Biomedical subjects

G J Dempsey

Publications and source records attributed to G J Dempsey.

5 recordsLinked to original sources

PubMed1995

Body surface ECG potential maps in acute myocardial infarction.

An algorithm for the early detection of acute myocardial infarction (MI) using body surface electrocardiographic potential mapping has been developed. The mapping system consists of a 64-hydrogel electrode harness applied rapidly to the anterior chest, from which electrocardiographic signals are stored on a memory card and processed by computer. At each of the 64 points, QRS and ST-T isointegrals and 10 other features of the QRST segment are measured. Using these measurements, new variables are derived that express the shape of the three-dimensional geometric surface of the map. The isointegrals, features, and shape variables are used in a variety of techniques to discriminate between MI and control subjects. Maps were recorded from 69 patients at initial presentation of chest pain suggestive of acute MI and from 80 healthy control subjects. Using a multiple logistic regression technique, 14 variables were identified that correctly classified 79 of the 80 control subjects (specificity, 98.8%) and 65 of the 69 MI patients (sensitivity, 94.2%). The algorithm based on these 14 variables was applied prospectively to maps recorded on a further 48 control subjects and 59 patients with acute MI. Of the MI patients, 31 had inferior, 13 inferoposterior, 10 anterior, 2 posterior, 1 lateral, 1 inferior with right bundle branch block, and 1 anterior non Q wave MI. The algorithm correctly classified all 48 control subjects (specificity, 100%) and 57 of the 59 MI patients (sensitivity, 96.6%). Marked differences in the three-dimensional geometric map surfaces between the control subjects and MI patients were demonstrated. Variables derived from these surfaces form the basis of an algorithm with a high sensitivity and specificity for the automated detection of acute MI. The design of adaptive algorithms and their application to patients with chest pain and atypical electrocardiographic changes, particularly ST depression, may lead to the earlier detection of MI and greater numbers of patients receiving thrombolytic therapy.

Adolescent↗

PubMed1995

An esophageal and gastric approach to ventricular pacing.

Using a unipolar esothoracic pacing system (where current passes from a point source positioned in the distal esophagus to a chest wall pad) and pulse duration of 50 msec, satisfactory 1:1 ventricular capture was obtained in 57 (86%) of 66 patients, with a mean threshold current of 27.7 mA at an optimal depth of 40.3 cm from the lower lip. When the unipolar esothoracic and bipolar transesophageal ventricular pacing systems were compared, the bipolar system was associated with a lower success rate and higher threshold current. When unipolar esothoracic pacing and gastrothoracic pacing (where current passes from a point source positioned in the stomach to a chest wall pad) were compared in 23 patients with bradyarrhythmia, ventricular capture was achieved using gastrothoracic pacing in 22 patients (96%) and esothoracic pacing in 21 (91%): gastrothoracic pacing required less current (16.0 mA +/- SD 7.2 vs 25.8 mA +/- SD 8.6). Optimal ventricular capture occurred using a unipolar gastrothoracic pacing electrode inserted to an average depth of 44.3 cm together with a high impedance chest pad (250 omega) placed in the fourth interspace at the left sternal edge, with 50-msec current pulses and a mean threshold of 16.0 mA. Thus, using a gastroesophageal electrode system, ventricular pacing can be achieved successfully, and the availability of such a system could play a major role in resuscitation of patients from severe bradyarrhythmias.

Bradycardia↗

PubMed1994

Discriminant function analysis of body surface potential maps in acute myocardial infarction.

Using a newly developed 64-electrode portable mapping device, QRS and ST-T isointegral maps were compared in 194 control subjects and 101 patients. One hundred ninety-four control subjects (mean age, 48 years; 120 men) with no history of cardiac disease were selected randomly and mapped. One hundred one patients (mean age, 62 years; 77 men) were mapped at presentation of chest pain suggestive of first myocardial infarction (MI); all patients had classic 12-lead electrocardiographic findings--46 with anterior and 55 with inferior MI. The diagnosis was confirmed in all cases by a significant rise in serial cardiac enzymes. The mean delay between onset of chest pain to map recording was 163 minutes. Of the 101 patients, 78 were first mapped outside the hospital. Applying discriminant function analysis to the isointegral measurements made on the control subjects and on the first map of MI patients achieved a correct classification of 97% of the control subjects (189 of 194) and 72% of the anterior (33 of 46) and 76% of the inferior (42 of 55) MI groups. This preliminary study suggests that discriminant function analysis, based on isointegral maps, not only provides a method of separating control subjects from MI patients but that it can also differentiate between types of infarct. Further studies are required to improve the predictive values of discriminant function and to extend the methodology to assess both the site and size of MI.

Adult↗

PubMed1994

Transesophageal electroventilation. Optimization and improvement.

For electroventilation, short duration pulse trains (0.1 ms) were applied between two axillary pads (transchest) and compared with transesophageal electroventilation where pulses passed between the same pads to an esophageal electrode in apneic, pentobarbitone-anesthetized pigs. Significantly greater tidal volumes were produced by transesophageal electroventilation in comparison with transchest. As measured by maintained tidal volumes, duration of inspiratory air flow, peak flow, percentage hemoglobin oxygen saturation (%SaO2), and end tidal carbon dioxide concentration (ETCO2), the optimal requirements for transesophageal electroventilation were pulse frequency 40 Hz, 0.7 s duration pulses, at 60 to 100 V, pulse width 0.1 ms, with the esophageal electrode proximal to the gastroesophageal junction without producing brachial plexus stimulation. The efficiency of transesophageal electroventilation falls off rapidly following ventricular fibrillation. Thus, the application of this technique would be in respiratory arrest with maintained circulation, eg, in drug-induced respiratory depression, severe smoke inhalation, severe emphysema, high cervical cord lesion, and weaning from prolonged mechanical ventilation.

Animals↗

PubMed1994

Portable cardiac mapping assessment of acute ischaemic injury.

A portable cardiac mapping system is used to improve the accuracy of diagnosis of acute ischaemic injury outside hospital. Patients presenting chest pain suggestive of myocardial infarction (MI) were mapped by attendant medical personnel operating from a mobile coronary unit. These first MI maps were compared against average normal maps using QRS and ST-T isointegral values. Discriminant function analysis performed on the parameters achieved a sensitivity of 90% and a specificity of 96%.

Body Surface Area↗