Pacing Interval Research Articles

Interference of apex locator, pulp tester and diathermy on pacemaker function.

Aim:The purpose of this study was to evaluate the effects of three electronic apex locators (EAL), electric pulp tester (EPT) and diathermy on pacemaker function in vitro.Materials and Methods:Three EALs: Root ZX (J. Morita Co., Tustin, CA, U.S.A.), Propex (Dentsply), Mini Apex locator (SybronEndo, Anaheim, CA, USA), EPT (Parkell pulp vitality tester Farmingdale, NY, USA) and Diathermy (Neomed 250 B) were tested for any interference with one pacemaker (A medtronic kappa KVDD901-serial number: PLE734632S). Directly connecting the pacemaker lead with the EAL/EPT/diathermy operating on a flat bench top, the telemetry wand was held directly over the pacemaker to monitor the pacing pattern for a period of 30 s. Pacemaker activity was continuously recorded on the telemetric programmer and electro gram (EGM) readings examined for pacer inhibition, noise reversion or inappropriate pacemaker pulses.Results:All the three apex locators showed no pacing interference or background noise during its function or at rest. The EGM readings of EPT showed varying levels of background noise in between pacing however, this did not affect the normal pacing pattern and the pacing interval remained constant. EGM readings of diathermy showed an increase in the pacing interval (irregular pacing pattern) followed by complete inhibition of the pacing system.Conclusion:The tested EALs do not interfere with cardiac pacemaker function. The tested EPT showed varying levels of background noise but does not interfere with cardiac pacemaker function. Use of Diathermy interfered with the normal pacing, leading to complete inhibition of the pacing system.

Reduced intrinsic heart rate is associated with reduced arrhythmic susceptibility in guinea-pig heart

Objectives. In the clinical setting, patients with slower resting heart rate are less prone to cardiovascular death compared with those with elevated heart rate. However, electrophysiological adaptations associated with reduced cardiac rhythm have not been thoroughly explored. In this study, relationships between intrinsic heart rate and arrhythmic susceptibility were examined by assessments of action potential duration (APD) rate adaptation and inducibility of repolarization alternans in sinoatrial node (SAN)-driven and atrioventricular (AV)-blocked guinea-pig hearts perfused with Langendorff apparatus. Design. Electrocardiograms, epicardial monophasic action potentials, and effective refractory periods (ERP) were assessed in normokalemic and hypokalemic conditions. Results. Slower basal heart rate in AV-blocked hearts was associated with prolonged ventricular repolarization during spontaneous beating, and with attenuated APD shortening at increased cardiac activation rates during dynamic pacing, when compared with SAN-driven hearts. During hypokalemic perfusion, the inducibility of repolarization alternans and tachyarrhythmia by rapid pacing was found to be lower in AV-blocked hearts. This difference was ascribed to prolonged ERP in the setting of reduced basal heart rate, which prevented ventricular capture at critically short pacing intervals required to induce arrhythmia. Conclusions. Reduced basal heart rate is associated with electrophysiological changes that prevent electrical instability upon an abrupt cardiac acceleration.

Control of Cardiac Arrhythmia by Nonlinear Spatiotemporal Delayed Feedback

The dynamic feedback control of the cardiac pacing interval has been widely used to suppress alternans. In this paper, temporally and spatially suppressing the alternans for cardiac tissue consisting of a one-dimensional chain of cardiac units is investigated. The model employed is a nonlinear partial difference equation. The model's fixed points and their stability conditions are determined, and bifurcations and chaos phenomenon have been studied by numerical simulations. The main objective of this paper is to stabilize the unstable fixed point of the model. The proposed approach is nonlinear spatiotemporal delayed feedback, and the appropriate interval for controller feedback gain is calculated using the linear stability analysis. It is proven that the proposed approach is robust with respect to all bifurcation parameter variations. Also, set point tracking is achieved by employing delayed feedback with an integrator. Finally, simulation results are provided to show the effectiveness of the proposed methodology.

Continuous-time control of alternans in long Purkinje fibers.

Alternans-an arrhythmic response of cardiac tissue to periodic pacing-often serves as a precursor to a more dangerous, and potentially lethal, state of fibrillation. Suppression of alternans using feedback control may be a plausible method to prevent fibrillation. Several approaches based on impulsive control have been proposed previously, where feedback is applied for a brief instance of time during each pacing interval. This paper presents a continuous-time approach, where feedback current is applied at all times, which is capable of suppressing alternans in fibers of significantly greater length (up to at least 4 cm), compared with impulsive control (less than 1 cm), and for a wide range of pacing cycle lengths.

Is the acetylcholine-regulated inwardly rectifying potassium current a viable antiarrhythmic target? Translational discrepancies of AZD2927 and A7071 in dogs and humans.

We aimed at examining the acetylcholine-dependent inward-rectifier current (IKAch) as a target for the management of atrial fibrillation (AF). The investigative agents AZD2927 and A7071 concentration-dependently blocked IKACh in vitro with minimal off-target activity. In anaesthetized dogs (n = 17) subjected to 8 weeks of rapid atrial pacing (RAP), the left atrial effective refractory period (LAERP) was maximally increased by 50 ± 7.4 and 50 ± 4.8 ms following infusion of AZD2927 and A7071. Ventricular refractoriness and the QT interval were unaltered. During sustained AF, both drugs significantly reduced AF frequency and effectively restored sinus rhythm. AZD2927 successfully restored sinus rhythm at 10/10 conversion attempts and A7071 at 14/14 attempts, whereas saline converted 4/17 episodes only (P<0.001 vs. AZD2927 and A7071). In atrial flutter patients (n = 18) undergoing an invasive investigation, AZD2927 did not change LAERP, the paced QT interval, or ventricular refractoriness when compared with placebo. To address the discrepancy on LAERP by IKACh blockade in man and dog and the hypothesis that atrial electrical remodelling is a prerequisite for IKACh blockade being efficient, six dogs were studied after 8 weeks of RAP followed by sinus rhythm for 4 weeks to reverse electrical remodelling. In these dogs, both AZD2927 and A7071 were as effective in increasing LAERP as in the dogs studied immediately after the 8-week RAP period. Based on the present series of experiments, an important role of IKACh in human atrial electrophysiology, as well as its potential as a viable target for effective management of AF, may be questioned.

Paced QT interval is a better predictor of mortality than the intrinsic QT interval: long-term follow-up study.

Prolongation of the corrected QT (QTc) interval on 12-lead electrocardiogram is related to total mortality and sudden cardiac death. The value of the paced QTc interval in predicting mortality has not been investigated. To evaluate the relationship between the paced QTc interval and mortality. Of 1440 patients who underwent pacemaker implantation from January 1990 to March 2010, 766 had a recorded intrinsic and ventricular paced rhythm and were included in this study. The intrinsic and paced QTc intervals were measured on 12-lead electrocardiogram before and 1-month after implantation. During a mean follow-up period of 7 ± 5 years, 189 (24.4%) patients died, of which 63 (8.1%) were cardiac deaths. Compared with patients in the first tertile of the paced QTc interval (<484 ms), patients in the third tertile (>511 ms) were significantly more likely to die (19% vs 29%; P < .05). A comparison of the third and first tertiles of the QTc interval showed that a prolonged paced QTc interval was a significant independent predictor of all-cause mortality (adjusted hazard ratio 2.08; 95% confidence interval 1.44-3.01; P < .001) and cardiac mortality (adjusted hazard ratio 2.53; 95% confidence interval 1.29-4.95; P = .007) and a better predictor than was a prolonged intrinsic QTc interval. When treated as a continuous variable, a prolonged paced QTc interval predicted increased total mortality and cardiac mortality. The paced QTc interval appears to be a more useful marker in predicting bad prognosis than does the intrinsic QTc interval in patients with indications for a permanent pacemaker.

Best clinical abstract

# 1365 Does atrial pacing lead to atrial fibrillation in patients with sick sinus syndrome? Insights from the DANPACE trial {#article-title-2} Purpose: Paroxysmal atrial fibrillation (AF) is common in patients with sick-sinus syndrome (SSS) and pacemakers leading to morbidity and an increased risk of stroke or death. Previous studies indicate that atrial pacing may precipitate atrial fibrillation (AF). We investigated the relation between atrial pacing and the occurrence of AF during long-term follow-up among patients with SSS, no prior AF, and DDDR pacemakers. Methods: We analysed data from 396 patients who received DDDR pacemakers in the DANPACE trial. The rate adaptive function was activated and programmed with a lower rate of 60 beats per minute and an upper rate of 130 beats per minute. The paced atrio-ventricular interval (AVI) was programmed to 140-220 ms according to a pre-specified algorithm. Follow-up took place after 3 months and again every year after implantation up to 10 years. The percentage of atrial pacing (%AP) was compared to the number of mode switch (MS) episodes collected by the pacemaker at each follow-up as an indicator of AF. Results: Mean follow-up was 4.2 ± 2.4 years. The mean proportion of atrial and ventricular pacing was 59±31 % and 65±33 %, respectively. A total of 333 patients (84 %) developed AF as indicated by MS episodes at some point during follow-up (figure). Unadjusted regression analysis indicated a relation between %AP and AF (P = 0.04), but after adjustment for possible confounders (sex, age, hypertension, diabetes, MI, PQ interval, and left atrial diameter) there was no significant relationship (P = 0.37). Conclusion: Atrial fibrillation is highly frequent among patients with SSS. No association between %AP and development of AF was found in patients with SSS. Future trials may randomise patients to different levels of AP exposure. ![Graphic][1] [1]: /embed/inline-graphic-1.gif

Individual differences in timing of discrete and continuous movements: a dimensional approach

This study investigated aspects of individual differences in timing of continuous and discontinuous movements to different pacing signals (auditory or visual), pacing intervals (500, 650, 800, 950 ms), and across effectors (dominant versus non-dominant hand). Correlation and principal component analysis demonstrated that a single statistical dimension accounted for up to 60% of the explained variance in discontinuous tasks and 25% of the variance in continuous tasks, when applied to performance obtained from tasks conducted with different effectors and at different pacing rates. Correlation analysis of factor scores representing effector and rate independent task performances showed that timing of discrete or continuous movements can be associated with modality independent mechanisms. Timing variability from discrete and continuous trials was not significantly correlated. This study goes beyond previous correlational work on individual differences in discrete and continuous movements, demonstrating that individual differences in discrete (event-based) or continuous (emergent) motor timing tasks can be modeled as distinctive statistical components with dissimilar capability to capture effector, rate, and modality independent variance.

Hearts of K Channel-Interacting Protein 2 Deficient Mice have Prolonged Action Potential Duration, and Reduced Outward Potassium Currents that are further reduced by Heart Failure

Cardiac myocytes exhibit a fast recovering transient outward potassium current (Ito,f) that is conducted by the channel proteins Kv4 + KChIP2. Heart failure (HF) is associated with a reduction of outward K+-currents and a downregulation of KChIP2. In this study, we investigated the electrophysiological role of KChIP2 in mice with HF.HF induced by transverse aortic constriction was defined as an ejection fraction below 50% evaluated by ultrasound. Action potentials were recorded by floating micro electrodes from the left ventricle in ex vivo perfused hearts. Whole-cell currents were recorded from disaggregated left ventricular cardiomyocytes.We found an equal reduction in the ejection fractions of wild-type (WT) and KChIP2-/- mouse hearts by transverse aortic constriction. Left ventricular action potential durations were prolonged by 32% in KChIP2-/- vs. WT at 90% repolarization (APD90) during 200 ms pacing intervals (P<0.05). Peak K+-current density was 18% lower in KChIP2-/- vs. WT (P<0.05). Induction of HF reduced peak K+-current density by 38% in KChIP2-/- and by 24% in WT (P<0.05 for both). K+-current recovery from inactivation was delayed in KChIP2-/- vs. WT, and further delayed by HF in KChIP2-/- but remained unchanged in WT.In conclusion, HF reduced K+-currents in WT, but did not abolish the KChIP2-dependent fast recovering current component. KChIP2-/- mice lack the fast recovering K+-current (Ito,f) leading to prolonged left ventricular action potentials. HF in KChIP2-/- mice induced a further loss of K+-currents and an additional delay of recovery from inactivation, suggesting a reduction of non-Ito,f K+-currents contributing to the electrophysiological changes in mouse HF.

Erratum to: Timing continuous or discontinuous movements across effectors specified by different pacing modalities and intervals

Erratum to: Timing continuous or discontinuous movements across effectors specified by different pacing modalities and intervals

Optimized temporary bi-ventricular pacing improves haemodynamic function after on-pump cardiac surgery in patients with severe left ventricular systolic dysfunction: a two-centre randomized control trial

OBJECTIVESOptimized temporary bi-ventricular (BiV) pacing may benefit heart failure patients after on-pump cardiac surgery compared with conventional dual-chamber right ventricular (RV) pacing. An improvement in haemodynamic function with BiV pacing may reduce the duration of ‘Level 3’ intensive care.METHODSThirty-eight patients in sinus rhythm, ejection fraction ≤35%, undergoing on-pump surgical revascularization, valve surgery or both were enrolled in this study. Before closing the sternum, temporary epicardial pacing wires were attached to the right atrium, RV outflow tract and basal posterolateral wall of the left ventricle. Patients were randomly assigned to postoperative BiV pacing with the optimization of the atrio- (AV) and inter-ventricular (VV) pacing intervals (Group 1) or conventional dual-chamber right AV pacing (Group 2). The primary end-point was the duration of ‘Level 3’ intensive care. Secondary end-points included cardiac output which was measured by thermodiluation at admission to the intensive care unit and at 6 and 18 h later, in five different pacing modes.RESULTSThe duration of ‘Level 3’ care was similar between groups (40 ± 35 vs 54 ± 63 h; Group 1 vs 2; P = 0.43). Cardiac output was similar in all pacing modes at baseline. At 18 h, cardiac output with BiV pacing (5.8 l/min) was 7% higher than atrial inhibited (5.4 l/min) and 9% higher than dual-chamber RV pacing (5.3 l/min; P = 0.02 and 0.001, respectively). Optimization of the VV interval produced a further 4% increase in cardiac output compared with baseline settings (P = 0.005).CONCLUSIONSPostoperative haemodynamic function may be enhanced by temporary BiV pacing of high-risk patients after on-pump cardiac surgery.

Facilitating assessment of QT interval duration during ventricular pacing

We aimed to facilitate the assessment of the QT interval duration during conventional right ventricular pacing (VP) by uncovering relationships with the underlying QT interval during intrinsic atrioventricular conduction (IC). The study patients (n = 122, age 68 ± 11 years) were dual-chamber device recipients with preserved IC and narrow QRS complexes. Patients were classified into either 'normal-QT' (n = 70) or 'prolonged-QT' (n = 52) group. Incremental atrial pacing rates were exercised to record serial QT/JT intervals over 5 min periods in IC mode and then in VP mode. Six different QT correction methods for heart rate were applied to assess the effect (i) of pacing mode (IC vs. VP) and (ii) of heart rate on the derived QT(c)/JT(c) intervals by mixed-effects linear models. Following VP, the uncorrected QT/JT intervals as well as the JTc intervals shortened (P < 0.001), whereas the QTc intervals prolonged (P < 0.001). In both patient groups, the Framingham and Nomogram methods demonstrated the optimal balance to assess QTc, with low heart rate dependence during VP and minimal interaction between pacing mode and heart rate. The Rautaharju formula provided excellent correction for the QT changes induced by VP, but the QTc interval responded differently to rate changes in IC vs. VP mode. Bazett's formula exaggerated QTc/JTc rate dependency during VP. The Framingham and Nomogram correction methods perform most reliably in assessing the underlying QT interval during IC from the ventricular paced QT interval.

Atrial septal pacing for the termination of atrial fibrillation: study in a biophysical model of human atria

While successful termination by pacing of organized atrial tachycardias has been observed in patients, single site rapid pacing has not yet led to conclusive results for the termination of atrial fibrillation (AF). The purpose of this study was to evaluate a novel atrial septal pacing algorithm for the termination of AF in a biophysical model of the human atria. Sustained AF was generated in a model based on human magnetic resonance images and membrane kinetics. Rapid pacing was applied from the septal area following a dual-stage scheme: (i) rapid pacing for 10-30 s at pacing intervals 62-70% of AF cycle length (AFCL), (ii) slow pacing for 1.5 s at 180% AFCL, initiated by a single stimulus at 130% AFCL. Atrial fibrillation termination success rates were computed. A mean success rate for AF termination of 10.2% was obtained for rapid septal pacing only. The addition of the slow pacing phase increased this rate to 20.2%. At an optimal pacing cycle length (64% AFCL) up to 29% of AF termination was observed. The proposed septal pacing algorithm could suppress AF reentries in a more robust way than classical single site rapid pacing. Experimental studies are now needed to determine whether similar termination mechanisms and rates can be observed in animals or humans, and in which types of AF this pacing strategy might be most effective.

Letter by Obeyesekere Regarding Article, “Functional Pace-Mapping Responses for Identification of Targets for Catheter Ablation of Scar-Mediated Ventricular Tachycardia”

HomeCirculation: Arrhythmia and ElectrophysiologyVol. 5, No. 5Letter by Obeyesekere Regarding Article, “Functional Pace-Mapping Responses for Identification of Targets for Catheter Ablation of Scar-Mediated Ventricular Tachycardia” Free AccessResearch ArticlePDF/EPUBAboutView PDFView EPUBSections ToolsAdd to favoritesDownload citationsTrack citationsPermissions ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toFree AccessResearch ArticlePDF/EPUBLetter by Obeyesekere Regarding Article, “Functional Pace-Mapping Responses for Identification of Targets for Catheter Ablation of Scar-Mediated Ventricular Tachycardia” Manoj N. Obeyesekere, MBBS Manoj N. ObeyesekereManoj N. Obeyesekere Mildura Cardiology, Victoria, Australia Search for more papers by this author Originally published1 Oct 2012https://doi.org/10.1161/CIRCEP.112.974055Circulation: Arrhythmia and Electrophysiology. 2012;5:e100To the Editor:The elegant study by Tung et al1 presents additional sites for ablation of scar-based ventricular tachycardia (VT). Pace-mapped induction sites predicted successful sites of termination during ablation. This study raises a hypothesis that pace-mapped induction may be viewed as a surrogate for entrainment.At induction as with at the end of entrainment, when pacing from within the scar and the exit site after the last paced impulse at induction is the same as the induced/entrained VT, conduction follows the same route, and the return cycle to the site of pacing may also be similar. Thus, the postpacing interval after entrainment may be the same as the postpacing interval measured from the last pacing stimulus that initiates VT (postpacing intervalInitiation). Similarly, the stimulus-QRS interval that initiates VT or during pacing is because of the same distance as the stimulus-QRS interval during entrainment if the exit is the same. In fact, the authors report that 71% of critical isthmus sites had a stimulus-QRS during pacing minus electrogram-QRS interval of <30 ms. Thus, the cycle at induction may provide comparable information to that derived after entrainment.2 This assumption can be confounded by decrement and concealed conduction at initiation, and remote site pace mapping may match VT morphology in up to 29% of sites.3 Could the authors provide data on analysis of the postpacing intervalInitiation minus tachycardia cycle length at pace-mapped induction sites, both when the last paced beat matched the VT and when it did not? Data on analysis of entrainment mapping at the 21 pace-mapped induction sites would also be valuable.DisclosuresNone.Manoj N. Obeyesekere, MBBSMildura CardiologyVictoria, Australia

Response to Letter Regarding Article, “Functional Pace-Mapping Responses for Identification of Targets for Catheter Ablation of Scar-Mediated Ventricular Tachycardia”

We appreciate the thoughtful comments raised by Dr Obeyesekere based on his work on the initiating post pacing interval (PPI) in differentiating mechanisms of supraventricular tachycardia. Our group has had an interest in this mechanistic concept as well, but we have observed disparate findings in the setting of scar-mediated ventricular tachycardia. Analysis of the initiating PPI at pace-mapped induction (PMI) sites fell into 3 categories: (1) inability to interpret a consistent electrogram to measure the initiating PPI; (2) likely resetting or entrainment rather than induction; and (3) suitable for analysis with a clear, distinguishable initiating beat. In 6 patients, a …

Timing continuous or discontinuous movements across effectors specified by different pacing modalities and intervals

Sensorimotor synchronization is hypothesized to arise through two different processes, associated with continuous or discontinuous rhythmic movements. This study investigated synchronization of continuous and discontinuous movements to different pacing signals (auditory or visual), pacing interval (500, 650, 800, 950ms) and across effectors (non-dominant vs. non-dominant hand). The results showed that mean and variability of asynchronization errors were consistently smaller for discontinuous movements compared to continuous movements. Furthermore, both movement types were timed more accurately with auditory pacing compared to visual pacing and were more accurate with the dominant hand. Shortening the pacing interval also improved sensorimotor synchronization accuracy in both continuous and discontinuous movements. These results show the dependency of temporal control of movements on the nature of the motor task, the type and rate of extrinsic sensory information as well as the efficiency of the motor actuators for sensory integration.

Long-term effectiveness of right septal pacing vs. right apical pacing in patients with atrioventricular block

BackgroundLong-term right ventricular apical (RVA) pacing increases the risk of heart failure (HF) by inducing ventricular dyssynchronization. Although recent studies suggest that right ventricular septal (RVS) pacing results in improved short-term outcomes, its long-term effectiveness remains unclear. Methods and resultsThis study investigated 149 consecutive patients who underwent implantation of a dual chamber pacemaker for atrioventricular block with either RVS-pacing between July 2007 and June 2010 or RVA-pacing between January 2003 and June 2007. The endpoint was defined as death and hospitalization due to heart failure (HF). The rates of mortality and hospitalization due to HF were significantly lower in the RVS-pacing group than that in the RVA-pacing group (event free RVS: 1 year, 98% and 2 years, 98%; RVA: 1 year, 85% and 2 years, 81%; p<0.05). None of the patients died from HF in the RVS-pacing group, while 4 patients died from HF in the RVA-pacing group within 2 years after pacemaker implantation. The paced QRS interval was significantly shorter with RVS pacing than with RVA pacing at different times after pacemaker implantation (RVS: immediately 157.8±24.0ms, after 3 months 157.3±17.5ms, after 6 months 153.6±21.7ms, after 12 months 153.6±19.4ms, after 24 months 149.3±24.0ms vs. RVA: immediately 168.3±23.7ms, after 3 months 168.7±26.0ms, after 6 months 168.0±22.8ms, after 12 months 171.2±22.3ms, after 24 months 176.1±25.5ms; p<0.05). ConclusionsRVS pacing is feasible and safe with more favorable clinical benefits than RVA pacing.

How to Approach Reentrant Atrial Tachycardia After Atrial Fibrillation Ablation

A 63-year-old male patient was admitted for catheter ablation of persistent atrial fibrillation (AF). On echocardiography, the left atrial (LA) size was 48 mm and the left ventricular function was normal. After electric cardioversion, ipsilateral pulmonary veins (PVs) were circumferentially ablated in sinus rhythm using double-Lasso (Lasso, Biosense Webster, Diamond Bar, CA) technique.1–3 Both ipsilateral PVs were simultaneously isolated. Two years later, the patient was admitted for the ablation of recurrent, drug-resistant atrial tachycardia (AT) (Figure 1A). Figure 1. A , Twelve-lead electrogram of the clinical atrial tachycardia. B , Entrainment mapping at right inferior pulmonary vein (RIPV) showed that postpacing interval tachycardia cycle length was 10 ms. RA indicates right atrium; CS, coronary sinus. The baseline tachycardia cycle length (TCL) was 350 ms. A 20-pole mapping catheter (Irvine Biomedical Inc, Irvine, CA) was inserted through the right jugular vein and positioned in the coronary sinus (CS). An 8-mm-tip ablation catheter (Japan Lifeline Inc, Tokyo, Japan) was advanced into the LA through a transseptal puncture. Mapping during AT revealed the resumption of conduction in the right PVs. On entrainment mapping, the Δ post pacing interval (PPI-TCL) was found to be 120, 70, 56, and 10 ms at the low lateral right atrium, anterior LA, bottom of LA, and left septum near the right PVs, respectively. On activation mapping using a 3D electroanatomic mapping system (Carto, Biosense Webster), earliest atrial activation was observed on the roof of right superior vein and the latest at the bottom of right inferior vein. Successful entrainment from the superior and inferior veins revealed that both sites were within the tachycardia circuit (Figure 1B and 2A). Entrainment from the LA septum near the right PVs demonstrated that septal myocardium was also a part of the reentrant circuit. Furthermore, P-wave morphology during entrainment …

Phase Relationship between Alternans of Early and Late Phases of Ventricular Action Potentials.

Background: Alternans of early phase and of duration of action potential (AP) critically affect dispersion of refractoriness through their influence on conduction and repolarization. We investigated the phase relationship between the two alternans and its effect on conduction. Methods and Results: Transmembrane potentials recorded from ventricles of eight swine and three canines during paced activation intervals of ≤300 ms were used to quantify alternans of maximum rate of depolarization (|dv/dt|max) and of action potential duration (APD). Incidence of APD alternans was 62 and 76% in swine and canines. Alternans of APD was frequently accompanied with alternans of |dv/dt|max. Of these, 4 and 26% were out of phase in swine and canines, i.e., low |dv/dt|max preceded long APD. Computer simulations show that out of phase alternans attenuate variation of wavelength and thus minimize formation of spatially discordant alternans. Conclusion: The spontaneous switching of phase relationship between alternans of depolarization and repolarization suggests that mechanisms underlying these alternans may operate independent of each other. The phase between these alternans can critically impact spatial dispersion of refractoriness and thus stability of conduction, with the in phase relation promoting transition from concord to discord while out of phase preventing formation of discord.

Continuous noninvasive arterial pressure

To assess the role of continuous noninvasive arterial pressure (CNAP) in elderly, high-risk patients with pronounced variation in arterial pressure (AP) under analgesic sedation. Twenty-nine patients were analyzed while undergoing elective transfemoral aortic valve implantation procedures during periods of normal blood pressure, hypotension, and hypertension with standard invasive arterial pressures (IAP). Systolic, diastolic, and mean IAP were compared with those obtained by CNAP. Data were analyzed to determine precision (i.e. measurement error) and accuracy (i.e. systematic error) during different periods of AP for agreement of the two methods. In addition, we compared the two methods during intervals of functional cardiac arrests (rapid pacing) in terms of amplitude and frequency of rapid changes in AP. No significant differences in precision were observed between CNAP measurements and IAP measurements. CNAP accuracy was -8.3*, 6.4, and 0.6 mmHg in normotensive, -20.5*, 4.4, and -5.5 mmHg in hypertensive, and -4.8, 9.4, and 4.5 mmHg in hypotensive conditions (*P<0.05). The frequency of AP pairs with a difference of ± 15 mmHg (limits of agreement) or less was 59.5, 71.7, and 76.5% in normotensive, 33.1, 72.9, and 66.9% in hypertensive, and 59.5, 71.7, and 76.5% in hypotensive periods for systolic, diastolic, and mean AP, respectively. Rapid pacing intervals showed a significant difference in systolic measurements; whereas the differences between CNAP and IAP for diastolic and mean AP were minimal. The agreement between the two techniques used in this study of elderly high-risk patients under analgesic sedation is similar to that found in studies performed under general anesthesia. The best agreement was detected in hypotensive periods.