Syncopes and brief spells of feeling faint: value of Holter monitoring?

A retrospective study of Holter monitoring of 250 patients referred for syncope and short spells of dizziness suspected of being cardiac in origin was undertaken to assess the diagnostic value of the investigation. The arrhythmias observed were classified in 3 groups, significant, suspect and physiological with respect to their true or potential severity and to previously reported results of Holter monitoring in healthy subjects. The following arrhythmias were classified as significant: supraventricular tachycardia with a ventricular rate greater than or equal to 200 bpm; sustained ventricular tachycardia (greater than 30 s and greater than or equal to 150 bpm), bradycardia (less than bpm), sinus arrest (waking greater than 2 s sleeping greater than or equal to 6 s), complete AV block with wide QRS complexes and pacemaker dysfunction. The following arrhythmias were classified as suspect: paroxysmal supraventricular tachycardia with a ventricular rate less than 200 bpm, salvos of ventricular tachycardia (120 greater than 150 bpm); R/T phenomenon and doublets (greater than or equal to 50/24 hours), sinus arrest of 2 to 6 seconds during sleep, complete AV block with narrow QRS complexes or second degree Mobitz II block. This classification led to a diagnosis of certitude in 20 patients (5.7%) with significant arrhythmias concomitant with syncope or a minor form in only 5 cases, supraventricular tachycardia (4 cases), ventricular tachycardia (4 cases), AV block (5 cases), sinus arrest (3 cases), pacemaker dysfunction (4 cases); a diagnosis of presumption in 74 patients (21.1%) with suspect arrhythmias in the absence of syncope or minor equivalent.(ABSTRACT TRUNCATED AT 250 WORDS)     

TRANSESOPHAGEAL ELECTROCARDIOGRAPHY AND ATRIAL PACING IN ACUTE CARDIAC CARE: DIAGNOSTIC AND THERAPEUTIC VALUE

The utility of transesophageal electrocardiography using a bipolar 'pill electrode' was assessed in 17 consecutive patients with tachycardia presenting to our casualty department. Standard 12-lead electrocardiography showed regular narrow QRS tachycardia in 12 patients, and five patients had wide QRS tachycardia. Esophageal atrial electrogram recordings were obtained in 14 patients (82%), and these were helpful in determining the mechanism of tachycardia in 11 patients (78%). Of these 11, seven patients fulfilled criteria for atrioventricular junctional (AVJ) tachycardia based on measurement of the minimum interval between the onset of ventricular depolarisation and earliest atrial (esophageal) activity. One of these patients had presented with a wide QRS tachycardia. The other four patients were diagnosed as having ventricular tachycardia (VT) following diagnosis of AV dissociation. Atrial overdrive pacing, via the pill electrode, successfully reverted four of the nine patients (44%) with narrow QRS tachycardia but no patient with VT. Esophageal recording during tachycardia is a simple, relatively non-invasive technique which is helpful in suggesting the mechanism of tachycardia both in patients with narrow and wide QRS tachycardia, and may have a therapeutic role in patients with AVJ tachycardia. (Aust NZ J Med 1989; 19: 11–15.)     

Late potentials and inducible ventricular tachycardia in surgically repaired congenital heart disease

We compared signal-averaged electrocardiography with invasive electrophysiological study in patients after surgical repair of congenital heart disease to determine if potentially useful correlations exist between the two methods for assessment of risk for ventricular tachycardia. Thirty-one patients (age, 1-49 years; mean, 10.6 years) with congenital heart disease repaired with right ventriculotomy or postrepair right bundle branch block (77% postoperative tetralogy of Fallot) who had electrophysiological study were studied with signal-averaged electrocardiography. Patients were classified by electrophysiological study results as having no inducible ventricular tachycardia, nonsustained ventricular tachycardia, or sustained ventricular tachycardia. Signal-averaged electrocardiograms were examined for the duration of low-amplitude (less than or equal to 40 microV) QRS signal, duration of total QRS, and root-mean-square voltage of the terminal 40 msec of the QRS. Low-amplitude terminal root-mean-square voltage of 100 microV or less had 91% sensitivity and 70% specificity for ventricular tachycardia inducible by electrophysiological study. Similar sensitivity but less specificity were seen using the criterion of 20 msec or more total low-amplitude QRS signal (initial plus terminal) or using total QRS duration of 128 msec or more. There was a weaker association between terminal low-amplitude QRS signal of 15 msec or more and inducible ventricular tachycardia.(ABSTRACT TRUNCATED AT 250 WORDS)     

Signal averaged ECG and mechanisms of sudden death

The aim of signal averaged electrocardiography is to detect late potentials (LP) which are markers of ventricular tachycardia. As sudden death is often due to ventricular fibrillation which can complicate ventricular tachycardia, some workers have suggested that the presence of LP may increase the risk of sudden death. We analysed the results of signal averaged ECG in 17 subjects who died suddenly and compared them with 8 patients who died from ventricular tachycardia. These two groups of patients were part of a general population of 450 subjects who underwent programmed ventricular stimulation and signal averaged ECG by Simson's method (25 Hz filter). Three parameters of this ECG were analysed: total QRS duration (Dur QRS), amplitude of the signal 40 ms before its termination (V 40), and the duration of the terminal activity less than 40 microV (Dur LP). The criteria of diagnosis of Lp were: Dur QRS greater than or equal to 120 ms, V 40 less than or equal to 20 microV, Dur LP greater than or equal to 40 ms. The results of signal averaged ECG of patients who died suddenly were different to those of patients who died from VT: Dur QRS 116 +/- 40 vs 140 +/- 25 ms, V 40 27 +/- 24 vs 7 +/- 8 microV, Dur LP 39 +/- 27 vs 59 +/- 14 ms. Only 8 patients who died suddenly had LP (47%) whereas all patients who died of VT had LP. A correlation was observed between the presence of LP and 2 factors: the LV ejection fraction which was significantly lower in patients with LP (28 +/- 8 vs 46 +/- 19%) and the results of programmed ventricular stimulation: patients with induced sustained VT less than 270/mn usually had LP (15/16). LP were usually absent (4/6) in cases of ventricular flutter (VT greater than or equal to 270/mn) or induced VF. The presence of LP in 2 patients could signify a risk of developing VT later on. In conclusion, 9/17 patients who died suddenly did not have LP. The risk of sudden death due to primary VF or V flutter cannot be predicted. Other causes of VF are even harder to identify.     

QRS interval in tricyclic antidepressant overdosage: inaccuracy as a toxicity indicator in emergency settings

Emergency department treatment and disposition of tricyclic antidepressant (TCA)-overdose patients remains a common and difficult problem. Various clinical findings have been proposed as toxicity indicators. To study the performance of QRS duration as a predictor of toxicity in our patient population, we retrospectively reviewed the cases of all patients presenting to our ED with TCA overdosage. The charts of 102 patients with quantitative or qualitative laboratory confirmation of TCA ingestion were reviewed for ED findings and hospital course with specific attention to the occurrence of ventricular arrhythmias (VAs) or seizures. The ED ECG revealed that 57 patients had a maximal 12-lead ECG QRS interval duration (QRS) of less than .10 seconds (Group 1). The remaining 45 patients had QRS greater than or equal to .10 seconds (Group 2). Three patients (5%) in Group 1 and three (6%) in Group 2 experienced VAs. Four patients (7%) in Group 1 and five (11%) in Group 2 experienced seizures. There was no significant difference in the rate of occurrence of VAs or seizures between the two groups. Of note was the fact that five of eight VAs and nine of 11 seizures occurred in the ED setting. We conclude that determination of QRS duration is not an accurate indicator of VA or seizure risk for all TCA-overdose populations. In particular, risk of toxic events during the emergency phase of TCA overdose does not appear to be indicated by evaluation of the QRS duration in the ED.     

Efficacy of propafenone in preventing ventricular tachycardia: inverse correlation with rate-related prolongation of conduction time

The efficacy of propafenone in preventing induction of ventricular tachycardia was evaluated in 25 consecutive patients (mean age 62 +/- 8 years) with remote myocardial infarction who underwent programmed electrical stimulation for ventricular arrhythmia using up to three extra-stimuli after basic drive at the right ventricular apex. In nine patients (Group A), propafenone prevented induction of sustained ventricular tachycardia (noninducible in four, nonsustained [less than 30 s] in five). In the other 16 patients (Group B), sustained ventricular tachycardia was still inducible; in 11 of the 16, the tachycardia configuration was unchanged but the cycle length was significantly longer (431 +/- 99 versus 284 +/- 44 ms, p less than 0.001). Propafenone did not significantly affect either sinus cycle length or AH and HV intervals. However, it prolonged QRS duration during sinus rhythm equally in both groups of patients. With ventricular pacing, propafenone also prolonged right ventricular effective and functional refractory periods and surface QRS duration. There was greater lengthening of the paced surface QRS duration when drug therapy was ineffective (for example, +35 +/- 12 ms in Group A versus +69 +/- 23 ms in Group B at a basic drive of 400 ms, p less than 0.01). Drug-induced prolongation of a paced QRS complex greater than 40 ms had a 94% positive predictive value for drug failure to prevent induction of ventricular tachycardia. Drug-induced percent prolongation of ventricular tachycardia cycle length in Group B did not correlate well with percent QRS prolongation.(ABSTRACT TRUNCATED AT 250 WORDS)     

The signal-averaged electrocardiogram as a screening test for inducibility of sustained ventricular tachycardia in high risk patients: a prospective study

The role of the signal-averaged electrocardiogram in predicting the induction of sustained monomorphic ventricular tachycardia in high risk patients was assessed prospectively in 100 consecutive patients. Presenting diagnoses were syncope (38 patients), nonsustained ventricular tachycardia (24 patients), sustained ventricular tachycardia (25 patients) and sudden cardiac arrest (13 patients). Using programmed ventricular stimulation, 71 patients (group I) did not have and 29 patients (group II) did have inducible sustained monomorphic ventricular tachycardia. Using the signal-averaged electrocardiogram with filtering (6 dB/octave) at high pass corner frequencies of 67 and 100 Hz, the two groups were compared. The signal-averaged electrocardiogram was considered abnormal if all of the following criteria were satisfied: 1) the total filtered QRS complex duration was greater than 120 ms, 2) the duration of the terminal QRS complex of less than or equal to 20 microV was greater than or equal to 30 ms, and 3) at least one deflection (late potential) was present in this region. Differences between groups I and II in these three measures were highly significant (p less than or equal to 0.001). The sensitivity and specificity of signal averaging for predicting the induction of sustained ventricular tachycardia were 93 and 94%, respectively. Stepwise logistic regression analysis identified the signal-averaged electrocardiogram as the best predictor of induction of sustained monomorphic ventricular tachycardia, independent of left ventricular ejection fraction, presence of ventricular aneurysm, myocardial infarction and other clinical variables (chi-square = 93.2, p less than 0.0001). The signal-averaged electrocardiogram is a sensitive and specific test for the induction of sustained monomorphic ventricular tachycardia, having independent predictive value.     

Signal averaging of the surface QRS complex predicts inducibility of ventricular tachycardia in patients with syncope of unknown origin: a prospective study

Forty patients with syncope of unknown origin underwent quantitative signal averaging of the surface QRS complex before invasive electrophysiologic testing with programmed ventricular stimulation. Of 34 patients without bundle branch block, 12 had inducible ventricular tachycardia (Group I) and 22 did not (Group II). The duration of low amplitude signals, the root mean square voltage of the terminal 40 ms and the signal-averaged QRS vector duration were measured in each case. One or more abnormal signal averaging variables were present in 92% of patients in Group I, but in only 27% of patients in Group II (p less than 0.005). An abnormal root mean square voltage of the terminal 40 ms was the most significant distinguishing variable, being present in 83% of Group I patients and in only 14% of Group II patients (p less than 0.005). The QRS vector duration was prolonged in 58% of Group I patients, but in only 9% of Group II patients (p less than 0.05). Likewise, the duration of low amplitude signals was prolonged in 58% of Group I patients, but in only 19% of Group II patients (p less than 0.05). When compared with 24 hour ambulatory electrocardiographic monitoring, the presence of abnormal signal averaging variables was more predictive of inducible ventricular tachycardia. Seven (32%) Group II patients had greater than or equal to 10 ventricular premature beats/h, couplets or episodes of nonsustained ventricular tachycardia; however, none had abnormal late potentials recorded. In contrast, three patients (25%) in Group I had less than 10 ventricular premature beats/h, although all in that group had one or more abnormal signal-averaged variables.(ABSTRACT TRUNCATED AT 250 WORDS)     

Signal averaging of the electrocardiogram in the remote differential diagnosis of broad complex tachycardias

The diagnosis of the origin of a broad complex tachycardia may be difficult, especially in the absence of a 12-lead electrocardiogram of the tachycardia. This study investigates the value of signal averaging in the differential diagnosis of broad complex tachycardia. Signal averaging during sinus rhythm was performed in 102 consecutive patients who presented with broad complex tachycardia (QRS width greater than 110 ms), in whom a definitive electrophysiological diagnosis was made. The presence of late potentials was determined on the basis of two definitions, the second including total QRS duration. The patients studied included 75 with ventricular tachycardia; 33 of these patients had suffered previous myocardial infarction, five had dilated cardiomyopathy, and 37 had a 'normal' heart. Of the 27 patients with supraventricular tachycardia, 22 had an atrioventricular accessory pathway (seven with a delta wave in sinus rhythm), three had atrioventricular nodal tachycardia and two had atrial tachycardia. The sensitivity of late potentials for the diagnosis of ventricular tachycardia was low utilizing both definitions (28% and 45%) although specificity was high (96% and 95%). The sensitivity for the diagnosis of ventricular tachycardia was higher for patients with ischaemic heart disease (43% and 70%) but very low for patients with ventricular tachycardia and a normal heart (16% and 22%). In conclusion, signal averaging in the remote diagnosis of broad complex tachycardia is specific but not sensitive for ventricular tachycardia, which limits its usefulness in selecting patients for electrophysiological study.     

Late ventricular potentials and spontaneous and electric stimulation-induced ventricular tachycardia

The purpose of this study was to compare the relation of signal averaged variables of the QRS complex to spontaneous and to inducible sustained ventricular tachycardia. Signal averaging of the surface QRS complex was performed in 96 patients with coronary artery disease and ventricular arrhythmias. Twenty eight of them were evaluated by programmed electrical stimulation. Signal average variables were considered abnormal as: 1) the QRS duration as the time from the onset to end point of the QRS vector complex greater than 120 ms, 2) the maximal amplitude of the terminal 40 ms of the QRS vector complex less than 25 microV, 3) the duration of low (less than 40 microV) amplitude signal of QRS vector complex less than or equal to 40 ms. The ventricular late potentials were defined as the pressure of 2 or 3 abnormal averaged variables. Programmed electrical stimulation was performed using single and double extrastimuli at sinus rhythm and at ventricular pacing rates 100, 120, 140 bpm, followed by ventricular burst pacing (3 and 10 consecutive beats) at sinus rhythm. If stimulation of the right ventricular apex did not initiate ventricular arrhythmias (sustained ventricular tachycardia, ventricular fibrillation or two repetitive nonsustained ventricular tachycardias) right ventricular outflow tract stimulation was performed. Sustained ventricular tachycardia was defined as ventricular tachycardia lasting 30 s or requiring termination because hemodynamic compromise. Quantitative comparison of signal averaged variables was performed in patients with inducible versus noninducible ventricular tachycardia and in patients with spontaneous versus non-spontaneous ventricular tachycardia.(ABSTRACT TRUNCATED AT 250 WORDS)     

Determinants of QRS alternans during narrow QRS tachycardia

This study was designed to prospectively determine the incidence of QRS alternans during various types of narrow QRS tachycardia and to clarify the determinants of QRS alternans. An electrophysiologic study was performed in 28 consecutive patients with a narrow QRS tachycardia. Persistent QRS alternans was observed in 6 (43%) of 14 patients during orthodromic reciprocating tachycardia, 5 (71%) of 7 patients during atrial tachycardia and 3 (43%) of 7 patients during atrioventricular (AV) node reentrant tachycardia. Incremental atrial pacing during sinus rhythm resulted in QRS alternans in patients who had QRS alternans during tachycardia, unless the shortest pacing cycle length associated with 1:1 AV conduction exceeded the tachycardia cycle length. In patients without QRS alternans during narrow QRS tachycardia, incremental atrial pacing during sinus rhythm resulted in persistent QRS alternans in five patients in whom the shortest pacing cycle length associated with 1:1 AV conduction was 60 to 180 ms less than the tachycardia cycle length. In an additional 20 patients without a narrow QRS tachycardia, persistent QRS alternans was observed during incremental atrial pacing in 11 (55%) of the patients. In six of six patients who had QRS alternans during abrupt rapid atrial pacing, QRS alternans was not observed when the same pacing rates were achieved gradually. Among the patients with narrow QRS tachycardia, the mean tachycardia cycle length in those who had QRS alternans (mean +/- SD 288 +/- 44 ms) was significantly shorter than in those who did not (369 +/- 52 ms, p less than 0.001). The presence of QRS alternans was not related to the tachycardia mechanism, relative or functional refractory period of the His-Purkinje system (at a drive cycle length of 500 ms), age, presence of structural heart disease, direction of input into the AV node or concealed retrograde conduction in the His-Purkinje system. In conclusion, QRS alternans during narrow QRS tachycardias is a rate-related phenomenon that depends on an abrupt increase to a critical rate and is independent of the tachycardia mechanism.     

Quantitative analysis of the high-frequency components of the signal-averaged QRS complex in patients with acute myocardial infarction: a prospective study

We performed a prospective study of the high-frequency components of the terminal portion of the QRS complex in 50 patients with acute myocardial infarction (AMI) (mean age 63 +/- 10 years) within 3.25 +/- 2.45 days of the acute event. Signal averaging (400 beats) at a filter setting of 80 to 300 Hz was performed and the duration of the low-amplitude signals of less than 40 microV in the terminal portion of the QRS, the root-mean-square (RMS) voltage of the terminal 40 msec of the QRS complex, and the total duration of the signal-averaged QRS vector complex were measured. The low-amplitude signals were abnormally prolonged in 22 of 50 patients (44%); the RMS-V was abnormal (less than 20 microV) in 21 of 50 patients (58%), and the signal-averaged vector complex was abnormal (greater than 120 msec) in 15 of 46 patients (33%) without bundle branch block. There was no significant correlation between any of the signal-averaged parameters and site of AMI or total creatine kinase (CK) and CK-MB values. On the basis of the occurrence of spontaneous ventricular tachycardia in the acute and postcoronary care phase of AMI, the patients were divided into two groups. Group I consisted of 31 patients (62%) who had no documented ventricular tachycardia and group II consisted of 19 patients (38%) who had one or more runs of ventricular tachycardia. Fourteen of the 19 patients in group II (73.6%) had nonsustained ventricular tachycardia and five patients (26.3%) suffered sustained ventricular tachycardia/ventricular fibrillation or sudden death.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ventricular arrhythmia and late potentials in patients with hypertrophic cardiomyopathy]

Holter monitoring (48 h) and registration of signal-averaged late potentials (method of Simson, high pass filter 40 Hz) were performed in outpatiens with hypertrophic cardiomyopathy. A prevalence of spontaneous ventricular arrhythmias could be determined in 51 patients; the results of 45 patients not taking antiarrhythmic drugs are presented here. 96% of these showed ventricular premature beats, 76% had multiform extrasystoles, 27% showed pairs of ectopic beats and 20% had runs of ventricular tachycardia (more than 3 QRS complexes). Absolute counts of premature beats were low in most patients, but important interindividual differences could be observed: M = 34 extrasystoles/24 h (0-4943). Ventricular tachycardias were of short duration (maximum 11 QRS) with heart rate ranging from 120 to 200/min. All patients were asymptomatic during tachycardia. Signal-averaged late potentials could be registered in 30 patients, 28 of them without antiarrhythmic drug therapy. Mean QRS duration (QRSdur) was 108 +/- 12 ms, mean duration of low amplitude signals (less than 40 microV) in the terminal portion of the QRS (LAdur) was 27 +/- 13 ms, and mean amplitude of the last 40 ms of the filtered QRS (LAamp) was 65 +/- 43 microV. A patient was considered to show late potentials if two of the following criteria were present: QRSdur greater than 120 ms, LAdur greater than or equal to 40 ms, LAamp less than 20 microV. This was found in four patients.(ABSTRACT TRUNCATED AT 250 WORDS)     

Experimental amitriptyline intoxication: treatment of cardiac toxicity with sodium bicarbonate

Overdose with amitriptyline and other tricyclic antidepressants can result in ventricular conduction abnormalities as well as severe ventricular arrhythmias. The arrhythmogenic effects of these compounds may be attributed to their direct local anesthetic actions in blocking sodium channels in cardiac membranes. Thus tricyclic-induced ventricular arrhythmias usually do not respond well to therapy with standard Class I antiarrhythmic drugs that also have the same direct local anesthetic action and may potentiate the adverse effects of tricyclic antidepressants. Cardiac toxicity was produced in dogs by the administration of amitriptyline, both orally and IV. At serum concentrations less than 2,000 ng/mL, sinus tachycardia occurred with widened QRS complexes. At higher concentrations, QRS duration became more markedly prolonged and was followed by ventricular tachyarrhythmias. Occurrence of ventricular tachyarrhythmias was associated with QRS durations of more than 0.11 second. Sodium bicarbonate (18 to 36 mEq) administered IV over either 30 seconds or two minutes rapidly converted ventricular tachycardia to normal sinus rhythm. Conversion was associated with abbreviation of the QRS complex and was accompanied by a rise in both systolic and diastolic pressures. The duration of sodium bicarbonate effect paralleled the duration of the changes in arterial pH and plasma bicarbonate concentrations. In vitro studies in cardiac Purkinje fibers suggested that reversal of amitriptyline-induced cardiac membrane effects by sodium bicarbonate may be attributed not only to alkalinization but also to increased in extracellular sodium concentration, diminishing the local anesthetic action of amitriptyline and resulting in less sodium channel block.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cardiac resynchronization therapy in patients with narrow QRS

Conduction delay affecting 30-50% of patients with NYHA class III-IV heart failure (HF) mainly results from left bundle branch block and leads to deterioration of cardiac contractility through intra- and interventricular dyssynchrony. Cardiac resynchronization therapy (CRT) has class I recommendation for the treatment of patients with severe systolic HF who have left ventricular ejection fraction less or equal to 35%, QRS duration greater than or equal to 120 ms. Nevertheless some studies have shown that systolic asynchrony is present in 27-43% of HF patients with narrow QRS complexes (defined as <120 ms). We present here results of CRT in 20 patients (13 male, 7 female). Main indication for CRT was ventricular dyssynchrony during basic cardiac rhythm or cardiac pacing independently of QRS width. In 4 patients width of QRS complex was less than 120 ms, in 3 QRS varied from 120 to 149 ms pts and in 13 it was equal to or exceeded 150 ms. CRT in patients with narrow QRS resulted in clinical improvement associated with increase of cardiac contractility and decrease of left ventricular end systolic volume. This allows to conclude that CRT can be beneficial for HF patients with narrow QRS and ventricular dyssynchrony.     

改良Brugada四步法诊断室性心动过速价值初探

为评价改良的Brugada四步法诊断室性心动过速（VT）的价值，对心电图表现为宽QRS波（QRS时限＞110ms），心动过速行射频消融术的连续病例24例（其中经心脏电生理检查证实VT19例，室上性心动过速5例）进行回顾性分析，结果显示改良的Brugada四步法对VT的敏感性为94．7％，特异性为80％，阳性预告值为94．7％。     

Value and limitations of adenosine in the diagnosis and treatment of narrow and broad complex tachycardias

The diagnostic and therapeutic potential of intravenous adenosine was studied in 64 patients during 92 episodes of regular sustained tachycardia. In 40 patients who had narrow complex tachycardias (QRS less than 0.12 s) adenosine (2.5-25 mg) restored sinus rhythm in 25 with junctional tachycardias (46 of 48 episodes) and produced atrioventricular block to reveal atrial or sinus tachycardia in 15. In 24 patients with broad complex tachycardias (QRS greater than or equal to 0.12 s) adenosine terminated the tachycardias in six patients and revealed atrial or sinus arrhythmias in four. The tachycardias persisted in 14 patients despite doses up to 20 mg, but adenosine allowed the diagnosis of ventricular tachycardia with retrograde atrial activation in two patients by producing transient ventriculoatrial dissociation. Diagnosis based on adenosine induced atrioventricular nodal block was correct in all patients with narrow complex tachycardias and in 92% of those with broad complex tachycardias, compared with correct electrocardiographic diagnoses in 90% and 75% respectively. Adenosine gave diagnostic information additional to the electrocardiogram in 25%. The response to adenosine in broad complex tachycardias identified those of supraventricular origin with 90% sensitivity, 93% specificity, and 92% predictive accuracy. Adenosine restored sinus rhythm in all patients with junctional reentrant tachycardias, but in 10 (35%) the arrhythmias recurred within two minutes. Symptomatic side effects (dyspnoea, chest pain, flushing, headache) were reported by 40 (63%) patients and, although transient, were severe in 23 (36%). There were ventricular pauses of over 2 s in 16% of patients, the longest pause being 6.1 s. Adenosine is of value in the diagnosis and treatment of narrow and broad complex tachycardias, but its use is limited by symptomatic side effects, a tenfold range in minimal effective dosage, occasional action at sites other than the atrioventricular node, and early recurrence or arrhythmia.     

Value and limitations of adenosine in the diagnosis and treatment of narrow and broad complex tachycardias.

The diagnostic and therapeutic potential of intravenous adenosine was studied in 64 patients during 92 episodes of regular sustained tachycardia. In 40 patients who had narrow complex tachycardias (QRS less than 0.12 s) adenosine (2.5-25 mg) restored sinus rhythm in 25 with junctional tachycardias (46 of 48 episodes) and produced atrioventricular block to reveal atrial or sinus tachycardia in 15. In 24 patients with broad complex tachycardias (QRS greater than or equal to 0.12 s) adenosine terminated the tachycardias in six patients and revealed atrial or sinus arrhythmias in four. The tachycardias persisted in 14 patients despite doses up to 20 mg, but adenosine allowed the diagnosis of ventricular tachycardia with retrograde atrial activation in two patients by producing transient ventriculoatrial dissociation. Diagnosis based on adenosine induced atrioventricular nodal block was correct in all patients with narrow complex tachycardias and in 92% of those with broad complex tachycardias, compared with correct electrocardiographic diagnoses in 90% and 75% respectively. Adenosine gave diagnostic information additional to the electrocardiogram in 25%. The response to adenosine in broad complex tachycardias identified those of supraventricular origin with 90% sensitivity, 93% specificity, and 92% predictive accuracy. Adenosine restored sinus rhythm in all patients with junctional reentrant tachycardias, but in 10 (35%) the arrhythmias recurred within two minutes. Symptomatic side effects (dyspnoea, chest pain, flushing, headache) were reported by 40 (63%) patients and, although transient, were severe in 23 (36%). There were ventricular pauses of over 2 s in 16% of patients, the longest pause being 6.1 s. Adenosine is of value in the diagnosis and treatment of narrow and broad complex tachycardias, but its use is limited by symptomatic side effects, a tenfold range in minimal effective dosage, occasional action at sites other than the atrioventricular node, and early recurrence or arrhythmia.     

Incessant ventricular tachycardia in infants: myocardial hamartomas and surgical cure

Infants with incessant ventricular tachycardia (occurring greater than 10% of the day) have generally been described in pathologic studies. This report describes 21 patients with incessant ventricular tachycardia present greater than 90% of the day and night; the age at diagnosis ranged from birth to 30 months (mean 10.5 months). The most common clinical presentation was cardiac arrest (11 patients, in 5 after digitalis for presumed supraventricular tachycardia); another 6 patients had congestive heart failure and 4 were asymptomatic. Three patients had coexisting Wolff-Parkinson-White syndrome. The rate of incessant ventricular tachycardia ranged from 167 to 440 (mean 260 beats/min) and the QRS duration from 0.06 to 0.11 second. The most common electrocardiographic (ECG) pattern (10 of 21) was right bundle branch block with left axis deviation, but other right and left bundle branch block patterns were observed. Conventional and investigational antiarrhythmic agents (nine patients received amiodarone) failed to eliminate incessant ventricular tachycardia in all. Electrophysiologic studies localized incessant ventricular tachycardia to the left ventricle in 17 (to the apex in 2, the free wall in 9 and the septum in 6) and to the right ventricular septum in 4. No structural abnormalities were found on the echocardiogram or angiocardiogram. All 21 patients had surgery at an age of 3.5 to 31 months (mean 16). In 15 a tumor was found: 13 myocardial hamartomas (9 discrete, 4 diffuse throughout both ventricles) and 2 rhabdomyomas (1 multiple). Myocarditis was found in one patient (the oldest). In four, only myocardial fibrosis was found; results of one biopsy were normal.(ABSTRACT TRUNCATED AT 250 WORDS)     

Improving the predictive ability of the signal-averaged electrocardiogram with a linear logistic model incorporating clinical variables

To improve the predictive accuracy of the signal-averaged electrocardiogram, we created a linear logistic model for predicting ventricular tachycardia during electrophysiologic testing. This signal-averaged electrocardiographic model was created from data obtained from 214 patients undergoing electrophysiologic testing (70 had ventricular tachycardia during electrophysiologic testing) by using stepwise logistic regression to rank eight clinical and nine signal-averaged electrocardiographic variables. The best predictors were ejection fraction, history of infarction, ventricular ectopic pairs or nonsustained ventricular tachycardia on Holter monitoring, QRS duration after 25-Hz filtering, and root mean square voltage of the terminal 40 msec of the QRS complex after 40- and 80-Hz filtering. Cross validation (a statistical technique that can be used to accurately evaluate how a predictive model will perform on a prospective patient population) was used to validate the model. After cross validation, the model's sensitivity was 91% and specificity was 59% for predicting ventricular tachycardia during electrophysiologic testing. This model compared favorably with established 25-Hz late-potential criteria (QRS duration of more than 110 msec and root mean square voltage of less than 25 microV of the terminal 40 msec of the QRS complex; sensitivity, 64%; specificity, 85%) and with established 40-Hz late-potential criteria (QRS duration of more than 114 msec or root mean square voltage of less than 20 microV of the terminal 40 msec of the QRS complex or duration of the low-amplitude signal less than 40 microV at the terminal QRS complex that is greater than 38 msec; sensitivity, 84%; specificity, 54%).(ABSTRACT TRUNCATED AT 250 WORDS)