Selective site right ventricular pacing.

The right ventricular apex (RVA) has been the elective site for placing endocardial pacing leads since 1959 when Furman described the use of the transvenous route for pacemaker implantation. This site was used because it is easily accessible, readily identified and associated with a stable position and reliable chronic pacing parameters. It was recognised, however, that pacing from the RVA did not reproduce normal ventricular conduction or contraction. With the advent of reliable active fixation leads, alternative right ventricular sites became accessible and began to be explored. In this review, the detrimental effects of RVA pacing are outlined, the right ventricular outflow tract is defined and the evidence for selective site pacing is discussed.

Association between serum free thyroxine concentration and atrial fibrillation.

BACKGROUND: Previous studies have suggested that minor changes in thyroid function are associated with risk of atrial fibrillation (AF). Our objective was to determine the relationship between thyroid function and presence of atrial fibrillation (AF) in older subjects. METHODS: A population-based study of 5860 subjects 65 years and older, which excluded those being treated for thyroid dysfunction and those with previous hyperthyroidism. Main outcome measures included tests of thyroid function (serum free thyroxine [T(4)] and thyrotropin [TSH]) and the presence of AF on resting electrocardiogram. RESULTS: Fourteen subjects (0.2%) had previously undiagnosed overt hyperthyroidism and 126 (2.2%), subclinical hyperthyroidism; 5519 (94.4%) were euthyroid; and 167 (2.9%) had subclinical hypothyroidism and 23 (0.4%), overt hypothyroidism. The prevalence of AF in the whole cohort was 6.6% in men and 3.1% in women (odds ratio, 2.23; P<.001). After adjusting for sex, logistic regression showed a higher prevalence of AF in those with subclinical hyperthyroidism compared with euthyroid subjects (9.5% vs 4.7%; adjusted odds ratio, 2.27; P=.01). Median serum free T(4) concentration was higher in those with AF than in those without (1.14 ng/dL; interquartile range [IQR], 1.05-1.27 ng/dL [14.7 pmol/L; IQR, 13.5-16.4 pmol/L] vs 1.10 ng/dL; IQR, 1.00-1.22 ng/dL [14.2 pmol/L; IQR, 12.9-15.7 pmol/L]; P<.001), and higher in those with AF when analysis was limited to euthyroid subjects (1.13 ng/dL; IQR, 1.05-1.26 ng/dL [14.6 pmol/L; IQR, 13.5-16.2 pmol/L] vs 1.10 ng/dL; IQR, 1.01-1.21 ng/dL [14.2 pmol/L; IQR, 13.0-15.6 pmol/L]; P=.001). Logistic regression showed serum free T(4) concentration, increasing category of age, and male sex all to be independently associated with AF. Similar independent associations were observed when analysis was confined to euthyroid subjects with normal TSH values. CONCLUSIONS: The biochemical finding of subclinical hyperthyroidism is associated with AF on resting electrocardiogram. Even in euthyroid subjects with normal serum TSH levels, serum free T(4) concentration is independently associated with AF.

Ablate and pace revisited: long term survival and predictors of permanent atrial fibrillation.

OBJECTIVE: To assess long term mortality and identify factors associated with the development of permanent atrial fibrillation after atrioventricular (AV) node ablation for drug refractory paroxysmal atrial fibrillation. DESIGN: Retrospective cohort study. SETTING: UK tertiary centre teaching hospital. PATIENTS: Patients admitted to the University Hospital Birmingham between January 1995 and December 2000. INTERVENTIONS: AV node ablation and dual chamber mode switching pacing. MAIN OUTCOME MEASURES: Long term mortality and predictors of permanent atrial fibrillation, assessed through Kaplan-Meier curves and logistic regression. RESULTS: 114 patients (1995-2000) were included: age (mean (SD)), 65 (9) years; 55 (48%) male; left atrial diameter 4 (1) cm; left ventricular end diastolic diameter 5 (1) cm; ejection fraction 54 (17)%. Indications for AV node ablation were paroxysmal atrial fibrillation in 95 (83%) and paroxysmal atrial fibrillation/flutter in 19 (17%). The survival curve showed a low overall mortality after 72 months (10.5%). Fifty two per cent of patients progressed to permanent atrial fibrillation within 72 months. There was no difference in progression to permanency between paroxysmal atrial fibrillation and paroxysmal atrial fibrillation/flutter (log rank 0.06, p = 0.8). Logistic regression did not show any association between the variables collected and the development of permanent atrial fibrillation, although age over 80 years showed a trend (p = 0.07). CONCLUSIONS: Ablate and pace is associated with a low overall mortality. No predictors of permanent atrial fibrillation were identified, but 48% of patients were still in sinus rhythm at 72 months. These results support the use of dual chamber pacing for paroxysmal atrial fibrillation patients after ablate and pace.

The electromechanical effects of pacing at different sites within the right atrium.

AIMS: To compare high right atrium (HRA) with right atrial appendage (RAA) pacing with respect to atrial electromechanical function. METHODS: Eleven patients undergoing elective electrophysiological studies were studied in order directly to compare atrial conduction acutely associated with HRA and RAA pacing. Twenty-five patients with chronically implanted, active fixation leads in the HRA were compared with an age and sex matched group of 25 patients with chronically implanted, passive fixation leads in the RAA. For both studies recordings were taken in sinus rhythm then repeated when paced. Measured time intervals were intra- and interatrial activation times. P wave duration and time to onset of atrial systolic blood flow. RESULTS: Right atrial pacing, when compared with sinus rhythm, significantly prolongs the interatrial activation time, the P wave duration and the time to onset of right and left atrial blood flow irrespective of site paced. Comparing the RAA group with the HRA group, there were no statistical differences for any of the measured parameters. CONCLUSION: High right atrial free wall or the right atrial appendage pacing, when compared with sinus rhythm, is significantly detrimental to atrial electromechanical function. There is, however, no demonstrable difference between the two sites.

Thyroid disease and its treatment: short-term and long-term cardiovascular consequences.

Thyroid hormones exert important effects on the cardiovascular system, including effects on cardiac systolic and diastolic function, peripheral vascular resistance and arrhythmogenesis. Hyperthyroidism and hypothyroidism often cause opposing effects on cardiovascular physiology in the short term. Increasing evidence suggests that long-term vascular morbidity and mortality occurs in both overt and subclinical thyroid disease.

Prospective randomized study of ablation and pacing versus medical therapy for paroxysmal atrial fibrillation: effects of pacing mode and mode-switch algorithm.

BACKGROUND: Atrioventricular (AV) node ablation and pacing has become accepted therapy for drug-refractory paroxysmal atrial fibrillation (PAF). However, few data demonstrate its superiority over continued medical therapy. The influence of pacing mode and mode-switch algorithm has not been investigated. METHODS AND RESULTS: Symptomatic patients who had tried >/=2 drugs for PAF were randomized to continue medical therapy (n=19) or AV junction ablation and implantation of dual-chamber mode-switching (DDDR/MS) pacemakers (slow algorithm [n=19] or fast algorithm [n=18]). Follow-up over 18 weeks was at 6-week intervals and used quality-of-life questionnaires (Psychological General Well Being [PGWB], McMaster Health Index [MHI], cardiac symptom score), exercise testing, echocardiography, and Holter monitoring. Paced patients were randomized to DDDR/MS or VVIR and subsequently crossed over. Ablation and DDDR/MS pacing produced better scores than drug therapy for overall symptoms (-41%, P<0.01), palpitations (-58%, P=0. 0001), and dyspnea (-37%, P<0.05). Changes in score from baseline were better with ablation and DDDR/MS pacing for overall symptoms (-48% versus -4%, P<0.005), palpitation (-62% versus -5%, P<0.001), dyspnea (-44% versus -3%, P<0.005), and PGWB (+12% versus +0.5%, P<0. 05). DDDR/MS was better than VVIR pacing for overall symptoms (-21%, P<0.05), dyspnea (-30%, P<0.005), and MHI (+5%, P<0.03). There were no differences between algorithms. More patients developed persistent AF with ablation and pacing than with drugs at 6 weeks (12 of 37 versus 0 of 19, P<0.01). CONCLUSIONS: Ablation and DDDR/MS pacing produces more symptomatic benefit than medical therapy or ablation and VVIR pacing but may result in early development of persistent AF.

Mode switching in dual chamber pacemakers: effect of onset criteria on arrhythmia-related symptoms.

AIMS: Various mode-switching algorithms are available with different tachyarrhythmia detection criteria to be satisfied to initiate mode-switching. This study evaluated three different mode-switching algorithms in patients with paroxysmal atrial fibrillation. METHODS AND RESULTS: Seventeen patients completed the study. Three mode-switching algorithms were downloaded as software into the pacemaker, each for 1 month in a single-blind, randomized sequence. The criteria to initiate mode-switching were: mean atrial rate ('standard'), '4-of-7' or '1-of-1' atrial intervals to exceed the atrial detection rate. Symptoms for each were measured using the Symptom Checklist Frequency and Severity index. The median number of mode-switch episodes increased from 20 for 'standard' to 39 for '4-of-7' (P=0.029 vs 'standard') and 103 for '1-of-1' (P=0.0012 vs 'standard') onset criteria. Median duration of episodes decreased from 2.5 min with 'standard' to 1.4 min with '4-of-7' and 0.4 min with '1-of-1' onset criteria. Frequency of symptoms was lower using '4-of-7' (18.2 +/- 12.0 vs 23 +/- 12.0, P=0.08) or '1-of-1' (20.4 +/- 12.4 vs 23 +/- 12.0, P=0.07) than 'standard' onset criteria. Severity of arrhythmia tended to be less with either '4-of-7' (16 +/- 10.4 vs 19.1 +/- 19.4, P=0.12) or '1-of-1' (17.5 +/- 10.3 vs 19.1 +/- 9.4, P=0.18) than with 'standard' onset criteria. CONCLUSIONS: The more sensitive onset criteria for detection of atrial tachyarrhythmias were associated with lower frequency and severity of symptoms.

Placement of atrial pacing leads during atrial fibrillation. Feasibility and subsequent lead performance.

AIMS: To assess the feasibility of placing permanent atrial pacing leads during atrial fibrillation (AF) and whether such leads function satisfactorily. METHODS AND RESULTS: Prospective study of 17 consecutive patients in whom permanent atrial leads were positioned during an episode of paroxysmal AF. Fluoroscopic position ('figure of 8' or side-to-side movement and anterior position in RAO projection), lead impedance (> 300 but < 1000 ohms) and intracardiac electrogram (average peak to peak amplitude > 1 mV) were used to define an acceptable lead position. At 8 weeks post implant we measured: pulse duration pacing threshold at 5 V; lead impedance at 5 V and 0.5 ms; intracardiac electrogram (EGM) signal amplitude. At the end of the study we reviewed patients to establish whether AF had become permanent. In all patients, follow-up demonstrated satisfactory lead function. All leads had impedances between 300 and 1000 ohms. Pacing thresholds were all < 0.1 ms at 5 V. Mean atrial EGM amplitude seen in sinus rhythm was 3.3 mV (range 1.2-8.4); in patients where all follow-up was in AF in was 2.1 mV (range 1.5-2.5). Nine patients (53%) developed permanent AF. CONCLUSION: Placing atrial leads during AF is feasible using the technique described. However, some patients progress to chronic AF, eliminating the benefits of atrial pacing.

Experience with a lead fixation/suture sleeve.

Current anchoring systems on pacemaker leads are crude in comparison to the lead technology. Poor anchoring technique may cause damage to the lead or early displacement from incorrect suture tension. We describe experience with a locking anchoring sleeve that applies a constant gripping force to the lead body. This can be locked and unlocked to allow optimal positioning after fixation of the sleeve to underlying tissues. The sleeve was fitted to a 55D polyurethane lead (Medtronic 4024, 7 Fr, bipolar, steroid eluting) implanted in the ventricular position in 22 patients at four European centers. All implants were uncomplicated; data were collected on handling and ease of use. Assessments were made using a scale of 1-10 (10 = excellent, 5 = equivalent to conventional sleeve). Overall ease of use compared to conventional sleeve was 7.79 +/- 0.62 (mean +/- SD). Mean scoring of flexibility of the lead at the transition points was 7.92 +/- 0.72; ability to lock/unlock the sleeve scored 6.28 +/- 1.78. Ease of suturing around the sleeve scored 8.07 +/- 0.77, and ability to slide the sleeve along the lead body scored 6.48 +/- 1.99. Chest X rays at 6 weeks showed no change in lead position with respect to postimplant films, and all leads showed a straight path on either side of the sleeve with no evidence of conductor distortion. Follow-up to 3 years has been without problem. All leads remain intact and in place, with stable thresholds and no evidence of erosion. There have been no complaints of patient discomfort. We conclude that this device is safe and effective and offers a significant advance in lead fixation.

Atrioventricular nodal ablation and implantation of mode switching dual chamber pacemakers: effective treatment for drug refractory paroxysmal atrial fibrillation.

OBJECTIVE: To assess the effect of atrioventricular node ablation and implantation of a dual chamber, mode switching pacemaker on quality of life, exercise capacity, and left ventricular systolic function in patients with drug refractory paroxysmal atrial fibrillation. PATIENTS: 18 consecutive patients with drug refractory paroxysmal atrial fibrillation. METHODS: Quality of life was assessed before and after the procedure using the psychological general wellbeing index (PGWB), the McMaster health index (MHI), and a visual analogue scale for cardiac symptoms. Nine of the patients also underwent symptom limited exercise tests and echocardiography to assess left ventricular systolic function. RESULTS: The procedure allowed a reduction in antiarrhythmic drug treatment (p < 0.01). PGWB and symptom scores improved (p < 0.01) but the MHI score did not change. Left ventricular systolic function and exercise capacity were unchanged. CONCLUSIONS: Atrioventricular node ablation and implantation of a DDDR/MS pacemaker is effective treatment for refractory paroxysmal atrial fibrillation, producing improved quality of life while allowing a reduction in drug burden. The popularity of the treatment is justified, but further studies are needed to determine optimum timing of intervention.

Clinical experience with Thera DR rate-drop response pacing algorithm in carotid sinus syndrome and vasovagal syncope. The International Rate-Drop Investigators Group.

This study examined the effectiveness of cardiac pacing using the Thera DR rate-drop response algorithm for prevention of recurrent symptoms in patients with carotid sinus syndrome (CSS) or vasovagal syncope. The algorithm comprises both diagnostic and treatment elements. The diagnostic element consists of a programmable "window" used to identify heart rate changes compatible with an evolving neurally mediated syncopal episode. The treatment arm consists of pacing at a selectable rate and for a programmable duration. Forty-three patients (mean age 53 +/- 20.4 years) with CSS alone (n = 8), CSS in conjunction with vasovagal syncope (n = 4), or vasovagal syncope alone (n = 31) were included. Thirty-nine had recurrent syncope, while the remaining four reported multiple presyncopal events. Prior to pacing, 40 +/- 152 syncopal episodes (range from 1 to approximately 1,000 syncopal events) over the preceding 56 +/- 84.5 months. Postpacing follow-up duration was 204 +/- 172 days. Three patients have been lost to follow-up and in one patient the algorithm was disabled. Among the remaining 39 individuals, 31 (80%) indicated absence or diminished frequency of symptoms, or less severe symptoms. Twenty-three patients (23/29, or 59%) were asymptomatic with respect to syncope or presyncope. Sixteen patients had symptom recurrences. Of these, seven experienced syncope (7/39, or 18%) and 9 (29%) had presyncope: the majority of patients with recurrences (6/7 syncope and 7/9 presyncope) were individuals with a history of vasovagal syncope. Consequently, although symptoms were observed during postpacing follow-up, they appeared to be of reduced frequency and severity. Thus, our findings suggest that a transient period of high rate pacing triggered by the Thera DR rate-drop response algorithm was beneficial in a large proportion of highly symptomatic patients with CSS or vasovagal syncope.