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Beginning November 6, 1996, Food and Drug Administration regulation 21 CFR 50.24 has allowed research without consent in limited circumstances while requiring additional patient protection in the form of community consultation and disclosure. We report our experience in complying with these regulations in Multicenter Vest CPR protocol, the first investigational device study done under this new ruling. We found uncertainty in inter-pretation of the requirements for community consultation. The acceptance of research without consent varied among the parties exposed to this protocol, but neither physicians nor the lay public expressed major reservations. The consultation process was time-consuming, demanding, and relatively costly. Further clarification of the community consultation standard and additional dialogue on this important topic will help to foster additional research in cardiopulmonary resuscitation.

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ECG signal averaging can detect low amplitude diastolic potentials in sinus rhythm. We, therefore, recorded signal-averaged ECGs during eight episodes of inducible uniform sustained VT with coincident atrial pacing to look for continuous diastolic electrical activity. Simultaneous AV pacing in seven patients served as controls. The number of QRS complexes averaged (187 +/- 47 vs 183 +/- 63), the noise level (1.26 +/- 0.88 vs 1.39 +/- 0.47) and cycle length (385 +/- 52 vs 404 +/- 40) did not differ between VT and paced recordings. In each lead the difference in onset between the unfiltered surface recording and the filtered data (40 Hz bidirectional) was significantly greater in VT than the paced recordings (25 +/- 16 vs 11 +/- 8 msec, P = 0.0012). These late diastolic (pre-QRS) potentials were greater than 15 msec duration in 65% of the leads in VT versus 20% of paced recording (P = 0.021). The maximum value was greater than 20 msec in six VT (75%) versus one (14%) paced recording (P = 0.019). The earliest filtered onset in any lead preceeded the earliest surface activity by greater than 12 msec, in 6 VT versus one paced recording (P = 0.019). Early diastolic (post-QRS) potentials were also longer in VT than pacing (49 +/- 40 versus 5 +/- 20, P = 0.001) and exceeded 38 msec in seven of the VTs but none of the paced recordings (P = 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

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Electrocardiographic signal-averaging during sinus rhythm (61 to 99 beats/min) and atrial pacing (100 to 171 beats/min) were performed to determine the effect of heart rate on late potentials in 15 patients without (group 1) and 7 patients with (group 2) inducible sustained ventricular tachycardia (VT). In sinus rhythm (79 +/- 12 vs 77 +/- 12 beats/min, difference not significant), the duration of the low-amplitude signal less than 40 microV was longer in group 2 than group 1 (43 +/- 21 vs 26 +/- 8 ms, p = 0.034) and more patients had late potentials (57 vs 7%, p = 0.021), but QRS duration (121 +/- 32 vs 98 +/- 19 ms) and terminal voltage (33 +/- 33 vs 50 +/- 26 ms) were not significantly different. With atrial pacing in group 1 (128 +/- 16 beats/min), 3 patients developed a simultaneous decrease in terminal voltage and an increase in terminal QRS duration consistent with a late potential, but mean total and terminal durations were unchanged. Terminal voltage increased (50 +/- 26 to 59 +/- 40) but not significantly. With atrial pacing in group 2 (119 +/- 12 beats/min) all patients either had a late potential or developed a simultaneous decrease in terminal voltage and an increase in terminal QRS duration (p = 0.001 vs group 1). Root mean square (p = 0.001 vs group 1). Root mean square voltage decreased (33 +/- 23 to 22 +/- 23) and became significantly different from group 1 (p = 0.017). Mean QRS duration, root mean square terminal voltage and low-amplitude terminal QRS duration, however, were unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

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The timing of entrainment onset has been shown to correlate with the conduction time to critical elements of a tachycardia circuit in a pacemaker model of reentrant ventricular tachycardia (VT). The utility of this method in evaluating clinical reentrant tachycardias was therefore evaluated in 24 patients with symptomatic Wolff-Parkinson-White syndrome and single bypass tracts (left free wall in 17, posteroseptal in 5, anteroseptal in 1, and right free wall in 1). Right ventricular apex (RVA) pacing during orthodromic atrioventricular reentrant tachycardia (oAVRT) at 10-70 msec less than tachycardia cycle length demonstrated concealed entrainment of the tachycardia in all patients studied. An entrainment index (EI), defined as the minimal prematurity of the ventricular stimulus that first resulted in atrial reset, was calculated from multiple entrainments in each patient. The EI was 121 +/- 25, 83 +/- 19, and 55 msec for left free wall, septal, and right free-wall bypass tracts, respectively (P = 0.004 for difference between left free wall and septal). A corrected EI, derived by subtracting the amount of atrial reset from the EI, gave values of 108 +/- 22 and 71 +/- 17 msec for left free wall and septal bypass tracts (P = 0.001). These values were compared to the preexcitation index (PI) by linear regression analysis in these patients. The PI correlated closely with both the EI and the corrected EI (r = 0.90 and 0.93, respectively), but the PI could only be derived in 12/17 (71%) left free-wall tachycardias versus the EI in 17/17 (100%) (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

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We investigated entrainment in a pacemaker model of reentrant ventricular tachycardia (VT) created in the intact dog heart using a VAT pacemaker with both electrodes on the ventricular epicardium. This produced an incessant wide QRS tachycardia originating from the pacing site with a cycle length equal to the conduction time between the sensing and pacing site plus the pacemaker AV delay. The conduction time between entrainment sites and the critical elements of the reentrant pathway (sensing and pacing sites) was determined by pacing at a comparable cycle length during sinus rhythm. Entrainment was achieved in 12 tachycardias with pacing at 1-4 sites at cycle lengths 10-100 msec shorter than tachycardia and confirmed by constant QRS fusion, progressive QRS fusion, and coupling of the first nonpaced QRS or intracardiac electrogram at the entraining cycle length. By least squares regression, the timing of entrainment onset (first reset of pacing or sensing site electrogram) measured by the prematurity of the local electrogram at the entraining site was highly correlated to the shortest conduction time between the entraining site and the circuit (F value of 84.7 and R = 0.752 [P less than 0.001]). Therefore, the timing of entrainment onset maybe useful in predicting the conduction time from the entraining site to critical elements of a reentrant circuit and may assist in localization of the reentrant pathway.

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In patients after myocardial infarction, survival is influenced by the presence or absence of anterograde flow in the infarct artery, and late potentials on signal-averaged electrocardiography identify those at risk for tachyarrhythmias and sudden death. To assess the frequency of late potentials in survivors of first infarction, coronary arteriography and signal-averaged electrocardiography were performed in 109 subjects (64 men, 45 women, aged 30 to 77 years), 49 with (group I) and 60 without (group II) anterograde flow in the infarct artery. The groups were similar in age, sex, infarct artery, severity of coronary artery disease and left ventricular function. However, only 4 (8%) of group I had late potentials, whereas 24 (40%) of group II had late potentials (p less than 0.001). Thus, anterograde flow in the infarct artery after myocardial infarction is associated with a low incidence of late potentials on signal-averaged electrocardiography, whereas the absence of anterograde flow is more often associated with late potentials.

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Entrainment of ventricular tachycardia (VT) may be manifest as fixed and progressive QRS fusion with ventricular and, rarely, atrial pacing. Only a single example of spontaneous VT entrainment by another rhythm, rapid atrioventricular nodal tachycardia, has been reported. This article describes an example of fixed and progressive QRS fusion between conducted sinus rhythm and VT consistent with entrainment. In contrast to entrainment with pacing, entrainment of VT by sinus rhythm occurred with drug-mediated arrhythmia slowing and demonstrated progressive QRS fusion at a constant cycle length. However, it did not demonstrate unfused but entrained QRS complexes. The resulting short PR interval and wide QRS mimicked a preexcited rhythm.

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Sudden death claims an estimated 350,000 lives per year in the United States. When death occurs within 1 hour of the onset of symptoms, 90% are the result of ventricular tachyarrhythmias. The majority of victims are middle-aged men with coronary artery disease, but in approximately 25%, sudden death is the presenting manifestation of their problem. In some populations, the detection of premature ventricular complexes (PVCs) by ambulatory monitoring is predictive of an increased risk of sudden death. However, the arrhythmia that best predicts this risk is unclear, and ambient arrhythmias are only a modest marker of this risk. Therapy to suppress asymptomatic PVCs has not been shown to be effective in preventing sudden death, and in some cases, lethal arrhythmias can be prevented without significant effects on ambient arrhythmias. Other risk markers such as depressed left ventricular function and the presence of low-amplitude, long-duration, late potentials recorded on a signal averaged electrocardiogram are more powerful predictors of risk than are PVCs. These latter findings in particular support the presence of areas of slow electrical conduction (a requirement for reentrant mechanism arrhythmias) and suggest that an abnormal electrical environment or "substrate" is the most important factor in this problem. The management of patients at risk for sudden death is controversial. While postinfarct survivors with arrhythmias constitute a population at increased risk, the absolute risk is only about 5% in the first year and has not been shown to be improved by conventional antiarrhythmic drugs. Small study size, arrhythmia variability, ill-defined end points, and proarrhythmia may partially explain this apparent lack of efficacy. The prophylactic use of antiarrhythmic drugs other than beta-blockers to prevent sudden death in asymptomatic populations at risk is therefore of unproven benefit. By contrast, patients who have survived a life-threatening arrhythmia unrelated to an acute myocardial infarction have an approximately 30% risk of recurrence in the following year. In these patients, the use of ambulatory monitoring to guide therapy is limited by the high incidence of false-negative responses (lethal arrhythmia recurrence despite ambient arrhythmia suppression) and the lack of frequent spontaneous arrhythmias in many patients. In this patient population, electrophysiological testing can be used to prognosticate recurrence and gain insight into arrhythmia mechanism, stability, and hemodynamic tolerance. The technique is also useful in guiding both pharmacological and nonpharmacological therapy.(ABSTRACT TRUNCATED AT 400 WORDS)

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The electrocardiograms (ECGs) of 80 ventricular tachycardias (VTs) occurring in 52 patients with a normal baseline QRS duration (group 1) were compared with 26 VTs in 18 patients with preexisting bundle branch block (group 2). The effects of bundle branch block on the sensitivity of previously defined electrocardiographic criteria for differentiating VT from supraventricular tachycardia with aberration were under investigation. Specificity was examined by comparing VT to the baseline ECG in group 2 patients. The VTs in groups 1 and 2 were comparable with respect to rate, bundle branch pattern, R-wave pattern in V1 with right bundle, frequency of an R/S ratio less than 1 in V6 with right bundle, Q-wave frequency in V6 with left bundle and quadrant of the frontal plane axis. Precordial QRS concordance was more frequent (35 vs 15%, p = 0.045) and a greater than 30 ms R wave in V1 or V2 with left bundle pattern was less frequent (18 vs 63%, p = 0.015) in group 2 vs group 1 arrhythmias. Right bundle pattern VT usually had a monophasic R wave in V1 (69%), whereas preexisting right bundle usually had a biphasic R wave in V1 (82%, p = 0.001). The quadrant of the frontal plane axis was significantly different between the VT ECGs and the ECGs with preexisting bundle branch block (p = 0.029) with a right superior quadrant axis only seen in VT (19%). A greater than 30 ms R wave in V1 or V2 with left bundle was also only seen in VT (52 vs 0%, p = 0.052).(ABSTRACT TRUNCATED AT 250 WORDS)

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Sudden cardiac death caused by ventricular tachyarrhythmias claims about 360,000 lives a year in the United States. The premature ventricular complex (PVC) hypothesis has been the cornerstone for understanding this problem, but it is now recognized as an incomplete explanation for this catastrophy. The recognition of the importance of structural heart disease in this process has led to the development of the Substrate Hypothesis as an alternative explanation. In this construct, PVCs may trigger lethal arrhythmias but only if an abnormal electrophysiologic substrate is present. This hypothesis more completely describes the pathophysiology of the process, provides the basis for understanding the value and limitations of the techniques used for risk assessment and management, and helps clarify the potential endpoints and potential adverse effects of therapy to prevent arrhythmias. Since no single diagnostic technique is ideal and no therapeutic modality is universally effective, an approach to the management of this problem must be multidimensional and based on a firm understanding of the actual risk of a life threatening arrhythmia, the potential but unproven benefits and uncertain endpoints of drug therapy, the cost, and the potential for arrhythmia exacerbation or significant side effect.

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The mechanism of ventricular tachycardia (VT) in postoperative tetralogy of Fallot has been ascribed to both reentry and triggered automaticity. We performed electrophysiologic studies on a patient with this condition and induced sustained uniform ventricular tachycardia by programmed extrastimulation. Pacing during the tachycardia at multiple cycle lengths from the right ventricular apex (RVA) and outflow tract (RVOT) produced constant but progressive fusion between the paced and tachycardia QRS. With termination of pacing, the last captured complex was unfused but coupled at the paced cycle length and then the tachycardia resumed at its intrinsic rate. Therefore, the VT was entrained. In addition, an area of slow conduction between the RVOT and RVA was demonstrated. These findings support a reentrant mechanism of this arrhythmia.

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The role of cycle length and cycle length alternans in the induction of tachycardia-related QRS electrical alternans was investigated using an atrial pacing protocol in 16 patients. Pacing was performed at a cycle length less than 400 ms in 5 patients, greater than 400 ms in 5 and at both in 6 with 0, 6, 10, 20, 40 and 60 ms of atrial cycle length alternans. A 12-lead electrocardiogram and high right atrial, His bundle and right ventricular apical electrograms were simultaneously recorded after 30 to 60 seconds of pacing. Alternans was produced in 88% of patients. Alternans was 3 times more frequent at short (less than 400 ms) than long paced cycle lengths (greater than 400 ms) (66% vs 22%, p less than 0.0001). Alternans increased with increasing cycle length alternans and occurred with very little (less than or equal to 10 ms) atrioventricular nodal, His-Purkinje and ventricular cycle length alternans when paced cycle length was short. Alternans was more frequent in the precordial than the limb leads (45% vs 17%, p less than 0.001) and was most frequent in V3 and V2 (sensitivity 69% and 65%) and least frequent in leads I and aVL (sensitivity 4% and 10%). More leads per electrocardiogram showed alternans at short compared with long paced cycle lengths and the number of leads per electrocardiogram increased with increasing cycle length alternans. Occurrence of alternans was highly related to QRS amplitude by Spearman rank correlation (p less than 0.0005).(ABSTRACT TRUNCATED AT 250 WORDS)

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Two patients with Wolff-Parkinson-White syndrome and surgically mapped anterior left free wall atrioventricular bypass tracts had orthodromic atrioventricular reentry tachycardia conducted with complete left bundle branch block (CLBBB), complete right bundle block (CRBBB), left anterior fascicular block (LAFB), and a narrow QRS. Ventriculoatrial conduction increased by 35 and 85 ms with CLBBB compatible with the left free wall location of the bypass tracts. In one patient, resolution of CLBBB occurred in two stages. Initially, left posterior fascicular block (LPFB) resolved, decreasing VA conduction by 20 ms. With resolution of the remaining LAFB, there was a further 15 ms decrease in VA conduction. In the other patient, the isolated occurrence of LAFB increased ventriculoatrial conduction by 30 ms. These changes confirmed the location of the bypass tracts in the anterior portion of the left ventricular free wall. Changes in VA conduction with fascicular block can help localize the ventricular insertion of atrioventricular bypass tracts.

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In patients with atherosclerotic coronary artery disease, cigarette smoking increases myocardial oxygen demand but may cause an inappropriate decrease in coronary blood flow and myocardial oxygen supply. This study was performed to explore the mechanism of smoking-induced coronary vasoconstriction and, specifically, to determine if smoking causes an alpha-adrenergically mediated increase in coronary artery tone. In 36 chronic smokers with coronary artery disease (27 men and nine women, 50 +/- 9 [mean +/- SD] years old), heart rate-systolic arterial pressure double product and coronary sinus blood flow (by thermodilution) were measured before and during smoking both before and after (1) normal saline (n = 5, control subjects), (2) an alpha-adrenergic-blocking agent, phentolamine, 5 mg (n = 15), (3) a beta-adrenergic-blocking agent, propranolol, 0.1 mg/kg (n = 12), or (4) sodium nitroprusside, 0.4 to 0.8 micrograms/kg/min, given in a dose sufficient to diminish systolic arterial pressure by 15% (n = 4). During the initial smoking period, rate-pressure product increased and coronary sinus blood flow was unchanged by smoking in all groups. After 30 to 75 min, saline, phentolamine, propranolol, or sodium nitroprusside was given, and measurements were repeated. In the control subjects, rate-pressure product and coronary sinus blood flow responded in a similar manner to that observed previously. In those receiving phentolamine, rate-pressure product was unchanged, but coronary sinus blood flow rose substantially with smoking (percent change +2 +/- 15% during the first smoking period [before phentolamine] and +32 +/- 17% during the second smoking period [after phentolamine]; p less than .01).(ABSTRACT TRUNCATED AT 250 WORDS)

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The occurrence of electrical alternation of 0.1 mV or greater of the QRS or T wave was analyzed in 156 electrocardiograms that showed wide QRS complex tachycardias from 91 patients. One hundred thirty-six ventricular tachycardias (VT) were recorded from 74 patients and 20 supraventricular tachycardias (SVT) from 17 patients. Alternans was present in 42 tracings (27%) from 35 patients (38%) and was equally frequent in the patients with VT (39%) and those with SVT (35%). Alternans occurred in 36 VTs (27%) and 6 SVTs (30%). Tachycardias with alternans had a shorter mean cycle length than tachycardias without alternans (339 +/- 53 vs 368 +/- 85 ms, p less than 0.05), but were not associated with a particular QRS morphology or axis. Alternans was most frequent in leads V2 and V3 and was seen in more leads during SVT than VT (7.2 +/- 2.6 vs 3.7 +/- 2.5, p less than 0.005). All SVTs with alternans incorporated an atrioventricular bypass tract. Electrical alternans occurs frequently in wide QRS tachycardias. Alone, it does not help differentiate VT from SVT. SVTs utilizing bypass tracts frequently show alternans even if the QRS is wide, and this finding may be useful in determining the mechanism of SVTs with aberrant intraventricular conduction.

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We have examined the effects of trifluperazine and fluphenazine on action potentials and transient depolarizations of rabbit ventricular cells. Isolated myocytes were prepared by perfusing rabbit hearts with low calcium enzyme-containing solutions, and action potentials were stimulated at 1 Hz and recorded using patch-type pipettes. In normal saline, 10 microM trifluperazine or fluphenazine shifted the action potential plateau to more negative potentials and increased the rate of phase 2 repolarization. Transient diastolic depolarizations appeared in solutions containing 50 nM isoproterenol plus 1 microM strophanthidin. These transient depolarizations were abolished by the addition of 10 microM trifluperazine or fluphenazine. In addition, spontaneous transient depolarizations were occasionally observed, and these too were abolished by the phenothiazines. Because these compounds are potent inhibitors of calmodulin, these data raise the possibility that calcium-calmodulin-regulated processes are important in the generation of arrhythmogenic transient depolarizations.

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