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Dirk Q Feild

Publications and source records attributed to Dirk Q Feild.

5 recordsLinked to original sources
PubMed2003

Comparison of waveforms in conventional 12-lead ECGs and those derived from EASI leads in children.

To investigate the possibility of simplifying electrocardiogram (ECG) recording in children, we compared waveforms in conventional 12-lead ECGs to those derived from EASI leads in 221 children of various ages. The conventional 12-lead ECGs and the ECGs using EASI electrode positions were collected simultaneously. We developed and determined the value of age-specific transformation coefficients for use in deriving 12-lead ECGs from the signals recorded at the EASI sites. We compared the results of using age-specific coefficients to the results of using adult coefficients and studied the "goodness-of-fit" between the conventional and the derived 12-lead ECGs. The age-specific coefficients performed slightly better than the adult coefficients, and good agreement was usually attained between the conventional 12-lead ECG and the EASI-derived 12-lead ECG. Our conclusion is that EASI leads in children have the same high levels of "goodness-of-fit" to replicate conventional 12-lead ECG waveforms, as reported earlier in adults.

Adolescent↗
PubMed2002

Improved EASI coefficients: their derivation, values, and performance.

The EASI lead system, which is based on the dipole hypothesis of vectorcardiography, offers the possibility of deriving the standard 12-lead electrocardiogram (ECG) and other desired leads from ECGs recorded at only 4 sites; it uses the Frank E, A, and I electrode locations, a fourth electrode location (S) at the manubrium, and a reference electrode. Accordingly, the electrodes of this system can be applied rapidly on easy-to-locate, stable anatomical sites that leave the precordium free for other diagnostic procedures. In early EASI implementations, the derived leads differed from actual leads by more than some clinicians found acceptable. As these differences were thought to be caused by the fact that the coefficients that were used had been derived from a limited data set, we have calculated a new set of EASI coefficients for the standard 12 leads, and several other leads, by using a data set of 983 adult subjects with 120-lead ECGs and well-documented diagnoses. This database is a concatenation of 2 previously described ones: one consisting of 892 persons (normal subjects, postmyocardial-infarction patients with and without arrhythmias, and patients with ventricular arrhythmias but no history of myocardial infarction) and the other consisting of 91 patients with single-vessel coronary artery disease who underwent coronary balloon-inflation angioplasty. In addition to the coefficients for the standard 12 leads (derived for standard limb leads as well as for Mason-Likar leads), we derived coefficients for six additional unipolar leads (posterior V(7)-V(9), and right-sided V(3)R-V(5)R), the Frank orthogonal leads, and three bipolar, vessel-specific leads that have been previously shown to exhibit optimal sensitivity for acute myocardial ischemia. We also derived coefficients for the modified electrode locations of the EASI system that must be used with patients who have undergone a midline sternotomy. Optimal coefficients for lead transformations were determined by maximizing the ensemble average (over the entire data set) of the correlation between the derived and the true lead for the chosen interval of the averaged complex. For derived standard limb leads, the amplitude was adjusted to give the best root-mean-square fit over the entire PQRST interval, whereas for derived Mason-Likar leads it was adjusted to give the best ST-segment fit. The entire set of coefficients and their corresponding goodness-of-fit measures are presented.

Adult↗
PubMed2002

Comparability of 12-lead ECGs derived from EASI leads with standard 12-lead ECGS in the classification of acute myocardial ischemia and old myocardial infarction.

We compared 12-lead electrocardiograms (ECGs) derived with an improved transformation matrix from EASI leads and standard 12-lead ECGs in the detection of acute myocardial ischemia and old infarction (MI). For the ischemia test, we used ECGs of 40 patients recorded prior to and at peak inflation during percutaneous transluminal coronary angioplasty, and for old MI we used test ECGs of 382 non-MI subjects and of 472 patients with prior MI documented by enzyme findings. Two experienced ECG readers served as separate, independent standards for lead-set comparisons, and the Philips ECG analysis program also classified the ECGs. The results showed no significant differences between the two lead sets in the detection of acute inflation-induced ischemia or of old MI according to coding by the electrocardiographers or the computer program. No significant differences were found between the electrocardiographers and the lead sets for acute ischemia. Classification differences between the electrocardiographers were larger than those between the lead sets for acute and old MI and were significant for the latter (P <.001). A more detailed comparison of the lead sets suggested a possible need for modified old-MI criteria and optimization of ST classification thresholds for acute ischemic injury, specific for the EASI 12-lead ECG. We conclude that the EASI-derived 12-lead ECG deserves serious consideration as an alternative to the standard 12-lead ECG in emergency situations and for monitoring in acute-care setting.

Electrocardiography↗
PubMed2002

Statistical and deterministic approaches to designing transformations of electrocardiographic leads.

Two different approaches can be used to investigate the relationships among electrocardiographic leads: a statistical one, based on the analysis of recorded electrocardiograms (ECGs), and a deterministic one, based on physical principles that govern the current flow in irregularly shaped volume conductors such as the human body. The purpose of this study was to compare these two approaches. For the statistical investigation, the data set consisted of 120-lead ECGs recorded in a population including normal subjects (n = 290), post-myocardial-infarction patients (n = 497), patients with a history of ventricular tachycardia but no evidence of a previous myocardial infarction (n = 105), and patients with a single-vessel coronary artery disease who underwent coronary angioplasty (n = 91). Lead transformations of interest were obtained by fitting the multiple-regression model to this data set by the least-squares method. For the deterministic investigation, we used a boundary-element model of the human torso to simulate body-surface potentials in response to three orthogonal unit dipoles placed consecutively at 1,239 ventricular source locations, and the resulting body-surface potential distributions (instead of the recorded ECGs) were then fitted by the multiple-regression model. The results suggest that the lead transformations should be preferably designed by statistical analysis of recorded ECGs. Regression models with a small number of predictors (eg, those based on three ECG leads) are the most reliable; those using more predictors are fraught with the danger of collinearity when predictors are highly correlated (as occurs in the standard 12-lead ECG). Model-derived deterministic transformations are compatible with statistically derived ones, provided that the distributed character of the cardiac sources is taken into account. We conclude that statistical associations among electrocardiographic leads can be reliably quantified in sufficiently large and diverse databases of recorded data; the causality of these associations can be supported by appropriate deterministic models based on the laws of physics.

Angioplasty, Balloon, Coronary↗