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 diagnostic value of ATP testing in patients with unexplained syncope

A minority of patients with unexplained syncope has an increased susceptibility to adenosine triphosphate (ATP) injection. In these 'hypersensitive' patients, owing to its powerful cardiac and hypotensive effects, endogenous adenosine released under physiological and pathological conditions could trigger bradycardia and/or hypotension and cause syncope. This hypothesis still needs to be proven. However, there is some evidence that the ATP test identifies a group of patients with otherwise unexplained syncope with definite clinical features, absence of structural heart disease and benign prognosis. The mechanism of syncope is heterogeneous; indeed, in cases of electrocardiographic documentation of spontaneous syncope, either a long ventricular pause (mainly due to paroxysmal atrioventricular (AV) block) or no rhythm variations or even tachycardia were documented. ATP-positive patients have clinical features and mechanisms of syncope which are different from tilt-positive patients. Owing to its low positive predictive value, the ATP test is of little value in selecting treatment. A favourable outcome suggests a strategy of postponing treatment, in particular pacemaker therapy, until a definite diagnosis can be made by documenting a spontaneous syncopal relapse.

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.

A standardized conventional evaluation of the mechanism of syncope in patients with bundle branch block

BACKGROUND

The finding of bundle branch block in patients with syncope suggests that paroxysmal AV block may be the cause of syncope, even though its prevalence is unknown.

METHODS

We evaluated 55 consecutive patients with syncope and bundle branch block (mean age 75 +/- 8 years; median of two syncopal episodes per patient) referred to three Syncope Units. The hierarchy and appropriateness of diagnostic tests and the definitions of the final diagnoses followed standardized predefined criteria.

RESULTS

Cardiac syncope was diagnosed in 25 patients (45%): AV block in 20, sick sinus syndrome in 2, sustained ventricular tachycardia in 1, aortic stenosis in 2. Neurally mediated syncope was diagnosed in 22 (40%): carotid sinus syndrome in 5, tilt-induced syncope in 15, adenosine-sensitive syncope in 2. Syncope remained unexplained in 8 (15%).

CONCLUSIONS

Less than half of the patients with bundle branch block have a final diagnosis of cardiac syncope; in these patients, paroxysmal AV block is the most frequent but not the only mechanism supposed.

The application of a standardized strategy of evaluation in patients with syncope referred to three syncope units

BACKGROUND

The appropriate diagnostic work-up of patients with syncope is not well defined. We applied the guidelines of Italian 'Associazione Nazionale Medici Cardiologi Ospedalieri' to a group of consecutive patients with syncope referred to three Syncope Units. The aim of the study was to evaluate the applicability of those guidelines in the 'real world' and their impact on the use of the tests.

METHODS

We evaluated 308 consecutive patients with syncope (mean age 61 +/- 20 years; median of three syncopal episodes per patient). The hierarchy and appropriateness of diagnostic tests and the definitions of the final diagnosis followed standardized predefined criteria. In brief, all patients underwent initial evaluation consisting of history, physical examination, supine and upright blood pressure measurement and standard electrocardiogram (ECG) (only in patients > 45 years or with history of heart disease). Any subsequent investigations were based on the findings of the initial evaluation. Priority was given to cardiological tests (prolonged ECG monitoring, exercise test, electrophysiological study), or to neurally mediated tests (carotid sinus massage, tilt test, ATP test), or to neuro-psychiatric tests, as appropriate.

FINDINGS

The initial evaluation alone was diagnostic in 72 patients (23%). One further test was necessary for diagnosis in 65 patients (21%), > or = 2 tests in 64 (21%) and > or = 3 tests in 50 (16%). The diagnostic yield was 10% for ECG, 3% for echocardiogram, 16% for Holter, 5% for exercise test, 27% for electrophysiological study, 57% for carotid sinus massage, 52% for tilt testing and 15% for ATP test. At the end of the work-up the mechanism of syncope remained unexplained in 57 patients (18%).

CONCLUSIONS

When standardized criteria based on the appropriateness of indications are used, few simple tests are usually needed for diagnosis of 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.

Mechanism of syncope in patients with bundle branch block and negative electrophysiological test

BACKGROUND

In patients with syncope and bundle branch block (BBB), syncope is suspected to be attributable to a paroxysmal atrioventricular (AV) block, but little is known of its mechanism when electrophysiological study is negative.

METHODS AND RESULTS

We applied an implantable loop recorder in 52 patients with BBB and negative conventional workup. During a follow-up of 3 to 15 months, syncope recurred in 22 patients (42%), the event being documented in 19 patients after a median of 48 days. The most frequent finding, recorded in 17 patients, was one or more prolonged asystolic pause mainly attributable to AV block; the remaining 2 patients had normal sinus rhythm or sinus tachycardia. The onset of the bradycardic episodes was always sudden but was sometimes preceded by ventricular premature beats. The median duration of the arrhythmic event was 47 seconds. An additional 3 patients developed nonsyncopal persistent III-degree AV block, and 2 patients had presyncope attributable to AV block with asystole. No patients suffered injury attributable to syncopal relapse.

CONCLUSIONS

In patients with BBB and negative electrophysiological study, most syncopal recurrences have a homogeneous mechanism that is characterized by prolonged asystolic pauses, mainly attributable to sudden-onset paroxysmal AV block.

[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.