Efficacy of Ventricular Rate Stabilization by Right Ventricular Pacing During Atrial Fibrillation

To assess the effect of right ventricular pacing on rate regularity during exercise and daily life activities, 16 patients with sinoatrial disease and chronic atrial fibrillation (AF) were studied. Incremental ventricular pacing was commenced at 40 beats/min until > 95% of ventricular pacing were achieved during supine, sitting, and standing. Thirteen patients also underwent randomized paired submaximal exercise tests in either a fixed rate mode (VVI) or a ventricular rate stabilization (VRS) mode in which the pacingrate was set manually at 10 beats/min above the average AF rate duringthe last minute of each exercise stage. The pacing interval for rate regularization was shortest during standing (692 ± 26 ms) compared with either supine or sitting (757 ± 30 and 705 ± 26 ms, respectively, P < 0.05). During exercise, VRS pacing significantly increased the maximum rate (119 ± 5.2 vs 106 ± 4.2 ms, P < 0.05), percent of ventricular pacing (85%± 5% vs 23%± 7%, P < 0.05), rate regularity index (5.8%± 1.6% vs 13.4%± 1.9%, P < 0.05), and maximum level of oxygen consumption (12.4 ± 0.5 vs 11.3 ± 0.5 ml/kg, P < 0.05) compared with VVI pacing. There was no change in oxygen pulse or difference in symptom scores in this acute study between the two pacing modes. It is concluded that right ventricular pacing may significantly improve rate regularity and cardiopulmonary performance in patients with chronic AF. This may be incorporated in a pacing device for rate regularization of AF using an algorithm that is rate adaptive to postural and exercise stresses.     

Monophasic Action Potential Duration During Programmed Electrical Stimulation

To examine changes in monophasic action potential duration (APD) with a pacing protocol similar to that used during electrophysiological testing, action potentials were recorded in vivo from the left ventricular apical endocardium of 12 normal mongrel dogs. The atrioventricular node was ablated and the dogs paced from the anterior right ventricle at a baseline cycle length of 1000 ms between interventions. Mean steady-state APD (APDss) was 266 +/- 7 ms at a pacing cycle length (PCL) of 1000 ms. Two pacing protocols were used. The first consisted of a sudden acceleration in pacing from a cycle length of 1000 ms to one between 300 and 600 ms. The second consisted of an 8-beat train at a cycle length of 400 ms followed by a premature beat at a coupling interval of 280 ms followed by a pause. The inter-train pause varied between 1 second and 32 seconds. With a sudden acceleration in pacing rate, steady-state values for APD at the faster PCLs were significantly smaller than APDss at 1000 ms with a change to cycle lengths of 600 ms (247 +/- 29 ms), 500 ms (229 +/- 21 ms), 400 ms (220 +/- 17 ms), and 300 ms (203 +/- 31 ms; P less than 0.01 for all comparisons). The time constant of the change in APD was shorter at a PCL of 300 ms (14.9 +/- 0.8 s) than 600 ms (20.3 +/- 4.7 s; P less than 0.05). With drive train pacing and incorporating an inter-train pause, the percent drop in steady-state APD compared to APD for the first train ranged from 10.1% with a 1-second inter-train pause to 2.1% with a 32-second pause. The difference in APD between the first drive train and drive trains after at least 3 minutes of pacing when APD had stabilized was not significant for an inter-train pause exceeding 8 seconds. In conclusion: (1) with a sudden acceleration in pacing rate, endocardial APD in vivo decreases exponentially. The faster the new rate, the shorter the new steady-state APD and the shorter the time constant. (2) When pacing using an 8-beat drive train and an inter-train pause, there is a decremental shortening in APD for pause lengths shorter than 16 seconds. Thus, while performing programmed stimulation using a pause, a conditioning period of at least 2 minutes should be used prior to diastole scanning to allow APD to achieve a steady state.     

Clinical Application of a Microcomputer System for Analysis of Monophasic Action Potentials

Computerized analysis of monophasic action potentials (MAPs) has rarely been reported in clinical setting. We developed a computer system featuring on-line acquisition and user-monitored automatic measurement of multichannel MAPs with the capability of manual corrections. This system has been used in 34 patients in whom two-channel MAPs and 1-lead ECG were digitized during sinus rhythm, pacing, and programmed stimulation (PS). In total, 41,413 MAPs in 212 data files were measured. The correct determination rate was 100% for MAP onset and plateau, 99.78% (95.76% during PS) for MAP baseline, and 99.96% (54.29% during PS) for QRS onset. The comparison between the computerized and manual measurements in 292 MAPs showed that the former highly agreed with the latter, with the limits of agreement, defined as mean difference ± 2 SD, being from -4.8-4.9 ms for activation time and from – 4.1-6.0 ms for MAP duration measurements. Using this system, two-channel MAPs of more than 300 consecutive beats can be measured in a few minutes, which made it possible to determine the steady state of MAP duration individually, and evaluate the MAP changes during intervention in detail. The clinical routine procedure for testing the effective refractory period and several new MAP parameters were also evaluated using this system. Conclusion: The MAP measurement using this computer system is reliable, rapid and accurate; it can therefore replace the manual method and provide more useful information for clinical research.     

Right Ventricular Monophasic Action Potentials in Healthy Young Men

The right ventricular repolarization phase was studied in 48 healthy men between 20 and 40 years of age. The assessment of the repolarization time included the measurement of ventricular effective refractory periods and monophasic action potentials during constant ventricular stimulation. Computer-based analysis of the monophasic action potential allowed the duration at 90% and 50% repolarization, the amplitude, the maximal upstroke velocity and the total rise time of the depolarization to be determined. These results may serve as reference values in further studies on ventricular repolarization using the same monophasic action potential recording technique.     

Recording Atrial Monophasic Action Potentials Using Standard Pacemaker Leads:

AF leads to electrophysiological changes, but it is not known if similar alterations also appear before the onset of the first episode of AF because invasive electrophysiological studies are not justified in otherwise symptom-free patients. To address this question requires a safe method of obtaining atrial electrophysiological parameters at no extra risk or discomfort for the patient. The aim of this study was to test if recording of monophasic action potentials (MAPs) is feasible during pacemaker implantation. The study included 22 patients undergoing pacemaker implantation for symptomatic bradycardia without any history of AF. Using a custommade amplifier and a minor modification of the routine procedure for intraoperatively measured P waves, atrial electrograms could be recorded using a standard active pacemaker lead. MAP-like electrograms were obtained in 15 patients. MAP amplitude was 2.6 +/- 0.3 mV, mean action potential duration was 316 +/- 12 ms at a spontaneous heart rate of 67.2 +/- 3.2 beats/min. MAP duration was decreased when atria were stimulated at shorter cycle lengths (249 +/- 12 ms at 150 beats/min, P <0.05 vs sinus rhythm). In about two thirds of patients undergoing pacemaker implantation, recording of MAP-like electrograms was feasible with only minor modification of the atrial electrogram recording technique. The method should allow screening patients for electrophysiological alterations even before the onset of AF.     

An Automatic Microcomputer System for Analysis of Monophasic Action Potentials

A computer system for rapid measurement and analysis of monophasic action potentials (MAPs) recorded in vivo was developed. MAPs recorded from the epicardium of mongrel dogs using a contact electrode were digitized by analog-to-digital conversion at a sampling rate of 1 kHz per channel for computer data acquisition. Activation time was detected using a sliding 10-point window at the location where the average positive dV/dT exceeds an adjustable threshold value in order to eliminate spurious detection due to baseline variability or motion artifact. Action potential duration (APD) was determined at 50% and 90% (APD50, APD90) repolarization levels at the first sample point below these detection levels. In addition, a tangent algorithm (APDtan) that detects peak negative dV/dT during repolarization was developed. APDtan was determined from the location of onset of activation to the intersection of tangent and baseline. APDtan allowed estimation of APD in the presence of subsequent premature beats when APD90 was not measurable. To validate activation time measurements, 4,600 action potentials were analyzed during fixed rate pacing. Over a range of paced coupling intervals from 200 to 1000 msec, an R2 value of 0.99968 and a slope of 0.9959 were obtained by linear regression between paced and calculated intervals. To validate APD measurements, 5035 action potentials were analyzed in five animals during fixed rate pacing (longer than 3 minutes) when action potential duration should be constant. Average coefficient of variation of 1.25%, 1.65%, and 1.14% were obtained for APD50, APD90, and APDtan, respectively. This algorithm provides a rapid and accurate method to analyze MAP activation and duration for basic physiological studies such as the determination of initiation of arrhythmias.     

Electrical Atrial Remodeling Assessed by Monophasic Action Potential and Atrial Refractoriness in Patients with Structural Heart Disease

The present study was performed to assess the effect of induced atrial fibrillation (AF) on atrial monophasic action potentials (MAPs) and atrial refractory period (ERP) in patients with structural heart disease. An electrode MAP catheter was placed in the right atrium to continuously measure atrial potential duration (APD₉₀) in 13 patients (coronary artery disease, 10 patients; dilated cardiomyopathy, 2 patients; hypertrophic cardiomyopathy, 1 patient) without spontaneous AF episodes. AF was induced by rapid atrial stimulation (300–1500/min). If sinus rhythm returned within 10 minutes, AF was reinduced. The atrial ERP was measured during atrial pacing at a basic cycle length of 550 ms before AF induction and after its conversion. Results: The mean atrial ERP and the atrial APD₉₀ before AF was 242 ± 34 ms and 256 ± 23 ms, respectively. ERP and APD_go shortening was observed after 3 minutes of AF. After 11 ± 0.5 min (10 min 20 s-13 min 10 s) of AF, ERP and APD₉₀ reached their minimal values of 72%± 13% and 71%± 10% of baseline, respectively. ERP and APD₉₀ returned to their initial values within 10 minutes after conversion of AF. A tendency toward longer duration of consecutive AF episodes and facilitation of their induction was observed. Conclusion: The present study confirms that short episodes of AF modify the electrophysiological properties of the atria in humans. In patients with structural heart disease, induced atrial fibrillation shortens the atrial ERP as well as the atrial APD₉₀. The changes were reversible within 10 minutes after arrhythmia termination.     

A Comparison of Ventricular Function During High Right Ventricular Septal and Apical Pacing after His-Bundle Ablation for Refractory Atrial Fibrillation

This study compares LV performance during high right ventricular septal (RVS) and apical (RVA) pacing in patients with LV dysfunction who underwent His-bundle ablation for chronic AF. We inserted a passive fixation pacing electrode into the RVA and an active fixation electrode in the RVS. A dual chamber, rate responsive pulse generator stimulated the RVA through the ventricular port and the RVS via the atrial port. Patients were randomized to initial RVA (VVIR) or RVS (AAIR) pacing for 2 months. The pacing site was reversed during the next 2 months. At the 2 and 4 month follow-up visit, each patient underwent a transthoracic echocardiographical study and a rest/exercise first pass radionuclide ventriculogram. We studied nine men and three women (mean age of 68 +/- 7 years) with congestive heart failure functional Class (NYHA Classification): I (3 patients), II (7 patients), and III (2 patients). The QRS duration was shorter during RVS stimulation (158 +/- 10 vs 170 +/- 11 ms, P < 0.001). Chronic capture threshold and lead impedance did not significantly differ. LV fractional shortening improved during RVS pacing (0.31 +/- 0.05 vs 0.26 +/- 0.07, P < 0.01). RVS activation increased the resting first pass LV ejection fraction (0.51 +/- 0.14 vs 0.43 +/- 0.10, P < 0.01). No significant difference was observed during RVS and RVA pacing in the exercise time (5.6 +/- 3.2 vs 5.4 +/- 3.1, P = 0.6) or the exercise first pass LV ejection fraction (0.58 +/- 0.15 vs 0.55 +/- 0.16, P = 0.2). The relative changes in QRS duration and LV ejection fraction at both pacing sites showed a significant correlation (P < 0.01). We conclude that RVS pacing produces shorter QRS duration and better chronic LV function than RVA pacing in patients with mild to moderate LV dysfunction and chronic AF after His-bundle ablation.     

Arrhythmia Risk: Eiectrophysiological Studies and Monophasic Action Potentials

Shortly after in the introduction of progrommed electrical stimulotion (PES) of the heart to study and localize cardiac arrhythmias in the intact human heart, the technique was used for risk stratification of the arrhythmia patient. Two decades later we have to conclude that especially in ventricular arrhythmias the technique of PES did not live up to our expectations and the left ventricular function is a better long-term predictor than the induction of ventricular arrhythmias or the ability to find an antiarrhythmic drug able to prevent the initiation of the classically documented ventricular arrhythmia. Another sobering finding come from the analysis of the characteristics of the patient dying suddenly out-of-hospital, which showed that most of those patients could not be classified before the event as being at high risk using noninvasive or invasive testing, not even in those with o previous cardiac history. Monomorphic action potential (MAP) recordings have been of importance in our understanding of torsade de pointe arrhythmias in congenital and acquired QT prolongation. A major problem in case of a less generalized electrophysiological abnormality is the identification of the appropriate place where to put the MAP-electrode.     

Microvolt T-Wave Alternans During Atrial and Ventricular Pacing

Introduction: Assessment of microvolt T-wave alternans (MTWA) by the spectral analysis (SA) method requires the heart rate to be stable within a certain range. This can be achieved by ventricular pacing (VP). We compared MTWA during short-term VP versus atrial pacing (AP).
Methods: Patients presenting for evaluation of risk of sudden cardiac death underwent an invasive electrophysiologic study. The concordance of results of MTWA-VP with MTWA-AP was evaluated, as well as the specificity, sensitivity, negative, and positive predictive values of MTWA-VP versus MTWA-AP. The maximum recorded amplitude of MTWA (MValt) in concordant positive results, as well as noise levels in all, were compared in both pacing modes.
Results: We studied 42 consecutive patients, of whom 31 completed both tests (32 by AP, 40 by VP). Compared to AP, VP—MTWA SA had a sensitivity of 93%, specificity of 71%, negative predictive value of 92%, and positive predictive value of 72%. The results were concordant in 25 patients (80%, κ= 0.62, P < 0.001). The noise level was significantly higher during VP than AP (1.4 ± 0.8 vs 1± 0.8, P< 0.01), and there was a trend toward a higher amplitude of TWA by VP (10.7 ± 5.3 vs 7.8 ± 3.9, P = 0.058).
Conclusions: MTWA SA is more likely to be completed during VP than AP. Overall there was concordance between both tests. VP generates higher amplitudes and noise, and a higher percentage of nonnegative results.     

高胆固醇血症家兔心脏单相动作电位及钙电流的特征

目的观察高胆固醇血症对家兔心脏单相动作电位及钙电流的影响。方法24只家兔分为高胆固醇饮食组和对照组各12只,分别给予高胆固醇饲料和标准饲料饲养10周后,检测血脂、心电图和室颤阈值,记录离体灌流心脏单相动作电位,并记录心室肌细胞的L型钙通道电流。结果高胆固醇饮食组兔的血脂水平明显高于对照组(P<0.01);室颤阈值(10.2±1.7)V,低于对照组的(13.9±1.3)V(P<0.05);单相动作电位复极90%的时程(MAPD90)较对照组延长并呈更明显的逆频率依赖性,在1500ms起搏时MAPD90为(348±21)ms,而对照组为(271±16)ms;心室肌细胞的L型钙通道电流密度为(14.7±0.8)pA/pF,明显高于对照组的(10.9±1.1)pA/pF(P<0.01)。结论高胆固醇血症家兔的心脏单相动作电位及心肌细胞L型钙通道电流明显改变,复极时程延长,室颤阈值降低。     

Clinical Significance of QRS Duration During Ventricular Pacing

To clarify the clinical significance of an abnormally prolonged paced QRS duration, we studied 114 patients who had undergone pacing for atrioventricular block (AVB). Patients were divided into two groups: group I consisted of 29 patients with at least one paced QRS duration greater than or equal to 180 msec during the follow-up period; group II consisted of 85 patients with paced QRS durations less than 180 msec. The clinical background, QRS complexes before pacing, and the echocardiographic findings were assessed. Males (P less than 0.05), those with H-V block (P less than 0.05) and a wider QRS complex of conducted and escape beats (both P less than 0.01) were dominant in group I. The incidence of underlying heart disease was greater in group I than in group II (83% vs 32%, P less than 0.01). Reduced left ventricular ejection fraction (LVEF) and increased left ventricular end-diastolic dimension (LVDd) were more prominent in group I than in group II (LVEF 0.49 +/- 0.17 vs 0.68 +/- 0.10, P less than 0.01, LVDd 57.1 +/- 7.9 mm vs 48.5 +/- 5.6 mm, P less than 0.01). The paced QRS duration correlated with LVEF (r = -0.61) and LVDd (r = 0.81). A paced QRS duration greater than or equal to 180 msec was sensitive and specific for a LVEF less than 0.5 (83.3% and 85.2%) and LVDd greater than or equal to 60 mm (100% and 81.4%). We conclude that patients with a prolonged paced QRS duration have more serious heart disease, and the paced QRS duration can be a useful indicator of impaired LV function.     

Relationship of the Effective Refractory Period and Monophasic Action Potential Duration after a Step Increase in Pacing Frequency

Adaptation of effective refractory period (ERP) and monophasic action potential (MAP) shortening after a step increase in drive frequency was determined at adjacent endocardial sites in the right ventricle of six patients without myocardial disease. ERP and MAP shortening occurred simultaneously. ERP shortening and MAP shortening were similar in time course in individuals, although the degree of shortening varied between individuals as the size of the step increase in pacing frequency varied. Shortening of both ERP and MAP was complete after a mean of 67 +/- 7.5 seconds. To allow group analysis, the percent change from baseline of action potential duration and ERP was calculated for each patient at intervals during adaptation and mean percent change for the group plotted against time from the beginning of the step rate increase. A mean step increase in pacing frequency of 49.3% of baseline for the group caused the ERP to shorten by a mean of 18.12%, and MAP90 by 17.43% of baseline. There was no significant difference (P = 0.05) between the action potential and ERP adaptation curves of the group. We conclude that in normal myocardium, there is a close relationship between shortening of ventricular ERP and action potential duration after a change in rate.     

Impact of Right Ventricular Pacing Sites on Exercise Capacity during Ventricular Rate Regularization in Patients with Permanent Atrial Fibrillation

Background: The deleterious effects of right ventricular apical (RVA) pacing may offset the potential benefit of ventricular rate (VR) regularization and rate adaptation during an exercise in patient's atrial fibrillation (AF). Methods: We studied 30 patients with permanent AF and symptomatic bradycardia who receive pacemaker implantation with RVA (n = 15) or right ventricular septal (RVS, n = 15) pacing. All the patients underwent an acute cardiopulmonary exercise testing using VVI‐mode (VVI‐OFF) and VVI‐mode with VR regularization (VRR) algorithm on (VVI‐ON). Results: There were no significant differences in the baseline characteristics between the two groups, except pacing QRS duration was significantly shorter during RVS pacing than RVA pacing (138.9 ± 5 vs 158.4 ± 6.1 ms, P = 0.035). Overall, VVI‐ON mode increased the peak exercise VR, exercise time, metabolic equivalents (METs), and peak oxygen consumption (VO₂max), and decreased the VR variability compared with VVI‐OFF mode during exercise (P < 0.05), suggesting that VRR pacing improved exercise capacity during exercise. However, further analysis on the impact of VRR pacing with different pacing sites revealed that only patients with RVS pacing but not patients with RVA pacing had significant increased exercise time, METs, and VO₂max during VVI‐ON compared with VVI‐OFF, despite similar changes in peaked exercise VR and VR variability. Conclusion: In patients with permanent AF, VRR pacing at RVS, but not at RVA, improved exercise capacity during exercise.     

A Method of Esophageal Electrogram Recording for Diagnostic Atrial and Ventricular Pacing

This study evaluates improvement of the electrogram sensed via an esophageal catheter with the sensing electrode adjacent to the stimulating electrode with and without a specialized artifact suppression system. In 100 patients (65 men and 35 women) aged 16-60 years (mean 48 years), esophageal recordings of left atrial activity were obtained during simultaneous transesophageal atrial pacing. Transesophageal ventricular pacing was performed in an additional 34 patients. Without the suppression system, ventricular paced activity, recorded from the esophagus, was not suitable for interpretation. About 10% of the atrial electrogram response could be recorded and evaluated during atrial pacing. With the stimulus artifact suppression system, interpretable recordings were obtained 100% of the time during atrial and ventricular recordings. The method described allows use of transesophageal diagnostic testing where previously only the intracardiac route was possible.     

Relationship Between Beat-to-Beat Changes in Hemodynamic State and Action Potential Duration of the Left Ventricle During Rapid Ventricular Pacing in Man

A relationship between beat-to-beat changes in hemodynamic state and action potential duration (APD) of the left ventricle was studied by pacing the right ventricle with a constant cycle length (400 msec) for 3 minutes and recording simultaneously the intraarterial pressure and left ventricular monophasic action potential in 16 patients (mean age 51 +/- 8 years) undergoing routine cardiac catheterization. The APD measured at the point of 90% repolarization (APD-90) shortened gradually from a baseline value of 305 +/- 25 msec to a minimum of 246 +/- 25 msec (P less than 0.001) by 160 +/- 10 seconds after the onset of pacing. After reaching the minimum duration, the APD and blood pressure were measured from 30 consecutive beats. The magnitude of beat-to-beat variation in the APD was directly correlated to variation in the mean arterial blood pressure (r = 0.65, P less than 0.01). Beat-to-beat changes in hemodynamic and electrical state were related in that an increase of at least 10 mmHg in the blood pressure of one beat was associated with an increase in the APD of the concomitant beat by at least 5 msec. In six patients with ventriculoatrial dissociation during the rapid ventricular pacing, the sequential ventriculoatrial pacing decreased the beat-to-beat variation of APD from 2.8% +/- 1.4% to 0.8% +/- 0.7% (P less than 0.01) and variation of blood pressure from 6.4% +/- 3.2% to 1.4% +/- 0.9% (P less than 0.01). The observed association between beat-to-beat changes in hemodynamic state and APD of the left ventricle demonstrates that an immediate force-interval relationship exists in the human left ventricle.     

Intermittent Ventricular Standstill During Chronic Atrial Fibrillation in Patients with Dizziness or Syncope

Thirty-two patients with atrial fibrillation and normal ventricular rates who complained of dizziness or loss of consciousness underwent 24-hour ambulatory electrocardiographic monitoring. A control group of 25 patients in atrial fibrillation but without symptoms of dizziness or loss of consciousness was likewise investigated. All patients remained in atrial fibrillation; periods of ventricular standstill (mean, 2.9; range, 1.8-8.0) were present in 31 symptomatic patients but in only three of the control patients (mean, 1.9 s; range, 1.7-2.4). Twenty-three symptomatic patients with pauses greater than or equal to 2.0 s received a demand pacemaker. Following pacing, nineteen became completely asymptomatic; four patients continued to have dizziness but three of these, who also experienced syncope, no longer did so (mean follow-up, 13 months; range, 6-30). It is suggested that ventricular standstill may commonly occur in patients with controlled atrial fibrillation who complain of dizziness or syncope and that the majority will benefit from permanent cardiac pacing.     

Simultaneous Recordings of the Monophasic Action Potential with Silver Chloride- and Ir-Coated Electrodes

Ag AgCI and Ir-coated electrodes allow the recording of the monophasic action potential (MAP) due to their electrical properties like non-polarisability. This study investigates the correlation of MAP recorded with both types of electrodes. In 20 mongrel dogs (18 ± 6 kg) an Ag/AgCI and an Ir-coated catheter (Ir) were placed endo-cardially in the apex of the right ventricle. The effects of isoproterenol and verapamil were investigated during spontaneous rhythm and stimulation simultaneously recorded with both types of electrodes in 10 dogs without AV-node ablation. The correlation at different heart rates were investigated in 10 other dogs with complete AV-block. The morphology and amplitudes of MAP were comparable (AgCl: 15±7 mV; Ir: 13±8 mV). Following an i.v. bolus of 2μg/kg isoproterenol the spontaneous rate increased (175±18 to 245±25 bpm). During stimulation with 250 ms cycle length the duration shortened (MAPd90: AgCl: 160 ± 11 to 130 ± 12 ms; Ir: 154 ± 18 to 128±15 ms). The alterations reversed after 20 mm. An i.v. bolus of 0.2 mg/kg verapamil decreased the spontaneous rate (167±11 to 104 ± 23 bpm) and lengthened the MAPd90 (AgCl: 182 ± 14 to 220±13 ms; Ir: 174 ± 16 to 216, 21 ms) at 300 ms stimulation. The correlation between the MAPd90 of both lead types was r=0.98 during all measurements. Under the effect of beta-agonist and Ca²⁺ -antagonist medication MAP showed a strong correlation recorded with both types of electrodes. Thus, both leads allow the recording of MAP but only the Ir-electrodes with their long-term stability are implantable and allows us to control the effects of drugs with implantable devices.     

Optimizing the Geometry of Implantable Leads for Recording the Monophasic Action Potential with Fractally Coated Electrodes

This study investigates the influence of various lead geometry on intracardial signals like the monophasic action potential (MAP) to optimize the geometry of implantable MAP leads. The experimental results were compared with a field theoretical approach to the origin of MAP from the transmembrane potential (TAP). During the experiments several lead geometries (tip surface: 1.3 to 12 mm²; tip-ring distance: 0.8 mm to 25 cm; ring surface: 1.8mm² to 40 mm²) were investigated in endo- and epicardial positions in 12 dogs (17±9 kg). The electrodes were fixed passively (tines) or actively (screws). MAP was recorded during several interventions and correlated with MAP measured using an Ag-AgCl MAP catheter. The experimental results showed that small tips provided high MAP amplitudes with less pressure. No difference was observed using active and passive fixations. A tip-ring distance smaller than 5 mm with a ring surface smaller than the tip (<5 mm²) avoided artifacts in the repolarization course. For the theoretical approach the quasistatic, anisotropic bidomain model was calculated in smalt unity volumes V_i where the TAP φ_m was constant and represented by the current density J. Two solutions for electrode positions at and outside the heart were achieved. By superposition of each solution φ_ei the summed potential at the electrode position was calculated. The theoretical findings show in good correlation with the experimental results that a larger distance than 10 mm leads to distortions in repolarization course by signals proportional to φ_out.     

Global Repolarization Sequence of the Ventricular Endocardium: Monophasic Action Potential Mapping in Swine and Humans

The aim of this study was to evaluate the global sequence of repolarization over the ventricular endocardium. Disturbances in myocardial repolarization are associated with the genesis of arrhythmias. However, little is known about the global sequence of repolarization. Monophasic action potentials (MAPs) were recordedfrom 61 +/- 18 LV and/or RV sites in ten healthy pigs and from 43 +/- 15 LV or RV sites in eight patients using the CARTO system. Local activation time (AT), end-of-repolarization (EOR) time, and MAP duration were calculated and three-dimensional global maps of AT, EOR, and MAP duration constructed. LV maps were obtained from all ten pigs and RV maps from three pigs. Five RV maps and five LV maps were obtained from the eight patients. (1) EOR sequence was recognizable in 12 of 13 pig maps and in all the patient maps. (2) EOR followed the sequence of activation in 12 of 13 pig maps and 8 of 10 patient maps. (3) The longest MAPs were recorded in or near the earliest activation area, and the shortest ones in or near the latest activation area in all the pig maps and in nine often and eight often patient maps, respectively. (4) In all maps, MAP duration and AT were negatively correlated, and EOR and AT positively correlated. In conclusion, repolarization gradients exist over the pig and the human ventricular endocardium. The activation sequence is a determinant for the repolarization sequence. The magnitude of the progressive MAP shortening with progressively later activation, relative to local AT, is a critical factor governing the direction and pattern of the EOR.