Successful epicardial ablation of idiopathic mitral annular ventricular tachycardia from the great cardiac vein

This case report describes idiopathic ventricular tachycardia (VT) originating from the anterolateral site of mitral annulus. Radiofrequency (RF) energy application at an endocardial site of mitral annulus could not eliminate the tachycardia. The earliest epicardial activation preceding the onset of the QRS complex by 34 ms was found at the great anterior cardiac vein just opposite to the endocardial ablation catheter, pace mapping provided an identical (12/12) match with the VT morphology at the site, and RF ablation effectively eliminated the VT from the great cardiac vein within the coronary venous system.     

Histopathology of Monopolar Transcatheter Radiofrequency Ablation at the Mitral Valve Annulus

Although monopolar radiofrequency (RF) ecitheter ablation is being used to interrupt leftsided accessory pathways in patients with tachyarrhythrma, little is known of the histologic effects from this method of treatment. RF ablation at the mitral valve (MV) annulus was performed in ten dogs to examine the histology of the lesion area. A custom 6 French ablation catheter with a 4 mm distal electrode was positioned beneath the MV adjacent to the annulus. Mean preablation atrial to ventricular electrogram ratio (A/V ratio) was 0.26 ± 0.17. Thirty ± 1 watts of RF power were applied for 53 ± 13 seconds between the distal electrode and a large skin electrode. Nine dogs were sacrificed 6 weeks and one dog 2 days following ablation. Annular lesions were seen in eight of the ten dogs. Lesion volume was 136 ± 41 mm³ and correlated with (he A/V ratio (r²= 0.74, P = 0.006). Lesions consisted of necrosis of the left ventricle with extension into the atrioventricular groove and left atrium. No injury to the coronary sinus or circumflex artery was observed. A small area of injury was noticed on the mitral leaflet in one dog. Monopolar RF ablation creates lesions at the MV annulus without injury to adjacent vascular structures.     

Proximity of Right Coronary Artery to Cavotricuspid Isthmus as Determined by Computed Tomography

Background: Radiofrequency ablation of atrial flutter is a commonly performed procedure. Ablation success depends upon complete transmural atrial tissue injury to achieve bidirectional cavotricuspid isthmus (CTI) block. Transmural ablation increases risk of injury to the adjacent right coronary artery (RCA). Distance between the RCA and the endocardium within the CTI area is not well described. We aimed to perform in vivo measurements of the distance between the CTI area and adjacent RCA. Methods: Thirty‐three consecutive patients underwent electrocardiogram‐gated contrast‐enhanced computed tomography. CTI area was divided into nine segments based on three common catheter locations (paraseptal, central, and lateral or 5, 6, and 7 o'clock) and ventricular to atrial ablation line. Results: Mean age was 64 ± 11 years and 97% of the participants were male. Paraseptal, central, and lateral measurements at the tricuspid annulus ridge showed endocardial to RCA distance 9 ± 3, 6 ± 2, and 5 ± 3 mm, respectively (range 2–17 mm). Corresponding measurements for the ventricular side were 5 ± 3, 4 ± 2, and 4 ± 2 mm and atrial side measurements were 3 ± 2, 3 ± 2, and 3 ± 3 mm. Distance was ≤2 mm in 14% of segments on the ventricular side and 39% of segments on the atrial side. Paired t‐test showed significant difference (P < 0.001) between tricuspid annulus ridge measurements and adjacent atrial or ventricular measurements. Conclusions: Distance between endocardium and RCA lumen is reduced in areas adjacent to the tricuspid annulus ridge. (PACE 2010; 1319–1323)     

Novel Form of Atrial Tachycardia Originating at the Atrioventricular Annulus

We report two patients with reentrant atrial tachycardia that originated at the AV annulus. Atrial tachycardia originated in the posterior portion of mitral annulus in one patient (case 1) and the posterolateral portion of tricuspid annulus in one patient (case 2). Tachycardia was successfully eliminated by RF catheter ablation in both patients, with the catheter placed underneath the mitral valve in case 1 and on the tricuspid annulus in case 2. Spiky potentials were recorded in the diastolic phase of the atrium during tachycardia at the sites of successful ablation. Spiky potentials were also recorded after atrial electrogram during sinus rhythm, and showed decremental properties during atrial pacing. An accelerated atrial rhythm was observed during RF application, and tachycardia could not be induced after ablation in either patient. Tachycardia in these patients seemed to be due to reentrant tachycardia originating in the accessory AV node (Mahaim fiber) without ventricular connection.     

应用多普勒组织成像评价单纯性风湿性二尖瓣狭窄患者的左室长轴收缩功能

目的探讨应用多普勒组织成像(DTI)评价单纯性风湿性二尖瓣狭窄患者左室长轴收缩功能的意义。方法23例单纯性风湿性二尖瓣狭窄患者与26例健康志愿者行常规超声心动图及DTI检查。DTI测定二尖瓣环的室间隔、侧壁、下壁、前壁、前间隔、后壁处各位点的收缩期峰值运动速度(Vs)。结果两组间左室射血分数(LVEF)差异无显著性意义。与对照组相比,患者组各节段Vs及平均Vs(AVs)显著降低。患者组AVs与LVEF呈高度正相关,与二尖瓣口面积无显著相关。患者组侧壁、前壁、后壁Vs与AVs的相关性较好。结论患者组虽然左室整体收缩功能正常,但其左室长轴收缩功能显著受损,其受损与风湿性二尖瓣狭窄的程度无关。AVs可定量评价患者左室长轴收缩功能,二尖瓣环侧壁、前壁、后壁均是定量评价左室长轴收缩功能的较好节段。     

Activation during ventricular defibrillation in open-chest dogs. Evidence of complete cessation and regeneration of ventricular fibrillation after unsuccessful shocks.

To test the hypothesis that a defibrillation shock is unsuccessful because it fails to annihilate activation fronts within a critical mass of myocardium, we recorded epicardial and transmural activation in 11 open-chest dogs during electrically induced ventricular fibrillation (VF). Shocks of 1-30 J were delivered through defibrillation electrodes on the left ventricular apex and right atrium. Simultaneous recordings were made from septal, intramural, and epicardial electrodes in various combinations. Immediately after all 104 unsuccessful and 116 successful defibrillation shocks, an isoelectric interval much longer than that observed during preshock VF occurred. During this time no epicardial, septal, or intramural activations were observed. This isoelectric window averaged 64 +/- 22 ms after unsuccessful defibrillation and 339 +/- 292 ms after successful defibrillation (P less than 0.02). After the isoelectric window of unsuccessful shocks, earliest activation was recorded from the base of the ventricles, which was the area farthest from the apical defibrillation electrode. Activation was synchronized for one or two cycles following unsuccessful shocks, after which VF regenerated. Thus, after both successful and unsuccessful defibrillation with epicardial shocks of greater than or equal to 1 J, an isoelectric window occurs during which no activation fronts are present; the postshock isoelectric window is shorter for unsuccessful than for successful defibrillation; unsuccessful shocks transiently synchronize activation before fibrillation regenerates; activation leading to the regeneration of VF after the isoelectric window for unsuccessful shocks originates in areas away from the defibrillation electrodes. The isoelectric window does not support the hypothesis that defibrillation fails solely because activation fronts are not halted within a critical mass of myocardium. Rather, unsuccessful epicardial shocks of greater than or equal to 1 J halt all activation fronts after which VF regenerates.     

Surgical open-chest ventricular defibrillation: triphasic waveforms are superior to biphasic waveforms

Triphasic shocks have been evaluated for endocardial defibrillation but not for open-chest epicardial defibrillation. The purpose of this study was to compare the efficacy and safety of biphasic versus triphasic shocks for epicardial defibrillation in a porcine model. Twenty-two adult swine (18-28 kg) were deeply anesthetized and intubated. After 30 seconds electrically induced VF, each pig received truncated exponential biphasic (7.2-ms positive pulse duration and 7.2-ms negative pulse duration, total waveform duration 14.4 ms) and triphasic (4.8/4.8/4.8 ms, total waveform duration 14.4 ms) epicardial shocks. Pigs in group 1 (n = 11) received epicardial biphasic and triphasic shocks from large hand held paddle electrodes (44.2 cm2); pigs in group 2 (n = 11) received shocks from small paddle electrodes (15.9 cm2). Shocks were given at five selected energy levels (3-30 J) in random sequence. Four shocks were delivered at each energy level to construct an energy versus percentage of success curve. In group 1 (large paddle electrodes), percentage of shock success was significantly higher for triphasic shocks at the energy levels of 3, 5, 10, and 20 J compared to biphasic shocks. In group 2 (small paddle electrodes), triphasic shocks yielded a significantly higher percentage of shock success than biphasic shocks at the energy levels of 5, 10, and 20 J). Shock induced ventricular tachycardia was similar for both waveforms; asystole was rare. For open-chest defibrillation, triphasic waveform shocks were superior to biphasic waveform shocks for VF termination at energy levels of 3-20 J and were as safe as biphasic shocks.     

Factors Predicting Success in DC Catheter Ablation of Accessory Pathways

In a series of 33 patients with accessory pathways, 26 had successful catheter ablation (fulguration [23 patients] or modification [3 patients]) of their accessory pathway conduction, and could be considered as a clinical success. One hundred thirteen single discharge or double discharge shocks were delivered, and each shock was studied to reveal which parameters were important to predict the success or failure of catheter ablation. Double discharge shocks resulted in successful accessory pathway modification or ablation twice as often as single discharge shocks (32% vs 16%). This effect was more pronounced in left lateral accessory pathways (48% vs 4%). Shocks in the electro physiologically defined ventricular zone were more likely to be successful (33%) than shocks delivered in the atrial zone (14%), irrespective of accessory pathway location. The presence of a probable Kent potential was the parameter most strongly associated with success. The parameter most strongly associated with failure, with a 100% negative predictive value, was the absence of earliest activation recorded on the ablating catheter prior to shock delivery. An AV interval of < 60 msec significantly divided the successful from the unsuccessful shocks (P = 0.01). The VA interval during orthodromic reciprocating tachycardia or right ventricular stimulation did not allow for significant division into successful and unsuccessful attempts in this relatively short series. VA intervals, when longer, were predictive of failure but, when shorter, had low positive predictive value. Mean follow-up in 25 successful patients was 15 ± 6 months. All patients did well in the followup period. Neither those patients with ablation nor modification of the accessory pathway had recurrent episodes of tachycardia or required pharmacological treatment for control of arrhythmias.     

High and Low Strength Nonsynchronized Shocks Given During Canine Ventricular Tachycardia

Cardioversion shocks given during ventricular tachycardia may cause ventricular fibrillation or acceleration of ventricular tachycardia, or arrest the tachycardia. A recently proposed theory may explain why the former two phenomena may occur. Briefly, this theory states that potential gradient shock fields of a critical strength delivered to tissue with a critical degree of refractoriness will cause circulating wave fronts of ventricular activation ("rotors") manifest as ventricular arrhythmia. We tested this theory by delivering nonsynchronized shocks 50% higher than defibrillation threshold or 50% lower than defibrillation threshold during 275 episodes of ventricular tachycardia in eight dogs with 5- to 7-day-old myocardial infarcts. Shocks stronger than the defibrillation threshold are likely to create shock fields in the ventricles everywhere stronger than this critical value, and therefore would not generate rotors. Shocks less strong than the defibrillation threshold may create shock fields within the ventricles that include the critical value, and therefore cause rotors if given when critically refractory tissue is present. Nonsynchronized shocks were used to increase the likelihood of encountering tissue with a critical degree of refractoriness. Ventricular fibrillation or acceleration of ventricular tachycardia occurred following 83 of 138 (60%) low strength shocks and following 20 of 137 (14.6%) high strength shocks. The pooled odds ratio for induction of ventricular fibrillation or accelerated ventricular tachycardia after low strength shocks as compared to high strength shocks was 8.9. Conclusion: when given during ventricular tachycardia, low strength shocks are much more likely to cause ventricular fibrillation or accelerated ventricular tachycardia than are high strength shocks (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Safety of Transvenous Low Energy Cardioversion of Atrial Fibrillation in Patients with a History of Ventricular Tachycardia: Effects of Rate and Repolarization Time on Proarrhythmic Risk

The objective of this study was to assess the safety and efficacy of transvenous low energy cardioversion of atrial fibrillation in patients with ventricular tachycardia and atrial fibrillation and to study the mechanisms ofproarrhythmia. Previous studies have demonstrated that Cardioversion of atrial fibrillation using low energy, R wave synchronized, direct current shocks applied between catheters in the coronary sinus and right atrium is feasible. However, few data are available regarding the risk of ventricular proarrhythmia posed by internal atrial defibrillation shocks among patients with ventricular arrhythmias or structural heart disease. Atrial defibrillation was performed on 32 patients with monomorphic ventricular tachycardia and left ventricular dysfunction. Shocks were administered during atrial fibrillation (baseline shocks), isoproterenol infusion, ventricular pacing, ventricular tachycardia, and atrial pacing. Baseline shocks were also administered to 29 patients with a history of atrial fibrillation but no ventricular arrhythmias. A total of 932 baseline shocks were administered. No ventricular proarrhythmia was observed after well-synchronized baseline shocks, although rare inductions of ventricular fibrillation occurred after inappropriate T wave sensing. Shocks administered during wide-complex rhythms (ventricularpacing or ventricular tachycardia) frequently induced ventricular arrhythmias, but shocks administered during atrial pacing at identical ventricular rates did not cause proarrhythmia. The risk of ventricular proarrhythmia after well-synchronized atrial defibrillation shocks administered during narrow-complex rhythms is low, even in patients with a history of ventricular tachycardia. The mechanism of proarrhythmia during wide-complex rhythms appears not to be related to ventricular rate per se, but rather to the temporal relationship between shock delivery and the repolarization time of the previous QRS complex.     

Localization of Left Free-Wall and Posteroseptal Accessory Atrioventricular Pathways by Direct Recording of Accessory Pathway Activation

With the advent of catheter ablation techniques, precise localization of accessory AV pathways (AP) assumes greater importance. In an efort to define the course of AP fibers, we attempted to record activation of 56 left free-wall and 23 posteroseptal APs in 62 patients undergoing eiectrophysiological study. The coronary sinus (CS) and great cardiac vein (GCV) were mapped using orthogonal catheter electrodes, which provide a recording dipole perpendicular to the AV groove. The tricuspid annulus (TA) was mapped using a 2 mm spaced octapolar electrode catheter. Potentials were considered to represent AP activation only if they could be dissociated from both atrial and ventricular activation by programmed stimulation. Orthogonal catheter electrodes in the CS and GCV were advanced heyond the site of earliest retrograde atrial activation and/or earliest antegrade ventricular activation in 45 of the 56 left free-wall APs, and AP potentials were recorded from 42 (93%). An oblique course was identified in 36 APs, with the ventricular insertion being recorded 4–30 mm (median 15 mm) distal or anterior to the atrial insertion. In three patients, antegrade and retrograde conduction proceeded over different (but close) parallel fibers. AP potentials were recorded from 19 of 23 posteroseptal pathways. Ten pathways (left posteroseptal) were recorded from the CS, beginning 5–11 mm (median 9 mm) distal to the os, with potentials extending 8–18 mm (median 11 mm) distally. Four pathways (midseptal) were recorded along the TA, anterior to the CS ostium and posterior to the His bundle catheter. Five pathways (right posteroseptal) were recorded along the TA, directly opposite or immediately posterior to the CS ostium. One of the patients had both midseptal and left posteroseptal pathways and three patients had both right posteroseptal and left posteroseptal pathways. We conclude: 1) left free-wall APs transit the AV groove obliquely and may be comprised of multiple, closely spaced, parallel fihers; 2) the anatomical location of “posteroseptal” pathways is variable and the presence of fibers at multiple sites is common; and 3) direct recordings of AP activation facilitate tracking of the accessory pathway along its course from atrium to ventricle and help identify the presence of multiple fibers.     

ST-segment deviation following implantable cardioverter defibrillator shocks: incidence,timing, and clinical significance

GUREVITZ, O., et al. : ST-Segment Deviation Following Implantable Cardioverter Defibrillator Shocks: Incidence, Timing, and Clinical Significance. ST-segment analysis is frequently used during surgical procedures, while ST deviation is considered a sign of myocardial injury. ST deviations were reported following transthoracic and epicardial electrical shocks. The prevalence, timing, and clinical significance of ST-segment deviation following endocardial ICD shocks are discussed in this article. Twenty-eight patients undergoing 125 shock episodes during ICD implantation or testing were included. A 12-lead ECG was recorded at baseline, continuously during the first 3–10 seconds, 1 minute after test shocks, 3–10 seconds and 1 and 5 minutes after each shock given to terminate VF. ST deviation was diagnosed when the ST-segment was displaced ≥ 1 mm in at least one lead compared to baseline. ST-segment deviations were observed after 49 (39%) of all shock episodes in 17 (61%) of patients. ST elevation was observed after 30 (24%) of all shock episodes, and ST depression after 31 (25%). Following 13 shock episodes in seven patients, ST-elevation and depression were observed. ST depressions occurred more frequently after shocks given to terminate VF than after lower energy test shocks (28% vs 18% respectively,  P = 0.045  ). However, there was no significant difference in the prevalence of ST elevations between the lower or higher energy shocks. No adverse clinical events were observed in patients with or without postshock ST-segment deviation. ST-segment deviation following endocardial ICD shocks is a frequent phenomenon, occurring acutely and resolving during the first few minutes postshock. It may have no prognostic implications.     

Cryoablation at Growing Myocardium: No Evidence of Coronary Artery Obstruction or Intimal Plaque Formation Early and Late after Energy Application

Background: Animal studies and clinical observations have demonstrated that radiofrequency current application at growing myocardium may result in coronary artery obstruction. Recently, cryoenergy has emerged as an effective alternative to radiofrequency ablation of arrhythmogenic substrates in pediatric patients. Up to now, there has been a lack of experimental data concerning the effects of cryoenergy application at growing myocardium.
Methods: During general anesthesia, selective coronary angiography of the right and left coronary artery was performed in 10 piglets (age: 6 weeks, body weight: 14–18 kg). Subsequently, cryoenergy was delivered at −75°C for 4 minutes using a 7-F catheter with a 6-mm-tip electrode at the atrial aspect of the tricuspid valve annulus in a posterior and lateral position. Additional cryoenergy lesions were induced via a retrograde approach at the lateral and posterior atrial and ventricular aspect of the mitral valve annulus, respectively. Five animals were restudied after 48 hours by coronary angiography and intracoronary ultrasound and in the remaining five piglets after 3 and 6 months, respectively.
Results: Selective coronary angiography and intracoronary ultrasound studies did not demonstrate any evidence for coronary artery obstruction after 48 hours, 3 months, or 6 months after cryoenergy application. In addition, histological examinations of the cryolesions after 48 hours and after 6 months did not demonstrate any intimal proliferations of the coronary arteries, respectively.
Conclusions: By means of the present study, we did not observe any affection of the coronary arteries after cryoenergy application at growing myocardium in young piglets.     

定量组织速度成像测量二尖瓣环运动速度

目的　应用定量组织速度成像测量二尖瓣环运动速度评价扩张型心肌病患者左室舒张功能。方法　定量组织速度成像测量 14例正常人和 14例扩张型心肌病患者二尖瓣环 6个节段 (后间隔和侧壁、前间隔和后壁、前壁和下壁 )舒张早期峰值速度Ve、左房收缩期峰值速度Va ,计算Ve Va ;多普勒超声心动图测量二尖瓣口血流快速充盈速度E峰、左房收缩充盈速度A峰 ,计算E A值。结果　正常人和扩张型心肌病患者两组间E A无显著统计学差异 ,而扩张型心肌病组二尖瓣环平均Ve Va、平均Ve较正常组显著减低 (Ve Va :0 .89± 0 .11vs 1.76± 0 .76,P =0 .0 0 1;Ve :-4 .79± 2 .2 2vs -8.42± 2 .2 7,P<0 .0 0 0 1) ;正常组中二尖瓣环平均Ve Va与E A显著相关 (r =0 .63 ,P =0 .0 0 8) ,而扩张型心肌病组二尖瓣环平均Ve Va与E A无显著相关。结论　扩张型心肌病患者二尖瓣口血流频谱表现为假性正常化 ,定量组织速度成像测量二尖瓣环运动速度可准确评价其左室舒张功能。     

Low Energy Endocardial Cardioversion of Atrial Arrhythmias in Humans

We assessed the feasibility of low energy endocardial defibrillation in patients with atrial fibrillation or atrial flutter who had failed a trial of pharmacological reversion with amiodarone. Low energy endocardial defibrillation under general anesthesia was attempted in 9 patients, 5 with atrial flutter and 4 with atrial fibrillation (median duration of arrhythmia 3.75 months). Two large surface area endocardial leads were introduced percutaneousiy and sited in the right atrial appendage and at the right ventricular apex. A cutaneous patch electrode was placed on the left thorax. Biphasic shocks synchronized to the ventricular electrogram were used to terminate atrial arrhythmias. Three electrode configurations were evaluated in the following sequence at each energy level: atrial cathode to ventricular anode; ventricular cathode to atrial anode; atrial cathode to a combined ventricular and cutaneous anode. If endocardial defibrillation failed (0.5–10 J), transthoracic defibrillation using 200 joules followed by 360 joules, if required, was performed. Endocardial defibrillation was successful in all five patients with atrial flutter (0.5 J, 1.0 J, 1.0 J, 4.0 J, and 10,0 J) but in only one patient with atrial fibrillation (10 J). On no occasion did successful defibrillation occur with one configuration when it had failed with an alternate configuration at that particular energy level. Ventricular fibrillation did not occur, and there were no other significant complications. Low energy endocardial defibrillation is feasible in patients with atrial flutter using large surface area electrodes. Although the success rate of atrial defibrillation was low, further work is required, particularly in patients with more recent onset of the arrhythmia and using a right to left electrode configuration.     

Ablation of a Left-Sided Free-Wall Accessory Pathway by Percutaneous Catheter Application of Radiofrequency Current in a Patient with the Wolff-Parkinson-White Syndrome

A case is presented of a 20-year-old woman with a history of three episodes of syncope within the last 4 years, which was caused by a rapid ventricular response to atrial fibrillation via a left-sided posterior accessory pathway. A variety of antiarrhythmic agents had failed to control the arrhythmia. Using a novel dual catheter approach, with one catheter in the coronary sinus and an adjacent catheter in the left ventricle close to the mitral annulus, accessory pathway conduction was successfully interrupted by two radio-frequency current applications between the tip electrodes of the two catheters. During follow-up, 12-lead electrocardiograms have been normal and the patient has been asymptomatic.     

Mitral annulus velocity in the evaluation of left ventricular diastolic function in atrial fibrillation.

This study assessed the clinical utility of mitral annulus velocity in the evaluation of left ventricular diastolic function in patients with atrial fibrillation. Atrial fibrillation is the most common sustained arrhythmia encountered in clinical practice. The clinical usefulness of conventional Doppler indexes is limited in atrial fibrillation because of the altered left atrial pressure and loss of synchronized atrial contraction. Mitral inflow and mitral annulus velocities were measured simultaneously with tau in 27 patients with nonrheumatic atrial fibrillation at the cardiac catheterization laboratory. Among deceleration time of mitral inflow, peak mitral inflow velocity (E), and peak diastolic mitral annulus velocity (E), only E correlated with tau (r = 0.51, P =.007). Prolonged tau (>/=50 ms) could be predicted by E <8 cm/s with a sensitivity of 73% (16 of 22) and a specificity of 100% (5 of 5). The E/E ratio correlated with left ventricular filling pressure (r = 0.79, P <.001). The E/E ratio of >/=11 could predict elevated left ventricular filling pressure (>/=15 mm Hg) with a sensitivity of 75% (9 of 12) and a specificity of 93% (14 of 15). Mitral annulus velocity is useful in the detection of impaired left ventricular relaxation and estimation of filling pressure even in patients with atrial fibrillation.     

Myocardial damage after repetitive direct current shock in the dog: correlation between left ventricular end-diastolic pressure and extent of myocardial necrosis

Acute myocardial necrosis was produced in 27 anesthetized dogs by repetitive DC 75 joule shock delivered with one electrode in the left ventricular cavity and the other on the left chest wall. A total of 1 shock/kg body weight delivered at 10 sec intervals resulted in discrete anterior wall necrosis of 7% to 31% (mean, 17.6%) of the mass of left ventricular myocardium. After some transient bradycardia, normal sinus rhythm was restored. Depression of left ventricular function 15 min after shock (rise in LVEDP from 4.0 +/- 1.5 to 17 +/- 2 mm Hg and fall in cardiac output from 2.29 +/- 0.24 to 1.82 +/- 0.12 L/min) recovered only slightly during the ensuing 2 hr. A significant correlation (r=0.85) was observed between the LVEDP at 2 hr after shock and the extent of necrosis determined histochemically and histologically at the time of sacrifice 3 hr after shock. Thus, in this form of acute myocardial damage, pump dysfunction is closely related to the area of necrosis.     

Effects of Defibrillation Shocks Delivered Directly Over a Major Coronary Artery

This study investigated the influence of defibrillator shocks delivered directly over a coronary artery, independent of ventricular fibrillation, on cardiac hemodynamics. Thirty-six open chest, halothane anesthetized pigs were randomized to receive six shocks at one of 5,0, 7.5, or 10.0 joules (J). Shocks were delivered between two mesh electrodes (Medtronic TX-7) sutured onto the epicardium, one over the left anterior descending coronary artery and the second directly opposite on the posterobasal ventricular surface. Shock delivery was synchronized to the R wave of the cardiac cycle, to reduce the risk of inducing fibrillation, with a 5-minute stabilization period between successive shocks. Pressure from the left ventricle, the left anterior descending coronary artery, distal to the mesh electrode and the left circumflex (control) artery and contractility in the regions perfused by both arteries were measured. The shocks invariably produced an immediate (2-second postshock), but transient, depression in systolic pressure of the same magnitude for the left anterior descending coronary artery, circumflex artery and the left ventricle that recovered by 5-minute postshock. There was no dose dependent relationship to energy. Also there was no clear difference in myocardial wall motion between the area perfused by the left anterior descending coronary artery and that perfused by the circumflex artery. These results suggest that shocks up to 10 J delivered over an epicardial artery do not cause arterial spasm and do not compromise coronary artery blood flow.     

速度向量成像与定量组织速度成像技术评价犬急性心肌缺血状态下左心室收缩功能

目的以心导管测量左室压力上升速度最大值( dp/dtmax)为标准,探讨应用速度向量成像(VVI)与定量组织速度成像(QTVI)评价犬急性心肌缺血状态左室收缩功能。方法健康杂种犬6只,开胸后游离左冠状动脉回旋支或前降支,使用自制动脉血管缩窄器制备不同程度冠状动脉狭窄。测量不同血流状况下二尖瓣环水平4个心室壁处(左室间隔、下壁、侧壁、前壁)心肌收缩速度,同时进行心导管检查,测量 dp/dtmax。结果使用VVI技术测量,二尖瓣环水平心肌收缩速度与左室 dp/dtmax呈正相关(r=0.883),P<0.001;使用QTVI技术测量,二尖瓣环处心肌收缩速度与 dp/dtmax呈正相关(r=0.715),P<0.001,两相关系数行Z检验,Z=2.981,P=0.0028。结论VVI或QTVI技术测定二尖瓣环水平心肌收缩速度均是评价左心室收缩功能的好方法。相对于QTVI而言,VVI与 dp/dtmax的相关性更高,可能更加适用于对左室收缩功能的测定。