Isoarea distributions during ectopic stimulation of isolated rabbit hearts

Statistical accuracy of a moving equivalent dipole method to identify sites of origin of cardiac electrical activation

While radio frequency (RF) catheter ablation (RCA) procedures for treating ventricular arrhythmias have evolved significantly over the past several years, the use of RCA has been limited to treating slow ventricular tachycardias (VTs). In this paper, we present preliminary results from computer and animal studies to evaluate the accuracy of an algorithm that uses the single equivalent moving dipole (SEMD) model in an infinite homogeneous volume conductor to guide the RF catheter to the site of origin of the arrhythmia. Our method involves measuring body surface electrocardiographic (ECG) signals generated by arrhythmic activity and by bipolar current pulses emanating from a catheter tip, and representing each of them by a SEMD model source at each instant of the cardiac cycle, thus enabling rapid repositioning of the catheter tip requiring only a few cycles of the arrhythmia. We found that the SEMD model accurately reproduced body surface ECG signals with a correlation coefficients > 0.95. We used a variety of methods to estimate the uncertainty of the SEMD parameters due to measurement noise and found that at the time when the arrhythmia is mostly localized during the cardiac cycle, the estimates of the uncertainty of the spatial SEMD parameters (from ECG signals) are between 1 and 3 mm. We used pacing data from spatially separated epicardial sites in a swine model as surrogates for focal ventricular arrhythmic sources and found that the spatial SEMD estimates of the two pacing sites agreed with both their physical separation and orientation with respect to each other. In conclusion, our algorithm to estimate the SEMD parameters from body surface ECG can potentially be a useful method for rapidly positioning the catheter tip to the arrhythmic focus during an RCA procedure.

Correlation between various parameters derived from body surface maps and ejection fraction in patients with anterior myocardial infarction

To determine the best map parameter to predict cardiac function, various map parameters were correlated with the left ventricular ejection fraction (EF) in patients with a previous (between 3 months and 1 year) anterior myocardial infarction, but without overt congestive heart failure or ventricular dyssynergy. From 300 consecutive patients with a previous myocardial infarction, 82 patients with only an anterior infarction and who underwent cardiac catheterization and body surface mapping were selected for this study. The maps from 100 healthy subjects were used as normal controls. Body surface maps using 87 unipolar electrodes were recorded and various parameters were derived from the Q map, the QRS departure maps, the QRS isointegral (IQRS) map, and the QRST isointegral (IQRST) maps. They were compared with the angiographically determined EF. The EF was correlated with nQ (r = -0.72), four parameters derived from the QRS departure map (r ranged from -0.73 to -0.79), two parameters derived from the IQRS map (r = -0.90 and -0.86), and two parameters derived from the IQRST map (r = -0.84 and -0.85). Some parameters derived from body surface maps were found to have a very high correlation with the EF in patients who had a previous anterior myocardial infarction.

Effects of myocardial infarction on cardiac electrical field properties using a numerical expansion technique

This study was undertaken to quantify basic cardiac electrical field properties using the Karhounen-Loeve (K-L) numerical expansion technique after experimental myocardial infarction. Transmural anterior myocardial infarction was produced in seven dogs by injection of liquid latex into the anterior descending artery; posterior myocardial infarction was produced in five dogs by injection of the circumflex artery. Body surface potentials from 84 electrodes were recorded during sinus rhythm prior to and 1 week after infarction. Electrical field properties during the QRS, ST, and QRST intervals were computed by the K-L method based upon areas calculated for each lead. The ratio of the sum of magnitude of the first three eigenvectors to the sum of all computed eigenvectors expressed as a percentage was used as a measure analogous to field dipolarity. Values before infarction were high during the QRS (97.1% +/- 2.0%, mean +/- 1SD), ST (96.0% +/- 5.1%), and QRST (97.7% +/- 2.7%) intervals, with no significant difference between the three periods. After infarction, the ratio during QRS decreased significantly, with lower values after posterior (61.9% +/- 11.7%) than after anterior (91.1% +/- 6.0%) infarction (p less than 0.001). Values during ST and QRST intervals were not significantly changed by infarction. Spatial patterns of the first eigenvector indicated that the derived QRS area electric field is directed away from the myocardial lesion for both anterior and posterior infarcts. Thus, experimental myocardial infarction produces significant changes in cardiac electrical field properties as measured by the K-L technique.

Detection of myocardial infarction in the presence of Wolff-Parkinson-White syndrome by QRST isoarea map in dogs

The possibility of detecting myocardial infarction (MI) in the presence of Wolff-Parkinson-White (WPW) syndrome by means of body surface QRST isoarea maps was studied in eight dogs. Eighty-seven body surface ECGs were recorded simultaneously. Recordings were taken during right atrial (RA) and right atrial and right ventricular (RA + RV) sequential pacing, which simulated WPW syndrome, during control periods and at 1-hour intervals for up to 5 hours after occlusion of the left anterior descending coronary artery. In ECGs during the RA drive, diagnostic findings of MI such as abnormal Q waves were observed but became obscure during the RA + RV drive. On the contrary, the QRST values over the anterior chest during both drives were positive soon after coronary occlusion, decreased gradually as time passed, and became abnormally negative after 5 hours. The QRST isoarea maps during RA and RA + RV pacing showed quite similar patterns and were highly correlated with each other throughout this study (r greater than 0.95). These findings demonstrate that localized abnormalities resulting from MI are evident in QRST isoarea maps even in the presence of preexcitation and fusion.

Diagnostic value of QRST isointegral maps in detecting myocardial infarction complicated by bundle branch block

The clinical usefulness of QRST isointegral maps (IQRST map) for detecting myocardial infarction that was complicated by intraventricular conduction disturbances was evaluated in patients with right bundle branch block (group RBBB, 64 patients) and left bundle branch block (group LBBB, 40 patients) by comparison with the normal mean IQRST map derived from 50 normal subjects. Myocardial infarction complicated the conduction disturbances in 24 of the 64 RBBB and in 18 of the 40 LBBB patients. A correlation coefficient was used for assessing the similarity of each map pattern with the normal mean IQRST map. The difference map was made by subtracting the average normal IQRST map from each abnormal IQRST map, and those differences that were less than 2 SD from the mean were retained as a significant area. The number of leads and their sum of differences were used to represent the size of the difference map. Correlation coefficients were significantly (p less than 0.001) smaller in patients with bundle branch block complicated by myocardial infarction than in patients with conduction disturbances not complicated by myocardial infarction. A significant area emerged in the difference map in all patients with myocardial infarction complicated by conduction disturbances. The emergence of a significant area revealed high diagnostic accuracy for detecting myocardial infarction in group RBBB (89.1%). The size of a significant area in a difference map was significantly larger in cases with complicated myocardial infarction than in cases with uncomplicated myocardial infarction in either group RBBB or group LBBB (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

The ventricular depolarization gradient: effects of exercise, pacing rate, epinephrine, and intrinsic heart rate control on the right ventricular evoked response

A new pacing technique is described that permits high fidelity recording of the paced ventricular evoked response, including cardiac depolarization. Integration of the paced R wave yields the ventricular depolarization gradient (GD), which is dependent on activation sequence and the spatial dispersion of activation times. GD was studied in 27 dogs to determine the effects of treadmill exercise at fixed rate pacing (n = 10), elevation of heart rate in the absence of stress (n = 20), epinephrine at fixed rate (n = 6), and exercise in the presence of normal chronotrophic response (n = 7). Low level exercise (1 mph, 2 min, 15 degrees) at a fixed heart rate produced significant (P less than 0.0005) decreases in GD that averaged -10.8 +/- 4.0% (mean +/- SD). The rate of change in GD was faster at the onset of exercise than at its cessation (P less than 0.0005). Artificial elevation of heart rate at rest produced significant (P less than 0.0005) increases in GD; mean sensitivity of GD to rate was 0.27 +/- 0.12%/beats/min. Intravenous injection of epinephrine produced significant (P less than 0.001) decreases in GD at two dosage levels (2.5 and 5.0 micrograms/kg) when evaluated at two baseline pacing rates (150 and 190 beats/min); mean changes in GD were -20.64 +/- 0.53% (2.5 micrograms/kg at 150 beats/min), -25.19 +/- 4.20% (5.0 micrograms/kg at 150 beats/min), -14.18 +/- 5.19% (2.5 micrograms/kg at 190 beats/min), and -24.22 +/- 4.94% (5.0 micrograms/kg at 190 beats/min). Sensitivity of GD to epinephrine was dose-dependent (P less than 0.01) at each baseline rate, but was independent (P greater than 0.05) of the rate itself. In the presence of a normal chronotropic response, GD remained unchanged (P greater than 0.5) during exercise in spite of significant elevation in heart rate (105.0 to 167.1 beats/min, P less than 0.001). These data suggest the presence of an intrinsic negative-feedback control mechanism that maintains GD constant in the healthy heart during homeostatic disturbance. Applications in closed-loop rate adaptive pacing are described.

Effects of coronary occlusion on cardiac and body surface PQRST isoarea maps of dogs with abnormal activation simulating left bundle branch block

The possibility of detecting myocardial infarction in the presence of left bundle branch block by analysis of cardiac and body surface PQRST isoarea maps was studied in nine open-chest and six closed-chest dogs. Recordings were taken during supraventricular drive or right atrial plus right ventricular pacing in control periods and at intervals for up to 10 hr after left anterior descending coronary artery occlusion. Right ventricular pacing was used to simulate left bundle branch block. Myocardial infarction was documented with triphenyl tetrazolium staining. The PQRST areas during supraventricular drive and right atrial plus right ventricular pacing were highly correlated to each other both before and after coronary occlusion. The PQRST isoarea maps after coronary occlusion showed a strong pole overlying the ischemic area on the cardiac surface in open-chest animals and over the left anterior thorax in closed-chest animals. The PQRST pole was positive during the first 1 to 2 hr of occlusion and became negative after several hours. The findings demonstrate that localized abnormalities due to ischemia and infarction are manifest in body and cardiac surface PQRST isoarea maps of both supraventricular complexes and right ventricular paced complexes. The findings suggest that PQRST isoarea maps may aid in identification and localization of ischemic or infarcted myocardium in the setting of abnormal activation such as left bundle branch block.

Manifest orientation: the theoretical link between the anatomy of the heart and the clinical electrocardiogram

Einthoven related the apparent direction of the heart's electrical activity to the potential differences manifest in the limb leads and the axes of their orientation. From this beginning the linked concepts of heart vector and lead vector, equivalent dipole and lead field, complex heart source and complex volume conductor have continued the electrocardiographer's search for deeper insight into cardiac function from examination of the surface expression. However, this conceptual evolution has been uneven and has littered practical interpretation with diagnostic criteria that depend on assumptions of uneven validity. The good news is that some of the criteria are surprisingly helpful and that the shattering and reassembling of the conceptual framework relating the heart to the electrocardiogram may facilitate the construction of a more comprehensive and effective diagnostic approach.