Exercise-induced uncommon atrioventricular nodal reentrant tachycardia with sick sinus syndrome: a case report.
(17/1706)
Exercise seldom provokes tachycardia in patients with paroxysmal supraventricular tachycardia (PSVT). This report presents a case of exercise-induced uncommon atrioventricular nodal reentrant tachycardia (AVNRT) with sick sinus syndrome. Treadmill exercise testing provoked AVNRT of long RP' with good reproducibility. Uncommon AVNRT was confirmed by the lack of atrial pre-excitation during PSVT and para-Hisian pacing. The patient has been successfully treated with verapamil and DDD pacing for 5 years. (+info)
Electrophysiologic parameters to predict clinical recurrence of ventricular tachycardia in patients under electrophysiologic study-guided effective pharmacological therapy.
(18/1706)
Although an electrophysiologic study (EPS) is the most reliable method for selecting the treatment for a patient with sustained ventricular tachycardia (VT), VT recurrence may occur even during EPS-guided effective therapy. Electrophysiologic parameters were compared between patients with and without arrhythmic events under EPS-guided effective therapy to identify the predictive parameters of VT recurrence during the clinical course. The study population consisted of 77 consecutive patients with sustained VT who were receiving long-term pharmacological therapy that was demonstrated to be effective by the EPS assessment. The VT induction protocol employed 1-3 extrastimuli and rapid ventricular pacing at 2 right ventricular sites and 1 left ventricular site, and isoproterenol was infused when VT was not induced. To determine the 'effective' antiarrhythmic drug, all sustained ventricular arrhythmias had to be prevented during the whole induction protocol, but repetitive ventricular responses (RVR) were allowed to remain for up to 5 beats when they were in the same QRS configurations as the clinical VT and up to 12 beats when they were in polymorphic QRS configurations. The effective refractory periods (ERPs) at the 3 ventricular pacing sites and their difference (i.e., ERP-dispersion) and the maximum number of RVR beats were evaluated in an EPS during the control state and at the time of drug assessment. In the comparison of patients with and without VT recurrence, there was no significant difference in clinical characteristics or ERPs, but the deltaERP-dispersion (i.e., the increase in ERP-dispersion caused by the antiarrhythmic drug) and the maximum number of RVRs were significantly smaller in the group of patients without VT recurrence (deltaERP-dis, -3+/-8 vs. 6+/-12, p = 0.0027; maxRVR, 3+/-3 vs. 5+/-4, p = 0.0160). The VT recurrence rate was significantly lower in the patients with deltaERP-dis < or =0 or maxRVR<6 in comparison with the others (p = 0.01 14 and p = 0.0360). Patients with VT recurrence showed greater deltaERP-disp and a longer duration of RVRs at the time of drug assessment in comparison with the patients without VT recurrence. The prognosis of patients under EPS-guided therapy may be improved by the use of stricter criteria for drug assessment in the EPS, although this may decrease the number of drug responders determined in the EPS. (+info)
Mechanical remodeling of the left atrium after loss of atrioventricular synchrony. A long-term study in humans.
(19/1706)
BACKGROUND: Tachycardia-mediated mechanical remodeling of the atrium is considered central to the pathogenesis of thromboembolism associated with chronic atrial fibrillation. Whether atrial mechanical remodeling also occurs in response to atrial stretch induced by chronic asynchronous ventricular pacing in patients with permanent pacemakers is unknown. METHODS AND RESULTS: The study design was a prospective randomized comparison between 21 patients paced chronically in the VVI mode and 11 patients paced chronically in the DDD mode for 3 months. Left atrial appendage (LAA) function and the presence of spontaneous echo contrast (SEC) were determined with transesophageal echocardiography (TEE) within 24 hours of pacemaker implantation and after 3 months. The VVI patients were then programmed to DDD and underwent a third TEE after DDD pacing for an additional 3 months. After chronic VVI pacing, LAA velocity decreased from 82.4+/-29.0 to 42.1+/-25.4 cm/s (P<0.01), LAA fractional area change decreased from 74.9+/-17.2% to 49.8+/-22.0% (P<0.01), and 4 patients (19%) developed left atrial SEC (P<0.05). With the reestablishment of chronic AV synchrony, LAA velocity increased to 61.6+/-18.5 cm/s (P<0.01), LAA fractional area change increased to 76.4+/-18.1% (P<0.01), and SEC resolved. In the 11 patients undergoing chronic DDD pacing, no significant changes in LAA velocity (baseline, 86.0+/-28.8 cm/s versus 3 months, 79.6+/-14. 9 cm/s) or LAA fractional area change (baseline, 76.2+/-19.4% versus 72.5+/-15.7%) were demonstrated, and SEC did not develop. CONCLUSIONS: Chronic loss of AV synchrony induced by VVI pacing is associated with mechanical remodeling of the left atrium, which may reverse after the reestablishment of AV synchrony with DDD pacing. This process may be partly responsible for the higher incidence of thromboembolism observed in patients undergoing VVI pacing compared with AV sequential pacing. (+info)
Electrical remodeling of the atria following loss of atrioventricular synchrony: a long-term study in humans.
(20/1706)
BACKGROUND: Evidence suggests that an increased incidence of atrial fibrillation occurs in patients undergoing single-chamber ventricular pacing (VVI) when compared with those undergoing single-chamber atrial pacing (AAI) or those having dual-chamber atrioventricular pacing (DDD). The mechanism for this is unknown. We hypothesized that long-term loss of atrioventricular (AV) synchrony leads to atrial electrical remodeling: a potential explanation for this difference. METHODS AND RESULTS: The study was a prospective, randomized comparison between 18 patients paced in VVI mode and 12 patients paced in DDD mode for 3 months. Under autonomic blockade, effective refractory periods (ERPs) from the lateral right atrium (RA), RA appendage, RA septum, and coronary sinus-corrected sinus node recovery times (cSNRTs), as well as P-wave duration (PWD), and biatrial diameters were measured at baseline and 3 months. The VVI group was then programmed to DDD pacing and reevaluated after a further 3 months. After long-term VVI pacing, ERPs at all 4 atrial sites increased significantly in a nonuniform fashion in association with biatrial dilatation. PWD and cSNRTs also prolonged significantly. With the reestablishment of AV synchrony, ERPs, PWD, cSNRTs, and biatrial dimensions returned to baseline levels. In the 12 patients who underwent long-term DDD pacing from baseline, no significant changes in atrial electrophysiology or biatrial dimensions were demonstrated. CONCLUSIONS: Long-term loss of AV synchrony induced by VVI pacing is associated with atrial electrical remodeling, which is reversible after the reestablishment of AV synchrony with DDD pacing. This process may be partly responsible for the higher incidence of atrial fibrillation in patients undergoing VVI pacing compared with AV sequential pacing. (+info)
Surgical management of the patient with an implanted cardiac device: implications of electromagnetic interference.
(21/1706)
OBJECTIVE: To identify the sources of electromagnetic interference (EMI) that may alter the performance of implanted cardiac devices and develop strategies to minimize their effects on patient hemodynamic status. SUMMARY BACKGROUND DATA: Since the development of the sensing demand pacemaker, EMI in the clinical setting has concerned physicians treating patients with such devices. Implanted cardiovertor defibrillators (ICDs) and ventricular assist devices (VADs) can also be affected by EMI. METHODS: All known sources of interference to pacemakers, ICDs, and VADs were evaluated and preventative strategies were devised. RESULTS: All devices should be thoroughly evaluated before and after surgery to make sure that its function has not been permanently damaged or changed. If electrocautery is to be used, pacemakers should be placed in a triggered or asynchronous mode; ICDs should have arrhythmia detection suspended before surgery. If defibrillation is to be used, the current flow between the paddles should be kept as far away from and perpendicular to the lead system as possible. Both pacemakers and ICDs should be properly shielded if magnetic resonance imaging, positron emission tomography, or radiation therapy is to be used. The effect of EMI on VADs depends on the model. Magnetic resonance imaging adversely affects all VADs except the Abiomed VAD, and therefore its use should be avoided in this population of patients. CONCLUSIONS: The patient with an implanted cardiac device can safely undergo surgery as long as certain precautions are taken. (+info)
Effect of pacing site on ventricular fibrillation initiation by shocks during the vulnerable period.
(22/1706)
The critical point hypothesis for the upper limit of vulnerability (ULV) states that the site of S1 pacing should not affect the ULV S2 shock strength for a single S2 shock electrode configuration but may affect the S1-S2 interval at which sub-ULV shocks induce ventricular fibrillation (VF). Furthermore, early post-S2 activations leading to VF should arise in areas with low potential gradients of similar magnitude, regardless of the S1 site. This hypothesis was tested in 10 pigs by determining ULVs for three S1 sites [left ventricular apex (LVA), LV base (LVB), and right ventricular outflow tract (RVOT)] with one S2 configuration (LVA patch to superior vena cava catheter). T-wave scanning was performed with biphasic S2 shocks incremented from 60 V in 40-V steps and stepped up or down in 20- and 10-V steps. Activations and S2 potential gradients were recorded at 528 epicardial sites. Although shocks just below the ULV induced VF significantly earlier in the T wave when the S1 site was the RVOT than when it was the LVA or LVB, ULVs were not significantly different for the three S1 pacing sites. Early post-S2 activations arose closer to the S2 electrode for weak S2s but moved to distant low potential gradient areas as the S2 strengthened. Just below the ULV, early post-S2 activations arose in the RVOT when the S1 site was the LVA or LVB but arose along the RV base when the S1 site was the RVOT. Early site potential gradients were not significantly different just below the ULV (LVA: 8.2 +/- 4.1 V/cm; LVB: 8.6 +/- 4. 9 V/cm; RVOT: 8.7 +/- 4.4 V/cm). At the ULV, early post-S2 activations arose from the same areas but did not induce VF. The results support the critical point hypothesis for the ULV. For this S2 configuration, no single point in the T wave could be used to determine the ULV for all S1 sites. (+info)
Risks of spontaneous injury and extraction of an active fixation pacemaker lead: report of the Accufix Multicenter Clinical Study and Worldwide Registry.
(23/1706)
BACKGROUND: The Telectronics Accufix pacing leads were recalled in November 1994 after 2 deaths and 2 nonfatal injuries were reported. This multicenter clinical study (MCS) of patients with Accufix leads was designed to determine the rate of spontaneous injury related to the J retention wire and results of lead extraction. METHODS AND RESULTS: The MCS included 2589 patients with Accufix atrial pacing leads that were implanted at or who were followed up at 12 medical centers. Patients underwent cinefluoroscopic imaging of their lead every 6 months. The risk of J retention wire fracture was approximately 5.6%/y at 5 years and 4.7%/y at 10 years after implantation. The annual risk of protrusion was 1.5%. A total of 40 spontaneous injuries were reported to a worldwide registry (WWR) that included data from 34 672 patients (34 892 Accufix leads), including pericardial tamponade (n=19), pericardial effusion (n=5), atrial perforation (n=3), J retention wire embolization (n=4), and death (n=6). The risk of injury was 0.02%/y (95% CI, 0.0025 to 0. 072) in the MCS and 0.048%/y (95% CI, 0.035 to 0.067) in the WWR. A total of 5299 leads (13%) have been extracted worldwide. After recall in the WWR, fatal extraction complications occurred in 0.4% of intravascular procedures (16 of 4023), with life-threatening complications in 0.5% (n=21). Extraction complications increased with implant duration, female sex, and J retention wire protrusion. CONCLUSIONS: Accufix pacing leads pose a low, ongoing risk of injury. Extraction is associated with substantially higher risks, and a conservative management approach is indicated for most patients. (+info)
Long-term follow-up of patients with long-QT syndrome treated with beta-blockers and continuous pacing.
(24/1706)
BACKGROUND: The long-QT syndrome is associated with sudden cardiac death. Combination of beta-blocker and pacing therapy has been proposed for treatment of drug-resistant patients. The purpose of this study was to summarize our long-term experience with combined therapy in patients with long-QT syndrome. METHODS AND RESULTS: A total of 37 patients with idiopathic long-QT syndrome were treated with combined therapy consisting of continuous cardiac pacing and maximally tolerated beta-blocker therapy and followed up for 6.3+/-4. 6 years (mean+/-SD). The group consisted of 32 female and 5 male patients with a mean age of 31.6 years. The mean paced rate was 82+/-7 bpm (range, 60 to 100 bpm). On follow-up, recurrent symptoms caused by pacemaker malfunction were documented in 3 patients. Four patients died during the follow-up period: 2 adolescents stopped beta-blocker therapy, 1 patient died suddenly while treated with combined therapy, and 1 patient died of unrelated causes. In addition, 3 patients had resuscitated cardiac arrest while on combined therapy, and 1 patient had repeated, appropriate implantable cardioverter-defibrillator discharges on follow-up. CONCLUSIONS: Because 28 of 37 patients remain without symptoms with beta-blocker therapy and continuous pacing, combined therapy appears to provide reasonable, long-term control for this high-risk group. However, the incidence of sudden death and aborted sudden death (24% in all patients and 17% in compliant patients) strongly suggests the use of a "back-up" defibrillator, particularly in noncompliant adolescent patients. Implantable cardioverter-defibrillator therapy, however, may be associated with recurrent shocks in susceptible patients. (+info)