猪急性心肌梗死模型发生心室颤动的相关因素分析

目的探讨猪冠状动脉前降支(LAD)结扎后发生室颤的特点及其相关因素,以期提高猪急性心肌梗死模型的成活率。方法57只小型猪开胸结扎心脏LAD不同位点,对室颤和体重、性别、术前心率、术前左室射血分数(LVEF)、开胸径路(旁正中/肋间)、手术时间、结扎百分位点、术后心率、术后发生室早或短阵室速等因素进行单因素相关分析和Logistic回归分析,进而对室颤的发生时间、室颤前心电图特点等进行评价。结果57例动物手术过程发生室颤18例,死亡11例。室颤均发生在结扎冠脉后35 min内,高峰时间为结扎冠脉后5 min和20 min;心率快于160 bpm或慢于60 bpm时容易诱发室颤。与非室颤组动物比较,室颤组动物的结扎位点高,术后最快心率>60 bpm的动物较多,短阵室速发生率高(P<0.01)。Logistic回归分析显示结扎位点过高是急性心肌梗死后发生室颤唯一的独立危险因素。结论结扎位点过高是猪急性心肌梗死后发生室颤的最重要危险因素;冠脉结扎后30 min内应该严密心电监护,特别注意结扎冠脉后5 min和20 min二个时间点、>160 bpm或<60 bpm二种心率、以及短阵室速等先兆事件。     

Mechanisms and models of cardiac sodium channel inactivation

Shortly after cardiac Na⁺ channels activate and initiate the action potential, inactivation ensues within milliseconds, attenuating the peak Na⁺ current, I_Na, and allowing the cell membrane to repolarize. A very limited number of Na⁺ channels that do not inactivate carry a persistent I_Na, or late I_Na. While late I_Na is only a small fraction of peak magnitude, it significantly prolongs ventricular action potential duration, which predisposes patients to arrhythmia. Here, we review our current understanding of inactivation mechanisms, their regulation, and how they have been modeled computationally. Based on this body of work, we conclude that inactivation and its connection to late I_Na would be best modeled with a “feet-on-the-door” approach where multiple channel components participate in determining inactivation and late I_Na. This model reflects experimental findings showing that perturbation of many channel locations can destabilize inactivation and cause pathological late I_Na.     

Ca2+-activated chloride channel activity during Ca2+ alternans in ventricular myocytes

Cardiac alternans, defined beat-to-beat alternations in contraction, action potential (AP) morphology or cytosolic Ca transient (CaT) amplitude, is a high risk indicator for cardiac arrhythmias. We investigated mechanisms of cardiac alternans in single rabbit ventricular myocytes. CaTs were monitored simultaneously with membrane currents or APs recorded with the patch clamp technique. A strong correlation between beat-to-beat alternations of AP morphology and CaT alternans was observed. During CaT alternans application of voltage clamp protocols in form of pre-recorded APs revealed a prominent Ca²⁺-dependent membrane current consisting of a large outward component coinciding with AP phases 1 and 2, followed by an inward current during AP repolarization. Approximately 85% of the initial outward current was blocked by Cl^? channel blocker DIDS or lowering external Cl^? concentration identifying it as a Ca²⁺-activated Cl^? current (I_CaCC). The data suggest that I_CaCC plays a critical role in shaping beat-to-beat alternations in AP morphology during alternans.     

Effect of the ventricular folds in a synthetic larynx model

Within the human larynx, the ventricular folds serve primarily as a protecting valve during swallowing. They are located directly above the sound-generating vocal folds. During normal phonation, the ventricular folds are passive structures that are not excited to periodical oscillations. However, the impact of the ventricular folds on the phonation process has not yet been finally clarified.An experimental synthetic human larynx model was used to investigate the effect of the ventricular folds on the phonation process. The model includes self-oscillating vocal fold models and allows the comparison of the pressure distribution at multiple locations in the larynx for configurations with and without ventricular folds.The results indicate that the ventricular folds increase the efficiency of the phonation process by reducing the phonation threshold level of the pressure below the vocal folds. Two effects caused by the ventricular folds could be identified as reasons: (1) a decrease in the mean pressure level in the region between vocal and ventricular folds (ventricles) and (2) an increase in the glottal flow resistance.The reason for the first effect is a reduction of the pressure level in the ventricles due to the jet entrainment and the low static pressure in the glottal jet. The second effect results from an increase in the glottal flow resistance that enhances the aerodynamic energy transfer into the vocal folds. This effect reduces the onset threshold of the pressure difference across the glottis.     

Isthmus Dependent Atrial Flutter Cycle Length Correlates with Right Atrial Cross-Sectional Area

Background

Right atrial flutter cycle length can prolong in the presence of antiarrhythmic drug therapy. We hypothesized that the cycle length of right atrial isthmus dependent flutter would correlate with right atrial cross-sectional area measurements.

Methods

60 patients who underwent ablation for electrophysiologically proven isthmus dependent right atrial flutter, who were not on Class I or Class III antiarrhythmic drugs and had recent 2-dimensional echocardiographic data comprised the study group. Right atrial length and width were measured in the apical four chamber view. Cross-sectional area was estimated by multiplying the length and width. 35 patients had an atrial flutter rate ≥ 250 bpm (Normal Flutter Group) and 25 patients had an atrial flutter rate < 250 bpm (Slow Flutter Group).

Results

Mean atrial flutter rate was 283 bpm in the normal flutter group and 227 bpm in the slow flutter group. Mean atrial flutter cycle length was 213 ms in the Normal Flutter Group and 265 ms in the Slow Flutter Group (p< 0.0001). Mean right atrial cross sectional area was 1845 mm² in the Normal Flutter group and 2378 mm² in the Slow Flutter Group, (p< 0.0001). Using linear regression, CSA was a significant predictor of cycle length (β =0.014 p = 0.0045). For every 1 mm² increase in cross-sectional area, cycle length is 0.014 ms longer.

Conclusions

In the absence of antiarrhythmic medications, right atrial cross sectional area enlargement correlates with atrial flutter cycle length. These findings provide further evidence that historical rate-related definitions of typical isthmus dependent right atrial are not mechanistically valid.     

Tp-e间期、P波离散度对室性心律失常病情的预测价值

摘要 目的：探讨Tp-e间期、P波离散度(Pd)对室性心律失常病情的预测价值。方法：2016年6月到2018年6月选择在本院诊治的心绞痛患者110例,所有患者都给予动态心电图检查,记录Tp-e间期、Pd值与室性心律失常发生情况。随访患者的心绞痛复发情况,并判定预测价值。结果：在110例患者中,发生室性心律失常48例(失常组),发生率为43.6 %,其中偶发室早21例、频发室早19例、室早4例、心室颤动3例、室性心动过速1例。失常组的Tp-e间期、Pd值都显著高于非失常组(P<0.05)。随访至今,失常组的心绞痛复发率为45.8 %,显著低于对照组的8.1 %(P<0.05)。在失常组中,单因素与多因素logistics回归分析显示Tp-e间期、Pd都为影响患者心绞痛复发的重要因素(P<0.05)。ROC曲线分析显示Tp-e间期、Pd预测心绞痛复发的敏感性与特异性都在85.0 %以上。结论：心绞痛合并室性心律失常患者多伴随有Tp-e间期、Pd增加,也会增加患者的复发率,Tp-e间期、Pd对预测室性心律失常复发情况具有重要价值。     

Cardiac pacemaker battery discharge after external electrical cardioversion for broad QRS Complex Tachycardia

External electrical cardioversion or defibrillation may be necessary in patients with implanted cardiac pacemaker (PM) or implantable cardioverter defibrillator (ICD). Sudden discharge of high electrical energy employed in direct current (DC) transthoracic countershock may damage the PM/ICD system resulting in a series of possible device malfunctions. For this reason, when defibrillation or cardioversion must be attempted in a patient with a PM or ICD, some precautions should be taken, particularly in PM dependent patients, in order to prevent damage to the device. We report the case of a 76-year-old woman with a dual chamber PM implanted in the right subclavicular region, who received two consecutive transthoracic DC shocks to treat haemodynamically unstable broad QRS complex tachycardia after cardiac surgery performed with a standard sternotomic approach. Because of the sternal wound and thoracic drainage tubes together with the severe clinical compromise, the anterior paddle was positioned near the pulse generator. At the following PM test, a complete battery discharge was detected.     

Occurrence of Torsade de Pointes prior to complete lead connection during pacemaker implantation

Torsade de Pointes (TdP) can be triggered by a pacing spike on the T-wave, due to pacemaker undersensing. However, it is not widely known that this phenomenon can occur even during pacemaker implantation. An 84-year-old woman underwent pacemaker implantation for the treatment of a complete atrioventricular block with dyspnea. During the procedure, immediately following ventricular lead insertion and before torque wrench tightening, TdP was observed. Ventricular pacing was initiated by inserting the lead into the header of the generator; however, sensing remained unstable. T-waves associated with undersensed PVCs and ventricular pacing occurred simultaneously, resulting in a spike on the T-wave and TdP.     

Ventricular tachycardia ablation in children

IntroductionThe ablation of ventricular tachycardia, including premature ventricular contractions, is an approved, albeit infrequent procedure in pediatric patients. Data are scarce regarding the outcomes of this procedure. The purpose of this study was to share a high-volume center experience and patient outcomes for catheter ablation of ventricular ectopy and ventricular tachycardia in pediatric population.MethodsData were retrieved from the institutional data bank. Outcomes over time were evaluated, and procedural details were compared.ResultsA total of 116 procedures were performed on 102 pediatric patients between July 2009 and May 2021 at the Rajaie Cardiovascular Medical and Research Center in Tehran, Iran. Ablation was not performed in 4 procedures (3.4%) due to high-risk substrates. Of the remaining 112 ablations performed, 99 (88.4%) were successful. However, one patient died due to a coronary complication. There were no significant differences observed in early ablation results based on patients' age, sex, cardiac anatomy, or ablation substrates (P > 0.05). Follow-up records were available for 80 procedures, and 13 (16.3%) of those experienced recurrence. During long-term follow-up, none of the variables mentioned above were statistically different between patients with or without arrhythmia recurrence.ConclusionThe overall success rate of pediatric ventricular arrhythmia ablation is favorable. We found no significant predictor for the procedural success rate concerning acute and late outcomes. Larger multicenter studies are needed to elucidate the predictors and outcomes of the procedure.