[Dual atrioventricular nodal pathways: physiology, arrhythmic findings, and electrocardiographic manifestations]. / Doppia via nodale: basi fisiologiche, risvolti aritmologici ed espressioni elettrocardiografiche.

The atrioventricular (AV) node is an anatomically well-defined structure, conveniently housed in the triangle of Koch. There are two distinct atrial impulse approaches to the AV node, one of which (in the anterior portion of triangle of Koch) has a faster conduction, while the other one (in the posterior portion) has a slower conduction. However, it is not said that such a conductive duality translates into any arrhythmic phenomena. Actually, these arrhythmias are due to an imbalance of the two pathways electrophysiological properties, which does not always exist. In the presence of such an imbalance, the dual AV nodal physiology is, however, the substrate for various arrhythmias and curious electrocardiographic behaviors. Often the fast pathway is characterized by a relatively long refractory period. In contrast, the slow approach is often characterized by shorter refractoriness.The unbalanced refractoriness of the two nodal pathways constitutes the prerequisite for the most common form of paroxysmal supraventricular tachycardia: the AV nodal reentrant tachycardia (AVNRT). In subjects prone to this type of arrhythmia, during sinus rhythm, nodal conduction usually occurs from the anterior approach (fast pathway). However, a premature atrial beat may find this pathway refractory and cross the AV node through the posterior approach (slow pathway), resulting in a sudden prolongation of the AV conduction time ("jump"). This allows the impulse, once it reaches the common end, to excitate the fast pathway in a retrograde direction and to return backwards to the atrium, thus triggering a circus movement that can result in a "slow-fast" AVNRT. More rarely, an AVNRT can take place in an opposite direction of the reentrant impulse ("fast-slow" variety of AVNRT). A paroxysmal supraventricular tachycardia may seldom occur with a regularly alternating RR cycle, if the reentrant mechanism involves retrogradely an accessory AV pathway and, in anterograde direction, a fast and a slow AV nodal pathway, alternately. Among the mechanisms underlying the total RR irregularity during atrial fibrillation, there is probably also the possibility that the AV node may offer to the atrial impulses two distinct pathways to reach the His bundle. Not too rarely, a dual AV nodal physiology can occur during sinus rhythm, through unexpected and sudden changes in the AV conduction time, so that two distinct PR families can be observed. It is likely that the presence of dual AV nodal pathways can facilitate or promote a Wenckebach conduction mechanism at nodal site.

Antiarrhythmic medication is superior to catheter ablation in suppressing supraventricular ectopic complexes in patients with atrial fibrillation.

BACKGROUND: Supraventricular ectopic complexes (SVEC) originating in the pulmonary veins are known triggers of atrial fibrillation (AF) which led to the development of pulmonary vein isolation for AF. However, the long-term prevalence of SVEC after catheter ablation (CA) as compared to antiarrhythmic medication (AAD) is unknown. Our aims were to compare the prevalence of SVEC after AAD and CA and to estimate the association between baseline SVEC burden and AF burden during 24months of follow-up. METHODS: Patients with paroxysmal AF (N=260) enrolled in the MANTRA PAF trial were treated with AAD (N=132) or CA (N=128). At baseline and 3, 6, 12, 18 and 24months follow-up patients underwent 7-day Holter monitoring to assess SVEC and AF burden. We compared SVEC burden between treatments with Wilcoxon sum rank test. RESULTS: Patients treated with AAD had significantly lower daily SVEC burden during follow-up as compared to CA (AAD: 19 [6-58] versus CA: 39 [14-125], p=0.003). SVEC burden increased post-procedurally followed by a decrease after CA whereas after AAD SVEC burden decreased and stabilized after 3months of follow-up. Patients with low SVEC burden had low AF burden after both treatments albeit this was more pronounced after CA at 24months of follow-up. CONCLUSION: AAD was superior to CA in suppressing SVEC burden after treatment of paroxysmal AF. After CA SVEC burden increased immediately post-procedural followed by a decrease whereas after AAD an early decrease was observed. Lower SVEC burden was highly associated with lower AF burden during follow-up especially after CA.

Prognostic Significance of Premature Atrial Complexes Burden in Prediction of Long-Term Outcome.

BACKGROUND: The prognostic significance of premature atrial complex (PAC) burden is not fully elucidated. We aimed to investigate the relationship between the burden of PACs and long-term outcome. METHODS AND RESULTS: We investigated the clinical characteristics of 5371 consecutive patients without atrial fibrillation (AF) or a permanent pacemaker (PPM) at baseline who underwent 24-hour electrocardiography monitoring between January 1, 2002, and December 31, 2004. Clinical event data were retrieved from the Bureau of National Health Insurance of Taiwan. During a mean follow-up duration of 10±1 years, there were 1209 deaths, 1166 cardiovascular-related hospitalizations, 3104 hospitalizations for any reason, 418 cases of new-onset AF, and 132 PPM implantations. The optimal cut-off of PAC burden for predicting mortality was 76 beats per day, with a sensitivity of 63.1% and a specificity of 63.5%. In multivariate analysis, a PAC burden >76 beats per day was an independent predictor of mortality (hazard ratio: 1.384, 95% CI: 1.230 to 1.558), cardiovascular hospitalization (hazard ratio: 1.284, 95% CI: 1.137 to 1.451), new-onset AF (hazard ratio: 1.757, 95% CI: 1.427 to 2.163), and PPM implantation (hazard ratio: 2.821, 95% CI: 1.898 to 4.192). Patients with frequent PAC had increased risk of mortality attributable to myocardial infarction, heart failure, and sudden cardiac death. Frequent PACs increased risk of PPM implantation owing to sick sinus syndrome, high-degree atrioventricular block, and/or AF. CONCLUSIONS: The burden of PACs is independently associated with mortality, cardiovascular hospitalization, new-onset AF, and PPM implantation in the long term.

Supraventricular premature beats and short atrial runs predict atrial fibrillation in continuously monitored patients with cryptogenic stroke.

BACKGROUND AND PURPOSE: Supraventricular premature beats (SPBs) may help to assess the risk of atrial fibrillation (AF) in patients with cryptogenic stroke and therefore guide therapy. METHODS: An internal loop recorder was implanted in consecutive patients with acute cryptogenic stroke. The occurrence and quantity of SPBs and short supraventricular runs (SVRs) in 24-hour ECG in patients with and without future AF were analyzed. We evaluated the relative risk of the upper quartile of SPB and SVR patients against the remainder and used binary logistic regression to evaluate a possible independent influence of SPBs and SVRs on AF occurrence. RESULTS: Twelve of 70 included patients (mean age, 59±13 years) experienced development of AF during a mean monitoring duration of 536±212 days. Patients with AF had a median of 22.8 SPBs/h versus 1.2 SPBs/h (P<0.0001) in patients without AF and a median of 0.7 SVRs/h (AF) versus 0 SVR/h (non-AF). Patients in the upper quartile of SPBs (>14.1/h) and SVRs (>0.2/h) demonstrated a relative risk of 4.0 (95% confidence interval, 1.1-14.6; P=0.04) and 6.9 (95% confidence interval, 1.8-26.7; P=0.005) for future AF, respectively. In binary logistic regression, SPBs (P=0.02) and SVRs (P=0.05) remained significant independent predictors for occurrence of AF. CONCLUSIONS: Numerous SPBs and SVRs demonstrated a high risk for future AF in patients with cryptogenic stroke.

Effect of continuous positive airway pressure on an atrial arrhythmia in a patient with mild obstructive sleep apnea.

Cardiac arrhythmias have been reported in up to half of individuals with obstructive sleep apnea (OSA) and have been proposed to be one of the factors contributing to their increased mortality. Several studies have demonstrated evidence of an association between OSA and a number of cardiac arrhythmias. The mechanisms of arrhythmogenesis in OSA may be due to enhanced vagal output triggered by a combination of apnea and hypoxemia. This case demonstrates a dose-dependent reduction in atrial ectopy with increasing continuous positive airway pressure (CPAP) in the setting of mild sleep apnea.

Acute effects of right ventricular apical pacing on left ventricular synchrony and mechanics.

BACKGROUND: Chronic right ventricular (RV) apical pacing has a detrimental effect on left ventricular (LV) function. However, the acute effects of RV apical pacing on LV mechanics remain unclear. The purpose of the study was to assess the acute impact of RV apical pacing on global LV function, evaluating LV contraction synchrony and LV shortening and twist, using 2D speckle-tracking strain imaging. METHODS AND RESULTS: A group of 25 patients with structural normal hearts referred for electrophysiological study were studied. Two-dimensional echocardiography was performed at baseline and during RV apical pacing at the time of the electrophysiological study. Changes in LV synchrony and mechanics (longitudinal shortening and twist) were assessed using speckle-tracking strain imaging. In addition, 25 controls matched by age, sex, and LV function were studied during sinus rhythm. The group of patients (44+/-12 years, 10 men) and the group of controls (48+/-3 years, 8 men) showed comparable LV synchrony, LV longitudinal shortening, and LV twist at baseline. However, during RV apical pacing, a more dyssynchronous LV contraction was observed in the patients (from 21 ms [Q(1):10, Q(3):53] to 91 ms [Q(1):40, Q(3):204], P<0.001) together with an impairment in LV longitudinal shortening (from -18.3+/-3.5% to -11.8+/-3.6%, P<0.001) and in LV twist (from 12.4+/-3.7 degrees to 9.7+/-2.6 degrees , P=0.001). CONCLUSIONS: During RV apical pacing, an acute induction of LV dyssynchrony is observed. In addition, LV longitudinal shortening and LV twist are acutely impaired.

[Fetal arrhythmias: premature atrial contractions and supraventricular tachycardia]. / Arythmies foetaltes: extrasystoles et tachycardies supraventriculaires.

Fetal arrhythmias form a complicating factor in 1-2% of all pregnancies and in 10% of those cases morbidity or even mortality is encountered. The most frequent occurring arrhythmias are premature atrial contractions (PAC). These are usually benign phenomena which resolve spontaneously, but require some follow-up to exclude the development of supraventricular tachycardias (SVT). SVTs are rare but are frequently complicated by fetal congestive heart failure or even fetal death. Timely prenatal pharmacotherapeutic intervention is generally advised to return to an adequate heart rate, preferably sinus rhythm. This study reports on the local experience with these forms of pathologies: of the 26 fetuses encountered with PAC or/and SVT between 2003 and 2005, none experienced serious complications, while 6 required pharmacotherapeutic intervention with sotalol.

Effects of right atrial pacing preference in prevention of paroxysmal atrial fibrillation: Atrial Pacing Preference study (APP study).

BACKGROUND: Several preliminary studies have indicated that atrial pacing can prevent atrial tachyarrhythmias. The suggested mechanisms by which pacing may be effective include suppression of premature atrial beats. METHODS AND RESULTS: The Atrial Pacing Preference (APP; Guidant, St Paul, MN, USA) algorithm allows the pacemaker to maintain a pacing rate slightly higher than the sinus rate. The preventive effects of APP on paroxysmal atrial fibrillation (AF) were studied in 51 patients (70+/-11 years). Nine patients did not complete the protocol. The pacemaker was programmed in random order to APP off and APP on at 3 different settings (ie, 8, 16 and 32 cycles) for 4 weeks each, using a cross-over design. Percentage atrial pacing was lower in APP off than at the other settings. Premature beat counts were greater in APP off than at the other settings. There was a significant difference in mode switch episode counts between APP off and the most effective setting (3,818+/-15,356 vs 596+/-1,719; p<0.01). CONCLUSIONS: The APP algorithm is a promising method for preventing atrial tachyarrhythmia in patients with an implanted pacemaker and AF. Optimizing the setting of the APP algorithm is an important issue in the prevention of AF.

Reversal of central nervous system and cardiac toxicity after local anesthetic intoxication by lipid emulsion injection.

A 91-yr-old man (57 kg, 156 cm, ASA III) received an infraclavicular brachial plexus block for surgery of bursitis of the olecranon. Twenty minutes after infraclavicular injection of 30 mL of mepivacaine 1% (Scandicain) and 5 min after supplementation of 10 mL of prilocaine 1% (Xylonest) using an axillary approach, the patient complained of agitation and dizziness and became unresponsive to verbal commands. In addition, supraventricular extrasystole with bigeminy occurred. Local anesthetic toxicity was suspected and a dose of 200 mL of a 20% lipid emulsion was infused. Symptoms of central nervous system and cardiac toxicity disappeared within 5 and 15 min after the first lipid injection, respectively. Plasma concentrations of local anesthetics were determined before, 20, and 40 min after lipid infusion and were 4.08, 2.30, and 1.73 microg/mL for mepivacaine and 0.92, 0.35, and 0.24 microg/mL for prilocaine. These concentrations are below previously reported thresholds of toxicity above 5 microg/mL for both local anesthetics. Signs of toxicity resolved and the patient underwent the scheduled surgical procedure uneventfully under brachial plexus blockade.

[Characterizations of atrial contractions triggering paroxysmal atrial fibrillation and the effect of atrial fibrillation prevention pacing].

OBJECTIVE: To evaluate the electrocardiographic characterizations of atrial contractions(AC) triggering paroxysmal atrial fibrillation(AF), and to explore the effects of AF prevention pacing on their electrocardiographic characterizations. METHODS: Twenty-four patients with the implantation of AF therapy pacemaker(Vitatron 900E) were analyzed by AC triggering paroxysmal AF with Holter monitoring in the study. AC compluing interval, compensatory pause and frequency 2 minutes before the AF or during the AC were compared between the induced paroxysmal AF group and noinduced paroxysmal AF group, and the preventive effect of AF on the post-PAC response program was investigated. RESULTS: There was significant difference in the AC compluing interval [(352.3 +/-30.4) vs (421.8 42.5)ms], compensatory pause [(963 +/-109) vs (733 +/-124) ms], and frequency [(34.8 +/-18.9) vs (12.7 +/-8.7)/min] 2 minutes before the AF or during the AC in the induced paroxysmal AF group, compared with those in the noinduced paroxysmal AF group (all P<0.05). The AF of 7 patients were controlled by atrial overdrive pacing therapy, 17 patients by post-AC-response or/and post-exercise control therapy, 6 patients by the above therapy combining with cordarone (0.2g/d). CONCLUSION: AC triggering paroxysmal AF is related to the compluing interval, compensatory pause and frequency 2 minutes before the paroxysmal AF or during the AC, AF prevention pacing may be helpful for the paroxysmal AF induced by AC.

Supraventricular ectopy and recurrence of atrial fibrillation after electrical cardioversion.

AIMS: Paroxysmal atrial fibrillation (AF) is usually preceded by a premature atrial complex (PAC). We hypothesized that patients with a high frequency of atrial ectopic activity after restoration of sinus rhythm following direct current cardioversion would be more likely to experience recurrence of AF. METHODS AND RESULTS: Forty-four patients with documented persistent AF were studied. A 24 h Holter recording was performed from the day of external direct current cardioversion. Patients were reviewed at 1 week, 1 month, and 6 months. After 6 months, 59% of patients had experienced a recurrence of AF. Neither the frequency of PACs nor the frequency or duration of supraventricular tachycardia (SVT) episodes predicted AF recurrence (P=0.60, 0.30, and 0.42, respectively). There was a trend towards maximum rate of SVT predicting recurrence of AF (P=0.08). CONCLUSION: Frequency of supraventricular ectopy or the number and length of SVT runs in the 24 h after restoration of sinus rhythm are not strong predictors of recurrence of AF after electrical cardioversion. A larger study would be required to detect a small predictive effect.

Acute antiarrhythmic effects of bi-level positive airway pressure ventilation in patients with acute respiratory failure caused by chronic obstructive pulmonary disease: a randomized clinical trial.

BACKGROUND: Cardiac arrhythmias are common in patients with chronic obstructive pulmonary disease (COPD) and acute respiratory failure (ARF) and may be life threatening. Recently, non-invasive positive pressure ventilation has been advanced as a useful tool in COPD patients with ARF. This method can affect global cardiac performance through its effects on many determinants of cardiac function and may be helpful in reducing arrhythmias. OBJECTIVE: To assess the role of bi-level positive pressure ventilation (BiPAP) in the management of cardiac arrhythmias in patients with ARF caused by COPD. METHODS: We studied 30 consecutive patients with ARF related to COPD diagnosed according to American Thoracic Society criteria. All subjects were smokers; the mean age was 68 +/- 7 years. They were randomly assigned to receive BiPAP plus standard therapy (group 1) or standard therapy alone (group 2). Patients randomized to receive BiPAP were first fitted with a nasal mask, and BiPAP was administered after 12 h of standard therapy. All subjects were studied using a computerized 24-hour Holter ECG. Blood gases, plasma electrolytes, respiratory rate and blood pressure were measured at study entry, at 30, 60 and 120 min and then every 3 h. RESULTS: Heart rate decreased from 86.08 +/- 7.86 to 74.92 +/- 5.39 in group 1 (p < 0.001) versus 82.77 +/- 8.78 to 75.82 +/- 6.76 in group 2 (p = 0.033). Ventricular premature complexes decreased from 564.38 +/- 737.36 to 166.15 +/- 266.26 in group 1 (p < 0.001) versus 523.38 +/- 685.75 to 353.54 +/- 469.93 in group 2 (p = 0.021). Atrial premature complexes decreased from 570.00 +/- 630.36 to 152.31 +/- 168.88 in group 1 (p < 0.001) versus 513.77 +/- 553.81 to 328.62 +/- 400.81 in group 2 (p = 0.021). CONCLUSIONS: Cardiac arrhythmias decreased significantly in both groups after the start of both treatments, although data obtained from group 1 revealed a more important statistical significance. Our data seem to support the hypothesis that BiPAP may be a useful tool in managing COPD patients with ARF and mild arrhythmias.

Paroxysmal atrial fibrillation: ectopic atrial activity and prevalence of severely symptomatic patients.

Catheter ablation is a promising approach in severely symptomatic patients with paroxysmal atrial fibrillation (PAF). Until this time it has only been performed in highly selected patients with weekly episodes and frequent premature atrial contractions (PACs). The aim of the present study was to estimate the prevalence of severely symptomatic patients with PAF and to evaluate the significance of PACs. The files of 7,447 consecutive patients were screened and 1,357 PAF patients identified. Holter recordings were performed in 108 patients with >/=2 spontaneous AF episodes. Despite antiarrhythmic treatment, 6.5% (1.8-11.1%) had a history of weekly PAF episodes. 29.2% of patients and 10% of healthy, age-matched controls had more than 700 PACs. The number of PACs was inversely related to the reported numbers of previous episodes and directly related to age and size of left atrium. We estimate that about 6.5% of patients with PAF are severely symptomatic and might benefit from catheter ablation. Our data suggest that the number of PACs should not be used as a selection criterion for catheter ablation. Frequent PACs are seen in a substantial proportion of elderly healthy individuals.

Initiation of atrial fibrillation by ectopic beats originating from the pulmonary veins: electrophysiological characteristics, pharmacological responses, and effects of radiofrequency ablation.

BACKGROUND: Atrial fibrillation (AF) can be initiated by ectopic beats originating from the atrial or great venous tissues. This study investigated the anatomic characteristics and electrophysiological properties of pulmonary veins (PVs), as well as the possible mechanisms and response to drugs of ectopic foci, and assessed the effects of radiofrequency (RF) ablation on AF initiated by ectopic beats originating from PVs. METHODS AND RESULTS: Seventy-nine patients with frequent episodes of paroxysmal AF and 10 control patients were included. Distal PVs showed the shortest effective refractory periods (ERPs), and right superior PVs showed a higher incidence of intra-PV conduction block than left superior PVs. Superior and left PVs had longer myocardial sleeves than inferior and right PVs, respectively. These electrophysiological characteristics were similar between AF and control patients. Propranolol, verapamil, and procainamide suppressed ectopic beats that originated from the PVs. Of 116 ectopic foci that initiated AF, 103 (88.8%) originated from PVs. A mean of 7+/-3 RF applications completely eliminated 110 ectopic foci (94.8%). During the 6+/-2-month follow-up period, 68 patients (86. 1%) were free of AF without any antiarrhythmic drugs. Follow-up transesophageal echocardiogram showed 42.4% of ablated PVs had focal stenosis. One patient had mild exertional dyspnea after ablation, but it resolved 3 months later; 1 patient had onset of mild exertional dyspnea 5 months after ablation. CONCLUSIONS: Electrophysiological characteristics of PVs are different from those in the atria. Ectopic beats from PVs can initiate AF, and beta-adrenergic receptor blocker, calcium channel blockers, and sodium channel blockers can suppress these ectopic beats. Careful mapping and elimination of these ectopic foci can cure paroxysmal AF.