The relationship between anatomy and electrical parameters in His bundle pacing

Background

The relationship between anatomy and electrical parameters of His bundle (HB) pacing has not been extensively studied.

Purpose

To characterize the anatomical location of the HB lead tip and its relationship with acute electrical parameters.

Methods

Consecutive patients who underwent HB lead implantation, guided by standard fluoroscopy and electrophysiology, were prospectively enrolled. The relationship between HB lead tip and tricuspid valve plane (TVP) was assessed with post-procedure transthoracic echocardiography.

Results

Twenty-five patients were studied. In 11 patients (44%), the HB lead tip did not cross the TVP (A group): in 7 cases it was screwed in the right atrium at a mean distance of −6.1 mm from the TVP and, in 4 cases, at the level of the tricuspid annulus. In the remaining 14 patients (56%), the lead tip crossed the TVP (V group): it was screwed in the right ventricle at a mean distance of 9.3 mm from the TVP. A and V groups had comparable HB capture thresholds (1.6±1 V vs 1.7±0.7 V, 1 ms pulse-width; p=0.66); selective HB capture was significantly more represented in the A group (91% vs 21%; p=0.001). Significantly higher R-wave amplitudes were seen in the V group (6.7±3 vs 2.5±1.7 mV; p=0.0004), and they positively correlated with the distance from the TVP (p=0.0038). Atrial oversensing was never observed.

Conclusion

In a consecutive cohort of HBP recipients, the rate of patients who had an effective HB capture in the atrium was substantial and was characterized by different electrophysiological properties than in the ventricle.

Funding Acknowledgement

Type of funding sources: None.

The relationship between anatomy and electrical parameters in His bundle pacing: A transthoracic echocardiography evaluation

PURPOSE

The implantation site of the His bundle (HB) lead may influence pacing parameters. Our aim was to characterize the anatomical location of the HB lead tip and its relationship with acute electrical parameters.

METHODS

Consecutive patients who underwent HB lead implantation, guided by standard fluoroscopy and electrophysiology, were prospectively enrolled. The relationship between HB lead tip and tricuspid valve plane (TVP) was assessed with post-procedure transthoracic echocardiography.

RESULTS

Twenty-five patients were studied. In 11 patients (44%), the HB lead tip did not cross the TVP (A group): in 7 cases it was screwed in the right atrium at a mean distance of -6.1 mm from the TVP and, in 4 cases, at the level of the tricuspid annulus. In the remaining 14 patients (56%), the lead tip crossed the TVP (V group): it was screwed in the right ventricle at a mean distance of 9.3 mm from the TVP. A and V groups had comparable HB capture thresholds (1.6 ± 1 V vs 1.7 ± 0.7 V, 1 ms pulse-width; p = 0.66); selective HB capture was significantly more represented in the A group (91% vs 21%; p = 0.001). Significantly higher R-wave amplitudes were seen in the V group (6.7 ± 3 vs 2.5 ± 1.7 mV; p = 0.0004), and they positively correlated with the distance from the TVP (p = 0.0038). Atrial oversensing was never observed.

CONCLUSION

In a consecutive cohort of HB pacing recipients, the rate of patients who had an effective HB capture in the atrium was substantial and was characterized by different electrophysiological properties than in the ventricle.

Is His-optimized superior to conventional cardiac resynchronization therapy in improving heart failure? Results from a propensity-matched study

BACKGROUND

His bundle pacing (HBP), alone or optimized in association with coronary sinus pacing (HBP+LV) has recently been proposed as an alternative to conventional cardiac resynchronization therapy (CRT). However, there is lack of controlled studies that assessed clinical outcome.

METHODS

We did a single-center, propensity-score matched, case-control study of comparison of HBP and HBP+LV versus conventional CRT in patients with heart failure (HF) and standard indications for CRT. The study group patients were consecutively enrolled in the year 2019. The control group patients were selected, by propensity score matching, among those CRT implantations performed in the years 2015-2018.

RESULTS

There were 27 patients in each group. In the active group, 12 (44%) patients received HBP alone and 12 (44%) patients HBP+LV pacing. HBP failed in three (11%) patients. In the control group, conventional CRT was achieved in 26 (96%) patients and failed in one. Paced QRS width was shorter in the active than in the control group (128 ± 18 vs. 148 ± 27 ms, p = .004). During a mean of 9.6 months of follow-up, a composite clinical outcome of death, hospitalization for HF or worsening HF occurred in three (11%) in the active group and in four (15%) in the control group, p = .58. No difference was also observed with softer endpoints: NYHA class (1.9 ± 0.7 vs. 2.1 ± 0.7), subjective improvement (74% vs. 74%) and LV ejection fraction (40.7% vs. 40.7%).

CONCLUSION

Compared with conventional CRT, a shorter QRS width can be obtained with HBP alone or in association with coronary sinus pacing but we were unable to show a better clinical outcome. There is urgent need for large, randomized trials.

Complementary effectiveness of carotid sinus massage and tilt testing for the diagnosis of reflex syncope in patients older than 40 years: a cohort study

AIMS

Indications, methodology, and diagnostic criteria for carotid sinus massage (CSM) and tilt testing (TT) have been standardized by the 2018 Guidelines on Syncope of the European Society of Cardiology. Aim of this study was to assess their effectiveness in a large cohort which reflects the performance under 'real-world' conditions.

METHODS AND RESULTS

We analysed all patients who had undergone CSM and TT in the years 2003-2019 for suspected reflex syncope. Carotid sinus massage was performed according to the 'Method of Symptoms'. Tilt testing was performed according to the 'Italian protocol' which consists of a passive phase followed by a sublingual nitroglycerine phase. For both tests, positive test was defined as reproduction of spontaneous symptoms in the presence of bradycardia and/or hypotension. Among 3293 patients (mean age 73 ± 12 years, 48% males), 2019 (61%) had at least one test positive. A bradycardic phenotype was found in 420 patients (13%); of these, 60% were identified by CSM, 37% by TT, and 3% had both test positive. A hypotensive phenotype was found in 1733 patients (53%); of these, 98% were identified by TT and 2% had both TT and CSM positive.

CONCLUSION

The overall diagnostic yield of the tests in patients >40-year-old with suspected reflex syncope was 61%. Both CSM and TT are useful for identifying those patients with a bradycardic phenotype, whereas CSM has a limited value for identifying the hypotensive phenotype. Since the overlap of responses between tests is minimal, both CSM and TT should be performed in every patient over 40 years receiving investigation for unexplained but possible reflex syncope.

Left bundle branch area pacing in a young athlete with progressive cardiac conduction (Lev-Lenegre) disease

We present the case of a professional soccer player affected by right bundle branch block and symptomatic 2:1 atrio-ventricular block during effort, due to progressive cardiac conduction disease (Lev-Lenegre disease), who received successful left bundle branch area pacing after a failed attempt at His bundle pacing. The electrocardiographic outcome of paced QRS was consistent with a rapid electrical activation of the left ventricle through the Purkinje system. The pursue of physiological pacing was preferred over conventional, given the young age of our patient and the expectedly high burden of stimulation, to reduce the long-term risk of pacing-induced cardiomyopathy.

Reproducibility of carotid sinus massage

AIMS

The reproducibility of carotid sinus massage (CSM) is debated. The aim of this study was to assess the reproducibility according to the methodology and diagnostic criteria defined by the guidelines on syncope of the European Society of Cardiology.

METHOD

Among 2800 patients with syncope who underwent CSM in the years 2005-2019, 109 patients (62 males; mean age 76 ± 10 years) had performed a second CSM after a median of 28 months. Carotid sinus hypersensitivity (CSH) was diagnosed when CSM elicited a pause of >3 s and/or a fall in systolic blood pressure >50 mm Hg without reproduction of spontaneous symptoms. Carotid sinus syndrome (CSS) was established when spontaneous symptoms were reproduced in the presence of bradycardia and/or hypotension.

RESULTS

The reproducibility of CSM was 78% for 18 CSS patients, 41% for 29 CSH patients, and 77% for 62 negative patients. The corresponding interrater agreement was good for CSS (kappa = 0.66), moderate for negative CSM (kappa = 0.42), and poor for CSH (kappa = 0.30). Combining CSH and negative tests, their reproducibility rose to 90% with kappa = 0.66.

CONCLUSION

CSS but not CSH has a good reproducibility. About half of patients with CSH had a negative response at the second test, thus suggesting a great overlap between them.

Long-Term Results After Single and Multiple Procedures of Ablation of Ventricular Tachycardia

INTRODUCTION

The aim of this study was to assess long-term results after single and multiple procedures of catheter ablation of ventricular tachycardia (VT). While it is generally accepted that multiple procedures are sometimes necessary in order to achieve long-term clinical success, the literature on this issue displays wide variability.

METHODS

We assessed the outcome of 160 consecutive patients who underwent 214 ablation procedures in the period 2008 to May 2015: 93 had overt structural heart disease (SHD) (previous myocardial infarction in 74 cases) and 67 had no SHD.

RESULTS

After the first procedure, the 1-year actuarial recurrence rates were 25% in patients with SHD and 5% in those without. However, recurrences increased progressively after the first year, reaching 46% and 35%, respectively, at 5 years. Overall, VT recurred in 35/93 (38%) patients with SHD and 22/67 (33%) patients without. Redo (1 to 4) procedures were performed in 28 (20%) patients with SHD and 18 (27%) patients without. After the last procedure, the 1-year actuarial recurrence rates were 5% in patients with SHD and 7% in those without, and the corresponding rates at 5 years were 23% and 7%. During follow-up, 21 patients died (all in the SHD group): no death was related to VT recurrence.

CONCLUSIONS

During long-term follow-up, VT frequently recurs after the first procedure, both in patients with SHD and in those without; multiple procedures are needed in order to increase the success rate.

Cardiac resynchronization therapy in patients undergoing atrioventricular junction ablation for permanent atrial fibrillation: a randomized trial

AIMS

On the basis of the current knowledge, cardiac resynchronization therapy (CRT) cannot be recommended as a first-line treatment for patients with severely symptomatic permanent atrial fibrillation undergoing atrioventricular (AV) junction ablation. We examined whether CRT was superior to conventional right ventricular (RV) pacing in reducing heart failure (HF) events.

METHODS AND RESULTS

In this prospective, multi-centre study, we randomly assigned 186 patients, in whom AV junction ablation and CRT device implantation had been successfully performed, to receive optimized echo-guided CRT (97 patients) or RV apical pacing (89 patients). The data were analysed according to the intention-to-treat principle. During a median follow-up of 20 months (interquartile range 11-24), the primary composite endpoint of death from HF, hospitalization due to HF, or worsening HF occurred in 11 (11%) patients in the CRT group and 23 (26%) patients in the RV group [CRT vs. RV group: sub-hazard ratio (SHR) 0.37 ( 95% CI 0.18-0.73), P = 0.005]. In the CRT group, compared with the RV group, fewer patients had worsening HF [SHR 0.27 (95% CI 0.12-0.58), P = 0.001] and hospitalizations for HF [SHR 0.20 (95% CI 0.06-0.72), P = 0.013]. Total mortality was similar in both groups [hazard ratio (HR) 1.57 (95% CI 0.58-4.27), P = 0.372]. The beneficial effects of CRT were consistent in patients who had ejection fraction ≤35%, New York Heart Association Class ≥III and QRS width ≥120 and in those who did not. At multi-variable Cox regression, only CRT mode remained an independent predictor of absence of clinical failure during the follow-up [HR = 0.23 (95% CI 0.08-0.66), P = 0.007].

CONCLUSIONS

In patients undergoing 'Ablate and Pace' therapy for severely symptomatic permanent atrial fibrillation, CRT is superior to RV apical pacing in reducing the clinical manifestations of HF. (ClinicalTrials.gov number: NCT00111527).

Usefulness of echo-guided cardiac resynchronization pacing in patients undergoing "ablate and pace" therapy for permanent atrial fibrillation and effects of heart rate regularization and left ventricular resynchronization

An acute comparative study of right ventricular (RV) pacing and echocardiographically guided cardiac resynchronization pacing (CRP) was performed in patients who underwent "ablate and pace" therapy for permanent atrial fibrillation. It was hypothesized that optimized CRP guided by tissue Doppler echocardiography would exert an additive beneficial hemodynamic effect to that of rate regularization achieved through atrioventricular junction ablation. An acute intrapatient comparison of echocardiographic parameters was performed between baseline preablation values and RV pacing and CRP (performed <24 hours after ablation) in 50 patients. Optimized CRP configuration was defined as the modality of pacing corresponding to that of the shortest intra-left ventricular (LV) delay among simultaneous biventricular pacing, sequential biventricular pacing, and single-chamber pacing. The intra-LV delay was defined as the difference between the longest and the shortest activation time in the six basal segments of the left ventricle. Compared with preablation measures, the ejection fraction increased by 10.8% during RV pacing (19% in patients with intra-LV delays <47.5 ms and 3% in those with intra-LV delays >47.5 ms). Compared with RV pacing, CRP caused a 9.2% increase in the ejection fraction, a 6.8% decrease in LV systolic diameter, and a 17.3% decrease in mitral regurgitation area; LV dyssynchrony was reduced from 52 +/- 27 to 21 +/- 12 ms. Similar results were observed in patients with and without depressed systolic function and in patients with and without left bundle branch block. In conclusion, rate regularization achieved through atrioventricular junction ablation and RV pacing provides a favorable hemodynamic effect that is inversely related to the level of LV dyssynchrony. Minimizing LV dyssynchrony by means of optimized CRP yields an additional important benefit.

[Comparative study of results of catheter ablation in ventricular tachycardia of different etiologies]

BACKGROUND

The aim of this study was to assess long-term results and adverse events in patients with ventricular tachycardia from different etiologies.

METHODS

The recurrence rate of tachycardia, consequent further therapies (other catheter ablation procedures, drug therapy and implantable defibrillator) and clinical events have been assessed in 60 consecutive patients undergoing ventricular tachycardia catheter ablation between January 2000 and December 2004.

RESULTS

During a median follow-up of 20 months (interquartile range 13-36 months), tachycardia recurred in 27 patients (45%) after a median of 3 months (interquartile range 1-12 months). A second procedure was performed in 11 patients; it was successful in 8 patients. Four patients underwent pharmacological therapy which was successful in all cases. Overall, after ablation (> or =1 procedures) and pharmacological therapy, tachycardia was cured in 75% of cases. All the 20 patients without structural heart disease were cured with ablation vs. 62% of patients with heart disease (p = 0.001). Patients with dilated cardiomyopathy reported worst results (33% success, p = 0.03). Recurrences were predicted by acute failure of procedure (p = 0.05), presence of heart disease (p = 0.006) and history of atrial arrhythmias (p = 0.02). On a multivariate analysis, only structural heart disease continued to be an independent predictor of ventricular tachycardia recurrence.

CONCLUSIONS

Catheter ablation of ventricular tachycardia has a high percentage of recurrences in patients with heart disease, whereas is curative in subjects without structural heart disease.

Seven-year follow-up after catheter ablation of atrioventricular nodal re-entrant tachycardia

BACKGROUND

Radiofrequency catheter ablation is considered to be a curative therapy for patients with atrioventricular nodal re-entrant tachycardia (AVNRT). Nevertheless, there is little information available with respect to long-term results and the consequences of catheter ablation. The present study aimed to assess the long-term results (a minimum of 5 years) and clinical events.

PATIENTS AND METHODS

The recurrence rate of AVNRT, the development of late atrioventricular block and the presence of other arrhythmias (atrial flutter and fibrillation) were assessed in 131 consecutive patients who were undergoing catheter ablation between January 1992 and December 1998.

RESULTS

During a mean follow-up of 7.2 +/- 2.5 years, tachycardia recurred in 13 patients (10%) after a median time of 6 months (interquartile range 4-24 months) and a second procedure was perfomed. Atrioventricular block occurred in two patients (1.5%) after 1 and 13 months. Atrial fibrillation recurred in seven (44%) of 16 patients in whom atrial fibrillation or flutter was present before ablation after a median of 12 months (interquartile range 9-15 months). Overall, all these events occurred after a median of 9 months (interquartile range 4-17 months). Subsequently, no event related to the arrhythmia or to the procedure was observed. A new onset atrial fibrillation, probably not related to AVNRT, occurred late in the follow-up in a further three patients.

CONCLUSIONS

Arrhythmic events are not infrequent after catheter ablation of AVNRT during the early years after ablation, but they are unlikely during the subsequent long-term follow-up.

The usage and diagnostic yield of the implantable loop-recorder in detection of the mechanism of syncope and in guiding effective antiarrhythmic therapy in older people

OBJECTIVES

To evaluate the usage and diagnostic yield of the implantable loop-recorder (ILR) in detection of the mechanism of syncope and in guiding therapy in patients aged >/=65 years and comparing them with those <65 years.

DESIGN

This was a two-hospital, observational, prospective study in consecutive patients with unexplained syncope who underwent an ILR implantation. Between November 1997 and December 2002, a total of 2052 patients with syncope were evaluated (local population of 590,000 inhabitants). The diagnosis remained unexplained in 371 (18%). Of these, 103 patients (5% of the total, 28% of those with unexplained syncope) received an ILR.

RESULTS

There were 70 (76%) patients aged >/=65 years and 25 (24%) <65 years. ILR implantation was 110 and 9 per million inhabitants per year, respectively. During a mean follow-up of 14+/-10 months, syncope was recorded in 52 patients. Compared with younger patients those older had a 2.7 higher syncope recurrence rate (56% vs 32%, P=0.03); arrhythmias were 3.1 times more likely to be responsible for syncope (44% vs 20%, P=0.03). More patients >/=65 years finally received ILR-guided therapy (42% vs 20%, P=0.04). Among the 29 patients (25 of those >/=65 years) who received specific antiarrhythmic therapy, only one (3%), had recurrence of syncope during the subsequent follow-up of 40+/-18 months.

CONCLUSIONS

In patients referred for investigation of unexplained syncope, the older subjects are more likely to have an indication for ILR implantation than those younger, ILR has a higher diagnostic value, an arrhythmia is more likely to be detected and successfully treated.

Incidence, diagnostic yield and safety of the implantable loop-recorder to detect the mechanism of syncope in patients with and without structural heart disease

AIM

To evaluate the incidence, diagnostic yield and safety of implantable loop recorders (ILRs) in patients with or without structural heart disease (SHD).

METHODS AND RESULTS

Two-hospitals, observational, prospective study in consecutive patients with unexplained syncope who underwent an ILR implantation. Between November 1997 and December 2002, a total of 2052 patients with syncope were evaluated (referral population of 590000 inhabitants). The diagnosis remained unexplained in 371 (18%). Of these, 103 patients (5% of total, 28% of unexplained syncope) received an ILR. SHD was present in 38 (37%), and absent in 65 (63%). During a median follow-up of 13 months, syncope was recorded in 52 patients. While patients with and without SHD had similar incidence of syncope recurrence, its mechanism was different. Patients with SHD more frequently had paroxysmal AV block and tachyarrhythmias and patients without SHD more frequently had sinus bradycardia/sinus arrest or no arrhythmia. More patients with SHD finally received an ILR-guided therapy. Sudden death occurred in one patient with SHD. Five syncope-related injuries were noted in 3 patients.

CONCLUSION

The mechanism of syncope is different in patients with and without SHD; diagnostic yield and safety are similar in both groups. About 28% of patients with unexplained syncope have an indication to ILR implantation. The need for ILR implantation in the general population is 34 implants/million inhabitants/year.

Outcome after cavo-tricuspid isthmus ablation in patients with recurrent atrial fibrillation and drug-related typical atrial flutter

This study evaluates the long-term clinical outcome of 56 consecutive patients affected by atrial fibrillation and drug-related typical atrial flutter who underwent cavo-tricuspid isthmus radiofrequency ablation. Symptomatic arrhythmic events recurred after ablation in 64% of the patients during follow-up of 19 +/- 9 months. Even in those who had recurrences, there was a substantial reduction in the incidence of episodes, quality of life was improved, and hospitalizations decreased.

Efficacy and feasibility of isometric arm counter-pressure manoeuvres to abort impending vasovagal syncope during real life

AIMS

Isometric arm exercises are able to increase blood pressure during the phase of impending vasovagal syncope. We evaluated their efficacy and feasibility during daily life in a group of 29 consecutive patients affected by vasovagal syncopes.

METHODS

The patients were trained to use arm tensing and/or handgrip in case of occurrence of symptoms of impending syncope.

RESULTS

During 14+/-6 months of follow-up, 260 episodes of impending syncope were reported by 19 patients; the manoeuvres were self-administered by these patients in 98% of cases and were able to abort syncope in 99.6% of cases. Overall, 5 episodes of syncope occurred in 5 patients (17%), in 4 cases without and in 1 with activation of the manoeuvres. Syncope recurred in 4 (40%) of 10 patients aged >65 years versus only 1 (5%) of 19 patients aged < or =65 years, p=0.03. The non-responders had more episodes of impending syncope than responders (37+/-32 vs 3+/-4, p=0.001). Among 19 clinical variables, age in years was the only significant predictor of syncopal recurrence. No patients had injury or other adverse morbidity related to the relapses.

CONCLUSIONS

Isometric arm counter-pressure manoeuvres are able to abort impending vasovagal syncope in most patients aged < or =65 years. Arm counter-pressure manoeuvres are feasible, safe and well accepted by the patients in the daily life.

Clinical and electrophysiological characteristics in patients with atrioventricular reentrant and atrioventricular nodal reentrant tachycardia

AIM

To compare clinical, electrophysiological characteristics and transcatheter ablation results between two groups of patients, one with atrioventricular reentrant tachycardia (AVRT) and the other with atrioventricular nodal reentrant tachycardia (AVNRT).

METHODS

The study population consisted of 94 consecutive patients who underwent endocavitary electrophysiological study and radiofrequency (RF) ablation: 46 patients had AVRT due to an accessory pathway with only retrograde conduction while 48 patients had AVNRT.

RESULTS

In relation to general and clinical characteristics, differences between the two groups emerged regarding the age of symptom onset (25+/-16 vs 37+/-17 years, p=0.001), the prevalence of heart disease (8 vs 31%, p=0.001) and the correct diagnosis on surface ECG (50 vs 79%, p=0.001). Clinical presentation was quite similar apart from a higher prevalence of fatigue and sweating in the AVNRT group. Transcatheter RF ablation therapy results were similar.

CONCLUSIONS

Patients with AVRT have a lower mean age at arrhythmia symptom onset compared with those with AVNRT and have fewer associated cardiac abnormalities. Clinical presentation is quite similar as well as their outcome after ablation. A correct diagnosis by standard ECG is more frequent in AVNRT.

Mechanism of syncope in patients with positive adenosine triphosphate tests

OBJECTIVES

We prospectively evaluated the mechanism of syncope in patients with positive adenosine triphosphate (ATP) tests (defined as the induction of atrioventricular [AV] block with a ventricular pause >/=6 s after an intravenous bolus of 20 mg ATP).

BACKGROUND

Patients with unexplained syncope tend to have more positive ATP tests results than those without syncope.

METHODS

An implantable loop recorder (ILR) was inserted in 36 ATP-positive patients (69 +/- 10 years; 22 women; median of 6 syncopal episodes); 15 of them also had a positive response to tilt testing.

RESULTS

During the follow-up of 18 +/- 9 months, 18 patients (50%) had syncopal recurrence and 16 (44%) had an electrocardiographically documented episode: AV block (n = 3: paroxysmal in 2 and permanent in 1), AV block followed by sinus arrest (n = 1), sinus arrest (n = 5), sinus bradycardia <40 beats/min (n = 2), normal sinus rhythm (n = 2), sinus tachycardia (n = 1), rapid atrial fibrillation (n = 1), and ectopic atrial tachycardia (n = 1). Bradycardia was documented in a total of 11 cases (69%), and a long ventricular pause (4 to 29 s) was present in eight cases (50%). All three patients with ILR-documented AV block had previously had a negative tilt test, whereas seven of eight with ILR-documented sinus bradycardia or sinus arrest had previously had a positive tilt test.

CONCLUSIONS

In patients with adenosine-sensitive syncope, the mechanism of syncope is heterogeneous, although bradycardia is the most frequent finding. Adenosine triphosphate-induced AV block predicts AV block as the mechanism of spontaneous syncope in only a few tilt-negative patients.

Isometric arm counter-pressure maneuvers to abort impending vasovagal syncope

OBJECTIVES

We hypothesized that isometric arm exercises were able to increase blood pressure (BP) during the phase of impending vasovagal syncope and allow the patient to avoid losing consciousness.

BACKGROUND

Hypotension is always present during the prodromal phase of vasovagal syncope.

METHODS

We evaluated the effect of handgrip (HG) and arm-tensing in 19 patients affected by tilt-induced vasovagal syncope. The study consisted of an acute single-blind, placebo-controlled, randomized, cross-over tilt-table efficacy study and a clinical follow-up feasibility study.

RESULTS

In the acute tilt study, HG was administered for 2 min, starting at the time of onset of symptoms of impending syncope. In the active arm, HG caused an increase in systolic blood pressure (SBP) from 92 +/- 10 mm Hg to 105 +/- 38 mm Hg, whereas in the placebo arm SBP decreased from 91 +/- 11 mm Hg to 73 +/- 21 mm Hg (p = 0.008). Heart rate behavior was similar in the two arms. In the active arm, 63% of patients became asymptomatic, versus 11% in the control arm (p = 0.02); conversely, only 5% of patients developed syncope, versus 47% in the control arm (p = 0.01). The patients were trained to self-administer arm-tensing treatment as soon as symptoms of impending syncope occurred. During 9 +/- 3 months of follow-up, the treatment was actually performed in 95/97 episodes of impending syncope (98%) and was successful in 94/95 (99%). No patients suffered injury or other adverse morbidity related to the relapses.

CONCLUSIONS

Isometric arm contraction is able to abort impending vasovagal syncope by increasing systemic BP. Arm counter-pressure maneuvers can be proposed as a new, feasible, safe, and well accepted first-line treatment for vasovagal syncope.

[Variables of arrhythmia risk in relation to pacemaker and implantable defibrillator]

Patients suffering from heart failure are at high risk of arrhythmic death. Conventional pacemakers have not shown to affect mortality in patients with chronic heart failure and sick sinus syndrome, while this issue is established in patients with III degree or advanced atrioventricular block. Biventricular pacing has recently been introduced in clinical practice and the experience is limited; to date, only an improvement in symptoms and quality of life has been shown. Biventricular pacing with implantable cardioverter-defibrillator back-up is promising. The implantable cardioverter-defibrillator is able to reduce total and sudden mortality in high risk patients, as clearly demonstrated by several randomized clinical trials.

[Comparison of clinical and electrophysiologic characteristics of patients with occult and manifest atrioventricular accessory pathway]

BACKGROUND

It is current opinion that concealed and manifest accessory pathways (APs) are indistinguishable with respect to their location and contribution to orthodromic reciprocating tachycardias. The aim of this study was to compare clinical and electrophysiological characteristics of two groups of patients.

METHODS

Between January 1999 and June 2000, 42 consecutive patients underwent radiofrequency catheter ablation for paroxysmal atrioventricular reciprocating tachycardia attributable to a concealed AP. Their clinical and electrophysiological characteristics were compared with a group of 48 consecutive patients with manifest AP and supraventricular tachyarrhythmias.

RESULTS

There were no differences regarding gender, the prevalence of heart disease and the age of onset of symptomatic tachycardias between the two groups. Compared to those with a manifest AP, the patients presenting with a tachyarrhythmia due to a concealed AP were older (48 +/- 15 vs 40 +/- 16 years, p < 0.05) and had a longer history of tachyarrhythmias (22 +/- 16 vs 13 +/- 13 years, p < 0.05). Atrial fibrillation was more frequent in patients with a manifest AP than in patients with a concealed AP (50 vs 9.5% respectively, p = 0.02). Atrioventricular reciprocating tachycardia was a cause of more hospitalizations (76 vs 35%, p = 0.01) and episodes of pre-syncope (47 vs 22%, p < 0.05) in the group of patients with a concealed AP. The anatomical site of concealed and manifest APs was significantly different: concealed APs were more frequently localized in the left side (93% left, 7% right), while manifest APs were seen in the left side in 64% of cases, in the right side in 29% and in the posteroseptal left + right region in 7% of cases. The retrograde electrophysiological properties and the inducibility of other types of reentrant arrhythmias were similar. Catheter ablation was similarly successful regardless of whether the AP was concealed or manifest, the rates of success being 91 and 88% respectively at the first attempt and with a similar number of energy applications (7 +/- 7 vs 10 +/- 9, p = NS). At a second attempt, the procedure was successful in 100 and 98% of cases respectively. Periprocedural complications occurred in 5% of patients with a concealed (1 ventricular fibrillation, 1 cerebral transient ischemic attack) and in 8% of patients with a manifest AP (2 pericardial effusion, 1 transient atrioventricular block, 1 anginal attack with spontaneous recovery) (p = NS). Complications occurred only for left-sided APs and were independent of the approach (transseptal or retrograde). Relapse of AP conduction was more frequent in the group of patients with a manifest than in those with a concealed AP (12 vs 5%), though not significantly. There were no late complications.

CONCLUSIONS

Those patients presenting with a tachyarrhythmia due to a concealed AP, compared to those with a manifest AP, were older and had a longer history of tachyarrhythmia. Atrial fibrillation was more frequent in patients with manifest AP. Atrioventricular reciprocating tachycardia episodes were longer-lasting and caused more hospitalizations and more frequently pre-syncope in the group of patients with a concealed AP. Almost all concealed APs were localized in the left side. The retrograde electrophysiological properties were similar. The results of radiofrequency catheter ablation were comparable in both groups.

Effects of left ventricular pacing on cardiac performance and on quality of life in patients with drug refractory heart failure

We assessed the effects of left ventricular pacing on echocardiographic and clinical parameters in 13 consecutive patients with heart failure and bundle branch block by means of a controlled acute and medium-term evaluation. Left ventricular pacing induced a significant improvement in left ventricular ejection fraction, Minnesota Living with Heart Failure Questionnaire score, New York Heart Association class, and 6-minute walking test compared with sinus rhythm or right ventricular pacing.

Adenosine-induced atrioventricular block in patients with unexplained syncope: the diagnostic value of ATP testing

BACKGROUND

ATP and its related nucleoside, adenosine, are ubiquitous biological compounds with potent depressant activity on the atrioventricular node. We hypothesized that an increased susceptibility of the atrioventricular node to adenosine may, in some cases, play a role in the genesis of syncope.

METHODS AND RESULTS

The study was performed in two parts. In part 1, we evaluated the effects of a bolus injection of 20 mg ATP in a group of 60 patients (57+/-19 years, 31 men) with syncope of unexplained origin and in 90 control subjects without syncope (55+/-17 years, 46 men). In control subjects, the upper 95th percentile of the maximum RR interval distribution, during ATP-induced atrioventricular block (AVB), was 6000 ms. In the syncope group, 28% of patients had a maximum RR interval above this limit (P=.000). The distribution of the maximum RR interval below the 95th percentile was similar in the two groups. In part 2, we validated the ATP test in 24 patients who had the fortuitous ECG recording of a spontaneous syncope caused by a transient asystolic pause (AVB in 15 and sinus arrest in 9). The ATP test caused AVB with an asystolic pause of > or = 6000 ms in 53% of the patients with documented AVB but in none (0%) of the patients with documented sinus arrest (P=.01). Among the patients with spontaneous AVB, the ATP test was abnormal in 6 of the 7 patients (86%) in whom all conventional investigations for syncope had been negative and in 2 of the 8 patients (25%) who had shown positivity (P=.03).

CONCLUSIONS

An increased susceptibility to ATP testing is present in patients with SUO and patients with syncope due to paroxysmal AVB. Thus, a logical inference is that ATP testing can be used to identify patients with syncope due to paroxysmal AVB. The results of this study form the necessary background for future prospective studies with an aim to validate this assumption.

A patient with syncopal ventricular tachycardia (noninducible on electrophysiologic study) and coronary artery disease

The case of a 63-year-old patient with coronary artery disease presenting with syncopal sustained ventricular tachycardia is reported. He had very poor ventricular function, an extensive myocardial scar, and limited area of reversible ischemia. Coronary angiographic examination showed a left main equivalent coronary artery disease with critical stenosis. Although this patient should theoretically benefit from revascularization, we decided against this due to the high estimated perioperative mortality rate for coronary artery bypass grafting in such a patient. Therefore, we intensively treated myocardial ischemia and pump failure with digoxon, furosemide, dihydralazine, nitrates, and warfarin and prescribed a back-up defibrillator implant.

Value of head-up tilt testing potentiated with sublingual nitroglycerin to assess the origin of unexplained syncope

This study was undertaken to assess the value of sublingual nitroglycerin administration during upright tilt as a simple practical test for the diagnosis of vasovagal syncope. To this purpose, 235 patients with syncope of unknown origin and no evidence of organic heart disease (110 men, mean age 52 +/- 20 years) and 35 asymptomatic control subjects underwent head-up tilt testing with nitroglycerin challenge. Patients and subjects were tilted at 60 degrees for 45 + 20 minutes; the initial 45 minutes were without medication and the final 20 minutes after 300 micrograms of sublingual nitroglycerin. During the drug-free phase of the test, 59 patients (25%) and no controls had a positive response. After drug administration, a positive response (syncope in association with sudden hypotension and bradycardia) occurred in 60 patients (26%) and in 2 controls (6%), whereas an exaggerated or false-positive response (minor or different symptoms in association with slowly increasing hypotension alone) was observed in 33 patients (14%) and in 5 controls (14%). We conclude that the sublingual nitroglycerin head-up tilt test is a useful tool to unmask the vasovagal origin of unexplained syncope in patients without organic heart disease. The addition of nitroglycerin to upright tilt allows the positive rate of passive tilting to be doubled (51% vs 25%) while maintaining a high specificity (94% vs 100%).

Mechanisms of syncope caused by transient bradycardia and the diagnostic value of electrophysiologic testing and cardiovascular reflexivity maneuvers

Transient bradycardia may be intrinsic because of sinus node or atrioventricular (AV) conduction abnormalities, or extrinsic because of abnormal vagal reflex. Twenty-five consecutive patients, referred to us for study of unexplained syncope, who, during electrocardiographic monitoring, had a documented episode of intermittent bradycardia that caused syncope, underwent a full electrophysiologic study, carotid sinus massage, and the head-up tilt test. A prolonged ventricular asystole (5 to 20 seconds) was documented during syncope in all patients: sinus arrest in 13, AV block in 7, sinus arrest plus AV block in 3, and asystolic pause during atrial fibrillation in 2. Abnormal electrophysiologic findings suggested the correct diagnosis in 6 patients (24%): block within the bundle of His in 5 and sick sinus syndrome in 1. An abnormal response to carotid sinus massage or to the head-up tilt test suggested a neurally mediated mechanism in 17 patients (68%). Overall, electrophysiologic study and vasovagal maneuvers were able to identify the mechanism of spontaneous syncope in 23 patients (92%). Thus, in patients affected by syncope due to transient bradycardia, the most likely mechanism of syncope is neurogenic, whereas it is cardiogenic only in a few instances. Electrophysiologic testing, carotid sinus massage, and the head-up tilt test can identify most of these patients. Conversely, when all these tests are negative, it is unlikely that transient bradycardia is the cause of syncope. Because of the different mechanisms involved, electrophysiologic study and vasovagal maneuvers are complementary diagnostic tools.

[The re-evaluation of the vasodepressive component in the carotid sinus syndrome]

BACKGROUND

The evaluation of the vasodepressor (VD) reflex of the carotid sinus syndrome is usually inaccurate, due to the difficulty in blood pressure measurement.

AIM

To study the VD reflex with a beat-to-beat not invasive technique.

METHODS

We investigated 68 patients (49 males, 19 females; mean age 70 +/- 11 years) affected by carotid sinus syndrome: cardioinhibitory (CI) form was present in 47 patients, mixed (M) form in 10 patients and VD form in 11 patients. The control group consisted of 9 patients (6 male, mean age 71 +/- 8 years) affected by third degree atrioventricular block who had received the implant of a permanent pacemaker and were pacemaker-dependent with a prolonged asystole at time of temporary inhibition of the pacemaker itself. The study of the VD reflex was performed in the supine position; beat-to-beat arterial systolic pressure was monitored by a photoplethysmographic method using a finger cuff (Finapres technique).

RESULTS

In all the patients the carotid sinus massage caused a marked fall in systolic blood pressure which was greatest at the end of the massage: from 143 +/- 25 mm Hg to 74 +/- 20 mm Hg in the patients with CI form, from 144 +/- 14 mm Hg to 76 +/- 18 mm Hg in those with M form and from 125 +/- 26 mm Hg to 65 +/- 13 mm Hg in those with VD form. A decrease in systolic blood pressure > or = 50 mm Hg occurred in 84% of cases. Afterwards, the patients with CI form had a progressive increase of systolic blood pressure that reached the initial value after a mean of 27 seconds. In the patients with VD form systolic blood pressure was significantly (p < or = 0.5) lower than that observed in all the other groups, beginning from the third second after the end of the massage; mean systolic blood pressure value remained significantly lower than the initial value for more than 27 seconds. The patients with M form showed an intermediate pattern. Also control group patients showed a fall in systolic blood pressure immediately after pacemaker inhibition (from 152 +/- 29 mm Hg to 87 +/- 25 mm Hg) that was of similar extent than that observed in carotid sinus syndrome patients, but pressure returned to initial value within 9 seconds.

CONCLUSIONS

An important VD reflex is present in most patients with carotid sinus syndrome. It lasts more than the CI reflex and it persists for several seconds after the end of the massage. The initial fall of systolic blood pressure is of similar extent in all the forms of carotid sinus syndrome, but the patients with the VD form are characterized by a longer duration and greater entity of the decrease. These results point out the importance of the VD reflex in patients with the carotid sinus syndrome.

Carotid sinus syncope: the most frequent neurally mediated syncope in the elderly

The present work reviews current literature and the authors' experience of carotid sinus syndrome (CSS), which is considered to be the most common cause of neurally mediated acute disorders of consciousness in the elderly. Although no definitive consensus about its nosology has yet been reached, most groups agree that three features fulfill the diagnosis: anamnestic presence of syncope or its minor equivalents, and their reproduction by carotid sinus massage associated with defined values of cardioinhibition or vasodepression or both. The technique for performing carotid sinus massage used by the authors is described; this manoeuvre seems very safe and reproducible as long as simple rules are followed, and it allows the classification of CSS types. The treatment of CSS is varied, according to several factors. No pharmacological therapy has yet been demonstrated to be effective. While severe cardioinhibitory forms require an appropriate pacing, vasodepressive ones and types with only minor symptoms show a more favourable natural history. Pacing is advised in mixed CSS with either frequent and invalidating relapses, or 'high risk' attacks (severe, abrupt, with major traumas, etc.). Finally, the protocol for choosing the adequate mode of pacing is illustrated. In most cases VVI is sufficient, but the decision requires a careful individual examination.

Radiofrequency catheter ablation and modulation of atrioventricular conduction in patients with atrial fibrillation

We attempted radiofrequency ablation of the AV junction with a sequential right- and left-sided approach in 78 patients affected by severely symptomatic, drug refractory atrial fibrillation. Stable third-degree AV block was obtained in 99% of cases and, after 3 months, persisted in 92% of cases. Single session, stepwise, radiofrequency modulation of the AV node was attempted in 13 patients with paroxysmal atrial fibrillation. During sinus rhythm, ablation of the slow and fast AV node pathways was performed in order to increase the nodal refractory period or to slow conduction. Clinically successful modulation of AV conduction was achieved in 15% of cases and persisted during a 3-month follow-up. In conclusion, AV junction ablation is a well-established means of treating atrial fibrillation, but implies the implant of a permanent pacemaker. AV node modulation avoids the pacemaker implant, but is efficacious only in a minority of patients. Thus, in patients affected by paroxysmal atrial fibrillation, AV modulation should be attempted first; if this is ineffective, AV ablation can be performed during the same session.

The effect of exogenous adenosine in patients with neurally-mediated syncope and sick sinus syndrome

The effects of a 20-mg i.v., bolus of adenosine 5' triphosphate (ATP) on the heart rhythm was studied in 79 patients affected by neurally-mediated syncope (26 cases) or sick sinus syndrome (22 cases) or both syndromes (31 cases) and in 31 healthy control subjects in order to examine the sensitivity of cardiac purinoceptors in such circumstances. During ATP infusion, the sinus cycle lengthened to > 2 seconds in no control, in 1 (4%) patient with neurally-mediated syncope, in 5 (23%) patients with sick sinus syndrome, and in 13 (42%) patients with both neurally-mediated and sick sinus syndromes (P = 0.01). Atrioventricular block occurred in 14 (45%) of controls, in 10 (38%) patients with neurally-mediated syncope, in 4 (18%) patients with sick sinus syndrome, and in 13 (42%) patients with both neurally-mediated syncope and sick sinus syndrome (n.s.). Thus, exogenous ATP exerts different effects on patients with neurally-mediated syncope and patients with sick sinus syndrome. In fact, intrisic disease of the sinus node is necessary to modulate an abnormal adenosine-mediated sinus arrest, whereas patients affected by neurally-mediated syncope alone show a normal sensitivity to the drug administration. The effect of ATP on atrioventricular conduction is greater than that on sinus node and is of similar magnitude in patients and controls; thus the clinical meaning of ATP induced atrioventricular block remains uncertain.

A new pacemaker for paroxysmal atrial fibrillation treated with radiofrequency ablation of the AV junction

Atrial fibrillation is a relative contraindication to atrial synchronous pacing because of the risk of the tracking of rapid atrial rhythms by the pacemaker. In this study, we describe the clinical results of an AV synchronous rate responsive pacemaker with an original algorithm, which is able to sense pathological increments in atrial rate and automatically to switch into a non-AV synchronous mode of pacing. This pacemaker was implanted in 12 patients who had undergone radiofrequency ablation of the AV junction in order to cure severely symptomatic, drug refractory, paroxysmal atrial fibrillation. In an acute, intrapatient comparison between the standard AV synchronous mode and the automatic switching mode, ventricular tracking of atrial fibrillation occurred in 35% and 4% of total beats at rest and in 24% and 2% of total beats during exercise, respectively (P < 0.001). During 5 +/- 4 months of follow-up, no further tachyarrhythmia related symptoms occurred. In conclusion, the standard DDDR mode is unable to eliminate ventricular tracking of atrial fibrillation, thus undermining the efficacy of AV junction ablation therapy. The automatic switching mode eliminates this adverse effect of dual chamber pacing.

Influence of atrioventricular junction radiofrequency ablation in patients with chronic atrial fibrillation and flutter on quality of life and cardiac performance

The purpose of this study was to evaluate the effects of atrioventricular junction radiofrequency ablation on the quality of life, exercise performance, and echocardiographic parameters in 23 patients with chronic, severely symptomatic, drug-refractory atrial fibrillation or flutter. Initially, patients were randomized to receive ablation plus pacemaker therapy (n = 12) or pacemaker therapy alone (n = 11). After 15 days, palpitations decreased by 92% and 37% (p = 0.004), rest dyspnea by 79% and 40% (p = NS), effort dyspnea by 65% and 30% (p = 0.03), exercise intolerance by 54% and 17% (p = 0.005), and asthenia by 67% and 31% (p = 0.02) in the 2 groups, respectively. At the end of this short-term study, control patients also underwent ablation therapy, and a 3-month intrapatient follow-up study was performed in 22 patients. New York Heart Association functional class > or = 3 was present in 14 patients (64%) before, but in only 3 patients (14%) after ablation therapy (p = 0.002); specific activity scale functional class > or = 3 was present in 9 patients (41%) before, but in only 5 (23%) after ablation therapy (p = NS). Exercise duration during standardized stress testing increased by a mean of 63 +/- 93 seconds (15% increase) (p = 0.001). In the 9 patients with depressed left ventricular systolic function, echocardiographic fractional shortening increased by 34% (from 23 +/- 5% to 31 +/- 9%) (p = 0.003). In the remaining 13 patients with normal systolic function, fractional shortening decreased by 10% (from 40 +/- 5% to 36 +/- 6%) (p = 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

[Progression to 2d and 3d grade atrioventricular block in patients after electrostimulation for bundle-branch block and syncope: a long-term study]

BACKGROUND

Patients with bundle branch block and syncope, especially those with abnormal electrophysiologic study, are at high risk of progression to second-or third-degree atrioventricular block and therefore they often receive a permanent back-up pacemaker. The aim of this study was to evaluate of the incidence of bundle branch block progression to second or third-degree atrioventricular block during long-term follow-up.

METHODS

A retrospective study was performed on 60 patients (49 males, age 77 +/- 9 years) with bundle branch block and permanent back-up pacemaker. The patients were subdivided into 3 groups: 13 patients, at pre-implant electrophysiologic study had HV interval > or = 100 msec and/or second- or third-degree atrioventricular block induced by ajmaline i.v. administration (Group 1); 20 patients with HV interval of 70-100 msec and/or HV > or = 120 msec after ajmaline administration (Group 2); 27 patients who had received a permanent pacemaker because of carotid sinus syndrome or sick sinus syndrome (22 patients) or because of recurrent syncopes and negative electrophysiologic study (5 patients) (Group 3).

RESULTS

During a mean follow-up of 62 +/- 41 months, 17/60 patients (28%) had progression to second- (n = 4) or third-degree (n = 13) atrioventricular block: atrioventricular block occurred in 54% of Group 1 patients in 25% of Group 2 patients and in 19% of Group 3 patients. The actuarial rate of progression to atrioventricular block for the overall population was, at 5 and 10 years, 25% and 58% respectively; in Group 1 it was 46% and 62%; in Group 2 it was 22% and 55% and in Group 3 it was 21% and 59% (p = 0.06). The patients with right bundle branch block and left anterior hemiblock were at higher risk of progression to atrioventricular block than those with right bundle branch block or left bundle branch block (risk 42% vs 14%, p = 0.06). The presence of an abnormal electrophysiologic study did not increase the progression rate either in the patients with right bundle branch block and left anterior hemiblock (risk of 43%), nor did it in those patients with other types of bundle branch block (risk of 18%). Moreover, the induction of second- or third-degree atrioventricular block during ajmaline administration was associated with a higher risk of block during the follow-up (60% vs 25%, p = 0.06).

CONCLUSIONS

Patients treated with pacemaker because of symptomatic bundle branch block have a high risk of progression to second- or third-degree atrioventricular block in the long-term follow-up. The results argue against the practical usefulness of electrophysiological study since a risk stratification could be obtained by the simpler surface electrocardiogram; moreover, risk of block was also present in the patients affected by carotid sinus syndrome or sick sinus syndrome, and in those affected by unexplained syncope with negative electrophysiologic study.

Follow-up of asystolic episodes in patients with cardioinhibitory, neurally mediated syncope and VVI pacemaker

The occurrence rate of spontaneous asystolic episodes during long-term follow-up in patients with abnormal asystolic responses induced by means of vasovagal maneuvers was evaluated. The heart rate of 23 patients (mean age 64 +/- 12 years; 6 women and 17 men) affected by neurally mediated syncope (mean 4.3 +/- 4.9 episodes) was continuously monitored by a specially designed implanted pacemaker able to detect and store in its memory all asystolic episodes lasting 3 to 6 or > 6 seconds. Asystolic, neurally mediated syncope was diagnosed when a reflex asystole of > 3 seconds was induced during carotid sinus massage (n = 22), eyeball compression test (n = 3) or head-up tilt test (n = 2). During a total of 357 months (mean 15 +/- 7) of monitoring, asystolic episodes occurred in 17 patients (74%): 1,765 episodes of 3- to 6-second (median 3) duration occurred in 14 patients, and 47 episodes of > 6-second (median 2) duration occurred in 11. The actuarial estimates of occurrence of asystolic episodes of > 3 and > 6 seconds were 82 and 53%, respectively, after 2 years of follow-up. Only 12 episodes of 3 to 6 seconds (0.7%), and 20 episodes of > 6 seconds (43%) resulted in presyncopal or syncopal symptoms. Thus, an asystolic response to vasovagal maneuvers predicts the occurrence of spontaneous asystolic episodes during follow-up. With few exceptions, spontaneous episodes are asymptomatic and their incidence is low.

Role of autonomic reflexes in syncope associated with paroxysmal atrial fibrillation

OBJECTIVES

The purpose of this study was to evaluate the role of autonomic reflexes in the genesis of syncope associated with the onset of paroxysmal atrial fibrillation.

BACKGROUND

Syncope associated with paroxysmal atrial fibrillation has been interpreted as an ominous finding predictive of rapid ventricular rates. However, various mechanisms may be involved when heart rate is not particularly high.

METHODS

Forty patients (age 60 +/- 14 years, 20 men, 20 women) with syncope and atrial fibrillation were compared with atrial fibrillation without syncope. Carotid sinus massage and head-up tilt testing (at 60 degrees for 60 min at baseline and during isoproterenol infusion) were performed during sinus rhythm. A positive response was defined as the induction of syncope. Atrial fibrillation was also induced on a tilt table at 60 degrees by means of short bursts of atrial pacing.

RESULTS

Results of carotid sinus massage were positive in 15 (37%) of 40 patients but in no control subjects (p = 0.002). Head-up tilt test findings were positive in 25 (66%) of 38 patients and in 2 (12%) of 16 control subjects (p = 0.0004). The induction of atrial fibrillation in the upright position elicited syncope in 16 (42%) of 38 patients but in none of 16 control subjects (p = 0.001). At the beginning of atrial fibrillation, systolic blood pressure was lower in patients than in control subjects (88 +/- 32 vs. 127 +/- 32 mm Hg), whereas mean heart rate was similar (142 +/- 35 vs. 134 +/- 25 beats/min). The correlation between heart rate and systolic blood pressure was weak (r = 0.35), and in five patients syncope occurred at a heart rate < or = 130 beats/min. At the time of syncope, heart rate decreased (-12 +/- 21 beats/min) in patients with induced syncope, whereas it remained unchanged in patients without induced syncope (+1 +/- 17 beats/min, p = 0.04) or slightly increased in control subjects (+9 +/- 21 beats/min, p = 0.009).

CONCLUSIONS

Patients with syncope associated with paroxysmal atrial fibrillation are predisposed to an abnormal neural response during both sinus rhythm and arrhythmia. In some patients the onset of atrial fibrillation triggers vasovagal syncope.