Biomedical subjects

M Shenasa

Publications and source records attributed to M Shenasa.

At least 73 records · Page 4Linked to original sources

PubMed1990

Predictors of survival and sudden death in patients with stable severe congestive heart failure due to ischemic and nonischemic causes: a prospective long term study of 200 patients.

This prospective study of 200 stable outpatients with New York Hospital Association (NYHA) class III congestive heart failure on maximal medical therapy was done to determine which factors affect survival, to record the incidence of sudden death, and to identify prognostic features which characterize patients at high risk of sudden death. Congestive heart failure was due to coronary artery disease in 151 patients (76%). After an average follow-up of 40 months, 96 patients (48%) had died: 30 (15%) suddenly, 41 (22%) of low output, and 25 (13%) of other causes. Of the 30 patients dying suddenly 12 had autopsies, and acute myocardial infarction was found in nine. Of the 41 patients dying of low output 15 had autopsies, and recent myocardial infarction was found in five. Nine of the 25 patients dying of other causes died of acute myocardial infarction. Multivariate stepwise analysis revealed that severity of ventricular arrhythmias (modified Lown classification), exercise tolerance and left ventricular ejection fraction were the most important determinants of survival. In patients with coronary artery disease, complex ventricular arrhythmias detected by ambulatory Holter monitoring were frequent in all groups and were not clinically useful in predicting which of these patients were at a higher risk of dying suddenly. In contrast, patients without coronary artery disease who died suddenly had a higher incidence of nonsustained ventricular tachycardia and a tendency towards more frequent ventricular arrhythmias in general. The authors conclude that in ambulatory patients with stable NYHA class III heart failure, the severity of ventricular arrhythmias is a predictor of survival.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗

PubMed1990

[The origin of late potentials in patients with ventricular tachycardia after myocardial infarction].

In order to study the origin of late potentials, their distribution was analyzed in 16 patients who had undergone surgery for arrhythmia due to ventricular tachycardia following myocardial infarction. The potentials were measured in sinus rhythm using 63 unipolar leads placed on the chest before the operation, then on the epicardium and endocardium during the operation. Epicardial and/or endocardial activity extending beyond the QRS complex measured from unfiltered chest signals and characterized by slowed propagation at the edge or inside of necrotic regions, stable from one beat to the next, and showing simple (39 per cent), double (34 per cent) or fragmented (27 per cent) deflections on the electrocardiograms were observed in 5/6 patients without bundle-branch block and in 5/10 patients with block. Similar activity but which did not extend after the QRS was detected in the 6 other patients. For signals filtered at 55 Hz, a close correlation between the distribution of chest, epicardial and endocardial potentials was observed, thus allowing approximate location of the origin of late potentials from the chest. Anterior or apical sites corresponded to close extrema in the precordial region, whereas the other sites were associated with more distant extrema. An analysis of potential distribution thus gives a better understanding of the electrogenesis of late potentials as well as their detection on the chest.

Aged↗

PubMed1989

Electrophysiologic effects of intravenous propafenone in Wolff-Parkinson-White syndrome.

The electrophysiologic effects of intravenous propafenone were studied in 15 consecutive patients with accessory pathways. Thirteen patients had sustained orthodromic supraventricular tachycardia induced during baseline study, and two patients needed isoproterenol to render it sustained. In all except one patient, propafenone, 2 mg/kg given intravenously over a 10-minute period, was successful in converting the arrhythmia to sinus rhythm. Atrial fibrillation was inducible in 10 patients before propafenone, but was no longer inducible in seven of these patients after the drug. The HV interval (23 +/- 20 to 41 +/- 25 msec) and the anterograde (310 +/- 96 to 509 +/- 145 msec) and retrograde (256 +/- 30 to 334 +/- 105 msec) effective refractory periods of the bypass tract were all significantly prolonged after the drug. The pacing cycle length that produced conduction block over the bypass tract anterogradely (319 +/- 126 to 446 +/- 150 msec) and retrogradely (272 +/- 25 to 360 +/- 97 msec) was also increased. During orthodromic tachycardia, propafenone increased conduction time in both the anterograde and retrograde limbs of the tachycardia. Tachycardia terminated in the retrograde limb in 64% of the patients. We conclude that propafenone is very effective in terminating orthodromic tachycardia when given intravenously and that it should be considered in patients initially seen with atrial fibrillation and short refractory periods.

Adult↗

PubMed1989

Performance degradation of the coherent averaging technique by a molding effect.

In coherent averaging, we show that when temporal alignment is performed by matched filtering, the SNR improvement may reach a stable limit after a certain number of averaged events. The source of this degradation lies in the noise that can be contained in the template of the matched filter. This effect depends on the SNR and the morphology of the signal and it can be reduced by a multipass averaging procedure or by a template updating technique.

Computer Simulation↗

PubMed1989

Differential effects of abrupt cycle length changes on the refractoriness of accessory pathway, His-Purkinje system, atrial and ventricular myocardium in Wolff-Parkinson-White syndrome.

We compared the response of the accessory pathway (AP), the atrial myocardium, the His-Purkinje system (HPS) and the ventricular myocardium during steady state (constant cycle length) and following an abrupt alteration in cycle length in 23 patients with Wolff-Parkinson-White syndrome. The durations of the anterograde and retrograde refractory periods were measured during constant drive cycle lengths of 600 and 400 ms (Method I) and during an abrupt change in cycle length of either short-to-long (400 to 600 ms) (Method II) or long-to-short (600 to 400 ms) (Method III) just before the extra stimulus. The mean durations of the anterograde effective refractory periods of the APs were 295 +/- 43, 243 +/- 39 and 273 +/- 37 ms at 600, 400 and 400 to 600 ms cycle lengths, respectively. For the atrial effective refractory periods at the three cycles, they were 238 +/- 18, 217 +/- 11 and 241 +/- 17 ms, respectively. During ventricular stimulation, the mean durations of the retrograde effective refractory periods of the APs were 263 +/- 25, 245 +/- 19 and 253 +/- 21 ms at cycle lengths of 600, 400 and 400 to 600 ms, respectively. For the relative refractory periods of the HPS, they were 335 +/- 29, 239 +/- 23 and 367 +/- 38 ms, respectively and, for the effective refractory periods of the ventricular myocardium, they were 227 +/- 17, 206 +/- 15 and 215 +/- 18 ms, respectively. The retrograde effective refractory period of the HPS could be measured in only five patients at the three cycles (600, 400 and 400 to 600 ms) and the mean values were 265 +/- 57, 225 +/- 14 and 305 +/- 27 ms, respectively. With Method III, AP and ventricular myocardium responded in a cumulative manner while HPS demonstrated paradoxical effect. Compared to Method I, changes with Methods II and III were statistically significant for all variables measured. During all three cycles, the retrograde effective refractory period of the HPS exceeded the effective refractory period of the AP; and the HPS demonstrated progressive conduction delay while the AP responded to no or minimal delays when the V1V2 intervals were similar. An abrupt cycle length change of the short-to-long type facilitated the induction of orthodromic tachycardia during ventricular pacing.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

PubMed1989

Surgical treatment of ventricular tachycardia. Regional cryoablation guided by computerized epicardial and endocardial mapping.

Extended cryoablation as a single method of myocardial ablation was used for surgical treatment of 33 patients with ventricular tachycardia associated with coronary artery disease. Surgery was guided by roving-probe mapping in 14 patients and by computerized epicardial and computerized, left ventricular, endocardial, multielectrode mapping in 19 patients. In the latter group, the anatomic correlation between sites of the earliest epicardial activation (EA-EPI) and those of the earliest endocardial activation (EA-ENDO) was found to be consistent in the apical region. In contrast, the EA-ENDO corresponding to the EA-EPI localized in the left anterolateral and posterobasal free-wall regions could be localized either in an underlying area or on the septum. All tachycardias with EA-EPI in anterior and posterior right ventricular regions had their corresponding EA-ENDOs in the interventricular septum. EA-ENDO preceded EA-EPI in 33 of 41 tachycardias studied. The converse was observed in the remaining eight tachycardias. Cryoablation was applied regionally in areas corresponding to EA-ENDO, along with standard aneurysmectomy and coronary artery bypass grafting when indicated. Among the entire group of 33 patients, there were two (6%) operative deaths. Ventricular tachycardias recurred spontaneously in two (6%) patients and remained inducible in four (13%), of whom one (3%) died suddenly. After hospital deaths were taken into account, actuarial survival was 74 +/- 9% (mean +/- SD) at 48 months after operation. Among the 10 patients who had an EA-EPI on the right ventricle and an EA-ENDO on the interventricular septum, deep septal involvement was suspected, and arrhythmic failure occurred in five patients; in contrast, complete surgical success was obtained in all nine patients who did not display this pattern during intraoperative investigation. We conclude that regional cryoablation alone in areas of the earliest left ventricular activation is highly effective for treatment of ventricular tachycardia, except in a subset of patients with specific markers of deep septal involvement, which can be detected by computerized epicardial and endocardial mapping.

Action Potentials↗

PubMed1989

Long term efficacy and toxicity of amiodarone in the treatment of refractory cardiac arrhythmias.

Amiodarone has remarkable efficacy, but it also has a high incidence of severe side effects. Nevertheless, it is extensively used. The findings of an amiodarone treatment follow-up period of one to 72 months (mean 19 +/- 17) in 95 patients with recurrent life threatening arrhythmias resistant to other antiarrhythmic drugs are described. The mean loading dose of 800 mg/day for one week was followed by an average dose of 600 mg/day for two weeks. The long term daily dose was 400 mg in 80 patients and 200 mg in the remaining 15 patients. Amiodarone was particularly effective in suppressing complex ventricular arrhythmias. It also decreased premature ventricular beats by 83% and atrial premature beats by 41%. Supraventricular tachycardias were completely controlled and the ventricular response to atrial fibrillation was slowed. Twelve of the 95 patients (12.6%) died while taking amiodarone, two of sudden death and 10 of heart failure. Side effects were recorded in 77 (81%) patients. They were generally dose related and subsided with a decrease in dose or discontinuation of the medication. There was a correlation between the concentration of rT3 and the significance of the side effects. Thirty-nine patients stopped taking amiodarone, however, only 14 of these stopped because of toxicity: five developed pulmonary fibrosis; three had neurological toxicity; two had bradyarrhythmias; two developed hepatic dysfunction; one had hypothyroidism; and one patient suffered an aggravation of a pre-existent heart failure. It was concluded that amiodarone is a very effective treatment for supraventricular and ventricular arrhythmias. However, it does have numerous and severe side effects.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1988

Wide QRS complex tachycardia. Reappraisal of a common clinical problem.

BACKGROUND AND PURPOSE: Despite available criteria, diagnosis of the mechanisms of wide complex tachycardia is often incorrect. We aimed in this study to identify reasons for misdiagnoses and the value and limitations of clinical and surface electrocardiographic criteria. DATA IDENTIFICATION: The analyzed data of 150 consecutive patients with wide QRS tachycardia from this study and a literature search of key papers in English since 1960 on clinical and surface electrocardiographic criteria form the basis of this report. The final correct diagnosis was made with intracardiac electrograms. DATA EXTRACTION AND ANALYSIS: Among the 150 patients, 122 had ventricular tachycardia, 21 had supraventricular tachycardia with aberrant conduction, and 7 had accessory pathway conduction. Only 39 of 122 patients with ventricular tachycardia were correctly diagnosed initially. In others, the diagnoses were supraventricular tachycardia with aberrant conduction (43 of 122) or simply a wide QRS tachycardia (40 of 122). Misdiagnosis in patients with aberrant or accessory pathway conduction was also common. Standard electrocardiographic criteria for ventricular tachycardia had unacceptable sensitivity, poor specificity, or both. Collectively such criteria allowed a correct diagnosis of ventricular tachycardia in 92% of cases. Diagnosis of ventricular tachycardia was also suggested by its association with structural heart disease. Criteria suggestive of ventricular tachycardia included atrioventricular dissociation, positive QRS concordance, axis less than -90 deg to +/- 180 deg, combination of left bundle branch block and right axis, QRS duration of greater than 140 ms with right bundle branch block and greater than 160 ms with left bundle branch block and, a different QRS during tachycardia compared to baseline preexisting bundle branch block. CONCLUSIONS: Ventricular tachycardia is the commonest underlying mechanism for wide QRS tachycardia. A correct diagnosis can usually be made from clinical and surface electrocardiographic criteria.

Adolescent↗

PubMed1988

Effect of intravenous and oral calcium antagonists (diltiazem and verapamil) on sustenance of atrial fibrillation.

Both verapamil and diltiazem are used to control ventricular response during atrial fibrillation (AF). Their effect on the maintenance of AF is not known. The effects of the intravenous and oral administration of verapamil and diltiazem were investigated in 35 patients, 18 with (group I) and 17 without (group II) documented paroxysmal AF. Programmed electrical stimulation, either extra-stimuli or burst atrial pacing, was used to induce AF. In group I, the mean values of the duration of AF before and after the intravenous and oral administration of the calcium antagonists were 31 +/- 12, 112 +/- 49 and 69 +/- 25 minutes, respectively. For group II, the values were 5 +/- 3.4, 39 +/- 13 and 14 +/- 7 minutes, respectively. The differences were statistically highly significant (p less than 0.001), after both oral and intravenous administration compared with the baseline value in both groups. The data suggest that both intravenously and orally administered calcium antagonists enhance sustenance of electrically induced AF, especially in patients with spontaneous arrhythmia. Thus, in patients with paroxysmal AF, verapamil or diltiazem should be administered cautiously, because these drugs may prolong the duration of arrhythmia. Further studies are warranted to investigate the role of calcium antagonists in spontaneously occurring paroxysmal AF.

Administration, Oral↗

PubMed1988

Effect of induced ventricular tachycardia on atrial natriuretic peptide in humans.

The effects of induced sustained ventricular tachycardia on the release of plasma-immunoreactive atrial natriuretic peptide were evaluated in 11 adult patients undergoing diagnostic electrophysiologic study. Plasma concentrations of atrial natriuretic peptide withdrawn from the right atrium before and during sustained ventricular tachycardia (mean tachycardia cycle length 320 +/- 68 ms, duration greater than 30 s) were determined by radioimmunoassay. Hemodynamic measurements included phasic femoral artery blood pressure and mean right atrial blood pressure before and during ventricular tachycardia. During ventricular tachycardia, atrial natriuretic peptide increased from 93 +/- 49 pg/ml to 234 +/- 195 pg/ml (p less than 0.05), systolic arterial blood pressure decreased from 120 +/- 16 to 70 +/- 23 mm Hg (p less than 0.001), diastolic arterial blood pressure decreased from 63 +/- 8 to 51 +/- 16 mm Hg (p = NS) and mean right atrial blood pressure increased from 3 +/- 1 to 8 +/- 5 mm Hg (p less than 0.02). In six patients, all hemodynamic variables and the atrial natriuretic peptide were measured during repeated stimulation protocols to investigate the effect of ventricular stimulation for ventricular tachycardia induction on atrial natriuretic factor release. Compared with the values obtained during sinus rhythm, there was no significant increase in atrial natriuretic factor during ventricular stimulation at a cycle length of 600 ms (45 +/- 20 versus 52 +/- 21 pg/ml) or at a cycle length of 400 ms (45 +/- 20 versus 57 +/- 18 pg/ml). No significant linear relation could be found among the changes in mean right atrial pressure, systolic arterial blood pressure and the increase in atrial natriuretic peptide.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1988

Atrioventricular nodal conduction and refractoriness following abrupt changes in cycle length.

The properties of the atrioventricular (AV) nodal conduction and effective refractory period in man are generally evaluated at a constant basic cycle length (CL) and, in most cases, they demonstrate an inverse relationship to the drive cycle. The response of AV node to abrupt change in CL is less defined. We therefore studied the effects of abrupt changes in CL on AV nodal conduction time and refractoriness in 18 patients. AV nodal conduction time, and effective and functional refractory periods were measured during: (1) a constant long CL, (2) a constant short CL, and (3) after an abrupt increase in CL just prior to the introduction of extrastimuli. In 10 of the 18 patients a constant long CL of 600 ms, a constant short CL of 400 ms and a sudden short-to-long change in CL (400 to 600 ms) were tested. AV nodal conduction times (A2H2) were measured at the shortest and longest comparable A1A2 intervals. The mean value of the shortest A2H2 intervals for constant CL of 600 ms was 144 +/- 18 ms; for a constant CL of 400 ms it was 162 +/- 17 ms; after a sudden short-to-long change in CL (400 to 600 ms) it was 142 +/- 14 ms. The mean value of the longest A2H2 intervals at a constant CL of 600 ms was 185 +/- 18 ms; at a constant CL of 400 ms it was 236 +/- 26 ms (p less than 0.01) and after a short-to-long change in CL (400 to 600 ms) 199 +/- 21 ms. AV nodal effective refractory periods measured at the same three CLs had mean values of 279 +/- 13 ms; 300 +/- 15 ms and 294 +/- 13 ms, respectively. Similar results were obtained when other CLs such as 700 to 900, 500 to 900, and 400 to 700 ms were tested. The data suggest that after abrupt short-to-long changes in CL, AV nodal function curves shift from long constant CL toward short constant CL as the coupling intervals decrease, indicating a cumulative pattern. Although the return to baseline conduction time after the fast basic rate is known to be slow, the limitation of this effect to the very early premature beat in the human has not been reported previously.

Adult↗

PubMed1988

Sinus rhythm mapping in a canine model of ventricular tachycardia.

The relationship between electrograms recorded during sinus rhythm and the activation sequence during ventricular tachycardia induced by programmed stimulation was investigated in a canine model of myocardial infarction. Thirteen dogs were studied 3 days (n = 10) or 14 days (n = 3) after coronary occlusion. Sixty-three unipolar electrograms were simultaneously recorded with a sock electrode array connected to a digital recording system, and analyzed by computer. Bipolar electrograms were recorded sequentially from the same sites with an analog recorder. Categories of unipolar electrograms were defined with reference to the QRS complex during sinus rhythm as follows: Class A included electrograms with an intrinsic deflection inscribed within the QRS complex, class B included those which did not exhibit any intrinsic rs deflection, and class C included those with an intrinsic deflection inscribed later than QRS. The epicardial distribution of each class of electrograms was significantly different between the preparations with, and those without inducible tachycardia (72% versus 63% of electrograms being in class A, 20% versus 35% in class B, and 8% versus 2% in class C; p less than 0.005). When tachycardia was inducible, class C epicardial electrograms were located in an area extending across the region of infarction, which corresponded to the common reentrant pathway of figure-of-eight patterns mapped during tachycardia. When ventricular tachycardia was not inducible, class B electrograms were recorded all over this region. The morphology of bipolar electrograms had no predictive value in identifying the common reentrant pathway. These results support the view that the inducibility of reentrant tachycardia is dependent upon critically located delayed activity detected during sinus rhythm by unipolar recordings.

Animals↗

PubMed1988

Catheter recording of left atrial activation from left pulmonary artery in the Wolff-Parkinson-White syndrome: validation of the technique with intraoperative mapping results.

Accurate localization of accessory pathways (AP) in the Wolff-Parkinson-White (WPW) syndrome requires detailed atrial mapping. Coronary sinus catheterization is so far the most accurate method of left atrial mapping, but it can be technically difficult in some patients. We evaluated the feasibility of left atrial mapping from the left pulmonary artery in 24 patients with WPW syndrome. All patients except one underwent surgical cryoablation of their AP and the results of intraoperative mapping are available for comparison. Mapping in sinus rhythm showed recording of atrial activity in the distal left pulmonary artery occurred 56 +/- 20 ms after activation of high right atrium and 24 +/- 4 ms after activation in the His bundle area, but coincident with left atrial activation in the distal coronary sinus (56 +/- 20 and 53 +/- 13, respectively). Mapping during ventricular pacing or orthodromic tachycardia could differentiate patients as having a right sided, left sided or paraseptal first site of activation. Eleven patients had a left lateral AP, four had a left posterior AP, five had left posteroseptal AP and one had a left anterior AP. The remaining three patients had a right sided AP. Intraoperative results correlated with pre-operative findings in 22 out of 23 (95%) patients who underwent surgical ablation of AP. Thus, recordings form the left pulmonary artery reflect left atrial activity and may be of aid in localizing an AP, especially when coronary sinus recordings cannot be obtained. This technique, however, should not replace the more accurate method of coronary sinus mapping.

Adult↗

PubMed1988

Demonstration of hysteresis in refractoriness of canine ventricular myocardium.

The properties and determinants of hysteresis during ventricular effective refractory period (VERP) measurements by an extrastimulus technique were determined in 15 anesthetized open-chest dogs as well as in isolated ventricular muscle (n = 6). VERP was determined both by decreasing the S1-S2 interval and also by increasing S1S2. Hysteresis was then calculated by subtracting the VERP obtained with the decreasing S1S2 from the VERP obtained with the increasing S1S2. The effects of basic cycle length, pulse width, stimulation intensity, and the number of basic drives on VERP and hysteresis were evaluated. VERP was shorter for long pulse width, high stimulation intensities, and shorter basic cycle lengths. These modifications were not associated with significant changes of hysteresis. VERP was shorter during decreasing S1S2 than during increasing S1S2. Hysteresis was greater with 6 basic drive cycles than with 12 (P less than 0.001) in both in vivo and in vitro preparations. The data suggest that 1) hysteresis occurs during VERP measurements; 2) hysteresis is independent of stimulation modality; and 3) hysteresis decreases with the number of basic drive cycles.

Animals↗

PubMed1988

PQRST isoarea maps from patients with the Wolff-Parkinson-White syndrome: an index for global alterations of ventricular repolarization.

Isoarea maps during the PQRST sequence were computed in 22 healthy subjects and 48 patients with Wolff-Parkinson-White (WPW) syndrome. Thirty-eight patients with WPW were on no medication and 10 were treated with class I, II, or III antiarrhythmic drugs. Seventeen isoarea maps were recorded before and 17 were recorded after accessory pathway ablation. One patient had intermittent preexcitation. Body surface maps from all healthy subjects were similar, although the magnitudes of the maxima and minima showed significant variability. In all patients with WPW who were on no medication and in those on class I and II agents, PQRST maps were normal. Two patients taking amiodarone had abnormal PQRST maps, as did patients early after surgery. In the patient with intermittent preexcitation, PQRST maps were very similar during normal and preexcited beats. In conclusion, our results support the theory that the PQRST time integral reflects intrinsic recovery properties of the heart and is independent of the activation sequence.

Adult↗

PubMed1988

Anisotropic conduction and functional dissociation of ischemic tissue during reentrant ventricular tachycardia in canine myocardial infarction.

We measured the conduction characteristics at the epicardial surface of the left anterior ventricular wall in the in situ canine heart before and 3 to 5 days (n = 9 dogs) after permanent occlusion of the left anterior descending coronary artery (LAD). During ventricular stimulation generating wavefronts conducted along the longitudinal or the transverse fiber direction, 61 unipolar electrograms were recorded with a fine-meshed plaque electrode. Before occlusion, the fastest conduction velocity was consistently found in a direction perpendicular to the nearby LAD segment (longitudinal direction), and the slowest velocity in a direction parallel to the LAD segment (transverse fiber direction). In 3- to 5-day-old infarct preparations, a layer of subepicardial muscle with 1 to 3 mm thickness survived over necrotic tissue. The velocities and directions of fast and of slow conduction measured in ischemic subepicardial muscle were not significantly different from preocclusion values during stimulation at a basic rate, but excitability was found to be depressed in response to premature stimuli. Premature impulses initiated in nonischemic myocardium and conducted into ischemic tissue in the longitudinal or in the transverse directions induced sustained (greater than 100 beats) monomorphic tachycardias during which figure-eight activation patterns were mapped with sock-array electrodes. During these tachycardias, the direction of the common reentrant wavefront of the figure-eight pattern was preferentially oriented along the longitudinal fiber direction, independently of the direction of the initiating impulse. When polymorphic beats were induced, tachycardia terminated spontaneously within 20 beats, or changed to a monomorphic pattern, as described above. In conclusion, the anisotropic organization of surviving subepicardial muscle overlying an infarct provides a spatial constraint that determines a preferential direction of reentrant propagation and may contribute to sustaining monomorphic tachycardia.

Animals↗

PubMed1988

Termination of sustained ventricular tachycardia by ultrarapid subthreshold stimulation in humans.

Our purpose was to investigate the efficacy, safety, and electrophysiological mechanism of ultrarapid subthreshold electrical stimulation in terminating sustained ventricular tachycardia (VT) in humans. Fifteen patients with inducible sustained hemodynamically stable VT and whose VT cycle length ranged between 295 and 440 msec (337 +/- 60 msec) were included in this study. The stimulation threshold and ventricular myocardial effective refractory period were determined during VT, and the values ranged between 0.4 and 1.2 mA (mean, 0.7 +/- 0.3 mA) and between 185 and 245 msec (mean, 225 +/- 20 msec), respectively. Trains of ultrarapid subthreshold stimulation were delivered with cycle lengths of 100 to 10 msec in decremental steps of 10 msec. A 5-second pause was allowed between each step (decrement). A 2-msec pulse width was used in all patients, and a 4-msec pulse width was also tested in eight patients. Any apparent captured beat was disregarded. In eight (53%) patients, ultrarapid subthreshold stimulation terminated VT, and in the remaining seven (47%) patients, it did not. The lowest subthreshold stimulation that effectively terminated VT was 0.05 mA. In 10 patients, the site of early activity during VT was determined by endocardial catheter mapping, and subthreshold stimulation more effectively terminated VT in eight patients when it was applied close to the site of early activity. In seven patients who underwent mapping-guided arrhythmia surgery, subthreshold stimulation was applied close to the site of early activity and successfully terminated VT. In no patient did subthreshold stimulation produce acceleration of VT or induce ventricular fibrillation.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1988

Tachycardia cycle length and maximum capacity of anterograde and retrograde atrioventricular conduction in paroxysmal supraventricular tachycardia.

Anterograde and retrograde pathways are the two major components of the reentry circuit in patients with paroxysmal supraventricular reentrant tachycardias. Therefore, the capacity of each pathway to maintain 1:1 conduction would be expected to determine the cycle length (CL) of the tachycardia. In this study, the possible relationship between the CL of reentrant tachycardia and the maximum capacities of anterograde and retrograde conduction in the maintenance of a 1:1 response during atrial and ventricular pacing were examined. This relationship was analyzed in 26 patients with orthodromic reentrant tachycardia due to Wolff-Parkinson-White syndrome (group 1) and compared with that in 26 patients with atrioventricular nodal reentrant tachycardia (group 2). There were no statistically significant differences between the two groups in the shortest tachycardia CLs (mean +/- SD, 325 +/- 44 versus 329 +/- 52 ms); in the shortest ventricular pacing CLs with 1:1 response (314 +/- 63 versus 319 +/- 38 ms); nor in the CLs that produced retrograde atrioventricular block (306 +/- 62 versus 301 +/- 37 ms). In contrast, the longest atrial pacing CL that produced Wenckebach's phenomenon and the shortest atrial pacing CL with 1:1 response were significantly shorter for group 1 than for group 2 patients (290 +/- 38 versus 390 +/- 88 ms, P less than 0.001) and (305 +/- 38 versus 406 +/- 90 ms, P less than 0.001), respectively. It was concluded that the CL of orthodromic tachycardia can best be predicted from the shortest atrial pacing CL that maintains 1:1 anterograde conduction via the normal pathway.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗