading prevailed. For major codes, the adjudicated reading prevailed.

Baseline and follow-up ECGs were compared. When two (adjudicated) ECGs were available from two separate visits, a determination was made at the CC as to whether the Minnesota code change criteria were met. Determination was made by a computer algorithm and not by Minnesota Coders. IDs that fit the change in criteria were examined side by side for serial ECG change at the Minnesota ECG Reading Center. Objective rules for side-by-side ECG evaluation were used to determine whether a Minnesota code change between ECG pairs was significant between visits, using the first clinic visit ECG as the referent.

All ECG technicians were certified and were required to take an average of 3 ECGs per week over a two-month period in order to remain familiar with the procedures and equipment. Each technician was observed quarterly by senior technicians while taking a participant’s ECG, and performance was documented. EPICARE checked the quality of the data.