Figure 1.
Generalized functional diagram for a typical 12-lead ECG system.
Figure 2.
Schematic summarizing all stages of ECG data processing by the system.
Table 1.
RMS difference values for all 10 patients' original versus re-digitized files when both the original and re-digitized files were collected on the same model of Cardiax ADC.
Table 2.
RMS difference values for all 10 patients' original versus re-digitized files when the original files were collected on a Cardiax ADC and the re-digitized files on a CorScience ADC.
Table 3.
Automated clinical diagnostic statements outputted by the Cardiax algorithm for the original versus re-digitized files when both files were collected on the same model of Cardiax ADC.
Figure 3.
“Worst case” result from a qualitative standpoint.
Original (A) and re-digitized (B) 12-lead ECG tracings from patient 2H as interpreted by the Leuven automated diagnostic algorithm when a Cardiax ADC was used to collect the original data and a CorScience ADC the re-digitized data. This was the only file amongst the 10 tested wherein a minor change was elicited in the automated interpretation of the re-digitized compared to the original file. This minor change occurred only when using the Leuven algorithm (a corresponding change did not occur for the automated interpretation when using the Cardiax algorithm under any circumstances), and occurred regardless of whether the re-digitized data were collected on a CorScience or Cardiax ADC. Note also the modest change in DC offset (which may have been a key contributor to the slight change in the automated interpretation) as well as the very minor differences between (A) and (B) in some intervals, axes and voltages as automatically determined.
Figure 4.
“Worst case” result from a quantitative standpoint.
Original (A) and re-digitized (B) 12-lead ECG tracings from patient 4D as interpreted by the Leuven automated diagnostic algorithm when a Cardiax ADC had been used to collect the original data and a CorScience ADC the re-digitized data. This patient has a left bundle branch block and the results shown in (B) represent the quantitative “worst case” encountered during the study inasmuch as the voltage differences between original and CorScience re-digitized files were the largest noted overall (Table 2). Consistent with the data in Table 2 (and in Table 1), the most pronounced differences between this patient's original and re-digitized files occurred in his leads V1–V3 (i.e., emanating from channels CR1–CR3), where, in the CorScience re-digitized compared to the original file, a slight additional concavity could also be visually noted in the ST segments.
Table 4.
Automated clinical diagnostic statement(s) outputted by the Leuven algorithm for the original vs. re-digitized files when the original file was collected on a Cardiax ADC and the re-digitized file on either a Cardiax or CorScience ADC.
Figure 5.
Effect of “true simultaneous” sampling.
(A) The study's standard “round-robin sampled” Cardiax-re-digitized file for the same patient 4D with a left bundle branch block whose original file is shown in Figure 4A. Possibly due in part to the higher sampling rate at Cardiax's compared to CorScience's ADC (i.e., 1000 Hz rather than 500 Hz), the visual differences in this patient's leads V1–V3 between the Cardiax re-digitized and original file are perhaps slightly less apparent than those between the CorScience re-digitized and original file as observed in Figure 4. (B) When using for re-digitization a just-released new Cardiax device briefly loaned to us after our formal study's completion that employs “true simultaneous” sampling via incorporation of Texas Instruments' ADS1298 chip, the visual differences in this same patient's V1–V3 complexes essentially “disappear” in conjunction with a ∼2–3 fold reduction in the RMS difference values for channels CR1, CR2 and CR3 to 9.4, 9.4 and 11.7 ADC counts, respectively. Compare these results to the corresponding results for CR1–CR3 for this patient as shown in Tables 1 and 2 when “non true-simultaneous sampling” was used for re-digitization.