Recurrent Episodes of Fluid Retention in a Patient with Heart Failure and Chronic Kidney Disease: The Additional Value of Implantable Monitoring Systems.

The additional role of continuous monitoring of filling pressures and impedance in heart failure patients with chronic kidney disease remains undetermined. In this case report, the effects of diuretic therapy and renal replacement therapy by hemodialysis upon right ventricular filling pressures and impedance are described in a patient with end-stage heart failure and end-stage chronic kidney disease (grade 5). We demonstrated that unloading of the heart by hemodialysis partly restored the blunted Frank-Starling relationship.

Impact of atrial programmed electrical stimulation techniques on unipolar electrogram morphology.

INTRODUCTION: Intra-atrial conduction abnormalities are associated with the development of atrial fibrillation (AF) and cause morphological changes of the unipolar atrial electrogram (U-AEGM). This study examined the impact of different atrial programmed electrical stimulation (APES) protocols on U-AEGM morphology to identify the most optimal APES protocol provoking conduction abnormalities. METHODS: APES techniques (14 protocols) were applied in 30 patients referred for an electrophysiology study, consisting of fixed rate, extra, and decremental stimuli at different frequencies. U-AEGM morphologies including width, amplitude, and fractionation for patients without (control group) and with a history of AF (AF group) were examined during APES. In addition, sinus rhythm (SR) U-AEGMs preceding different APES protocols were compared to evaluate the morphology stability over time. RESULTS: U-AEGM morphologies during SR before the APES protocols were comparable (all P > .396). Atrial refractoriness was longer in the AF group compared to the control group (298 ± 48 vs 255 ± 33 ms; P ≤ .020), but did not differ between AF patients with and without amiodarone therapy (278 ± 48 vs 311 ± 40 ms; P ≥ .126). Compared to the initial SR morphology, U-AEGM width, amplitude, and fractionation changed significantly during the 14 different APES protocols, particularly in the AF group. In both groups, U-AEGM changes in morphology were most pronounced during fixed-rate stimulation with extra stimuli (8S1-S2 = 400-250 ms). CONCLUSION: APES results in significant changes in U-AEGM morphology, including width, amplitude, and fractionation. The impact of APES differed between APES sequence and between patients with and without AF. These findings suggest that APES could be useful to identify AF-related conduction abnormalities in the individual patient.

Cardioversion of persistent atrial fibrillation is associated with a 24-hour relapse gap: Observations from prolonged postcardioversion rhythm monitoring.

BACKGROUND: Many recurrences occur after electrical cardioversion (ECV) of atrial fibrillation (AF). Assessment of extent of remodeling and continuous prolonged rhythm monitoring might reveal actionable recurrence mechanisms. HYPOTHESIS: After ECV of AF specific patterns of arrhythmia recurrence can be distinguished. METHODS: All patients who underwent successful ECV due to persistent AF were included. Tissue velocity echocardiography during AF was performed before ECV to study atrial fibrillatory cycle length and fibrillatory velocity. After ECV, the heart rhythm of all patients was monitored 3 times daily during 4 weeks, and timing of recurrence was noted. RESULTS: In total, 50 patients (68% male) were included; mean age was 68 ± 9 years. Median duration of the current AF episode was 102 (range, 74-152) days. Twenty-one (42%) patients showed recurrence of persistent AF. No recurrences occurred during the first 24 hours. There were no differences in clinical characteristics between patients with or without recurrence of AF. However, patients with early recurrence of AF had significantly higher precardioversion wall-motion velocity compared with patients who remained in sinus rhythm (2.8 [1.6-3.6] vs 1.4 [0.9-3.3] cm/s; P = 0.017), whereas atrial fibrillatory cycle length did not differ. CONCLUSIONS: In this study on 50 patients successfully cardioverted for persistent AF, there was a relapse gap of ≥24 hours. This phenomenon has not been well appreciated before and offers an AF-free window of opportunity for electrocardiographically triggered cardiac imaging or complex electrophysiological procedures. Echocardiographic tissue velocity imaging may visualize atrial remodeling relevant to AF recurrence.

Bipolar electrograms characteristics at the left atrial-pulmonary vein junction: Toward a new algorithm for automated verification of pulmonary vein isolation.

BACKGROUND: Verification of pulmonary vein isolation (PVI) is challenging because of the coexistence of PV and far-field potentials in bipolar electrograms recorded at the left atrial-pulmonary vein (LA-PV) junction. OBJECTIVE: The purpose of this study was to characterize algorithmically LA-PV potentials before and after PVI and to develop an algorithm to differentiate nonisolated from isolated PVs. METHODS: In 61 patients, we characterized-by type (morphology) and parameters-1440 electrograms recorded during sinus rhythm before and after PVI. Based on vein-dependent prevalence of a given type before and after PVI (first step) and based on vein- and type-dependent cutoff values in parameters specific for recordings before and after PVI (second step), we developed a 2-step algorithm to differentiate nonisolated from isolated PVs. We prospectively validated this algorithm in another dataset of 20 patients. RESULTS: Characteristics before and after PVI were as follows: low voltage (10% ± 7% vs 36% ± 15%), monophasic (13% ± 4% vs 27% ± 9%), biphasic (18% ± 4% vs 21% ± 9%), triphasic (22% ± 5% vs 11% ± 13%), multiphasic (26% ± 7% vs 3% ± 3%), double potentials (11% ± 5% vs 2% ± 1%), peak-to-peak amplitude (0.97 ± 0.21 mV vs 0.35 ± 0.23 mV), maximal slope (0.179 ± 0.033 mV/ms vs 0.071 ± 0.029 mV/ms), minimal slope (0.030 ± 0.003 mV/ms vs 0.024 ± 0.002 mV/ms), and sharpest peak (1.82° ± 0.26° vs 3.45° ± 0.85°, P < .01 for all except biphasic). Overall sensitivity and specificity of the 2-step algorithm was 100% and 87%, respectively. CONCLUSION: We algorithmically characterized LA-PV potentials before and after PVI in a large dataset (library of types and parameters). This library enabled us to develop an accurate 2-step algorithm to automatically differentiate nonisolated from isolated PVs. The 2-step algorithm is objective and reliable for assessing PV isolation without the need for pacing maneuvers.

Novel algorithmic methods in mapping of atrial and ventricular tachycardia.

BACKGROUND: Conventional methods to assess local activation time (LAT) detect the peak of the bipolar electrogram (B-LATPeak) or the maximal negative slope of the unipolar electrogram (U-LATSlope). We evaluated 3 novel methods to assess LAT: onset (B-LATOnset) and center of mass (B-LATCoM) of bipolar electrogram, and maximal negative slope of unipolar electrogram within a predefined bipolar window (U-LATSlope-hybrid). METHODS AND RESULTS: In 1753 atrial tachycardia and 1426 ventricular tachycardia recordings, the performance of the methods in detecting LAT was evaluated pair-wise (eg, B-LATPeak versus B-LATOnset). For each comparison, histogram analysis of the differences in LAT values was performed. Variation in differences (P95-P5) in low quality (LQ) was compared with high-quality electrograms. In a separate data set (12 atrial tachycardia and 10 ventricular tachycardia), we evaluated for each method the accuracy in algorithmic activation mapping. Both in atrial tachycardia and ventricular tachycardia, the variation in difference between the conventional and novel methods was larger in LQ electrograms. In contrast, variation in difference between the novel methods was comparable in LQ and high-quality electrograms. Except for LATSlope-hybrid, all methods showed decreased mapping accuracy with increasing percentage of LQ electrograms. U-LATSlope-hybrid accurately mapped activation in 16 out of 22 maps (versus B-LATCoM, 14; B-LATPeak, 14; B-LATOnset, 13; U-LATSlope, 4). CONCLUSIONS: In LQ atrial and ventricular electrograms, the novel LAT methods (B-LATOnset, B-LATCoM, and U-LATSlope-hybrid) show less variation than the conventional methods. The U-LATSlope-hybrid, a hybrid method that accurately detects the maximal negative unipolar slope, is associated with the highest accuracy in algorithmic mapping of atrial tachycardia/ventricular tachycardia.

Histogram analysis: a novel method to detect and differentiate fractionated electrograms during atrial fibrillation.

INTRODUCTION: Complex fractionated atrial electrograms (CFAEs) might identify the critical substrate maintaining AF. We developed a method based upon histogram analysis of interpeak intervals (IPIs) to automatically quantify fractionation and differentiate between subtypes of CFAEs. METHODS: Two experts classified 1,681 fibrillatory electrograms recorded in 13 patients with persistent AF into 3 categories (gold standard): normal electrograms, discontinuous CFAEs, or continuous CFAEs. Histogram analysis of IPI was performed to calculate the P5, P50, P95, and the mean of IPIs, in addition to the total number of IPI (N(Total)), and the number of IPI within predetermined ranges: 10-60 (N(Short)), 60-120 (N(Intermediate)), and >120 ms (N(Long)). RESULTS: P50 and N(Long) were higher in the normal electrograms compared to the other 2 categories (P < 0.001). N(Intermediate) was higher in the discontinuous CFAE category compared to the other 2 categories. P95, mean IPI, N(Total), and N(Short) were all significantly different among the 3 categories (P < 0.001) and correlated with the degree of fractionation (r =-0.52, -0.55, 0.68, and 0.67, respectively). Receiver operating characteristic (ROC) curves showed good diagnostic accuracy (area under curve, AUC > 0.8) of P50 and N(Long) to detect normal electrograms. An algorithm using N(Intermediate) showed good diagnostic accuracy (AUC > 0.7) to detect discontinuous CFAEs, whereas P95, mean, N(Total), and N(Short) all revealed high diagnostic accuracy (AUC > 0.85) to detect continuous CFAEs. This was confirmed in a prospective data set. CONCLUSIONS: Histogram analysis of IPI can differentiate between normal electrograms, discontinuous and continuous fractionated electrograms. This method might be used to standardize and optimize ablation strategies in AF.

Electropathological substrate of longstanding persistent atrial fibrillation in patients with structural heart disease: epicardial breakthrough.

BACKGROUND: During persistent atrial fibrillation (AF), waves with a focal spread of activation are frequently observed. The origin of these waves and their relevance for the persistence of AF are unknown. METHODS AND RESULTS: In 24 patients with longstanding persistent AF and structural heart disease, high-density mapping of the right and left atria was performed during cardiac surgery. In a reference group of 25 patients, AF was induced by rapid pacing. For data analysis, a mapping algorithm was developed that separated the fibrillatory process into its individual wavelets and identified waves with a focal origin. During persistent AF, the incidence of focal fibrillation waves in the right atrium was almost 4-fold higher than during acute AF (median, 0.46 versus 0.12 per cycle per 1 cm² (25th to 75th percentile, 0.40 to 0.77 and 0.01 to 0.27; P<0.0001). They were widely distributed over both atria and were recorded at 46 ± 18 of all electrodes. A large majority (90.5) occurred as single events. Repetitive focal activity (>3) happened in only 0.8. The coupling interval was not more than 11 ms shorter than the average AF cycle length (P=0.04), and they were not preceded by a long interval. Unipolar electrograms at the site of origin showed small but clear R waves. These data favor epicardial breakthrough rather than a cellular focal mechanism as the underlying mechanism. Often, conduction from a site of epicardial breakthrough was blocked in 1 or more directions. This generated separate multiple wave fronts propagating in different directions over the epicardium. CONCLUSIONS: Focal fibrillation waves are due to epicardial breakthrough of waves propagating in deeper layers of the atrial wall. In patients with longstanding AF, the frequency of epicardial breakthroughs was 4 times higher than during acute AF. Because they provide a constant source of independent fibrillation waves originating over the entire epicardial surface, they offer an adequate explanation for the high persistence of AF in patients with structural heart disease.

Electropathological substrate of long-standing persistent atrial fibrillation in patients with structural heart disease: longitudinal dissociation.

BACKGROUND: The electropathological substrate of persistent atrial fibrillation (AF) in humans is largely unknown. The aim of this study was to compare the spatiotemporal characteristics of the fibrillatory process in patients with normal sinus rhythm and long-standing persistent AF. METHODS AND RESULTS: During cardiac surgery, epicardial mapping (244 electrodes) of the right atrium (RA), the left lateral wall (LA), and the posterior left atrium (PV) was performed in 24 patients with long-standing persistent AF. Twenty-five patients with normal sinus rhythm, in whom AF was induced by rapid pacing, served as a reference group. A mapping algorithm was developed that separated the complex fibrillation process into its individual elements (wave mapping). Parameters used to characterize the substrate of AF were (1) the total length of interwave conduction block, (2) the number of fibrillation waves, and (3) the ratio of block to collision of fibrillation waves (dissociation index). In 4403 maps of persistent AF, no evidence for the presence of stable foci or rotors was found. Instead, many narrow wavelets propagated simultaneously through the atrial wall. The lateral boundaries of these waves were formed by lines of interwave conduction block, predominantly oriented parallel to the atrial musculature. Lines of block were not fixed but continuously changed on a beat-to-beat basis. In patients with persistent AF, the total length of block in the RA was more than 6-fold higher than during acute AF (median, 21.1 versus 3.4 mm/cm(2); P<0.0001). The highest degree of interwave conduction block was found in the PV area (33.0 mm/cm(2)). The number of fibrillation waves during persistent AF was 4.5/cm(2) compared with 2.3 during acute AF, and the dissociation index was 7.3 versus 1.5 (P<0.0001). The interindividual variation of these parameters among patients was high. CONCLUSIONS: Electric dissociation of neighboring atrial muscle bundles is a key element in the development of the substrate of human AF. The degree of the pathological changes can be measured on an individual basis by electrophysiological parameters in the spatial domain.

Continuous monitoring of intrathoracic impedance and right ventricular pressures in patients with heart failure.

BACKGROUND: Hemodynamic monitoring using implantable devices may provide early warning of volume overload in patients with heart failure (HF). This study was designed to prospectively compare information from intrathoracic impedance monitoring and continuous right ventricular pressure measurements in patients with HF. METHODS AND RESULTS: Sixteen patients with HF (age, 63.5+/-13.8 years; left ventricular ejection fraction, 23.2+/-11.3%; New York Heart Association, II and III) and a previous HF decompensation received both a cardiac resynchronization therapy defibrillator providing a daily average of intrathoracic impedance and an implantable hemodynamic monitor providing an estimate of the pulmonary artery diastolic pressure. At the end of a 6-month investigator-blinded period, baseline reference hemodynamic values were determined over 4 weeks during which the patient was clinically stable. A major HF event was defined as HF decompensation requiring hospitalization, IV diuretic treatment, or leading to death. Sixteen major HF events occurred in 10 patients. Within 30 days and 14 days before a major HF event, impedance decreased by 0.12+/-0.21 Omega/d and 0.20+/-0.20 Omega/d, respectively, whereas estimated pulmonary arterial diastolic pressure increased by 0.10+/-0.20 mm Hg/d and 0.16+/-0.15 mm Hg/d, respectively. During these periods, impedance decreased by 3.8+/-5.4 Omega (P<0.02) and 4.9+/-6.1 Omega (P<0.007), respectively, whereas estimated pulmonary arterial diastolic pressure increased by 5.8+/-5.7 mm Hg (P<0.002) and 6.8+/-6.1 mm Hg (P<0.001), respectively, compared with baseline. In all patients, impedance and estimated pulmonary arterial diastolic pressure were inversely correlated (r = -0.48+/-0.25). Within 30 days preceding a major HF event, this correlation improved to r =-0.58+/-0.24. CONCLUSIONS: Decompensated HF develops based on hemodynamic derangements and is preceded by significant changes in intrathoracic impedance and right ventricular pressures during the month prior to a major clinical event. Impedance and pressure changes are moderately correlated. Future research may establish the complementary contribution of both parameters to guide diagnosis and management of patients with HF by implantable devices.

Analysis of fractionated atrial fibrillation electrograms by wavelet decomposition.

This study introduces the use of wavelet decomposition of unipolar fibrillation electrograms for the automatic detection of local activation times during complex atrial fibrillation (AF). The purpose of this study was to evaluate this technique in patients with structural heart disease and longstanding persistent AF. In 46 patients undergoing cardiac surgery, unipolar fibrillation electrograms were recorded from the right atrium, using a mapping array of 244 electrodes. In 25 patients with normal sinus rhythm, AF was induced by rapid pacing, whereas 21 patients were in persistent AF. In patients with longstanding AF, the atrial electrograms showed a high degree of fractionation. In each patient, 12 s of AF were analyzed by wavelet transformation (15 scales). The finest scales (1-7) were used to reconstruct a "local" fibrillation electrogram, whereas with the coarse scales (9-15), a far-field signal was generated. With these local and far-field electrograms, the "primary" fibrillation potentials, due to wave propagation underneath the electrode, could be distinguished from double potentials and multiple components generated by remote wavefronts. Wavelet transformation resulted in AF histograms with a closely gaussian distribution and the automatically generated activation maps showed a good resemblance with fibrillation maps obtained by laborious manual editing. A special chaining algorithm was developed to detect multiple components in fractionated electrograms. The degree of fractionation showed a positive correlation with the complexity of fibrillation, thus providing an objective quantification of the degree of electrical dissociation of the atria. Wavelet transformation can be a useful technique to detect the primary potentials and quantify the degree of fractionation of fibrillation electrograms. This could enable real-time mapping of complex cases of human AF and classification of the underlying electropathological substrate.

QRS integral: an electrocardiographic indicator of mechanical interventricular asynchrony.

AIM: The aim of this study was to investigate whether interventricular asynchrony (IVA) can be measured by electrocardiography. METHODS: Sixty-two patients (New York Heart Association heart failure functional class III: age, mean +/- SD: 64 +/- 9 years; ejection fraction, mean +/- SD: 24% +/- 8%; dilative cardiomyopathy/ischemic cardiomyopathy, n = 39/23) with left bundle branch block (QRS duration, mean +/- SD: 165 +/- 21 milliseconds) underwent a 120-channel body surface mapping. QRS integral was analyzed and compared with IVA (echo). RESULTS: Interventricular asynchrony was associated with significantly decreased QRS integrals 15 cm cranial and 6 cm lateral from V1 in patients with normal axis (n = 36): At a cutoff value of -26 milliseconds mV, receiver operating characteristic analysis to predict IVA revealed a sensitivity of 89% and a specificity of 83% (area under curve, mean +/- SEM: 0.9 +/- 0.07; P < .001). In patients with left axis deviation (n = 26), IVA showed significantly decreased QRS integrals 10 cm caudal from V1: at a cutoff value of -89 milliseconds mV, receiver operating characteristic analysis to predict IVA revealed a sensitivity of 83% and a specificity of 100% (area under curve, mean +/- SEM: 0.9 +/- 0.07; P < .002). CONCLUSIONS: Interventricular asynchrony strongly correlates with QRS integral. Key lead positions, however, are axis dependent and outside standard leads.

Changes in P-wave area and P-wave duration after circumferential pulmonary vein isolation.

AIMS: The effect of circumferential pulmonary vein isolation (CPVI) on P-wave characteristics is not clear. We used the signal-averaged (SA) electrocardiogram (ECG) and the ECG derived vector cardiogram (dVCG) to study the influence of CPVI on P-wave duration (PWD) and P-wave area (PWA) and studied whether changes were associated with successful outcome after initial CPVI. METHODS AND RESULTS: Thirty-nine patients (56 +/- 10 years, 72% males) underwent CPVI for paroxysmal or persistent atrial fibrillation (AF). For each patient, an ECG recording was taken at the start and end of the ablation procedure. dVCG was derived using the inverse Dower transform. PWD was defined by manual annotation of earliest onset and latest offset of the SA-P-wave. PWA was calculated as the area under the SA-ECG curve averaged for the 12 ECG leads (PWA-ECG) and SA-dVCG curve (PWA-dVCG). Successful outcome after CPVI was defined as freedom from symptomatic and asymptomatic AF at the end of follow-up (11 +/- 5 months). Average PWD decreased from 132 +/- 14 to 126 +/- 16 ms (P < 0.01). PWA-ECG and PWA-dVCG decreased markedly from 4.64 +/- 1.40 to 3.65 +/- 1.61 mVms (P < 0.001) and from 4.27 +/- 1.66 to 2.48 +/- 1.59 mVms (P < 0.001). Parameters of PWA were not different between successes (n = 31) and failures (n = 8). In contrast, PWD after ablation was significantly shorter in patients with successful outcome (123 +/- 16 vs. 135 +/- 11 ms, P < 0.05). CONCLUSION: (i) CPVI results in a modest but significant shortening in PWD and a marked decrease in PWA. (ii) PWD was significantly shorter in cases of successful outcome after CPVI.

Improving sensing and detection performance in subcutaneous monitors.

Implantable loop recorders (ILRs) are used for continuous assessment of patients at risk for syncope and arrhythmia. Device accuracy depends on appropriate sensing of the patient's electrocardiogram (ECG) signal. However, current methods for sensing cardiac electrical activity rely on simple threshold detectors that are computationally efficient but nonspecific. We test the hypothesis that better ILR implant positions will increase detection accuracy. Ten healthy subjects were studied as they assumed 12 different postures. Body surface potential map (BSM) recordings were used to estimate bipolar R-wave amplitudes for 64 potential implant sites at 360 orientations per site. Optimal sites were identified as the combination of position and orientation that consistently gave the largest signal and the lowest variability during posture changes. Results showed that posture impacts the R-wave amplitude in both BSM and derived bipolar ECGs in healthy subjects. Specific postures are associated with significant drops in R-wave signal amplitude that could cause loss of signal detection in ILRs, especially in positions likely to displace the diaphragm. R-wave changes occurred abruptly as posture was changed. Optimal implant locations cluster near the center of the chest, aligned with the cardiac axis, consistent with the steeper isoelectric gradients known to be associated with these positions.

Incidence, timing, and characteristics of acute changes in heart rate during ongoing circumferential pulmonary vein isolation.

AIMS: Previous studies showed that catheter ablation of atrial fibrillation (AF) results in vagal denervation with an increase in average heart rate (HR) and a reduced overall HR variability (HRV) at follow-up. We analysed acute ablation-induced changes in HR and short-term HRV during percutaneous circumferential pulmonary vein isolation (CPVI). We also studied whether observed changes were predictors of successful outcome after first CPVI. METHODS AND RESULTS: A total of 46 patients (35 men, 55 +/- 10 years) undergoing CARTO and computed tomography-guided CPVI for symptomatic AF were studied. Circumferential pulmonary vein isolation was performed under general anaesthesia by widely encircling the left and right pulmonary veins during sinus rhythm (SR). Radiofrequency (RF) current (35W, 48 degrees C) was applied with a 3.5 mm open irrigated tip catheter (Navistar Thermocool, Biosense Webster, Diamond Bar, CA, USA). Time- and frequency-domain analysis of short-term HRV was performed using 5 min electrocardiogram (ECG) recordings obtained at the beginning and the end of the CPVI procedure. Sinus rhythm cycle length was monitored continuously during CPVI. Circumferential pulmonary vein isolation was performed with 119 +/- 25 RF applications. Mean HR increased from 54 +/- 8 to 62 +/- 9 bpm (P < 0.001). Heart rate variability was significantly reduced (SDNN from 34 +/- 30 ms to 14 +/- 17 ms, P < 0.001, RMSSD from 27 +/- 22 ms to 13 +/- 14 ms, P < 0.001) with a marked change in sympathovagal balance towards less vagal activity (low frequency (LF)/high frequency (HF) ratio from 3.94 +/- 0.33 to 4.20 +/- 0.17, P < 0.001). Changes in RR interval, SDNN, and LF/HF ratio correlated significantly with RR interval (R = 0.56, P < 0.001), SDNN (R = 0.84, P < 0.001), and LF/HF ratio (R = -0.74, P < 0.001) at baseline. There were acute changes during ablation in HR and HRV, at the antero-superior junction between the left atrium (LA) and the right superior pulmonary vein (RSPV) in 36 patients (78%). Both HR and HRV at baseline and changes in HR/HRV were comparable between successful (n = 36) and failed (n = 10) patients. CONCLUSION: (i) Percutaneous CPVI induces acute acceleration of HR and attenuation of short-term HRV (indicating vagal denervation during the procedure). (ii) Acute changes in HR and its variability invariably occur during RF energy delivery at the antero-superior junction between the LA and the RSPV. (iii) The degree of HR and short-term HRV changes depend on the vagal tone at the beginning of the procedure. (iv) In contrast to previously reported changes in overall HRV, acute changes in HR during the procedure are no predictors of long-term clinical outcome after CPVI.

Impact of sampling rate reduction on automatic ECG delineation.

Electrogram (EGM) delineation is an increasingly important task to be performed in implantable cardiac devices such as pacemakers and defibrillators. Reliable detection and classification of EGM components might help to minimize the risk of false detections. Efforts are therefore undertaken to examine whether existing ECG delineators can be adapted for the delineation of EGMs. One issue to be solved is the low sampling rate at which EGMs are acquired. In this study we investigate performance degradation of an existing wavelet-based ECG delineator by a stepwise reduction of the sampling rate. It is shown that for signals sampled at 1 kHz, no significant performance degradation occurs in P or T wave delineation. The performance of QRS delineation is affected only at the lowest sampling rate of 62.5 Hz. For signals originally sampled at 250 Hz, no degradation in delineation performance is observed. It is concluded that the automatic delineation of ECGs can be performed at sampling rates as low as 62.5 Hz and that the low sampling rate does not significantly degrade the reliability of automatic delineation.

Automatic mapping of human atrial fibrillation by template matching.

BACKGROUND: The high spatiotemporal variation in morphology of fibrillation electrograms makes mapping of atrial fibrillation (AF) a difficult and burdensome task. OBJECTIVES: The purpose of this study was to evaluate the results of automatic detection of fibrillation electrograms by a template matching technique. METHODS: During cardiac surgery in 25 patients without a history of AF, paroxysms of AF were induced by rapid atrial pacing. A mapping array of 244 unipolar electrodes (3.6-cm diameter, 2.25-mm interelectrode distance) was positioned on the free wall of the right atrium. All fibrillation electrograms were correlated with a mathematically constructed library of 128 potentials of different duration, RS ratio, and short double components. The moments of maximal correlation, coinciding with the negative deflection in the fibrillation potentials, were used to create fibrillation maps. RESULTS: In each patient, a segment of 18.6 +/- 3.8 seconds of AF was analyzed, resulting in 80 to 130 maps per patient. The output of the automatic algorithm was compared with careful manual analysis by an experienced investigator. Of the total database of 398,796 fibrillation potentials, 93.6% +/- 4.2% resulted in a good correlation with one of the templates in the library (correlation coefficient >= 0.7). At a correlation threshold of 0.6, on average template matching yielded slightly more false-positive than false-negative detections (sensitivity 96.6% +/- 2.5%, positive predictive value 94.3% +/- 5.4%). The majority of false-positive detections were due to electrotonic potentials recorded along the lateral boundaries of the fibrillation waves. This led to a slight overlap of fibrillation waves but not to false detection of nonexisting wavefronts. Undersensing was mainly due to the presence of long double and fractionated potentials (2.6%) that were not represented in the template library. Fractionated parts in the electrograms were identified by failure of template matching and can be analyzed separately. CONCLUSION: Template matching is a useful technique for characterizing unipolar fibrillation electrograms and for visualizing the complex activation patterns during AF. It allows automatic evaluation of the electropathologic substrate of AF on an individual basis.