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Biomedical subjects

Todor N Mazgalev

Publications and source records attributed to Todor N Mazgalev.

At least 19 recordsLinked to original sources
PubMed2006

Novel robotic catheter remote control system: feasibility and safety of transseptal puncture and endocardial catheter navigation.

OBJECTIVES: The aims of this study were to demonstrate the safety and the feasibility of the robotic catheter remote control system (CCS) in endocardial navigation in all cardiac chambers, as well as facilitation of the transseptal puncture. BACKGROUND: CCS has been developed to facilitate control and precise positioning of catheters within the cardiovascular system. METHODS: CCS consists of a remote catheter manipulator, a set up joint, a physician workstation, and a steerable guide catheter (SGC) and sheath. A conventional 4-mm tip catheter was inserted through the SGC to perform mapping of five predefined targets in each cardiac chamber. Seven mongrel dogs were used in this study. Intracardiac echocardiography and three-dimensional (3-D) electroanatomical mapping were integrated with CCS to facilitate catheter manipulation and to guide transseptal puncture. The time to complete the transseptal puncture and the time to complete access to the predefined targets in each cardiac chamber were measured. Gross and microscopic examinations of the accessed and ablation sites were performed to evaluate safety. RESULTS: Transseptal puncture was performed successfully in all animals with a mean time of 7 +/- 3 minutes. Procedure times to access the five targets in the right atrium, right ventricle, left atrium, and left ventricle were 5.6 +/- 1.7, 4.6 +/- 1.5, 13.5 +/- 11.0, 7.0 +/- 2.9 minutes, respectively. There were no intracardiac damages associated with catheter manipulation noted in the excised hearts. CONCLUSIONS: Endocardial catheter navigation and mapping using the robotic catheter remote control is safe and feasible. Moreover, the CCS could be used to perform transseptal puncture and left atrial instrumentation.

Animals↗
PubMed2006

Vagal denervation and atrial fibrillation inducibility: epicardial fat pad ablation does not have long-term effects.

BACKGROUND: Major epicardial fat pads contain cardiac ganglionated plexi of the autonomic, predominantly vagal nerves. Vagal denervation may improve the success rate of atrial fibrillation (AF) treatment. OBJECTIVES: The purpose of this study was to elucidate the long-term effects of fat pad ablation on the electrophysiologic characteristics of the atrium and AF inducibility. METHODS: Six mongrel dogs were studied. Cervical vagal stimulation was applied to determine effects on the sinus node, AV node, atrial effective refractory period (AERP), and AF inducibility. AERP and AF inducibility were evaluated at both the right atrial and left atrial appendages and at the right atrial and left atrial free walls. Radiofrequency energy was delivered epicardially to the entire areas of two major fat pads: right pulmonary vein fat pad and inferior vena cava-left atrium fat pad. Cervical vagal stimulation then was applied to confirm the acute effects of fat pad ablation. The same evaluation was repeated 4 weeks later. RESULTS: The effects of vagal stimulation on the sinus node, AV node, and AERP were significantly eliminated immediately after fat pad ablation. However, these denervation effects disappeared after 4 weeks. At baseline, AF inducibility was increased by vagal stimulation (right atrial appendage: 72% +/- 31% vs 4.8% +/- 12%; right atrial free wall: 75% +/- 31% vs 0.0% +/- 0.0%; left atrial appendage: 60% +/- 29% vs 0.0% +/- 0.0%; left atrial free wall: 65% +/- 42% vs 0.0% +/- 0.0%). Fat pad ablation significantly reduced this vagal stimulation effect (8.3% +/- 20%, 10% +/- 22%, 17% +/- 29%, and 25% +/- 29%, respectively). However, similar to baseline, AF inducibility was strongly augmented by vagal stimulation 4 weeks after fat pad ablation (96% +/- 10%, 100% +/- 0.0%, 100% +/- 0.0%, and 95% +/- 11%, respectively). CONCLUSION: Radiofrequency fat pad ablation may not achieve long-term suppression of AF induction in this canine model.

Adipose Tissue↗
PubMed2006

Avoiding microbubbles formation during radiofrequency left atrial ablation versus continuous microbubbles formation and standard radiofrequency ablation protocols: comparison of energy profiles and chronic lesion characteristics.

BACKGROUND: Radiofrequency (RF) energy parameters and chronic lesion characteristics associated with the microbubbles formation have not been yet fully elucidated. OBJECTIVES: The objective of this study was to compare the energy profiles and chronic lesion characteristics associated with RF ablation of the pulmonary vein antrum using three different ablation protocols: (1) avoiding microbubbles; (2) continuous microbubble formation; (3) temperature-guided ablation. METHODS: A 4-mm tip ablation catheter was used for creating RF ablation lesions in 15 adult mongrel dogs. All ablation lesions were created at the posterior aspect of the PV antrum in each animal. Avoiding microbubbles (group 1, n = 5 dogs, 23 lesions), continuous microbubble formation (group 2, n = 5 dogs, 22 lesions), and temperature-guided (group 3, n = 5 dogs, 19 lesions, target temperature 60 degrees C/power limit 50 W) ablation lesions were analyzed. RESULTS: Group 1 showed significantly lower power (19 +/- 8.6 W), lower temperature (50 +/- 4.8 degrees C), higher efficiency-of-heating index (2.9 +/- 0.8 degrees C/W), and lower impedance (109 +/- 24.4 Omega) than groups 2 (38 +/- 8.4 W; 63 +/- 10 degrees C; 1.8 +/- 0.8 degrees C/W; 148 +/- 34.4 Omega) and 3 (44 +/- 12 W; 57 +/- 2.4 degrees C; 1.4 +/- 0.5 degrees C/W; 139 +/- 23.1 Omega) (P < 0.001 vs groups 2 and 3). During ablation, no significant events were detected in group 1, but 11 cases of audible pop, 11 cases of catheter tip charring, and 1 case of fatal myocardial perforation were observed in groups 2 and 3. Transmural lesions were more frequently created in group 1. CONCLUSION: RF energy delivery applying "avoiding microbubbles" protocol seems to be associated with higher degree of safety and efficacy when compared to temperature-guided and continuous microbubble-formation ablation protocols.

Animals↗
PubMed2005

Chronic atrioventricular nodal vagal stimulation: first evidence for long-term ventricular rate control in canine atrial fibrillation model.

BACKGROUND: We have previously demonstrated that selective atrioventricular nodal (AVN) vagal stimulation (AVN-VS) can be used to control ventricular rate during atrial fibrillation (AF) in acute experiments. However, it is not known whether this approach could provide a long-term treatment in conscious animals. Thus, this study reports the first observations on the long-term efficacy and safety of this novel approach to control ventricular rate during AF in chronically instrumented dogs. METHODS AND RESULTS: In 18 dogs, custom-made bipolar patch electrodes were sutured to the epicardial AVN fat pad for delivery of selective AVN-VS by a subcutaneously implanted nerve stimulator (pulse width 100 micros or 1 ms, frequency 20 or 160 Hz, amplitude 6 to 10 V). Fast-rate right atrial pacing (600 bpm) was used to induce and maintain AF. ECG, blood pressure, and body temperature were monitored telemetrically. One week after the induction of AF, AVN-VS was delivered and maintained for at least 5 weeks. It was found that AVN-VS had a consistent effect on ventricular rate slowing (on average 45+/-13 bpm) over the entire period of observation. Echocardiography showed improvement of cardiac indices with ventricular rate slowing. AVN-VS was well tolerated by the animals, causing no signs of distress or discomfort. CONCLUSIONS: Beneficial long-term ventricular rate slowing during AF can be achieved by implantation of a nerve stimulator attached to the epicardial AVN fat pad. This novel concept is an attractive alternative to other methods of rate control and may be applicable in a selected group of patients.

Animals↗
PubMed2005

Differences in left ventricular long-axis function from mice to humans follow allometric scaling to ventricular size.

While the heart size maintains a constant proportion to body size, heart function parameters, such as heart rate and cardiac output, show a more complex scaling pattern. How these phenomena affect the long-axis left ventricular (LV) function is unknown. We studied 10 mice, 15 rats, 6 rabbits, 8 mongrel dogs and 38 human volunteers. Doppler tissue echocardiography data were postprocessed to reconstruct mitral annulus (MA) peak systolic velocity and displacement. The relationship between MA peak velocity, MA displacement and LV ejection time, and LV end-diastolic volume (and mass) were fit to an allometric (power-law) equation Y=kMbeta. LV mass varied from 0.062 to 255 g, while end-diastolic volume varied from 0.014 to 205 ml. beta values of the relation between LV ejection time and LV end-diastolic volume and mass were 0.247+/-0.017 and 0.267+/-0.018, respectively. beta values of the relationship between MA displacement and LV end-diastolic volume and mass were 0.358+/-0.047 and 0.390+/-0.051 (P<0.023 versus beta of LV ejection time). beta values of the relationship between MA peak systolic velocity and LV end-diastolic volume and mass were 0.096+/-0.012 and 0.100+/-0.013, respectively (P<0.0001 versus 0). Finally, beta values of the relationship between the long-to-short axis displacement ratio and LV end-diastolic volume and mass were 0.077+/-0.017 and 0.086+/-0.019 (P<0.0001 versus 0). We conclude that MA velocity, displacement, and long-to-short axis displacement ratio scale allometrically to heart size. This reduces the relative long-axis contribution to heart function in small mammals.

Animals↗
PubMed2005

Myocardial compliance was not altered after acute induction of atrial fibrillation in sheep.

BACKGROUND: Although left ventricular (LV) contractility in atrial fibrillation (Af) is known to change in a beat-to-beat fashion, little is known about the changes in LV compliance in Af. MATERIAL/METHODS: We experimentally induced tachycardic Af (average heart rate - 154 beats per minute) in 18 sheep. LV volume and pressure were simultaneously monitored using a conductance catheter. LV end-diastolic volume (V(ED)) and pressure (P(ED)) were plotted in a beat-to-beat fashion and fitted to the following exponential equation (P(ED)=gamma x e(b x V(ED))) in each animal. A random effects model was constructed to determine if the intercepts and slopes differ. RESULTS: In all animals, those plots after the induction of Af fit quite well to the exponential function (r=0.834+/-0.184) by gating short preceding interval (RR1) beats. By simply taking the natural logarithm of both sides in the equation, the linear relationship (ln(P(ED)) =alpha+ betaxV(ED), where a = lng) was observed in all animals before (normal sinus rhythm, NSR) and after the induction of Af. Only two of 18 intercepts and four of 18 slopes deviate between NSR and Af. Most interestingly, the random effects model clearly detailed that the average animal had intercepts and slopes that were not discernibly different between NSR and Af. CONCLUSIONS: Unlike LV contractility, myocardial compliance did not change after the acute induction of Af. These interesting results may give us insights into the understanding of the physiology in acute rapid Af.

Animals↗
PubMed2005

Giant flow reversal in pulmonary venous flow as a possible mechanism for asynchronous pacing-induced heart failure.

BACKGROUND: Mechanistic roles of the immediate increase in left atrial (LA) pressure in pacing-induced congestive heart failure have not been clearly understood. We evaluated the impact of asynchronous rapid ventricular pacing on LA hemodynamics in this model. METHODS: Transthoracic and transesophageal echocardiography and hemodynamic assessment were performed in 23 healthy mongrel dogs. Data were acquired before and 5 minutes after initiation of rapid right ventricular pacing (200/min). RESULTS: At 5 minutes after initiation of the pacing, giant pulmonary venous (PV) flow reversal (-76 cm/s) was observed in association with 1:1 ventriculoatrial conduction or complete atrioventricular dissociation. This giant PV flow reversal corresponded to an inappropriately timed atrial contraction, especially during systole. Cardiac output (3.21 vs 2.00 L/min, P < .001) was decreased corresponding to the decrease in the forward blood volumes as described by decrease in the Doppler left ventricular (LV) outflow (8.99 vs 4.73 cm, P < .0001), mitral inflow (6.89 vs 3.19 cm, P < .0001), and PV flow (14.15 vs 7.22 cm, P < .0001) velocity integrals. As a result, there was a marked elevation of the mean pulmonary capillary wedge (9.1 vs 17.1 mm Hg, P < .001) and LV end-diastolic (8.2 vs 17.4 mm Hg, P < .01) pressures leading to congestive heart failure. CONCLUSIONS: The giant PV flow reversal seen during asynchronous rapid right ventricular pacing corresponds to an inappropriate atrial contraction, immediately elevates LA pressure, and may initially promote congestive heart failure. The increase in LV end-diastolic pressure associated with decreased LV ejection fraction caused decrease in the LV filling volume leading to further increase in the LA pressure. This sustained marked elevation in the LA pressure and LV end-diastolic pressure could contribute to the heart failure process.

Animals↗
PubMed2004

Atrioventricular nodal fast pathway modification: mechanism for lack of ventricular rate slowing in atrial fibrillation.

OBJECTIVES: Atrioventricular node (AVN) modification is one of the alternatives for ventricular rate control in patients with drug refractory atrial fibrillation (AF). However, the underlying mechanisms, and in particular the role of the dual pathway electrophysiology is not clear. By using a novel index, His electrogram (HE) alternans, we have previously demonstrated in rabbits that both the slow (SP) and the fast pathways (FP) are involved in AVN conduction during AF. This electrophysiological-morphological study was designed to address the role of selective FP ablation on AVN conduction during AF. METHODS AND RESULTS: In 12 rabbit AVN preparations dual pathway conduction was confirmed by HE alternans during A1A2 pacing protocol, as well as during AF. On average 48% of the conducted beats during AF utilized the FP. Selective FP ablation (n=12) guided by HE alternans resulted in only-SP conduction, with longer AVN conduction time at basic beats, but without change of AVN effective refractory period (ERP). Interestingly, despite elimination of all FP-conducted beats during AF, the selective FP ablation allowed previously concealed SP beats to be conducted, resulting in little net effect on the ventricular rate (average His-His interval 199+/-10 ms before versus 201+/-13 ms after FP ablation, p>0.05). Morphological evidence indicated that FP ablation created lesions within the transitional cells of the superior approaches at the junction between the central fibrous body and the AVN. However, extension of FP ablation lesion into the compact AVN domain resulted in non-selective AVN modification and slowing of ventricular rate during AF. CONCLUSIONS: Despite its longer ERP, FP is responsible for a substantial number of ventricular beats during AF. However, selective FP ablation has a minor effect on ventricular rate. The most likely mechanism for this phenomenon is that FP ablation allows previously concealed SP beats to be conducted. On the other hand, ventricular rate slowdown could be achieved if FP ablations caused collateral damage in the compact node. This study highlights the usefulness of HE alternans as a novel tool to monitor dual pathway conduction during AF and to guide AVN modification.

Animals↗
PubMed2004

The pseudorestrictive pattern of transmitral Doppler flow pattern after conversion of atrial fibrillation to sinus rhythm: is atrial or ventricular dysfunction to blame?

Patients with paroxysmal atrial fibrillation (AF) who have recently converted from AF to sinus rhythm often exhibit a restrictive Doppler pattern in the transmitral flow (TMF) velocity. However, the mechanism of this phenomenon has not been well defined. We evaluated the temporal change of TMF pattern and hemodynamics after conversion of AF to in sinus rhythm in an animal model. Eight open-chest dogs underwent 3 hours of pacing-induced AF. TMF velocities and pressure data were acquired at baseline (sinus rhythm), immediately after conversion of AF, and every 10 minutes thereafter. Early diastolic TMF velocity was increased immediately after conversion and recovered to the baseline value in 20 minutes. Atrial systolic TMF velocity was reduced after AF and recovered to baseline value in 20 to 30 minutes. Early diastolic/atrial systolic TMF velocity was increased after conversion, and recovered to baseline value in 20 to 30 minutes. The mean left atrial (LA) pressure increased immediately, 10 and 20 minutes after the conversion of AF to sinus rhythm. The left ventricular end-diastolic pressure was increased and positive left ventricular dP/dt and tau were decreased immediately after AF, whereas they recovered within 10 minutes. In conclusion, a pseudorestrictive pattern of TMF after AF occurred as a result of transient LA mechanical functional impairment and increased LA pressure caused by LA stunning. Transient left ventricular diastolic dysfunction also effected the TMF velocity immediately after the conversion from AF to sinus rhythm, although it recovered faster than LA mechanical dysfunction.

Animals↗
PubMed2004

Achieving regular slow rhythm during atrial fibrillation without atrioventricular nodal ablation: selective vagal stimulation plus ventricular pacing.

OBJECTIVES: The aim of this study was to achieve regular slow ventricular rhythm during atrial fibrillation (AF) without destroying the AV node (AVN). BACKGROUND: Recent experimental and clinical studies have demonstrated that selective AVN vagal stimulation (AVN-VS) can be used to slow ventricular rate during AF; however, an irregular rhythm remains. Alternatively, ventricular on-demand (VVI) pacing achieves rate regularization but at rates faster than the already fast intrinsic rate during AF. We hypothesized that AVN-VS combined with VVI pacing would achieve slow, regular rhythm during AF without requiring AVN ablation. METHODS: AF was induced in eight dogs. AVN-VS was applied to the epicardial fat pad that projects vagal nerve fibers to the AVN. A computer-controlled algorithm adjusted AVN-VS intensity to achieve three levels of mean ventricular RR interval: 75%, 100%, or 125% of the spontaneous sinus cycle length. At each of the three levels, concomitant VVI pacing was delivered at a constant cycle length equal to the corresponding target. Hemodynamic measurements were performed during the study to elucidate the advantages of the proposed method. RESULTS: AF resulted in rapid, irregular ventricular rates (RR = 287 +/- 36 ms, or 56% of sinus cycle length). AVN-VS achieved average ventricular rate slowing to the three target levels in all dogs (RR increased to 381 +/- 41, 508 +/- 54, and 632 +/- 68 ms, respectively). At each of the three target rate levels, AVN-VS combined with VVI pacing fully eliminated rate irregularities. The regular slow ventricular rhythms during AF were associated with significant hemodynamic improvement. CONCLUSIONS: A novel approach combining AVN-VS with VVI pacing results in a regular, slow ventricular rhythm during AF that does not necessitate AVN ablation. Rate regularization achieved by this approach was associated with pronounced hemodynamic benefits during AF.

Algorithms↗
PubMed2004

Frank-Starling mechanism contributes modestly to ventricular performance during atrial fibrillation.

OBJECTIVES: The aim of this study was to assess whether Frank-Starling mechanism has an independent effect on left ventricular (LV) performance in atrial fibrillation (AF). BACKGROUND: Ventricular performance in AF depends on variable contractility through the interval-force mechanism based on the ratio of preceding and pre-preceding RR intervals (RR(p)/RR(pp)). The impact of end-diastolic volume (EDV) variability, through the Frank-Starling mechanism, is not well understood. METHODS: We induced AF in 16 open chest dogs. RR intervals, LV pressure, LV volume, and aortic flow were collected for >400 beats during rapid AF (ventricular cycle length 292 +/- 66 ms). In six of the dogs, additional data were collected while average ventricular cycle length was prolonged from 258 +/- 34 ms to 445 +/- 80 ms by selective vagal nerve stimulation of the AV node. RESULTS: The relations of maximal LV power (LVPower) and peak LV pressure derivative (dP/dt) versus RR(p)/RR(pp) were fitted to the equation y = A * (1 - EXP (RR(p)/RR(pp)min - RR(p)/RR(pp))/C) and the residuals (RES) of these relations were analyzed. LVPower and dP/dt strongly correlated with RR(p)/RR(pp) (r(2) = 0.67 +/- 0.12 and 0.66 +/- 0.12, P < .0001 for all correlations). Importantly, RES-LVPower and RES-dP/dt showed linear correlation with EDV (r(2) = 0.20 +/- 0.14 and r(2) = 0.24 +/- 0.17, P < .01 for all correlations). In the six dogs with slowed average ventricular rate, the slope of both residual relationships (RES-LVPower vs EDV and RES- dP/dt vs EDV) decreased (P < .03 for both). CONCLUSIONS: The Frank-Starling mechanism contributes to ventricular performance in AF independently of the interval-force effects of the beat-to-beat variability in cardiac contractility. The Frank-Starling mechanism is sensitive to the average ventricular rate.

Action Potentials↗
PubMed2004

Ventricular rate control during atrial fibrillation and AV node modifications: past, present, and future.

Atrial fibrillation (AF) is the most common arrhythmia. Currently there are two broad strategic treatment options for AF: rhythm control and rate control. For rhythm control, the treatment is directed toward restoring and maintaining the sinus rhythm. For rate control, the intention is to slow ventricular rate while allowing AF to continue. In both cases anticoagulation therapy is recommended. The results of currently available clinical trials demonstrated clearly that rate control is not inferior to rhythm control. Thus, rate control is an acceptable primary therapy for many AF patients. The rate control can be achieved essentially by depressing or modifying the filtering properties of the atrioventricular (AV) node. This can be attained by medications that depress the impulse transmission within the AV node, by anatomic modification of the AV communications, as well as by autonomic manipulations that produce AV node negative dromotropic effect. We are reviewing current clinical and newer experimental modalities aimed at enhancing the lifesaving function of this remarkable nodal structure.

Anti-Arrhythmia Agents↗
PubMed2003

Determinants of LV diastolic function during atrial fibrillation: beat-to-beat analysis in acute dog experiments.

Left ventricular (LV) diastolic function during atrial fibrillation (AF) remains poorly understood due to the complex interaction of factors and beat-to-beat variability. The purpose of the present study was to elucidate the physiological determinants of beat-to-beat changes in LV diastolic function during AF. The RR intervals preceding a given cardiac beat were measured from the right ventricular electrogram in 12 healthy open-chest mongrel dogs during AF. Doppler echocardiography and LV pressure and volume beat-to-beat analyses were performed. The LV filling time (FT) and early diastolic mitral inflow velocity-time integral (E(vti)) were measured using the pulsed Doppler method. The LV end-diastolic volume (EDV), peak systolic LV pressure (LVP), minimum value of the first derivative of LV pressure curve (dP/dt(min)), and the time constant of LV pressure decay (tau) were evaluated with the use of a conductance catheter for 100 consecutive cardiac cycles. Beat-to-beat analysis revealed a cascade of important causal relations. LV-FT showed a significant positive linear relationship with E(vti) (r = 0.87). Importantly, there was a significant positive linear relationship between the RR interval and LV-EDV in the same cardiac beat (r = 0.53). Consequently, there was a positive linear relationship between LV-EDV and subsequent peak systolic LVP (r = 0.82). Furthermore, there were significant positive linear and negative curvilinear relationships between peak systolic LVP and dP/dt(min) (r = 0.95) and tau (r = -0.85), respectively, in the same cardiac beat. In addition, there was a significant negative curvilinear relationship between dP/dt(min) and tau (r = -0.86). We have concluded that the determinants of LV diastolic function in individual beats during AF depend strongly on the peak systolic LVP. This suggests that the major benefit of slower ventricular rate appears related to lengthening of LV filling interval, promoting subsequent higher peak systolic LVP and greater LV relaxation.

Animals↗
PubMed2003

His electrogram alternans reveal dual atrioventricular nodal pathway conduction during atrial fibrillation: the role of slow-pathway modification.

BACKGROUND: Traditional tools to study dual-pathway atrioventricular nodal (AVN) electrophysiology are not applicable in subjects with permanent atrial fibrillation (AF). The presence of fast-pathway (FP) and slow-pathway (SP) wavefronts and their possible modification remain uncertain in this condition. We demonstrated previously that His electrogram (HE) alternans can determine whether the FP or the SP reaches the His bundle on a beat-by-beat basis. We have now applied this novel index to monitor dual-pathway conduction and the effects of SP modification during AF. METHODS AND RESULTS: In 12 rabbit AVN preparations, HE alternans were confirmed during a standard A(1)A(2) pacing protocol. During AF, in 9 of the 12 hearts, HE alternans indicated the presence of dual pathways. Successful SP modification guided by the HE alternans eliminated the SP, resulting in a predominantly FP conduction during AF in all hearts. This increased the average His-His interval (204+/-14 versus 276+/-51 ms, P<0.001). Morphological studies revealed that SP modification damaged only the posterior extension of the AVN. CONCLUSIONS: We have demonstrated for the first time in rabbits that HE alternans permit "visualization" of dual-pathway electrophysiology and confirmed the presence of both FP and SP wavefronts during AF. This novel index has been used in a selective SP ablation that resulted in a significant slowing of the ventricular rate. HE alternans provide a new insight into the mechanisms of AVN conduction and could guide AVN modification for ventricular rate control in AF clinically.

Animals↗
PubMed2003

Optical mapping technique applied to biventricular pacing: potential mechanisms of ventricular arrhythmias occurrence.

Although it has been suggested that multisite ventricular pacing alleviates heart failure by restoring ventricular electrical synchronization, the respective roles of voltage output, interventricular delay, and pacing sites in the development of ventricular arrhythmias occurrence have not been studied during biventricular pacing or LV pacing. Voltage-sensitive dye was used in eight ischemic Langerdorff-perfused guinea pig hearts to measure ventricular activation times and examine conduction patterns during multisite pacing from three RV and four LV sites. The hearts were stained with di-4-ANEPPS and mapped with a 16 x 16 photodiode array at a resolution of 625 microns per diode. Isochronal maps of RV and LV activation were plotted. Ischemia was produced by gradually halving the perfusion output over 5 minutes. Pacing the RV apex and the base of the LV anterior wall was associated with the most homogeneous and rapid activation pattern (28 +/- 9 vs 41 +/- 12 ms with the other configurations, P < 0.01), and no inducible arrhythmia. In six hearts, ventricular tachycardia could be induced when pacing from the right and left free walls with 20 ms of interventricular delay, at six times the pacing threshold output. In four hearts, simultaneous RV and LV pacing at high voltage output induced ventricular fibrillation with complex three-dimensional propagation patterns, independently of the pacing sites. During biventricular pacing with ischemia, pacing at high voltage output with a long interventricular delay is likely to induce ventricular arrhythmias, particularly when left and right pacing results in a conduction pattern orthogonal to the ventricular myocardial fibers orientation.

Animals↗
PubMed2003

The strength-duration relationship of monophasic waveforms with varying capacitance sizes in external defibrillation.

The shape of the shock waveform influences defibrillation efficacy. However, the optimal combination between capacitance size and truncation/tilt which can determine monophasic waveform's shape, has not been determined for external defibrillation. The purpose of this study was to assess the effects of varying capacitance and tilt on external defibrillation using exponential monophasic waveforms. In a pig model of external defibrillation (n = 10, 30 +/- 6 kg), nine exponential monophasic waveforms combining three capacitance values (30 microF, 60 microF, and 120 microF) and three tilt values (55%, 75%, and 95%) were tested randomly. The energy and leading edge voltage at 50% defibrillation success (E50 and V50) were used to evaluate defibrillation efficacy. E50 and V50 were determined by the Bayesian technique. The lowest stored E50 for the 30microF, 60 microF, and 120 microF waveforms were 90 +/- 12 J (95% tilt), 106 +/- 45 J (55% tilt), and 107 +/- 52 J (75% tilt), respectively. The lowest V50 for the 30 microF, 60 microF, and 120 microF waveforms were 2,439 +/- 166 V (95% tilt), 1,849 +/- 375 V (55% tilt), and 1,301 +/- 322 V (75% tilt), respectively. The average current at external defibrillation threshold demonstrated a strength versus pulse duration relationship similar to that seen with pacing. Reducing capacitance has the same effect as truncating the waveform. The E50 is more sensitive to tilt values changes in larger capacitance waveforms. This study suggests that the optimal combination between capacitance and tilt may be 120 microF and 55%-75% for external defibrillation.

Animals↗