Epicardial Mapping: Ventricular Epicardial Activation is Unaffected by Heart Position

Epicardial ventricular mapping was performed in five dogs during sinus rhythm with a sock array containing 41 bipolar electrodes. Maps were generated with a computer-assisted mapping system when the heart was in situ and when the heart was lifted by 44 degrees out of the chest. Times of earliest and latest epicardial activation in these two states did not differ. Despite a different frontal plane QRS axis, location of earliest activation was not affected by lifting the heart. In two of the five animals, the site of latest epicardial activation was minimally different from the heart in situ, but the general pattern of epicardial activation was unchanged. Therefore, the change in frontal plane QRS axis with lifting the heart was due to a change in heart position rather than a general change of heart activation.     

Steroid-Eluting Epicardial Leads in Pediatrics: Improved Epicardial Thresholds in the First Year

From 1986 to 1991, we evaluated the clinical use of three new epicardial lead designs incorporating a steroid-eluting electrode. Medtronic models SP2114 (bipolar high profile), 10320 (bipolar low profile), 10295A/4965 (unipolar low profile) steroid epicardial (SE) leads were used on either atrium or ventricle for a total of 21 lead placements in 17 patients. Energy thresholds (T) were calculated and compared with our most recent 16 nonsteroid epicardial (NE) Medtronic model 4951 lead implants for which T was available. SE leads demonstrated no acute T rise and continued T improvements at 1 year of follow-up. We conclude that epicardial application of SE lead technology offers a major improvement in pacing lead function and potential pacemaker longevity over NE leads in pediatric patients in whom endocardial pacing is precluded by size or anatomy.     

Epicardial versus parietal pericardial defibrillation

This study evaluated the energy requirements for porous electrodes implanted on the parietal pericardium versus those for porous electrodes implanted on the epicardial surface of the heart. Defibrillation with a 2.5-cm porous electrode implanted on the parietal pericardium was successful in 42% of all episodes of ventricular fibrillation. The minimal energy requirement ranged from 30-68 J, with an average of 46 J. Epicardial defibrillation was successful in approximately 80% of all episodes. The average maximal energy was 21.3 J. There was histological evidence of subepicardial damage in the parietal defibrillation group. This may be related to the higher energy required to defibrillate in this group. However, in this group frequent, large, external shocks were required to defibrillate the dogs' hearts. Theoretically, there may be some physiological and surgical advantages to an intact pericardium. However, the high energy requirement and the low success rate for defibrillation with a porous electrode on the parietal pericardium negate the feasibility of this route of defibrillation with a permanent implantable system.     

The Epicardial Field Potential in Dog: Implications for Recording Site Density During Epicardial Mapping

Investigations into mechanisms and successful surgical therapy of ventricular tachycardia (VT) depend upon accurate endocardial/epicardial mapping. Deduction of local activation is based upon parameters derived from the field potentiai (FP) (monopolar recording) or its first spatial derivative (bipolar recording). Adequate electrode spacing is an assumption fundamental to the mapping process, but the electrode spacing required for accurate representation of the FP is unknown. The purpose of this work is to derive the electrode spacing necessary to accurately describe the FP on the epicardium. In 11 dogs, electrograms from vertical (V) (base to apex h) bands having 40 electrodes and horizontal (H) bands having 40 to 80 electrodes were sampled at I kHz. The spatial handwidths (BW) were computed according lo two criteria: (1) the frequency yielding 2% mean squared error (MSE) computed at the time of the greatest integrated magnitudes of the Fourier transform; and (2) the highest frequency bounding 95% power computed at each msec throughout the beat. Implied electrode spacings were defined according to the sampling theorem. The 5th percentiles of the implied electrode spacing distributions were used to define the widest interelectrode distance required to prevent spatial aliasing. H-5th percentile and V-5th percentile were, respectively; 2% MSE (3.5 mm, 2.3 mm); 95% power (3.6 mm, 2.3 mm). Thus, a typical 20-kg dog requires more than 250 recording sites for accurate epicardial mapping. Extrapolating to man, these results suggest inadequate electrode density may partially be responsible for incomplete and ambiguous reentry patterns often observed during intraoperutive mapping.     

Electrocardiographic Patterns during Left Ventricular Epicardial Pacing

Background: There is a paucity of data concerning the use of QRS morphology patterns for identifying pacing sites during left ventricle (LV)‐only epicardial pacing in patients with a biventricular device. The objective of this study was to identify QRS patterns during LV‐only pacing, and to establish their relationship with LV lead position. In addition, to validate the diagnostic performance of such electrocardiogram (ECG) patterns for predicting posterolateral versus anterior and apical versus nonapical LV pacing site. Methods: The study retrospectively analyzed data from 376 cardiac resynchronization therapy device patients. Data analyzed included ECGs registered during LV‐only VVI pacing, fluoroscopic projections, and lateral chest roentgenograms that documented postimplantation LV lead position. Phase one of the study involved categorization of the ECG patterns of the first 66 study cases. Phase two of the study examined the association between ECG pattern and different LV lead positions. Results: As the LV epicardial pacing site became more anteroapical, the LV‐only paced QRS complexes in the precordial leads became more negative. Three ECG patterns were identified (posterolateral, intermediate, and anteroapical), and their distribution was found to be associated with LV lead position (P < 0.001). The posterolateral ECG pattern was mostly observed in cases where the LV lead was in the posterolateral area (diagnostic accuracy of 89.1% for predicting a nonapical LV lead position). The anteroapical ECG pattern was associated with LV leads in anteroapical segments (specificity of 98.5%, accuracy of 89.1% for predicting an anteroapical pacing site). Conclusions: Posterolateral and anteroapical ECG patterns are highly predictive of LV lead position. (PACE 2012; 35:1361–1368)     

Echocardiographic Assessment of Epicardial Defibrillator Patch Electrodes

We performed a blinded controlled analysis of transthoracic echocardiograms on IK patients before and after epicardial defibrillator patch electrode placement to determine the accuracy of echocardiography in identifying defibrillator patches and to determine possible echocardiographic findings that may correlate with defibrillator function or perioperative complications. The sensitivity of two-dimensional echocardiography in detecting defibrillator electrodes was 72% by one observer and 39% by a second observer. Corresponding specificities were 67% and 83%, respectively. The discordance rate was 27%. The echocardiographic finding of patch buckling was not observed, and echocardiographic estimates of the distance from patch to epicardium did not correlate with defibrillator threshold at the time of surgery. We conclude that: echocardiography is only moderately sensitive and specific in identifying epicardial defibrillator electrodes; significant interobserver variability does exist; and echocardiography therefore cannot be used reliably to assess for pericardia] changes or possible complications of patch electrode placement.     

Precipitous Exit Block with Epicardial Steroid-Eluting Leads

Between fanuary 1990 and October 1992, we implanted 16 steroid-eluting ventricular epicardial pacing leads (Medtronic 10295A and 10295B/4965) in 12 patients. There were 8 males and 4 females ranging in age from 3 months to 49 years (mean 8.7 ± 13.2, median 6.0years). Structural cardiac disease was present in 11 of 12 patients. Follow-up ranged from 3–73 months postimplant (mean 35.7 ± 22.3, median 28.5 months). Lead fracture (10295A) occurred in 1 of 12 patients. Of the remaining 11 patients, 8 of 11 have very low long-term pacing thresholds. Unexpectedly, 3 patients demonstrated precipitous threshold increases from 3 months to 3.5 years postimplant. Although no deaths resulted in these exit block patients, 1 of 3 exit block patients developed marked worsening of congestive heart failure. We reviewed and analyzed the data obtained at 4 weeks postimplant for all of the 10295A and 4965 patients in the entire Medtronic clinical study database. Using the criterion of a 4 week postimplant pacing threshold ≥ 0.12 ms (5 V), we found that the long-term risk of eventual exit block was 27.3% for the 10295A lead (P = 0.005) and 7.5% for the 10295B/4965 lead (P = 0.03). We, therefore, recommend that in patients implanted with the 4965 steroideluting epicardial lead, ventricular pacing thresholds ≥ 0.12 ms (5 V) measured at 4 weeks postimplant should prompt frequent threshold testing to detect late and potentially sudden ventricular pacing threshold increases.     

Epicardial adipose tissue in patients with heart failure

Purpose

The aim of this study was to evaluate the extent of epicardial adipose tissue (EAT) and its relationship with left ventricular (LV) parameters assessed by cardiovascular magnetic resonance (CMR) in patients with congestive heart failure (CHF) and healthy controls.

Background

EAT is the true visceral fat deposited around the heart which generates various bioactive molecules. Previous studies found that EAT is related to left ventricular mass (LVM) in healthy subjects. Further studies showed a constant EAT to myocardial mass ratio in normal, ischemic and hypertrophied hearts.

Methods

CMR was performed in 66 patients with CHF due to ischemic cardiomyopathy (ICM), or dilated cardiomyopathy (DCM) and 32 healthy controls. Ventricular volumes, dimensions and LV function were assessed. The amount of EAT was determined volumetrically and expressed as mass indexed to body surface area. Additionally, the EAT/LVM and the EAT/left ventricular remodelling index (LVRI) ratios were calculated.

Results

Patients with CHF had less indexed EAT mass than controls (22 ± 5 g/m² versus 34 ± 4 g/m², p < 0.0001). In the subgroup analysis there were no significant differences in indexed EAT mass between patients with ICM and DCM (21 ± 4 g/m² versus 23 ± 6 g/m², p = 0.14). Linear regression analysis showed that with increasing LV end-diastolic diameter (LV-EDD) (r = 0.42, p = 0.0004) and LV end-diastolic mass (LV-EDM) (r = 0.59, p < 0.0001), there was a significantly increased amount of EAT in patients with CHF. However, the ratio of EAT mass/LV-EDM was significantly reduced in patients with CHF compared to healthy controls (0.54 ± 0.1 versus 0.21 ± 0.1, p < 0.0001). In CHF patients higher indexed EAT/LVRI-ratios in CHF patients correlated best with a reduced LV-EF (r = 0.49, p < 0.0001).

Conclusion

Patients with CHF revealed significantly reduced amounts of EAT. An increase in LVM is significantly related to an increase in EAT in both patients with CHF and controls. However, different from previous reports the EAT/LVEDM-ratio in patients with CHF was significantly reduced compared to healthy controls. Furthermore, the LV function correlated best with the indexed EAT/LVRI ratio in CHF patients. Metabolic abnormalities and/or anatomic alterations due to disturbed cardiac function and geometry seem to play a key role and are a possible explanation for these findings.     

Epicardial Brugada syndrome ablation unmasking inferior J waves

Patients with Brugada syndrome are at risk of life‐threatening ventricular arrhythmias. Epicardial substrate ablation for Brugada syndrome has been described as a means of controlling these arrhythmias and recent reports describe elimination of the Brugada phenotype with ablation. We describe a unique case in which a patient developed inferior J waves with an early repolarization‐type electrocardiogram following successful epicardial infundibular substrate ablation (which eliminated the Brugada syndrome electrocardiogram on ajmaline challenge). We discuss the likely underlying pathophysiology responsible for this phenomenon, its relationship to the anatomic obstacles encountered during epicardial ablation, and the implications for long‐term arrhythmic risk.     

心外膜超声心动图在心脏外科围术期的应用价值

目的评价心外膜超声心动图在心脏手术中的应用价值。方法应用心外膜超声心动图对58例心脏手术患者术中超声监测，提供心脏瓣膜功能、左心室收缩功能等信息。结果12例(21％)超声发现右室流出道狭窄或肺动脉分支狭窄；9例(16％)瓣膜成形术因瓣膜返流或狭窄显著而改为瓣膜置换；10例(17％)超声提示左心室收缩功能减退。共15例因超声异常发现(26％)及时予以补救而避免了第二次开胸手术。结论心外膜超声心动图可简洁可靠地显示心脏的解剖结构和血流动力学异常，是心脏外科手术中的得力助手。     

Modification of Myocardial Test Probe for Epicardial Pacemaker Insertion

Modification of the myocardial test probe has proven voluable in reducing the danger of myocardial laceration and has improved the reliability of epicardial threshold measurements during epicordial pacemaker insertion. Angulation of the stylet to 30° and 60° allows application of the probe at an angle perpendicular to the epicardial surface of the heart, thus reducing readoul variotion and epicardiaJ trauma.     

Epicardial Reflection as a Cause of Incessant Ventricular Bigeminy

Incessant monomorphic ventricular bigeminy was studied in a young patient with no organic heart disease. The arrhythmia could not be controlled by drug therapy. Spontaneous and artificial variation of the heart rate showed that reentry was the most likely arrhythmogenic mechanism. Peroperative epicardial and transmural mapping revealed an epicardial focal origin which was cryoablated. Reflected reentry occurring in a small area of working myocardial cells appeared to be the most likely explanation for this arrhythmia.     

Epicardial Mapping: How to Measure Local Activation?

Epicardial ventricular mapping was performed in 5 dogs during sinus rhythm with a sock array containing 41 electrodes. Maps were generated with a computer-assisted mapping system using four different definitions of local epicardial activation: (1) maximal negative slope (intrinsic deflection) of the unipolar electrogram, (2) maximal slope of the bipolar electrogram, (3) maximal amplitude of the bipolar electrogram, and (4) first onset by 45 degrees from the baseline of the bipolar electrogram. The site of earliest and latest epicardial activation was identical with maximal negative slope in the unipolar electrogram and maximal slope and maximal amplitude of the bipolar electrogram in all five animals. Times of earliest and latest epicardial activation calculated with maximal amplitude of the bipolar electrogram were most similar to those evaluated with maximal negative slope of the unipolar electrogram. Using onset of the bipolar electrogram, activation times were measured 10 to 12 msec earlier than with each of the other three definitions of local activation, and in two of the five animals, first epicardial breakthrough was mapped to a different site than with the three other methods. Conclusions: (1) Maximal amplitude of the bipolar electrogram coincided with maximal negative slope of the unipolar electrogram; (2) Using onset of the bipolar electrogram, timing and location of earliest epicardial activation may be misinterpreted.     

300例心外膜超声的临床应用

在心血管手术，特别是复杂心脏病手术中，心外膜超声（ＩＥＥ），在术前进一步完善诊断；开放循环后立即对手术结果评价，这是常规检查方法所不能完成的。我们对３００例心脏病患者进行了ＩＥＥ检查，在体外循环前发现２５例同时合并其它畸形，开放循环后有３９例患者出现震颤、低心排表现，经ＩＥＥ诊断，１４例患者进行了再手术治疗。ＩＥＥ于转机前对各种检查遗漏的病变做出进一步诊断，并对手术疗效做出准确的评估，对矫正效果不佳的患者能明确病因，进行再手术治疗，同时本研究组对４２例患者进行压力容积环测量，推导出基本不受负荷影响准确测量左室收缩功能的指标，收缩末弹性模量（Ｅｅｓ），结合其它常用指标综合评价左心功能变化     

经心外膜聚焦超声消融治疗犬心房颤动的实验研究

目的 探讨聚焦超声经心外膜的环肺静脉消融(CPVa)和左房盒式消融(BOXa)对房颤的影响.方法 成年杂种犬20只,随机分为两组,建立肺静脉起源的阵发性房颤模型后,直视下分别行环肺静脉消融和左房盒式消融.消融前、后记录左房有效不应期(LA-ERP)、计算房颤诱发率、记录房颤持续时间,术毕行组织学检查.结果 所有犬均能诱发出肺静脉起源的阵发性房颤,房颤终止后的LA-ERP较基线水平显著缩短[CPVa组:(140±10)ms vs(102±10)ms,P＜0.01;BOXa组:(139±11)ms vs(105±8)ms,P＜0.01],但消融前后的LA-ERP并无显著性差异[CPVa组:(102±10)ms vs(110 8)ms,P=0.070;BOXa组:(106±7)ms vs(111±7)ms,P=0.225].消融后两组的房颤诱发率均较消融前显著降低[(98±4)%vs(28±10)%,P＜0.01,(97±4)%vs(14±7)%,P＜0.01],房颤持续时间均显著缩短[(233±40)s vs(70±29)s,P＜0.01;(240±41)s vs(34±22)s,P＜0.01];部分犬可见肺静脉一心房双向电传导阻滞;两组间消融前房颤诱发率、房颤持续时间无统计学差别,消融后BOXa组房颤诱发率和房颤持续时间低于/短于CPVa组(P＜0.05).消融后焦域内的组织呈凝固性坏死.结论 经心外膜聚焦超声环肺静脉消融可显著降低房颤诱发率和缩短房颤持续时间,而左房盒式消融则可进一步提高成功率.     

Preliminary Studies on a New Steroid Eluting Epicardial Electrode

Acute and chronic canine atrial and ventricular thresholds and sensing were compared for a steroid eluting epicardial plaque electrode, a similar steroid free plaque electrode and two standard leads. The steroid eluting electrode had low, stable thresbolds in atrium and ventricle compared to the steroid free plaque and standard leads. This new electrode also provided improved atrial sensing. Thus, the concept of a steroid eluting epicardial electrode shows promise for further evaluation.