Clinical Evaluation of Morphology Discrimination: An Algorithm for Rhythm Discrimination in Cardioverter Defibrillators

The aim of this study was to test the new morphology discrimination diagnostic algorithm for ICDs that differentiates supraventricular tachycardias (SVTs) from VTs by analysis of ventricular depolarization complexes morphology. Twenty-five patients implanted with a St. Jude Ventritex single chamber ICD were studied during electrophysiological evaluation at predischarge and were followed for 7 +/- 4 months. Sensitivity and specificity for VT detection and overall diagnostic accuracy of the morphology discrimination algorithm were calculated on 326 detected events. At electrophysiological evaluation, the algorithm was tested during 67 episodes of right atrial pacing, during 119 episodes of RV pacing (at basal interventricular septum and RV apex) and during 27 episodes of sustained AF: specificity was 98%, sensitivity was 66%, and diagnostic accuracy was 80%. All episodes of AF were correctly diagnosed as SVT. Exclusion of detections related to pacing at the basal interventricular septum, resulted in a specificity of 98%, a sensitivity of 85%, and a diagnostic accuracy of 93%. During follow-up, evaluation of the morphology discrimination algorithm on 113 spontaneous episodes (31 VTs, 31 AF, 7 SVTs, and 44 sinus tachycardias) exhibited a specificity of 89%, a sensitivity of 100%, and a diagnostic accuracy of 92%. In conclusion, the morphology discrimination algorithm exhibits a high specificity in discriminating VTs from SVTs, although with a corresponding reduction in sensitivity. The preliminary experience on spontaneous episodes is promising. To correct for the reduction in sensitivity, it is advisable to use this algorithm in parallel with other algorithms for rhythm discrimination (sudden onset, stability) coupled with extended high rate.     

射频消融术在儿科室上性心动过速中的应用

目的探讨射频消融术(radiofrequency catheter ablation，RFCA)在儿科阵发性室上性心动过速(paroxysmal superaventricular tachycardia，PSVT)中的应用特点，明确儿科PSVT心内电生理机制及其检查的特殊性。方法筛选1995年～2003年住院的25例18岁以下的PSVT患者，接受心内电生理检查及RFCA术，根据年龄与合作程度采用局麻或全身麻醉。结果25例患者经心内电生理检查，2例属房性心动过速，10例有房室结双径路，16例有旁道，其中3例同时具有旁道及房室结双径路。所有患者均行RFCA术治疗。结论RFCA作为一项治疗儿科心律失常的新技术，临床证明安全、有效，但由于青少年患者特殊的解剖生理特点，仍应严格掌握适应证，不断完善诊治技术、麻醉方式和防护措施。     

The treatment of intractable supraventricular tachycardia after open heart surgery by a continuous infusion of verapamil and ventricular pacing

Four patients who developed intractable supraventricular tachycardia (SVT) after open heart surgery were treated using a new therapeutic method of creating a pharmacological atrioventricular block by the continuous infusion of verapamil with ventricular pacing. Both the initial dose and the effective dose, being the verapamil dose necessary to maintain pharmacological atrioventricular block to prevent the recurrence of SVT, were surveyed with clinical results. The verapamil-induced hemodynamic changes observed 4 h and 8 b after treatment, as indicated by systolic arterial blood pressure, mean arteral blood pressure, heart rate, cardiac index, and urine volume, were compared with the values I h before treatment. After an initial low dose infusion of 0.07 ± 0.02 mg/kg · h had been given, an effective and safe dose of 0.11 ± 0.05 mg/ g · h was determined. Good hemodynamic and clinical results were achieved in all four patients who are now leading an active life. These results therefore encourage us to apply this therapeutic method for treating patients with intractable and recurrent SVT after open heart surgery.     

Structural heart disease: Its importance in association with antiarrhythmic drug therapy

The presence or absence of structural heart disease is an important factor to consider prior to initiating antiarrhythmic drug therapy with a class I or class III antiarrhythmic agent. An appropriate screen for structural heart disease and other associated proarrhythmic risk factors should include a complete history, physical examination, electrocardiogram (ECG), and echocardiogram in all patients; exercise test and Holter monitoring in many/most selected patients; and a signal-averaged ECG, chest x-ray, and invasive procedures only in selected/occasional patients. Whether and when to obtain the tests that are not indicated for all patients must be determined by each individual physician's practice strategy and philosophy, while keeping in mind the likelihood of finding an abnormality in a particular patient, the arrhythmia being treated, the nature of the drug to be used, and cost-effectiveness issues. Given the low incidence of proarrhythmia under most circumstances, screening for clinically unrecognized structural heart disease may appear difficult to justify in the current era of cost containment. However, due to the potential lethality of proarrhythmia, particularly in patients with structural heart disease, pre-drug assessment is prudent.     

Perioperative Cardiac Risk Reduction in Noncardiac Surgery

Major adverse cardiovascular events are a significant source of morbidity and mortality in the perioperative setting, estimated to occur in approximately 5% of patients undergoing nonemergent noncardiac surgery. To minimize the incidence and impact of these events, careful attention must be paid to preoperative cardiovascular assessment to identify patients at high risk of cardiovascular complications. Once identified, cardiovascular risk reduction is achieved through optimization of medical conditions, appropriate management of medication, and careful monitoring to allow for early identification of—and intervention for—any new conditions that would increase the risk of adverse cardiovascular outcomes. The major cardiovascular and anesthesiology societies in the United States, Europe, and Canada have published guidelines for perioperative management of patients undergoing noncardiac surgery. However, since publication of these guidelines, there has been a practice-changing evolution in the medical literature. In this review, we attempt to reconcile the recommendations made in these 3 comprehensive guidelines, while updating recommendations, based on new evidence, when available.     

Accuracy of arrhythmia recognition in paramedic treatment of paroxysmal supraventricular tachycardia: : A ten-year review

Objectives

To examine trends in paramedic rhythm misidentification rates in the use of adenosine for presumed paroxysmal supraventricular tachycardia (PSVT) over a ten-year period, and to determine variables associated with rhythm misidentification.

Methods

The authors conducted a retrospective analysis of all cases in which paramedics treated presumed PSVT with adenosine from 1993 to 2002. Rhythm strips were categorized as narrow or wide-complex and regular or irregular. Appropriate use of adenosine was defined as narrow-complex regular tachycardia with no visible P waves and rate greater than 140 beats/min.

Results

The authors studied 224 patients with a mean age of 60 years (range, 15-94 years); 157 (70%) were female and predominantly white. The majority (54%) of patients had initial heart rates of 161-200 beats/min. Forty-nine percent of the patients had a previous history of PSVT. Inappropriate use of adenosine occurred in 45 (20%) cases. Misidentification rates per year ranged from 9% to 31% with the lowest rate occurring after a targeted education program on tachydysrhythmias. An initial heart rate of <160 beats/min (χ² = 14.81, p<0.001) and absence of a medical history of either fast heart rate or palpitations (χ² = 11.35, p = 0.001) were associated with inappropriate use of adenosine.

Conclusion

Paramedics in this emergency medical services system are more likely to use adenosine appropriately for patients with initial heart rates of >160 beats/min and a history of rapid heart rate or palpitations. Further studies are required to identify factors associated with rhythm interpretation errors in the prehospital setting as well as to evaluate error reduction strategies.     

Evolution and Revolution in Drug Labeling: Regulation of Antiarrhythmic Drugs by the Food and Drug Administration 1962–1996

Between 1962, when the Kefauver-Harris Drug Amendments were passed, and 1996, 20 pharmaceutical compounds were approved and labeled by the FDA as effective antiarrhythmic drugs for some specified cardiac arrhythmia. Drug research and development in the 1970s and 1980s were focused on treatment of premature ventricular beats as a marker for sudden cardiac death and ventricular tachycardia. The Cardiac Arrhythmia Suppression Trial in 1989 irrevocably altered this approach. Recent drug development programs have targeted atrial fibrillation (AF) as epidemiologic data have predicted an increase in the incidence of AF as the United States population ages, and as treating premature ventricular beats has fallen from favor. The FDA, the scientific community, and the pharmaceutical industry have all participated in and been affected by this evolution in drug development.     

Electrophysiology of inducible atrial flutter in patients with atrioventricular nodal reentrant tachycardia

An association between atrial flutter and atrioventricular nodal reentrant tachycardia (AVNRT) has been observed, but the underlying mechanisms are poorly defined. This issue was therefore investigated by comparing the electrophysiological properties of AVNRT patients with and without inducible atrial flutter and those of patients with a history of flutter. Twenty-nine patients with clinically documented atrial flutter and 104 with AVNRT were studied. Atrial flutter was induced in 38 (37%) AVNRT patients during standardized electrophysiological testing before radiofrequency ablation. The atrial relative refractory periods in AVNRT patients with inducible flutter (260 +/- 30 ms) were significantly shorter than those of either patients with a history of flutter (282 +/- 30 ms; P = 0.02) or AVNRT patients without inducible flutter (284 +/- 38 ms; P = 0.006). The atrial effective refractory periods in AVNRT patients with inducible flutter (205 +/- 31 ms) were shorter than in AVNRT patients without inducible flutter (227 +/- 40 ms; P = 0.01). The maximum AH interval during premature atrial stimulation in patients with clinical flutter (239 +/- 94 ms) was shorter than in AVNRT patients either with (290 +/- 91 ms; P = 0.04) or without inducible flutter (313 +/- 101 ms; P = 0.002). However, no significant differences were found in the maximum AH interval achieved during incremental atrial pacing among different groups. Our data show that a non-clinical flutter could more often be induced in those who had short atrial refractoriness. Despite their anatomical proximity, the slow pathway conduction of AVNRT and the isthmus slow conduction of flutter may be related to different mechanisms.     

Mapping Guided Laser Catheter Ablation of the Atrioventricular Conduction in Dogs

Safety and efficacy of mapping guided laser catheter ablation of the AV junction was tested in a canine model. A total of 43 laser pulses (continuous wave, Nd:YAG, 1,064 nm, 30 W, irradiated spot diameter 2.0–2.5 mm) were delivered in 15 dogs (2–5 per dog) via a novel laser catheter system. Pulses were selectively aimed at: (1) the AV node: (2) the His bundle; and (3) the bundle branches. Laser pulses of 9.7 ± 1.1 seconds (n = 31) produced reversible conduction disturbances in the targeted segment of the AV conduction system, while pulses of 28.6 ± 7.9 seconds (n = 9) resulted in chronic block. The dogs survived the procedure without complications. Follow-up was 6.5–10.5 months. Histopathologically, lesions showed clear-cut oval-shaped areas of fibrosis of 0.5–18.0 mm in diameter and 0.5–3.5 mm (transmural) in depth, depending on the irradiation time. Pervenous mapping guided laser catheter irradiation of the AV junction can produce AV block consistently and selectively in the targeted segment of the right ventricular conduction system in dogs. The method is safe and can be performed in a controllable manner by using the catheter system presented.     

射频治疗室上性心动过速合并冠心病的初步经验

对6例室上速怀疑合并冠心病的患者射频术前行冠状动脉造影，证实冠脉有不同程度的狭窄病变。射频术前预先做好处置并补足液量，术中加强监护，射频治疗尽量从较小的能量开始，均取得成功。无1例术中和术后出现严重的并发症。术后随访3～8个月，平均4．5±1．8个月，无1例复发。结论：对怀疑合并冠心病的患者，术前应行冠脉造影，射频前补足液量。射频从小能量开始，既可减少并发症，又可减少术后的复发。