Incidence and significance of inducible supraventricular tachyarrhythmias in patients with chronic myocardial infarction

Linear systems analysis for laminar fMRI: Evaluating BOLD amplitude scaling for luminance contrast manipulations

A fundamental assumption of nearly all functional magnetic resonance imaging (fMRI) analyses is that the relationship between local neuronal activity and the blood oxygenation level dependent (BOLD) signal can be described as following linear systems theory. With the advent of ultra-high field (7T and higher) MRI scanners, it has become possible to perform sub-millimeter resolution fMRI in humans. A novel and promising application of sub-millimeter fMRI is measuring responses across cortical depth, i.e. laminar imaging. However, the cortical vasculature and associated directional blood pooling towards the pial surface strongly influence the cortical depth-dependent BOLD signal, particularly for gradient-echo BOLD. This directional pooling may potentially affect BOLD linearity across cortical depth. Here we assess whether the amplitude scaling assumption for linear systems theory holds across cortical depth. For this, we use stimuli with different luminance contrasts to elicit different BOLD response amplitudes. We find that BOLD amplitude across cortical depth scales with luminance contrast, and that this scaling is identical across cortical depth. Although nonlinearities may be present for different stimulus configurations and acquisition protocols, our results suggest that the amplitude scaling assumption for linear systems theory across cortical depth holds for luminance contrast manipulations in sub-millimeter laminar BOLD fMRI.

Prevalence of inducible paroxysmal supraventricular tachycardia during esophageal electrophysiologic study in patients with unexplained stroke

BACKGROUND

The relationships between stroke and atrial tachycardia or atrial fibrillation were previously reported. Electrophysiological study is one of the means, used to detect and evaluate these atrial tachyarrhythmias. But, some other arrhythmias as paroxysmal supraventricular tachycardia, can be induced during electrophysiologic study and their significance in stroke is unknown. The aim of the study was to assess the significance of inducible paroxysmal supraventricular tachycardia (PSVT) in stroke.

METHODS

One hundred thirty seven patients, aged 61+/-12 years had unexplained stroke (group I) and were compared to 60 subjects aged 45+/-18.5 years without stroke and history of tachycardia (group II); Holter monitoring (HM), echocardiogram and esophageal electrophysiologic study (EPS) in basal state and after isoproterenol were performed.

RESULTS

Heart disease was noted in 19 group I patients (14%) and 10 group II patients (17%). In group I, atrial fibrillation or tachycardia (AF-AT) was induced in 20 patients (15%) and PSVT was induced in 19 patients (14%) aged 66+/-12 years. In group II, AF/AT was induced in 3 patients (5%); no group II patient had induced PSVT. After 3+/-1 years, in group I, one of 98 patients without induced arrhythmias had new strokes and 2 had AF; 5 patients with induced AT/AF developed AF; 5 patients with induced PSVT had PSVT's, requiring ablation in 4 of them; 1 died from a new stroke; one had a second non-fatal stroke and 3 patients developed AF (16%). In group II, there were no events.

CONCLUSION

In 14% of patients with unexplained stroke, PSVT was inducible during esophageal electrophysiologic study. Further studies are warranted to assess the significance of this finding in patients with unexplained stroke.

Electrophysiologic characteristics of atria in patients without heart disease

BACKGROUND

The significance of atrial fibrillation or tachycardia (AF) induction remains debatable. Some believe that the presence of heart disease (HD) increases the sensitivity and decreases the specificity of programmed atrial stimulation (PAS). There are few data in patients without HD. The purpose of the study was to evaluate the results of PAS in asymptomatic patients without HD and in those with documented spontaneous AF, but without HD, to know the diagnosis value of the technique.

METHODS

A total of 4,900 PAS were consecutively performed. The control group (I, N=67) was defined by the absence of preexcitation syndrome, dizziness/syncope, hypertension, history of tachycardia, or other documented HD together with a normal 2D echocardiogram and 24-hour Holter monitoring. They were compared to a group (II) of 54 patients with documented paroxysmal AF and without HD. PAS used one and two extrastimuli, delivered during sinus rhythm and two drive rates (600, 400 ms). Atrial-effective refractory periods (ARP), their adaptation to cycle length, and conduction times were noted. AF induction was defined as the induction of AF lasting more than 1 minute.

RESULTS

Group I patients (1.4% of 4,900) were younger than group II (51 +/- 17 vs 65 +/- 11 years, P < 0.001). A single extrastimulus never induced sustained AF in group I, but did so in 11 group II patients (20%); sustained AF was induced by two extrastimuli in 15 group I patients (22%) and in 31 group II patients (57%) (P < 0.001). There were no ARP and conduction time differences in group I patients with and without inducible AF, but there was a longer sinus cycle length in patients with inducible AF (977 +/- 164 vs 838 +/- 141 ms, P < 0.02). There were no electrophysiological differences in group II patients with and without inducible AF. No group I patient developed spontaneous AF (follow-up 4 +/- 2 years). The sensitivity of PAS with one extrastimulus was 20% and the specificity 100%; the sensitivity of PAS with two extrastimuli was 57% and the specificity 78%.

CONCLUSION

Sustained AF was not induced by one extrastimulus in control patients without symptoms, nor heart disease, but sustained AF was induced by two extrastimuli in 22% of these patients. The induction of a sustained AF by two extrastimuli should be interpreted cautiously, particularly in patients with a relative sinus bradycardia. However, the sensitivity of PAS with one extrastimulus was very low and two extrastimuli were required in patients with spontaneous AF to induce the tachycardia. Other electrophysiological parameters were not useful to differentiate patients with and without inducible AF.

Utility of transesophageal atrial pacing in the diagnostic evaluation of patients with unexplained syncope associated or not with palpitations

BACKGROUND

Noninvasive studies are often negative in patients with syncope, normal surface ECG and without heart disease. The purpose of the study was to determine the diagnostic impact of an esophageal electrophysiological study performed during a consultation.

METHODS

A total of 154 patients aged from 16 to 87 years were consecutively recruited for unexplained syncope; they had a normal ECG in sinus rhythm, no documented arrhythmia and no patent heart disease. Half of them complained of palpitations. Electrophysiologic study was performed during a consultation by transesophageal route: rate of 2nd d AV block occurrence during atrial pacing and sinus node recovery time were determined; programmed atrial stimulation using one and two atrial extrastimuli were delivered in control state and then after infusion of 0.02-1 microg/min of isoproterenol; arterial blood pressure was monitored.

RESULTS

(1) Electrophysiologic study was positive in 107 patients (69%); (2) sinus node dysfunction was noted in 9 patients (6%); (3) atrioventricular conduction disturbances were noted in 2 patients (1%); (4) vasovagal reaction which associated a junctional bradycardia and a fall of arterial blood pressure and which reproduced spontaneous symptoms was provoked by isoproterenol infusion in 21 patients (14%); (5) sustained atrial fibrillation was induced in 23 patients (15%); and (6) paroxysmal junctional tachycardia was induced in 52 patients (34%). Patients with negative study were younger (44+/-21.5 years) than those with sinus node dysfunction or atrial fibrillation (71+/-9 and 63+/-14 years, respectively). The treatment was guided by these data: patients with inducible atrial fibrillation were treated by antiarrhythmic drugs and those with inducible paroxysmal junctional tachycardia by the radiofrequency ablation of reentrant circuit. Syncope disappeared in all patients but 2.

CONCLUSION

Esophageal electrophysiologic study performed during a consultation was a safe, rapid and economic means to detect an arrhythmia (sinus node dysfunction or supraventricular tachycardia) in patients with dizziness/syncope and palpitations in half cases. Supraventricular tachycardia was clearly an underestimated cause of syncope in this population.

Reproducibility of response to programmed atrial stimulation

The induction of atrial tachyarrhythmias (ATAs) is used to guide the medical or ablative treatment of these tachycardias. To date no information is available regarding the reproducibility of programmed atrial stimulation (PAS) induced ATA. The purpose of the study was to look for the reproducibility of PAS. Two baseline electrophysiological tests were performed in the drug-free state and within 6 months to 3 years of one another (mean 18 months) in 62 patients. Twenty-six patients had spontaneous documented ATAs (group I); 36 patients did not have spontaneous ATAs (group II). PAS used one and two extrastimuli delivered during three cycle lengths (sinus rhythm, 600 ms, 400 ms). The results were as follows. In group I, sustained (> 1 minute) ATA was induced in 23 patients on the first PAS and remained inducible in 22 patients in the second study. In three patients with noninducible ATA, PAS remained negative in only one; the reproducibility of PAS was 88%. In 17 (47%) group II patients, a sustained ATA was induced in the first study, and the ATA remained inducible in 10 patients in the second study. Nineteen other patients did not have inducible ATA on the first study, but 10 of them had an inducible ATA on the second PAS; the reproducibility of PAS was 53%. In conclusion, long-term reproducibility of PAS induced ATA in patients with spontaneous and documented ATA was good. In patients without spontaneous ATA, the reproducibility of PAS induced ATA was low and the induction of ATA in these patients should be interpreted cautiously in light of this observed variability in induced atrial arrhythmias.

Hypertrophic cardiomyopathy: value of atrial programmed electrical stimulation in patients with or without syncope with special reference to the role of atrial arrhythmias

Hypertrophic cardiomyopathy may be associated with both supraventricular and ventricular arrhythmias, which may play a role in the genesis of syncope. The aim of this study was to assess the findings of electrophysiological study and programmed atrial and ventricular stimulation and their possible role in syncope. Programmed atrial and ventricular stimulation using up to two extrastimuli in right atrium and three in right ventricle at three cycle lengths (600, 400 ms and spontaneous) was systematically performed in 56 patients with hypertrophic cardiomyopathy. Thirty seven had unexplained dizzinesses or syncopes (group I) and 19 did not present loss of consciousness (group II). Patients with syncopes had a higher prevalence of induced sustained supraventricular tachyarrhythmia (73%) than those of group II (16%) (P<0.05). Inducible supraventricular tachycardia was the only finding in 16 patients with syncopes. During the follow-up (3 years+/-6 months), empirical antiarrhythmic therapy suppressed the symptoms, except in two patients who developed atrial fibrillation despite therapy. The high incidence of inducible atrial tachycardia of these patients was not correlated with particular Holter findings or echocardiographic data. However, their mean age was rather high (58+/-12 years). In conclusion, atrial tachyarrhythmias may play a role in syncopes of middle-aged patients with hypertrophic cardiomyopathy. Moreover programmed atrial stimulation is an useful means to identify this syncope mechanism.

Significance and prevalence of inducible atrial tachyarrhythmias in patients undergoing electrophysiologic study for presyncope or syncope

The purpose of the study was to report the prevalence of inducible supraventricular tachyarrhythmias (SVTA) in 827 consecutive patients aged 17 to 90 years who did not have spontaneous documented SVTA and who had unexplained presyncope and/or syncope. The electrophysiologic study (EPS) included programmed atrial and ventricular stimulation up to two extrastimuli at three cycle lengths, and the study of sino-atrial and AV conduction. The results were as follows. EPS was normal in 386 patients. Inducible junctional tachycardia or atrial flutter and fibrillation was the only finding in 187 patients (23%). In the remaining patients we found ventricular tachycardia in 103 (12%), heart block in 67 (8%), sick sinus syndrome in 56 (7%) and increased vagal tone in 28 (3%). The presence of an underlying heart disease (47%) and salvos of atrial premature beats on Holter monitoring (39%) were significantly correlated with the induction of SVTA. However, the comparison with similar groups without syncope indicates that only the induction of SVTA in patients with hypertrophic cardiomyopathy and mitral valve prolapse was significantly correlated with the history of syncope. In patients without heart disease or with prior myocardial infarction or decreased left ventricular function, the induction of SVTA, which is not associated with hypotension in the supine position, could require an induction after head-up tilting, because of the lack of specificity of programmed stimulation in these patients. Programmed atrial stimulation should be systematically performed in patients with unexplained syncope, in particular in those with hypertropic cardiomyopathy and mitral valve prolapse, who require a specific treatment, if a SVTA is induced. In other patients the results of programmed atrial stimulation should be interpreted cautiously.