Atrioventricular Synchrony Research Articles

Predictors of inappropriate atrial sensing in long-term VDD-pacing systems

The efficacy and stability of the atrial electrode sensing function is essential for maintaining atrioventricular (AV) synchrony. This study aimed to explore the long-term reliability and causes of the long-term sensing failure of VDD systems. We enrolled all the patients with complete or high-degree AV block who received VDD pacemakers between August 1994 to January 2006 and who were followed up for more than 12 months. The interrogation parameters, including the atrial potentials (APs) and AV-synchrony ratio were acquired immediately post-implantation and at 3-6 month intervals thereafter. An inappropriate atrial sensing efficacy was defined as an AV-synchrony ratio of <90%. Totally 157 patients (70 +/- 12 years, 103 males) were enrolled into the study with a follow-up for 4.9 +/- 2.5 years. Twenty-six patients (16.6%) suffered from inappropriate atrial sensing. According to a Kaplan-Meier analysis, the incidence of inappropriate atrial sensing was higher in the patients with an age > or =72 years old (P = 0.047), mean AP during the implantation of <3.0 mV (P = 0.015), concomitant use of non-dihydropyridine calcium channel blockers (CCBs) (P = 0.003), and atrial fibrillation (AF) (P < 0.001). A Cox regression analysis showed that non-dihydropyridine CCBs (hazard ratio, 3.255; 95% confidence interval, 1.148-9.227, P = 0.026) and AF (hazard ratio, 6.507; 95% confidence interval, 2.478-17.104, P < 0.001) predicted inappropriate atrial sensing. VDD pacing is a reliable pacing modality. However, we should monitor the pacemaker sensing function in the patients with the concomitant use of non-dihydropyridine CCBs and AF.

Sincronía auriculo-ventricular en pacientes portadores de marcapasos con estimulación VDD. Estudio descriptivo de un periodo de 14 años

Objective To analyze the performance of VDD mode pacing in patients with complete AV block with special attention on maintaining AV synchrony. Design This is a descriptive, retrospective and observational study of a case series. Setting Intensive Medicine Department of a tertiary Hospital. Patients All patients with VDD pacemakers implanted between 1994 and 2008. Main measurements The cause of the rhythm disorder, time of atrioventricular synchrony, cause of its loss, number of pacemaker replacement and reason, age when the first implant was performed, incidence of failure of atrial sensing and atrial fibrillation. We compared patients with atrial fibrillation with the rest who maintained normal atrial activity. Results A total of 95 patients, 49 (51.6%) males and 46 (48.4%) female with mean age of 77.08±8.37 years, were analyzed. The most common symptom was dizziness and presyncope in 43 cases (45.3%), the most common rhythm disorder was the III AV block with wide QRS with 68 cases (71.6%). Average time of AV synchrony was maintained 73.01±4.2 months with no significant differences between different causes of synchrony loss. At the end of the study, 56 cases remained in AV synchrony (73.3%). Conclusions The preservation time of AV synchrony is high, the most important causes of loss being entry in atrial fibrillation and atrial infrasensing.

A Novel Method of Atrial Temporary Pacing as an Acute Treatment for Brady- and Tachy-arrhythmias in the Intensive Care Setting with Preservation of Atrio-ventricular Synchrony

A Novel Method of Atrial Temporary Pacing as an Acute Treatment for Brady- and Tachy-arrhythmias in the Intensive Care Setting with Preservation of Atrio-ventricular Synchrony

Ventricular pacing: to pace or not to pace

Pacing from the right ventricular apex has been the clinical standard for decades but has recently come into question with a growing trend towards reducing ventricular pacing as much as possible. The earliest devices provided asynchronous ventricular pacing in patients whose indication for pacing was asystolic complete heart block. RV apical pacing was literally the difference between life and death. Over the decades, as technology has advanced allowing the medical community to more closely model normal cardiac physiology, we have seen the progressive introduction of demand function, single-chamber atrial pacing, dual-chamber pacing, dual-chamber rate-modulated pacing, and in the past decade, cardiac resynchronization pacing. During this evolution, it has been noted that pacing from the right ventricular apex, even in the presence of high-grade AV block, may contribute to ventricular dysfunction associated with the disordered ventricular activation sequence associated with the paced left bundle branch block pattern. ‘Pacemaker syndrome’ or the adverse haemodynamics associated with a technically normal pacing system was rarely recognized in the late 1960s when complete heart block was the indication for implantation. Its recognition blossomed in the 1980s with the introduction of dual-chamber pacing systems and an increase in the relative indications for permanent pacing including individuals who only needed pacing on an intermittent basis or whose primary indication for pacing was sinus node dysfunction. Pacemaker syndrome was usually associated with a loss of appropriate atrial transport (atrioventricular synchrony) and was able to be corrected by upgrading a patient with a single-chamber VVI pacing system to a DDD pacing system.1–3 The standard location for the ventricular lead during the first four decades of cardiac pacing was the RV apex. The first generation of DDD pacemakers had limited AV delay programmability such that there was either full ventricular pacing or consistent ventricular fusion. On the … *Corresponding author. Tel: +1 818 493 2900, Fax: +1 818 362 2242, Email: plevine{at}sjm.com

Intravenous Induction of Therapeutic Hypothermia in the Management of Junctional Ectopic Tachycardia: A Pilot Study

Therapeutic hypothermia has been used to treat children with postcardiotomy junctional ectopic tachycardia (JET). However, cooling techniques have not been systematically studied. This pilot study investigates the safety and efficacy of intravenous cold saline infusions used to augment surface cooling to achieve a core temperature of 32-34 degrees C for pediatric patients with JET. For this study, 10 patients with JET were cooled using cooling blankets and 4 degrees C normal saline infusions to a target central temperature of 32-34 degrees C. Vital signs and central temperatures were monitored continuously during the cooling period. Comprehensive metabolic panels, complete blood counts, coagulation studies, and cultures were obtained per study protocol. Therapeutic hypothermia was achieved within 65 min (interquartile range [IQR], 45-75 min). The median heart rate decreased from 187 beats per min (bpm) (IQR, 184-190 bpm) to 158 bpm (IQR, 121-162 bpm). For all the patients, atrioventricular synchrony was restored either with conversion to normal sinus rhythm or with successful atrial pacing. No clinically significant electrolyte abnormalities or bleeding events occurred. Two deaths, not directly attributable to the cooling protocol, occurred. Intravenous induction of therapeutic hypothermia can be safely and effectively performed for children with JET. Further studies, powered for clinically relevant outcomes, should evaluate this potentially valuable therapeutic method.

Surgical Therapy of Arrhythmias in Single‐Ventricle Patients Undergoing Fontan or Fontan Conversion

Arrhythmia is detrimental to Fontan hemodynamics. Clinical outcomes among Fontan patients who underwent antiarrhythmic treatment were retrospectively reviewed. From January 1996 to January 2007, 182 patients underwent a Fontan procedure, including Fontan conversion. Thirty-nine of the 182 patients showed various arrhythmias pre- or post-Fontan operations, and were treated surgically including Fontan conversion (18 patients) or medically. The authors analyzed the outcomes of arrhythmia treatments retrospectively. Thirty-nine patients (21.4%) showed various arrhythmias, such as atrial flutter, atrial fibrillation, junctional rhythm, sinus node dysfunction, or brady tachyarrhythmia pre- or post-Fontan procedure. Follow-up duration was 13.1 +/- 8.7 years (11 months to 325 months).Atrial flutter and fibrillation only developed in 17 patients who received atriopulmonary connection Fontan, and who were treated by Fontan conversion with concomitant procedures such as Cox-maze procedure (two patients), right-side maze and pacemaker implantation (five patients), right atrial isthmus ablation (four patients), right atrial isthmus cryoablation and pacemaker implantation (five patients), and only pacemaker implantation (one patient). The 21 patients who showed arrhythmia at the time of the Fontan procedure underwent the following procedures concomitantly: right atrial isthmus cryoablation with pacemaker implantation (one patient), right atrial isthmus cryoablation (one patient), or pacemaker implantation (nine patients). The remaining 10 patients, who showed junctional rhythm, sinus bradycardia, or intermittent ectopic beats, were managed medically. There were two late mortalities due to protein-losing enteropathy. As a result, 33 patients (89.2%) maintained atrioventricular synchrony, 19 in sinus rhythm and 14 supported by a DDD-type pacemaker. The remaining four patients (10.8%) showed persistent junctional rhythm with a stable hemodynamic status. The various arrhythmias in Fontan patients were well controlled by aggressive surgical management.

Amiodarone as a First-Line Therapy for Postoperative Junctional Ectopic Tachycardia

Postoperative junctional ectopic tachycardia is a potentially life-threatening arrhythmia that is often resistant to conventional antiarrhythmic drugs. Amiodarone was suggested to be an adequate treatment; however, data regarding its efficacy and safety are limited. This study evaluated the efficacy of amiodarone in the first-line treatment of postoperative junctional ectopic tachycardia and assessed factors associated with failure of amiodarone therapy. The study included 40 pediatric cardiosurgical patients with postoperative junctional ectopic tachycardia. Intravenous amiodarone in 2-mg/kg boluses and, if necessary, as continuous infusion (10 to 15 mug/kg/min), were used as the first-line therapy. Restoration of sinus rhythm or slowing of junctional ectopic tachycardia to a rate that allowed atrial or atrioventricular sequential pacing was considered as efficacy of therapy. Amiodarone was effective in 18 patients (45%). Sinus rhythm was achieved in 7, and heart rate decreased in 11 patients from 180 (range, 173 to 200) to 142 (range, 133-155) beats/min (p < 0.0001) and allowed effective pacing with atrioventricular synchrony. Higher arteriovenous oxygen saturation difference (p = 0.007) and lower body temperature (p = 0.02) were associated with failure of amiodarone therapy. Amiodarone as the first-line treatment was effective in almost half of the patients with postoperative junctional ectopic tachycardia. Higher arteriovenous oxygen saturation difference and lower body temperature were associated with failure of amiodarone therapy, and their presence may suggest more aggressive initial approach consisting of amiodarone combined with hypothermia.

Postoperative junctional ectopic tachycardia

MOT CLE Tachycardie jonctionnelle ectopique A 3-month-old boy underwent surgery for correction of a ventricular septal defect. Three hours after the intervention the patient developed a regular narrow QRS complex tachycardia (Fig. 1) with a ventricular rate (V) of 195 bpm and slower, regular atrial activity (A) at 150 bpm. The QRS configuration was similar to previous sinus beats. An atrial electrocardiogram recorded by a postoperative temporary atrial epicardial electrode (lead I) clearly demonstrated dissociation between atrial activity (arrows) and ventricular activity (asterisks), leading to the diagnosis of postoperative junctional ectopic tachycardia (JET). The patient was treated with moderate hypothermia and atrial overdrive pacing. The QRS morphology of the paced beats was similar to that observed during the tachycardia. As expected, atrial pacing did not terminate the arrhythmia; however, the haemodynamic status of the patient improved and he recovered sinus rhythm 89 hours after the onset of tachycardia. The patient’s subsequent postoperative course was uneventful, and he has remained free of new arrhythmic events after five years of follow-up. Rapid (> 170 bpm) postoperative JET has been reported after 1% of congenital heart repairs. Its aetiology is thought to be related to mechanical irritation of the proximal conduction system during surgery. Despite being a transient phenomenon, postoperative JET may lead to serious haemodynamic compromise due to elevated heart rate and loss of atrioventricular synchrony. Electrocardiographic features include QRS configuration similar to conducted sinus or atrial paced beats, along with either atrioventricular dissociation with ventricular rate faster than the atrial rate or retrograde conduction. This arrhythmia does not respond to electrical cardioversion, atrial overdrive pacing or intravenous adenosine, and the efficacy of antiarrhythmic drugs is usually

Novel Method of Predicting the Optimal Atrioventricular Delay in Patients With Complete AV Block, Normal Left Ventricular Function and an Implanted DDD Pacemaker

The optimal atrioventricular (AV) delay setting is important for achieving optimal AV synchrony in patients with an implanted DDD pacemaker. Using pulsed Doppler echocardiography is the most common method of predicting the optimal AV delay, but it is a complicated and time-consuming method. Therefore, an automatic optimizing function of the AV delay at different atrial rates is desirable for achieving a favorable hemodynamic state. This study aimed to predict the optimal AV delay using phonocardiography. The amplitude of the first heart sound (S1) recorded on the phonocardiogram was measured with different AV delays in 6 patents with complete AV block, normal left ventricular function and an implanted DDD pacemaker. The correlation between the amplitude of S1 and the length of the AV delay was a cubic curve (y=974.15x(3)-23.084x(2)-8.0074x+0.7495, R2=0.9511). The length of the AV delay at the inflection point of the curve showed a significant positive correlation with the optimal AV delay determined by pulsed Doppler echocardiography (R=0.9254, P<0.01). This study demonstrated a novel simple method of predicting the optimal AV delay using phono-cardiography.

Dual Chamber Pacemaker Implantation in Dogs with Atrioventricular Block

Pacemaker implantation is the treatment of choice for symptomatic bradyarrhythmias. In dogs, a single chamber system is commonly used. In human patients with high-grade 2nd- or 3rd-degree atrioventricular (AV) block, physiologic pacing is recommended, because it improves cardiac output, blood pressure, exercise tolerance, and quality of life. In dogs, this type of pacing is seldom used. The implantation of a dual chamber pacemaker in dogs with AV block is a feasible procedure for restoring AV synchrony. Thirty-three privately owned dogs with high-grade 2nd- or 3rd-degree AV block were included. Patient data of all dogs with AV block presented for pacemaker implantation between December 1997 and November 2004 were reviewed. Dual chamber pacemaker implantation with AV synchronous stimulation was successfully performed in 33/33 dogs (100%). In 9/33 (27%) major and in 12/33 (36%) minor complications were observed. Mean survival time for the patients discharged from hospital (n = 32) was 33.6 +/- 20.4 months (range, 3.9-83.5 months). Dual chamber pacing is a feasible procedure in dogs with 2nd- or 3rd-degree AV block and is not associated with a higher complication rate compared with single chamber pacemaker systems. A major advantage over ventricular demand pacemaker systems is the restoration of AV synchrony for a substantial period of time.

Dexmedetomidine: A Novel Drug for the Treatment of Atrial and Junctional Tachyarrhythmias During the Perioperative Period for Congenital Cardiac Surgery: A Preliminary Study

Atrial and junctional tachyarrhythmias occur frequently during the perioperative period for congenital cardiac surgery and can be a cause of increased morbidity and mortality. These rhythm disturbances that may be well tolerated in a normal heart can cause significant hemodynamic instability in patients with congenital heart defects, particularly during the postcardiopulmonary bypass period. Management of these arrhythmias presents more of a challenge, since currently available antiarrhythmic drugs can be ineffective and poorly tolerated. In this study, we examined the possible effect of dexmedetomidine, a primarily sedative drug, on atrial and junctional tachyarrhythmias. Though some animal data have shown that it can prevent certain types of ventricular tachycardia, its therapeutic role during these types of arrhythmias has not been studied. This was a retrospective, nonrandomized, noncontrolled study. Fourteen patients admitted to the cardiac intensive care unit and who received dexmedetomidine for both, sedation/analgesia and for junctional ectopic tachycardia (JET), atrial ectopic tachycardia (AET), reentry type supraventricular tachycardia (Re-SVT), atrial flutter (AF) or junctional accelerated rhythm (JAR) were included. Dexmedetomidine was used as a primary drug or as a rescue if other antiarrhythmics had been used. Our primary end-points were (a) conversion to normal sinus rhythm (NSR) within 3 min for Re-SVT, and 2 h for all other arrhythmias or (b) heart rate (HR) reduction to improve hemodynamics; JET < or =170 bpm, AET > or =20%, AF < or =150 bpm and for JAR prevention of progression to JET. The mean age and weight were 2 +/- 3 mo and 4 +/- 1.5 kg, respectively. Most of the arrhythmias (79%) occurred during the postoperative period. Dexmedetomidine was used as a primary treatment in nine and as a rescue in five patients. Ten patients (71%) received an initial loading dose of 1.1 +/- 0.5 microg/kg. A continuous infusion, 0.9 +/- 0.3 microg x kg(-1) x h(-1) was administered in 12 patients. Thirteen patients' lungs were mechanically ventilated. Adverse effects were seen in four patients (28%). Three had hypotension that responded to fluid administration and one had a possible brief complete atrioventricular (AV) block. Nine of the 14 patients were transiently paced with atrial (seven) or AV sequential (two) pacing to improve AV synchrony. The primary outcome with rhythm and/or HR control was achieved in 13 patients (93%). JET rate decreased from 197 +/- 22 to 165 +/- 17 bpm within 67 +/- 75 min of dexmedetomidine administration. Five of these patients converted to NSR in 39 +/- 31 h and one remained in JAR. All four patients with Re-SVT had resolution of their tachyarrhythmia. Three converted to NSR and one to JAR. One patient with AET (220-270 bpm) responded well with decreasing HR to 120 bpm within 35 min and to NSR in 85 min. One patient with AF failed to respond. In two patients with JAR, neither progressed to JET and HR decreased from 158 +/- 11 to 129 +/- 1 bpm. This preliminary, observational report suggests that dexmedetomidine may have a potential therapeutic role in the acute phase of perioperative atrial and junctional tachyarrhythmias for either HR control or conversion to NSR.

The Impact of the Distance between the Atrial Electrode and the Atrial Wall on Atrial Undersensing in Patients with VDD Pacemakers: Long‐Term Follow‐Up

Atrial undersensing (AUS) in single-lead VDD pacemakers may be due to diminished P-wave amplitude secondary to local inflammation beneath the electrodes closer to atrial wall. The aim of this study was to assess the potential effect of distance between atrial electrode and atrial wall on immediate and long-term atrial sensing stability in VDD systems. A total of 275 patients with normal sinus node function who received VDD pacemakers were enrolled into the study and were followed up for a median duration of 33 months. During each control visit, a standard 12-lead electrocardiogram (ECG) was obtained and standard pacemaker function assessment was performed including testing for pacing threshold and atrioventricular synchrony. The distance between atrial electrode and atrial wall was measured from chest X-ray. Of the 275 patients, AUS was detected in 59 patients. Univariate predictors of AUS were use of closely spaced bipolar ring atrial electrode (CSBR) (P = 0.01), wider atrial ring-spacing (P = 0.03), and atrial sensitivity programmed to a higher level (P = 0.001). Use of CSBR (P = 0.04) and atrial sensitivity > or =0.3 mV (P = 0.02) were observed to be the independent predictors for AUS. When the distance between atrial electrode and atrial wall was <7 mm, AUS was less with diagonally arranged bipolar ring electrodes (DABR) than it was with CSBRs (P = 0.02). The distance between atrial electrode and atrial wall does not appear to affect AUS incidence in VDD pacemakers. For VDD electrodes closer to atrial wall, AUS was significantly less likely in DABR-type electrodes.

Bradycardia and B-type natriuretic peptide

Bradycardia and loss of atrioventricular synchrony can result inincreased natriuretic peptide secretion due to increased cardiac wall tension. Antihypertensive beta-blocker therapy has been shown to cause elevated natriuretic peptide levels, as well as to increase the frequency of atrial fibrillation in hypertensive patients. The measurement of natriuretic peptides might help solve the clinical challenge of predicting the patients with high risk for beta-blocker induced atrial fibrillation.

Effects of Pacing Modes on Cardiac Baroreflex Function in Permanently Paced Patients with Sinus Node Dysfunction

We compared, in patients with sick sinus syndrome, the effects of various pacing modes on baroreceptor (BR)-stroke volume (SV) reflex sensitivity, a method we have closely correlated with BR-heart rate (HR) reflex sensitivity. Impaired autonomic nervous function, such as decreased BR-HR reflex sensitivity, predicts sudden cardiac death. However, in patients with sick sinus syndrome, the effects of various pacing modes on autonomic function are unknown, since chronotropic incompetence precludes its evaluation by measurements of BR-HR reflex sensitivity. We studied 12 recipients of dual-chamber pacemakers with sick sinus syndrome (mean age = 73 +/- 8 years; 8 men). Beat-by-beat blood pressure (BP) and SV were measured during 5-minute runs of AAI, DDD, and VVI pacing, and spectrally analyzed to assess BR-SV reflex sensitivity. Systolic BP was significantly lower (P < 0.01) during VVI (109 +/- 24 mmHg) than during DDD (124 +/- 22 mmHg) or AAI (125 +/- 41 mmHg) pacing. SV was significantly smaller during VVI (36 +/- 23 mL) than during DDD (49 +/- 31 mL) pacing (P < 0.05). BR-SV reflex sensitivity was significantly lower (P < 0.05) during VVI (9.3 +/- 5.7% per mmHg) than during DDD (15.0 +/- 6.5% per mmHg) or AAI (15.5 +/- 6.2% per mmHg) pacing. BR-SV reflex sensitivity was significantly lower during VVI than during AAI or DDD pacing. Atrioventricular synchrony plays an important role in the preservation of BR-SV reflex sensitivity in pacemaker recipients.

Plasma levels of B-type natriuretic peptide in children and adolescents with high degree atrioventricular block

B-type natriuretic peptide (BNP) was measured in 43 children and adolescents with high-grade second degree or complete atrioventricular conduction block. BNP plasma level was significantly higher ( p < 0.01) in patients without pacemaker ( n = 21) than in patients with permanent pacemaker ( n = 26). In all four patients with measurement of BNP both before and after placement of a permanent pacemaker, individual plasma BNP decreased. Additionally, patients with dual-chamber pacing had significantly lower BNP values compared to those with single chamber ventricular pacing ( p < 0.05). Conclusively, high degree atrioventricular block can induce elevated plasma BNP levels and the loss of atrioventricular synchrony induce a further increase of plasma BNP.

Perioperative outcome of pacemaker patients undergoing non-cardiac surgery

Perioperative outcome of pacemaker patients undergoing non-cardiac surgery

Echo optimization of cardiac resynchronization therapy

Echocardiography has a prominent role in the era of cardiac resynchronization therapy (CRT) by virtue of its noninvasive nature with high feasibility and reproducibility. More importantly, it permits serial assessment for optimization of the therapy before and after device implantation [1]. First, echocardiography can optimize selection of CRT candidates by baseline evaluation of left ventricular (LV) dyssynchrony and myocardial contractility reserve. Second, it may be used to guide the LV lead position in order to avoid those areas with extensive scar. Finally, it is important in optimization of device programming, including atrioventricular (AV) and interventricular (VV) intervals. Although the clinical and echocardiographic benefits of CRT have been well demonstrated, about one-third of patients did not respond to the therapy, in whom the lack of systolic dyssynchrony before device implantation is mainly attributable [1,2]. Various advanced echo techniques, such as tissue Doppler imaging (TDI) and its postprocessing modalities, real-time 3-dimensional echocardiography (RT3DE) and 2-dimensional speckle tracking, have been proved to be able to detect LV dyssynchrony and predict acute or chronic favorable responses after CRT [3−5]. In addition, a certain myocardial reserve might also be necessary, as reflected by a positive result in stress echo or a preserved circumferential strain at baseline [6,7]. With rapidly evolving new technologies, more accurate identification of responders to CRT by echocardiography would be expected so as to reduce the number of nonresponders and improve the cost effectiveness of the therapy. Despite the presence of pre-implant LV dyssynchrony, recent data from MRI have demonstrated that patients with scar tissue in the posterolateral LV segments, where the LV lead is usually located, failed to show clinical and echocardiographic responses after CRT [8]. It suggests the importance of deploying the LV lead away from scar areas. However, it is unclear whether the assessment of scar region by use of echo methods would have predictive value, though the extent of scar tissue by contrast echo was shown to be inversely related to CRT responses [9]. It also needs more information whether discordance between the site of latest activation and the position of LV lead would give rise to a lesser degree of improvement after CRT, though being suggestive in observational and registry studies. Improvement of AV dyssynchrony is one of the mechanisms of benefit from CRT, which is particularly helpful in those patients with 1st AV block where diastolic filling time will be in further jeopardy [2]. Optimization of AV interval is in attempt to ensure AV synchrony and near 100% ventricular pacing in individual patient, which results in decrease in pre-systolic time, abolishment of diastolic mitral regurgitation, increase in LV filling time and gain in cardiac output. The two commonly employed methods by Doppler echocardiography are based on the principles of optimal LV diastolic filling or maximal cardiac output. Usually, AV interval optimization is performed shortly after the device implantation, ie. at the pre-discharge period. However, re-optimization of AV interval at intermediate (e.g. 3 months) and long-term (e.g.12−18 months) follow up may be necessary to further improvement in cardiac performance.[10] VV Optimization may further reduce ventricular dyssynchrony and hence improve systolic function. Currently, optimization of VV interval is commonly based on the reiterative cardiac output method, which is very time-consuming. However, the benefit of VV timing over conventional simultaneous biventricular pacing needs to be confirmed by large, prospective, randomized studies [11].

Prediction of Interatrial and Interventricular Electromechanical Delays from P/QRS Measurements: Value for Pacemaker Timing Optimization

Cardiac pacing creates spurious delays between and within the cardiac chambers. These are: 1. Left atrial (LA) transport delay (ATD) either sensed (s) or paced (p), (time from right atrial P-wave to the end of LA transport (mitral Doppler A-wave)). 2. Interventricular delay (IVD), (time from onsets of right (RV) to left ventricular (LV) contractions). 3. P-sense offset (PSO), (time from P-onset to P-detection). Thus, restoration of left heart atrioventricular (AV) synchrony can be accomplished by compensating above delays, according to a previously published equation: RAV = ATD-IVD-PSO, where RAV = right heart AV. To test the hypothesis that ATD could be predicted from Ps and Pp, and that interventricular delay (IVD) could be predicted from QRSp, using three-lead surface electrocardiograms (ECGs). Thirty-six patients aged 63.5 +/- 15.5 years, 64% males, all with previously implanted DDD pacemakers, were studied by echo-Doppler and surface ECG obtained with a pacemaker programmer. Measurements included Ps; Pp; intrinsic QRSs; and paced QRSp, ATDs, ATDp, and IVD (difference between RVp and RVs left preejection intervals, PEI). Regressions between ECG and echo-Doppler intervals were calculated. Regressions and correlation coefficients: ATD (s+p) = 0.96*P + 55 (R = 0.94, P < 0.0001); PEIp = 0.75 * QRSp + 34.8 (R = 0.89, P< 0.0001); IVD = 0.39 *QRSp - 7.9 ms (R = 0.87, P = 0.002). Inter-atrial and inter-ventricular electromechanical delays can be predicted from P-wave and QRS durations. These measurements allow AV delay optimization in DDD and cardiac resynchronization therapy devices with no need of Doppler echocardiography.

Long-term follow-up of patients paced in VDD mode for advanced atrioventricular block: a pilot study

The aim of this pilot study was to estimate the survival trend of patients implanted with VDD pacemakers, and to compare it with the survival curve of the general population of the same region. Ninety-seven patients (65 male, mean age 78 +/- 6 years) with advanced atrioventricular block referred to our institution were implanted with single-lead VDD pacemakers. All patients were stimulated at the right ventricular apex. At each follow-up visit, a clinical examination was performed and telemetric data collected. In case of death, the family was contacted to record the cause of death. Data on the survival probability of the general population in the Marche Region were obtained from the Italian Institute of Statistics (ISTAT). During the follow-up (mean 7 +/- 6 years), 17 patients (17.5%) died and eight patients (8.2%) developed atrial fibrillation. Atrioventricular synchrony was 97 +/- 3% in the overall patient population, excluding patients with atrial fibrillation. Only one patient was upgraded to DDD pacing owing to symptomatic loss of atrial sensing; after the upgrading procedure symptoms disappeared. During the follow-up period, 19 pacemakers were replaced for end of life of the battery. Patients who died during follow-up were aged 80 +/- 7 years at implantation and 85 +/- 6 years at death. The comparison between the trend line simulating the patient survival probability of the studied VDD population, and the survival probability of males in the Marche Region did not show any significant difference. In patients chronically paced with a single-lead VDD system, survival probability seems to be similar to that of the general population.

Surgery for Atrial Fibrillation

Atrial fibrillation (AF) is a common and serious arrhythmia that traditionally has been treated with antiarrhythmic drugs and warfarin for anticoagulation. Patients often are symptomatic. Normal cardiac function may be impaired due to loss of atrioventricular synchrony and the abnormal irregular ventricular activation. Despite the widespread use of medical therapy in these patients, a recent 21-year follow-up study of patients with AF treated medically showed no improvement in mortality risk over time and in fact showed a substantial excess risk of death.1 Thus, the goal of intervention has shifted over the last 30 years from efforts to improve ventricular rate control while leaving the atria in atrial fibrillation to attempting to permanently atrial fibrillation and restore the atria to sinus rhythm. The late 1970’s and early B0’s ushered in a variety of new invasive surgical procedures. Cox initially developed the atrial isolation designed to confine the atrial fibrillation to the left atrium and allow the heart to beat in sinus rhythm from the right atrium.2•4 Guiraudon created the corridor procedure that joined the sinus node to the atrioventricular node with an isolated strip of right atrial wall.5 In both procedures, the left atrium continued to fibrillate and posed a continued risk of thromboembolism. Open surgical ablation of the atrioventricular node with cryothermia and pacemaker implantation was performed by us in the late 1970’s in selected patients who had difficulty controlling their heart rate through medical therapy. This latter was soon superseded by catheter ablation of the His bundle that was reported by Scheinman in 1982.6 Warfarin continued to be required for rate-controlled atrial fibrillation. The development of a surgical cure for atrial fibrillation was delayed due to the erroneous belief that it was a microreentrant arrhythmia. The initial breakthrough in understanding the mechanism of atrial fibrillation was first achieved by Dr. James Cox and his electrophysiologist colleagues at Duke and then at Washington University. In a series of elegant experiments on dogs and humans, the precise patterns of atrial activation in atrial flutter and fibrillation were elucidated. A mapping computer with 256 electrodes on right and left atrial arrays clearly demonstrated that atrial fibrillation was a macroreentry arrhythmia and that microreentry and automaticity were not present in established atrial fibrillation.3•4 This was consistent with the earlier work published by Allessie on the mapping of atrial flutter in the isolated heart model, which demonstrated that multiple macroreentrant wave fronts were present during atrial flutter.7 Thus, surgical efforts were directed toward creating a series of atrial incisions that would allow normal activation of the entire left and right atria but would prevent propagation of macroreentrant circuits. The specific areas considered at high risk of supporting macroreentry were the vena caval orifices, the base of the left atrial appendage, the four pulmonary veins, the interatrial septum, and the tricuspid orifice. These studies and subsequent clinical experience led to the development of the Cox-Maze Ill procedure, which was introduced into clinical practice in 1991 and continues to be the gold standard for cure of atrial fibrillation. Even with the high cure rate reported by Dr. Cox and confirmed by other centers, the Cox-Maze was never widely adopted. This was due in part to a perception that it was difficult to learn. It also was a significant surgical procedure: Dr. Cox initially performed the operation by making multiple and extensive full-thickness atrial incisions that then had to be sutured.3•4 The introduction of new technologies such as high frequency ultrasound (HIFU) and bipolar radiofrequency devices has greatly simplified this process and made it easier to apply as a combined in patients with atrial fibrillation and structural heart disease such as coronary or valvular lesions. Despite the surgery’s safety record and long-term cure rate of over 95%, however, the need for an open surgical incision and the now-outdated perception of it being a major undertaking continues to limit its application as a freestanding procedure.