Sinus rhythm mapping in healed experimental myocardial infarction: contrasting activation patterns for inducing ventricular tachycardia versus fibrillation

Electrophysiologic characteristics at initiation of ventricular tachycardia and ventricular fibrillation in a canine infarct model

Local ventricular activation time and the conduction time during sinus rhythm at the induction of ventricular tachycardia (VT) and ventricular fibrillation (VF) were investigated using a canine model of chronic myocardial infarction. Of 26 dogs studied, 15 had inducible VT, 10 had inducible VF, and 1 had no inducible arrhythmias. Bipolar local ventricular electrograms were recorded during sinus rhythm from 136 sites in 10 dogs with VT and 164 sites in 11 dogs with VF. Mean activation time in dogs with inducible VT was significantly longer than in dogs with inducible VF. Furthermore, simultaneous local ventricular electrograms were recorded during the induction of VT (74 episodes) or VF (38 episodes) from the infarct border zone at the endocardium (B-EN), the epicardium (B-EP), and normal sites (N-EN, N-EP). During VT induction, the activation time at N-EN and N-EP was significantly longer than during VF induction (N-EN: 94 +/- 21, 70 +/- 19 ms; N-EP: 83 +/- 21, 64 +/- 10 ms; p < 0.05). Conduction time was measured at the initiation of VT or VF induced by orthodromic or antidromic pacing. The conduction times of the last paced beat between N-EN and B-EP (35 +/- 11, 62 +/- 24 ms), N-EN and N-EP (35 +/- 12, 14 +/- 13 ms), B-EN and B-EP (16 +/- 10, 38 +/- 25 ms), and B-EP and N-EP (77 +/- 27, 44 +/- 12 ms) were significantly different in dogs with inducible VT (p < 0.05), but not in dogs with VF.(ABSTRACT TRUNCATED AT 250 WORDS)

Differences between predictive characteristics of signal-averaged electrocardiographic variables for postinfarction sudden death and ventricular tachycardia

Several studies indicate that the electrophysiologic substrate for sustained ventricular tachycardia differs from that of ventricular fibrillation. This prospective study examined whether there were clinically relevant differences between the predictive values of the standard time-domain signal-averaged (SA) electrocardiographic (ECG) variables for ventricular tachycardia and sudden death after myocardial infarction. Predischarge SA electrocardiograms were recorded in 332 patients after infarction. During a follow-up period of greater than or equal to 6 months, there were 12 sudden deaths (3.6%), 14 patients (4.2%) developed spontaneous sustained ventricular tachycardia and 20 patients (6%) died of circulatory failure. The sensitivity, specificity and positive predictive accuracy of the numerical values of the time-domain SA electrocardiographic variables for predicting sudden death and ventricular tachycardia were compared. The optimal criteria for predicting ventricular tachycardia required the positivity of greater than or equal to 2 of the standard time-domain SA variables, whereas the optimal criteria for predicting sudden death required the positivity of all 3 variables. A high specificity was sustained over a wider range of sensitivity for sudden death than it was for ventricular tachycardia and the values of the variables which provided the same sensitivity for sudden death and ventricular tachycardia were different. For a sensitivity of 70%, the positive predictive accuracy was 31% for predicting sudden death and 13% for predicting ventricular tachycardia. The study concludes that differences in the predictive characteristics of variables for ventricular tachycardia and sudden death may be used to refine postinfarction risk stratification.

Noninvasive detection of patients with ischemic and nonischemic heart disease prone to ventricular fibrillation

Abnormalities in the fast Fourier transforms of signal-averaged electrocardiograms (ECGs) obtained during sinus rhythm appear to distinguish patients with ischemic heart disease and sustained monomorphic ventricular tachycardia from those without ventricular tachycardia. This study was performed to determine the power of frequency analysis to detect patients with a history of ventricular fibrillation, to determine the extent to which spectra of signal-averaged ECGs from patients with ischemic and nonischemic heart disease are comparable and to compare results of signal-averaged ECG analysis in patients with ventricular fibrillation with results of programmed ventricular stimulation. Signal-averaged ECGs were obtained during sinus rhythm from 60 patients with sustained ventricular tachycardia (Group I) and 34 patients with ventricular fibrillation (Group II). Results of signal-averaged ECG analysis were abnormal in 92% of patients with ventricular tachycardia and 85% of patients with ventricular fibrillation (p = NS). Abnormal spectra were detected in the signal-averaged ECGs from 90% of patients with ischemic and from 86% of patients with nonischemic heart disease (p = NS). In contrast, the results of programmed stimulation differed markedly between the two patient groups. Sustained ventricular arrhythmias were induced in 91% of the patients with ventricular tachycardia compared with only 46% of those with ventricular fibrillation (p less than 0.0001). Moreover, ventricular tachycardia was inducible in 81% of patients with ischemic heart disease compared with only 50% of those with nonischemic heart disease (p less than 0.02). Thus, abnormalities in the spectra of signal-averaged ECGs were found in the majority of patients with ventricular fibrillation and were detectable even in those whose arrhythmia was not inducible by programmed stimulation. These results broaden the potential clinical application of noninvasive interrogation of signal-averaged ECGs to include the prospective identification of patients with ischemic or nonischemic heart disease prone to ventricular tachycardia or ventricular fibrillation.

Signal-averaged electrocardiographic late potentials in resuscitated survivors of out-of-hospital ventricular fibrillation

The results of signal-averaged electrocardiography and programmed electrical stimulation were evaluated in 25 patients with recurrent sustained ventricular tachycardia (VT) and 46 patients with a history of out-of-hospital ventricular fibrillation (VF) to characterize the electrophysiologic substrate responsible for these different clinical arrhythmia presentations. Patients with VT had a higher incidence of late potentials (VT 83%, VF 50%, p = 0.005). Significant differences between these groups were also noted in response to programmed electrical stimulation. A sustained ventricular arrhythmia was induced in 24 of 25 (96%) patients with a history of VT but in only 27 of 46 (59%) of VF patients (p = 0.005). In addition, VF was induced in 11 (24%) patients in the VF group but in none of the patients in the VT group (p = 0.005). When the 2 groups were compared on the basis of select clinical characteristics, no significant difference in age, sex, presence of coronary artery disease or ejection fraction was noted. The frequency of prior myocardial infarction was significantly higher in the VT group (VT 20 of 25, 80%; VF 24 of 46, 52%; p = 0.03). Finally, no significant relation between the presence of late potentials and induced arrhythmias was noted in either group. The inability of signal-averaged electrocardiography to predict inducibility in VF patients may represent a significant limitation of this technique in identifying patients at risk for sudden cardiac death.

Inducible monomorphic sustained ventricular tachycardia in the conscious pig

Sustained monomorphic ventricular tachycardia (VT) is of clinical importance but has not been readily modeled in conscious animals. Eleven pigs had myocardial infarction induced by pulling snares previously placed around the left anterior descending (LAD) coronary artery. Six days after occlusion, bipolar pacing catheters were inserted in the right ventricular apex for induction of VT. Testing was repeated in conscious pigs on 6 out of 8 to 19 days after infarction. Monomorphic VT was induced in each animal during each session, using three to four extrastimuli. VT was terminated by burst pacing in 74% of trials; average VT rate was 362 +/- 26 beats/min. VT was prevented in four of eight animals by procainamide and in five of eight animals by magnesium, but was not prevented by lidocaine or metoprolol. The model may be useful in the study of potentially malignant ventricular tachyarrhythmias, important prodromes for sudden death.

Electrophysiological and anatomic differences between canine hearts with inducible ventricular tachycardia and fibrillation associated with chronic myocardial infarction

This study examined electrophysiological and anatomic differences between dogs with ventricular tachycardia (VT) and fibrillation (VF) inducible by programmed ventricular stimulation 7-21 days after left anterior descending coronary artery ligation. Of 106 dogs studied, 40 had inducible VT, 19 had inducible VF, and 47 had no inducible arrhythmias. Differences between these three groups of animals were examined with cardiac mapping (to determine ventricular activation time in sinus rhythm) and post-mortem pathology (to measure infarct size and to reconstruct the anatomy at the infarct edge). Animals with inducible VT had longer maximal epicardial activation time (127 +/- 8 msec) than did animals with inducible VF (91 +/- 8 msec, p less than 0.05) or animals with no inducible arrhythmias (75 +/- 2 msec, p less than 0.001). Delayed epicardial activation occurred in 90% of animals with VT, 42% of animals with VF, and in only 6% of animals with no inducible arrhythmias. Endocardial and myocardial activation times were similar for the VT and VF groups. Infarct size was 18 +/- 2% of the ventricles for the VT group, much higher than for the VF group (11 +/- 2%, p less than 0.001) or for the group with no inducible arrhythmias (9 +/- 1%, p less than 0.001). The maximum diameter of viable muscle bundles interdigitating with scar tissue at the infarct edge was much larger in animals with VT (2.4 +/- 0.2 mm) than in animals with VF (1.8 +/- 0.2 mm, p less than 0.05) or animals with no inducible arrhythmias (1.7 +/- 0.1 mm, p less than 0.01). Thus, when compared with animals with inducible VF, animals with inducible VT had longer epicardial activation time, larger infarct size and viable muscle bundles of larger diameter at the infarct edge.

Sinus rhythm mapping in a canine model of ventricular tachycardia

The relationship between electrograms recorded during sinus rhythm and the activation sequence during ventricular tachycardia induced by programmed stimulation was investigated in a canine model of myocardial infarction. Thirteen dogs were studied 3 days (n = 10) or 14 days (n = 3) after coronary occlusion. Sixty-three unipolar electrograms were simultaneously recorded with a sock electrode array connected to a digital recording system, and analyzed by computer. Bipolar electrograms were recorded sequentially from the same sites with an analog recorder. Categories of unipolar electrograms were defined with reference to the QRS complex during sinus rhythm as follows: Class A included electrograms with an intrinsic deflection inscribed within the QRS complex, class B included those which did not exhibit any intrinsic rs deflection, and class C included those with an intrinsic deflection inscribed later than QRS. The epicardial distribution of each class of electrograms was significantly different between the preparations with, and those without inducible tachycardia (72% versus 63% of electrograms being in class A, 20% versus 35% in class B, and 8% versus 2% in class C; p less than 0.005). When tachycardia was inducible, class C epicardial electrograms were located in an area extending across the region of infarction, which corresponded to the common reentrant pathway of figure-of-eight patterns mapped during tachycardia. When ventricular tachycardia was not inducible, class B electrograms were recorded all over this region. The morphology of bipolar electrograms had no predictive value in identifying the common reentrant pathway. These results support the view that the inducibility of reentrant tachycardia is dependent upon critically located delayed activity detected during sinus rhythm by unipolar recordings.

Differences between patients with ventricular tachycardia and ventricular fibrillation as assessed by signal-averaged electrocardiogram, radionuclide ventriculography and cardiac mapping

This study examined 65 patients with ventricular tachycardia or fibrillation late after myocardial infarction to determine whether they differed with respect to duration of ventricular activation in sinus rhythm and left ventricular ejection fraction. Patients with spontaneous ventricular tachycardia had a longer ventricular activation time in sinus rhythm than did patients with spontaneous ventricular fibrillation. This difference was detected with the signal-averaged electrocardiogram (ECG) (tachycardia 181 +/- 33 ms, fibrillation 152 +/- 23 ms, p less than 0.001) and at epicardial mapping (tachycardia 210 +/- 17 ms, fibrillation 192 +/- 17 ms, p less than 0.02). Left ventricular ejection fraction was lower in patients with spontaneous ventricular tachycardia (0.22 +/- 0.09) than in patients with spontaneous ventricular fibrillation (0.27 +/- 0.09) (p less than 0.05). The patients with both spontaneous and inducible ventricular fibrillation had a shorter ventricular activation time on the signal-averaged ECG (129 +/- 17 ms) and a higher ejection fraction (0.36 +/- 0.05) than did either patients with spontaneous ventricular fibrillation and inducible ventricular tachycardia (158 +/- 21 ms and 0.25 +/- 0.08, respectively, each p less than 0.01) or patients with both spontaneous and inducible ventricular tachycardia (181 +/- 33 ms and 0.22 +/- 0.09, respectively, each p less than 0.001). Of the patients with inducible ventricular tachycardia, presentation with tachycardia rather than fibrillation was associated with a longer ventricular activation time on the signal-averaged ECG (181 +/- 33 versus 158 +/- 21 ms, p less than 0.02) and a longer cycle length of inducible ventricular tachycardia (290 +/- 61 versus 259 +/- 44 ms, p = 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)