Utility and Limitations of Ablation Index for Guiding Therapy in Ventricular Myocardium.

BACKGROUND: Ablation index (AI) is used for guiding therapy during pulmonary vein isolation. However, its potential utility in ventricular myocardium is unknown. OBJECTIVES: This study sought to examine the correlation between AI and lesion dimensions in healthy and infarcted ventricles. METHODS: In ex vivo experiments using healthy swine ventricles, the correlation between AI (400-1,200) and lesion dimensions was examined at fixed power (30 W) and contact force (CF) (15 g). To examine the accuracy of AI in predicting lesion dimensions created by different combinations of ablation parameters, applications with a similar prespecified AI value created using different power (30 vs 40 W), CF (15 vs 25 g) or impedance (130-170 Ω) were created. In in vivo experiments, the correlation between AI and lesion dimensions was examined in healthy and infarcted myocardium. RESULTS: Ex vivo experiments (247 lesions, 36 hearts) showed good correlation between AI and lesion depth (R = 0.93; P < 0.001). However, in vivo experiments (9 healthy swine and 10 infarcted swine) showed moderate correlation in healthy myocardium (R = 0.64; P < 0.01) and poor correlation in infarcted myocardium (R = 0.23; P = 0.61). AI values achieved using different combinations of power, CF, and baseline impedance resulted in different lesion depths: Ablation at 30 W produced deeper lesions compared with 40 W, ablation with CF of 15 g produced deeper lesions compared with CF of 25 g, and ablation at lower impedance produced larger lesions at similar prespecified AI values (P < 0.01 for all). CONCLUSIONS: AI has limited value for guiding ablation in ventricular myocardium, particularly scar. This may be related to small proportional significance of application duration and complex tissue architecture.

Atrial Endocardial Unipolar Voltage Mapping for Detection of Viable Intramural Myocardium: A Proof-of-Concept Study.

BACKGROUND: Endocardial bipolar voltage amplitude is largely derived from endocardial and subendocardial wall layers. This may result in situations of low bipolar voltage amplitude despite the presence of mid-myocardial including epicardial (ie, intramural-epicardial) viable myocardium. This study examined the utility of endocardial unipolar voltage mapping for detection of viable intramural-epicardial atrial myocardium. METHODS: In 15 swine, an atrial intercaval ablation line with an intentional gap was created. Animals survived for 6 to 8 weeks before electroanatomical mapping followed by sacrifice. Gaps were determined by the presence of electrical conduction and classified based on the histopathologiclly layer(s) of viable myocardium into the following: (1) transmural, (2) endocardial, and (3) intramural-epicardial. Voltage data from healthy, scar, and gap points were exported into excel. The sensitivity and specificity of bipolar and unipolar voltage amplitude to detect intramural-epicardial gaps were compared using receiver operating characteristic analysis. RESULTS: In 9 of 15 (60%) swine, a focal ablation gap was detected in the intercaval line, while in the remainder 6 of 15 (40%), the line was complete without gaps. Gaps were classified into transmural (n=3), endocardial (n=3), or intramural-epicardial (n=3). Intramural-epicardial gaps were characterized by very low bipolar voltage amplitude that was similar to areas with transmural scar (P=0.91). In comparison, unipolar voltage amplitude in intramural-epicardial gaps was significantly higher compared to transmural scar (P<0.001). Unipolar voltage amplitude had higher sensitivity (93% versus 14%, respectively) and similar specificity (95% versus 98%, respectively) to bipolar voltage for detection of intramural-epicardial gaps. CONCLUSIONS: Atrial unipolar voltage mapping may be a useful technique for identifying viable intramural-epicardial myocardium in patients with endocardial scar.

Effect of Pulsed-Field and Radiofrequency Ablation on Heterogeneous Ventricular Scar in a Swine Model of Healed Myocardial Infarction.

BACKGROUND: Pulsed-field ablation (PFA) is a nonthermal energy with higher selectivity to myocardial tissue in comparison to radiofrequency ablation (RFA). We compared the effects of PFA and RFA on heterogeneous ventricular scar in a swine model of healed infarction. METHODS: In 9 swine, myocardial infarction was created by balloon occlusion of the left anterior descending artery. After a survival period of 8 to 10 weeks, ablation with PFA or RFA was performed at infarct border zones identified by abnormal electrograms. In the PFA group (4 swine), ablation was performed with a lattice catheter (Sphere-9, Affera, Inc). In the RFA group (5 swine), ablation was performed using a 3.5-mm tip catheter (Thermocool ST-SF; Biosense Webster). To further investigate the effect of RFA on temperature development in scar tissue, intramyocardial temperature was measured in healthy and infarcted myocardium using an ex vivo bath model. RESULTS: A total of 11 PFA and 15 RFA lesions were created at infarct border zones with heterogeneous scar. PFA produced uniform and well-demarcated lesions exhibiting irreversible injury characterized by cardiomyocyte death, contraction bands, and lymphocytic infiltration. This effect of PFA extended from the subendocardium through collagen and fat to the epicardial layers. In contrast, the effect of RFA is less uniform and largely limited to the subendocardium with minimal effect on viable myocardium deeper to separating layers of collagen and fat. PFA produced deeper and more transmural lesions (6.4 [interquartile range, 5.5-7.5) versus 5.4 [interquartile range, 4.8-5.9]), 72% versus 30%, respectively; P≤0.02 for each comparison). The limited effect of RFA on viable myocardium at deeper infarct layers was related to a lower intramyocardial maximal temperature compared with healthy myocardium (P=0.01). CONCLUSIONS: PFA may be advantageous for ablation in ventricular scar, producing lesions that unlike RFA are not limited to the subendocardium, but also eliminate viable myocardium separated from the catheter by collagen and fat.

Increasing Lesion Dimensions of Bipolar Ablation by Modulating the Surface Area of the Return Electrode.

OBJECTIVES: This study sought to examine the effect of the return electrode's surface area on bipolar RFA lesion size. BACKGROUND: Bipolar radiofrequency ablation (RFA) is typically performed between 2 3.5-mm tip catheters serving as active and return electrodes. We hypothesized that increasing the surface area of the return electrode would increase lesion dimensions by reducing the circuit impedance, thus increasing the current into a larger tissue volume enclosed between the electrodes. METHODS: In step 1, ex vivo bipolar RFA was performed between 3.5-mm and custom-made return electrodes with increasing surface areas (20, 80, 180 mm2). In step 2, ex vivo bipolar RFA was performed between 3.5-mm and 3.5-mm or 8-mm electrode catheters positioned perpendicular or parallel to the tissue. In step 3, in vivo bipolar RFA was performed between 3.5-mm and either 3.5-mm or 8-mm parallel electrode at the: 1) left ventricular summit; 2) interventricular septum; and 3) healed anterior infarction. RESULTS: In step 1, increasing the surface area of the return electrode resulted in lower circuit impedance (R = -0.65; P < 0.001), higher current (R = +0.80; P < 0.001), and larger lesion volume (R = +0.88; P < 0.001). In step 2, an 8-mm return electrode parallel to tissue produced larger and deeper lesions compared with a 3.5-mm return electrode (P = 0.014 and P = 0.02). Similarly, in step 3, compared with a 3.5-mm, bipolar RFA with an 8-mm return electrode produced larger (volume: 1,525 ± 871 mm3 vs 306 ± 310 mm3, respectively; P < 0.001) and more transmural lesions (88% vs 0%; P < 0.001). CONCLUSIONS: Bipolar RFA using an 8-mm return electrode positioned parallel to the tissue produces larger lesions in comparison with a 3.5-mm return electrode.

How to use bipolar and unipolar electrograms for selecting successful ablation sites of ventricular premature contractions.

BACKGROUND: Local activation time is often determined by the maximal negative of the extracellular unipolar potential (-dV/dTmax). While this is accurate in 2-dimensional uniform tissue, propagation through nonuniform or 3-dimensional structures have shown discordance between -dV/dTmax and local activation time. OBJECTIVE: The purpose of this study was to examine the relationship between bipolar and unipolar electrograms for selecting successful ablation sites of endocardial (superficial) vs intramural (deep) ventricular premature contractions (VPCs). METHODS: This cohort consisted of 66 patients with VPCs presenting for ablation in a bigeminy, trigeminy, or quadrigeminy pattern. VPCs were classified as endocardial if ablation at the earliest endocardial site resulted in immediate suppression (<10 seconds) or as intramural if ablation resulted in delayed suppression (≥10 seconds), required multiple applications, or was not achieved. Unipolar and bipolar electrograms were analyzed. RESULTS: In endocardial VPCs, the first rapid bipolar deflection corresponded with unipolar -dV/dTmax, occurring 20.5 ms (17.8-26.0 ms) and 16.0 ms (6.8-22.0 ms), respectively, before the QRS onset. In successfully ablated intramural VPCs, the first rapid bipolar deflection preceded the QRS onset by 14.0 ms (11.2-22.6 ms) and coincided with the first rapid unipolar deflection, although -dV/dTmax occurred 10.5 ms (0.0-20.8 ms) after the QRS onset and often coincided with far-field activity. In unsuccessfully ablated intramural VPCs, the first rapid bipolar deflection to QRS onset interval was shorter in comparison to successfully ablated intramural VPCs (1.5 ms vs 14.0 ms; P < .001) while the unipolar -dV/dTmax to QRS onset interval was similar (P = .095). CONCLUSION: Mapping of VPCs should be guided by the first rapid bipolar deflection that corresponds to a similarly early unipolar deflection but not with -dV/dTmax.

Direction-aware mapping algorithms have minimal impact on bipolar voltage maps created using high-resolution multielectrode catheters.

INTRODUCTION: Direction-aware mapping algorithms improve the accuracy of voltage mapping by measuring the maximal voltage amplitude recorded in the direction of wavefront propagation. While beneficial for stationary catheters, its utility for roving catheters collecting electrograms (EGMs) at multiple angles is unknown. OBJECTIVE: To compare the directional dependence of bipolar voltage amplitude between stationary and roving catheters. METHODS: In 10 swine, a transcaval ablation line with a gap was created. The gap was mapped using an array catheter (Optrell™; Biosense Webster). In Step 1, the array was kept stationary over the gap, and four voltage maps were created during activation of the gap from superior, inferior, septal, and lateral directions. In Step 2, four additional maps were created; however, the catheter was allowed to move with points acquired at multiple angles. In Step 3, the gap was remapped; however, bipoles were computed using a direction-aware mapping algorithm. RESULTS: In a stationary catheter position, bipolar voltage distribution was influenced by the direction of activation with maximal differences obtained between orthogonal directions 32% (13%-53%). However, roving the catheter produced similar bipolar voltage maps irrespective of the direction of activation 11% (5%-18%). A direction-aware mapping algorithm was beneficial for reducing the directional dependence of voltage maps created by stationary catheters but not by roving catheters. CONCLUSION: The directional dependency of bipolar voltage amplitude is greatest when the catheter is stationary. However, when the catheter is allowed to rove and collect EGMs at multiple angles as occurs clinically, the directional dependence of bipolar voltage is minimal.

Pulsed-Field Ablation in Ventricular Myocardium Using a Focal Catheter: The Impact of Application Repetition on Lesion Dimensions.

[Figure: see text].

Circular Multielectrode Pulsed Field Ablation Catheter Lasso Pulsed Field Ablation: Lesion Characteristics, Durability, and Effect on Neighboring Structures.

BACKGROUND: Pulsed field ablation (PFA) is a nonthermal energy with potential safety advantages over radiofrequency ablation. This study investigated a novel PFA system-a circular multielectrode catheter (PFA lasso) and a multichannel generator designed to work with Carto 3 mapping system. METHODS: A 7.5F bidirectional circular catheter with 10 electrodes and variable expansion was designed for PFA (biphasic, 1800 Volts). This study included a total of 16 swine used to investigate the following 3 experimental aims: Aim 1 examined the feasibility to create a right atrial ablation line of block from the superior vena cava to the inferior vena cava. Aim 2 examined the effect of PFA on lesion maturation including durability after a 30-day survival period. Aim 3 examined the effect of high-intensity PFA (10 applications) on esophageal and phrenic nerve tissue in comparison to normal intensity radiofrequency ablation (1-2 applications). Histopathologic analysis of all cardiac, esophageal, and phrenic nerve tissue was performed. RESULTS: Acute line of block was achieved in 12/12 swine (100%) and required a total PFA time of 14 seconds (interquartile range [IQR], 9-24.5) per line. Ablation line durability after 28±3 days was maintained in 11/12 (91.7%) swine. PFA resulted in transmural lesions in 179/183 (97.8%) sections and a median lesion width of 14.2 mm. High-intensity PFA (9 [IQR, 8-14] application) had no effect on the esophagus while standard intensity radiofrequency ablation (1.5 [IQR, 1-2] applications) resulted in deep esophageal tissue injury involving the muscularis propria and adventitia layers. High-intensity PFA (16 [IQR, 10-28] applications) has no effect on phrenic nerve function and structure while standard dose radiofrequency ablation (1.5 [IQR, 1-2] applications) resulted in acute phrenic nerve paralysis. CONCLUSIONS: In this preclinical model, a multielectrode circular catheter and multichannel generator produced durable atrial lesions with lower vulnerability to esophageal or phrenic nerve damage.

Temperature-Controlled Radiofrequency Ablation Using Irrigated Catheters: Maximizing Ventricular Lesion Dimensions While Reducing Steam-Pop Formation.

OBJECTIVES: The goal of this study was to examine the safety and efficacy of radiofrequency ablation (RFA) with irrigated catheters operated in a temperature-controlled mode for ventricular ablation. BACKGROUND: Techniques to increase RFA dimensions are associated with higher risk for steam-pops. A novel irrigated catheter with circumferential thermocouples embedded in its ablation surface provides real-time surface temperature data. This study hypothesized that RFA operated in a temperature-controlled mode may allow maximizing lesion dimensions while reducing the occurrence of steam-pops. METHODS: RFA with an irrigated catheter incorporating surface thermocouples was examined in 6 swine thigh muscle preparations and 15 beating ventricles at higher (50 W/60 s, Tmax50oC) and lower (50 W/60 s, Tmax45oC) temperature limits. Biophysical properties, lesion dimensions, and steam-pop occurrence were compared versus RFA with a standard catheter operated in power-control mode at higher (50 W/60 s) and lower (40W/60 s) power, and additionally at high power with half-normal saline (50 W/60 s). RESULTS: In the thigh muscle preparation, lesion depth and width were similar between all groups (p = 0.90 and p = 0.17, respectively). Steam-pops were most frequent with power-controlled ablation at 50 W/60 s (82%) and least frequent with temperature-controlled ablation at 50 W/60 s, Tmax45oC (0%; p < 0.001). In the beating ventricle, lesion depth was comparable between all RFA settings (p = 0.09). Steam-pops were most frequent using power-controlled ablation at 50 W/60 s (37%) and least frequent with temperature-controlled ablation at 50 W/60 s, Tmax45oC (7%; p < 0.001). Half-normal saline had no incremental effect on lesion dimensions at 50 W in either the thigh muscle or the beating heart. CONCLUSIONS: RFA using a novel irrigated catheter with surface thermocouples operated in a temperature-controlled mode can maximize lesion dimensions while reducing the risk for steam-pops.

High-Power and Short-Duration Ablation for Pulmonary Vein Isolation: Biophysical Characterization.

OBJECTIVES: This study sought to examine the biophysical properties of high-power and short-duration (HP-SD) radiofrequency ablation for pulmonary vein isolation. BACKGROUND: Pulmonary vein isolation is the cornerstone of atrial fibrillation ablation. However, pulmonary vein reconnection is frequent and is often the result of catheter instability, tissue edema, and a reversible nontransmural injury. We postulated that HP-SD ablation increases lesion-to-lesion uniformity and transmurality. METHODS: This study included 20 swine and a novel open-irrigated ablation catheter with a thermocouple system able to record temperature at the catheter-tissue interface (QDOT Micro Catheter). Step 1 compared 3 HP-SD ablation settings: 90 W/4 s, 90 W/6 s, and 70 W/8 s in a thigh muscle preparation. Ablation at 90 W/4 s was identified as the best compromise between lesion size and safety parameters, with no steam-pop or char. In step 2, a total of 174 single ablation applications were performed in the beating heart and resulted in 3 (1.7%) steam-pops, all occurring at catheter-tissue interface temperature ≥85°C. Additional 233 applications at 90 W/4 s and temperature limit of 65°C were applied without steam-pop. Step 3 compared the presence of gaps and lesion transmurality in atrial lines and pulmonary vein isolation between HP-SD (90 W/4 s, T ≤65°C) and standard (25 W/20 s) ablation. RESULTS: HP-SD ablation resulted in 100% contiguous lines with all transmural lesions, whereas standard ablation had linear gaps in 25% and partial thickness lesions in 29%. Ablation with HP-SD produced wider lesions (6.02 ± 0.2 mm vs. 4.43 ± 1.0 mm; p = 0.003) at similar depth (3.58 ± 0.3 mm vs. 3.53 ± 0.6 mm; p = 0.81) and improved lesion-to-lesion uniformity with comparable safety end points. CONCLUSIONS: In a preclinical model, HP-SD ablation (90 W/4 s, T ≤65°C) produced an improved lesion-to-lesion uniformity, linear contiguity, and transmurality at a similar safety profile of conventional ablation.

Safety and efficacy of delivering high-power short-duration radiofrequency ablation lesions utilizing a novel temperature sensing technology.

Aims: Delivery of high-power short-duration radiofrequency (RF) ablation lesions is not commonly used, in part because conventional thermocouple (TC) technology underestimates tissue temperature, increasing the risk of steam pop, and thrombus formation. We aimed to test whether utilization of an ablation catheter equipped with a highly accurate novel TC technology could facilitate safe and effective delivery of high-power RF lesions. Methods and results: Adult male Yorkshire swine were used for the study. High-power short-duration ablations (10-s total; 90 W for 4 s followed by 50 W for 6 s) were delivered using an irrigated force sensing catheter, equipped with six miniature TC sensors embedded in the tip electrode shell. Power modulation was automatically performed when the temperature reached 65°C. Ablation parameters were recorded and histopathological analysis was performed to assess lesion formation. One hundred and fourteen RF applications, delivered using the study ablation protocol in the ventricles of eight swine [53 in the right ventricle (RV), 61 in the left ventricle (LV)], were analysed. Average power delivered was 55.4 ± 5.3 W and none of the ablations resulted in a steam pop. Fourteen out of the 114 (12.3%) lesions were transmural. The mean lesion depth was 3.9 ± 1.1 mm for the 100 non-transmural lesions. Similar ablation parameters resulted in bigger impedance drop (11.6 Ω vs. 9.1 Ω, P = 0.009) and deeper lesions in the LV compared with the RV (4.3 ± 1.2 mm vs. 3.3 ± 0.8 mm, P < 0.001). Conclusion: Delivery of high-power short-duration RF energy applications, facilitated by a novel ablation catheter system equipped with advanced TC technology, is feasible, safe, and results in the formation of effective ablation lesions.

Evaluation of ablation catheter technology: Comparison between thigh preparation model and an in vivo beating heart.

BACKGROUND: An in vivo animal thigh model is the standard technique for evaluation of ablation catheter technologies, including efficacy and safety of ablation. However, the biophysics of ablation in a thigh model may not be similar to a beating heart. OBJECTIVE: The purpose of this study was to compare efficacy and safety of ablation between a thigh preparation model and a beating heart. METHODS: In 7 swine, radiofrequency ablation using a 3.5-mm open irrigated catheter (ThermoCool Smart Touch) was performed sequentially in a thigh muscle and in vivo beating ventricles. Ablation was performed at low (30 W for 40 s) and high (40 W for 60 s) energy settings and at similar contact force. Ablation lesions were scanned in high resolution and measured using electronic calipers. RESULTS: A total of 152 radiofrequency ablation lesions were measured (86 thigh and 66 heart). At low energy, lesion width was greater in the thigh model (12.19 ± 1.8 mm vs 8.99 ± 2.1 mm; P <.001), whereas lesion depth was similar between the thigh and heart (5.71 ± 0.8 mm vs 5.95 ± 1.3 mm, respectively; P = .18). The planar cross-sectional lesion area was greater in the thigh model (thigh 54.8 ± 10.8 mm2 vs heart 43.1 ± 16.1 mm2; P <.001). At the high-energy setting, lesion depth, width, and area were all greater in the thigh model (thigh 91.5 ± 16.8 mm2 vs heart 56.0 ± 15.5 mm2; P <.001). The incidence of steam pop and char formation was similar between the models. CONCLUSION: The thigh preparation model is a reasonable technique for evaluation of ablation catheter technology; however it often results in overestimation of lesion size, especially at higher energy settings.

Prediction of radiofrequency ablation lesion formation using a novel temperature sensing technology incorporated in a force sensing catheter.

BACKGROUND: Real-time radiofrequency (RF) ablation lesion assessment is a major unmet need in cardiac electrophysiology. OBJECTIVE: The purpose of this study was to assess whether improved temperature measurement using a novel thermocoupling (TC) technology combined with information derived from impedance change, contact force (CF) sensing, and catheter orientation allows accurate real-time prediction of ablation lesion formation. METHODS: RF ablation lesions were delivered in the ventricles of 15 swine using a novel externally irrigated-tip catheter containing 6 miniature TC sensors in addition to force sensing technology. Ablation duration, power, irrigation rate, impedance drop, CF, and temperature from each sensor were recorded. The catheter "orientation factor" was calculated using measurements from the different TC sensors. Information derived from all the sources was included in a mathematical model developed to predict lesion depth and validated against histologic measurements. RESULTS: A total of 143 ablation lesions were delivered to the left ventricle (n = 74) and right ventricle (n = 69). Mean CF applied during the ablations was 14.34 ± 3.55g, and mean impedance drop achieved during the ablations was 17.5 ± 6.41 Ω. Mean difference between predicted and measured ablation lesion depth was 0.72 ± 0.56 mm. In the majority of lesions (91.6%), the difference between estimated and measured depth was ≤1.5 mm. CONCLUSION: Accurate real-time prediction of RF lesion depth is feasible using a novel ablation catheter-based system in conjunction with a mathematical prediction model, combining elaborate temperature measurements with information derived from catheter orientation, CF sensing, impedance change, and additional ablation parameters.

High-Resolution Mapping of Ventricular Scar: Evaluation of a Novel Integrated Multielectrode Mapping and Ablation Catheter.

OBJECTIVES: This study sought to evaluate an investigational catheter that incorporates 3 microelectrodes embedded along the circumference of a standard 3.5-mm open-irrigated catheter. BACKGROUND: Mapping resolution is influenced by both electrode size and interelectrode spacing. Multielectrode mapping catheters enhance mapping resolution within scar compared with standard ablation catheters; however, this requires the use of 2 separate catheters for mapping and ablation. METHODS: Six swine with healed infarction and 2 healthy controls underwent mapping of the left ventricle using a THERMOCOOL SMARTTOUCH SF catheter with 3 additional microelectrodes (0.167 mm2) along its circumference (Qdot, Biosense Webster, Diamond Bar, California). Mapping resolution in healthy and scarred tissue was compared between the standard electrodes and microelectrodes using electrogram characteristics, cardiac magnetic resonance, and histology. RESULTS: In healthy myocardium, bipolar voltage amplitude was similar between the standard electrodes and microelectrodes, with a fifth percentile of 1.19 and 1.30 mV, respectively. In healed infarction, the area of low bipolar voltage (defined as <1.5 mV) was smaller with microelectrodes (16.8 cm2 vs. 25.3 cm2; p = 0.033). Specifically, the microelectrodes detected zones of increased bipolar voltage amplitude, with normal electrogram characteristics occurring at the end of or after the QRS, consistent with channels of preserved subendocardium. Identification of surviving subendocardium by the microelectrodes was consistent with cardiac magnetic resonance and histology. The microelectrodes also improved distinction between near-field and far-field electrograms, with more precise identification of scar border zones. CONCLUSIONS: This novel catheter combines high-resolution mapping and radiofrequency ablation with an open-irrigated, tissue contact-sensing technology. It improves scar mapping resolution while limiting the need for and cost associated with the use of a separate mapping catheter.

Reduction of the allylic substituents in Ni(I)(1,8-dipropenyl-1,4,8,11-tetraazacyclotetradecane)+ by the central Ni(I) in aqueous solutions.

The complex Ni(II)(1,8,-di-2-propenyl-1,4,8,11-tetraazacyclotetradecane)(2+), (NiL(1))(2+), was synthesized. X-ray crystallography demonstrates that the complex obtained is the trans-III isomer. The allylic substituents shift the redox couples (NiL(1))(3+/2+) and (NiL(1))(2+/+) anodically relative to the corresponding couples for Ni(II)(1,4,8,11-tetraazacyclotetradecane)(2+), (NiL(2))(2+), as expected. Surprisingly, the lifetime of (NiL(1))(+) in neutral aqueous solutions is shorter than that of (NiL(2))(+). Pulse radiolysis experiments reveal that the allylic substituents are reduced by the central Ni(I) ion. The first step in this reduction is a general acid catalyzed process. The results suggest that this step involves schematically the reaction Ni(I)[bond]NCH(2)CH[double bond]CH(2)(+) + H(+) --> Ni(III)[bond]NCH2CH2CH(2)(2+). The latter transient decomposes slowly with a half-life time of several minutes. Preliminary results support the suggestion that (NiL(2))(+), or other Ni(I)L complexes of this family, might reduce many alkenes present in the solution.