Biomedical subjects

D E Mann

Publications and source records attributed to D E Mann.

At least 37 records · Page 2Linked to original sources

PubMed1994

Implantation of an automatic defibrillator using a new nonthoracotomy approach.

Most current nonthoracotomy systems for defibrillator implantation use monophasic devices. To determine the safety and efficacy of a new nonthoracotomy lead configuration when used in conjunction with a device that used biphasic waveforms, 38 consecutive patients were taken to the operating room for implantation of a Cadence tiered therapy defibrillator system. The lead system consisted of a transvenous coil electrode positioned at the right atrial-superior vena caval junction, a bipolar endocardial right ventricular lead, and a large patch placed subcutaneously near the cardiac apex. Of the 38 nonthoracotomy defibrillator implantations attempted, 36 (95%) were completed with adequate defibrillation thresholds. The mean defibrillation threshold in these 36 patients was < or = 563 +/- 10 V (< or = 20 +/- 1 J). There was no perioperative mortality. Complications included coil lead migration (5), sensing lead migration (1), infection (3), pneumothorax (2), arterial embolism (1), and folding of the subcutaneous patch with an increase in defibrillation threshold (1). No patient died during a median follow-up period of 22 weeks. Fourteen patients (39%) had spontaneous sustained ventricular tachyarrhythmias, which were all successfully terminated by the implanted device. Shocks for nonsustained arrhythmias were aborted in eight patients (22%). Spurious discharges for sinus tachycardia or atrial fibrillation occurred in six patients (17%) and were readily diagnosed by examination of the stored electrograms. Thus, implantation of a biphasic tiered therapy defibrillator system using this nonthoracotomy approach is feasible in the majority of patients. The major complication associated with this procedure is lead dislodgment.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1994

Low dose disopyramide often fails to prevent neurogenic syncope during head-up tilt testing.

Low dose disopyramide has been used to prevent neurally-mediated syncope during head-up tilt testing but a correlation between blood levels and efficacy has not been described. We measured disopyramide levels in 15 patients with recurrent syncope and positive 70 degrees head-up tilt tests who underwent one or more repeat tests on the drug. There were 9 males and 6 females, age range 15-78 years. Fourteen of the 15 patients had structurally normal hearts. The daily disopyramide dose was 645 +/- 165 mg (mean +/- SD). Patients developed syncope during 9 tests and had no syncope during 12 tests. The mean disopyramide level in patients with positive tests was significantly lower than the level in patients with negative tests (2.4 +/- 0.15 mu/mL vs 3.2 +/- 0.22 mu/mL, P = 0.018). Six patients were tested twice on different disopyramide doses. Five of these six patients had syncope during head-up tilt testing on the lower dose and negative tests on the higher dose (disopyramide levels 2.2 +/- 0.17 mu/mL vs 3.2 +/- 0.17 mu/mL, P = 0.004). Thus, disopyramide is effective in preventing neurogenic syncope during head-up tilt testing, but higher blood levels are often necessary for efficacy. In a given patient, failure to respond to low dose disopyramide does not preclude success on higher doses.

Adolescent↗

PubMed1993

Mechanical correlates of contraction-excitation feedback during acute ventricular dilatation.

OBJECTIVE: The purpose was to examine the mechanical correlates of the electrophysiological changes that occur during acute left ventricular dilatation. METHODS: Ten isolated, retrogradely perfused, ejecting rabbit hearts were studied. Left ventricular volume was adjusted by varying left atrial perfusion pressure. Left ventricular pressure was measured directly. Changes in left ventricular chamber dimensions at the level of an epicardial electrode were evaluated with two dimensional echocardiography and wall stress was calculated from these measures. Regional left ventricular electrophysiological properties were measured at two left atrial perfusing pressures. RESULTS: Increases in left atrial perfusion pressure resulted in significant increases in left ventricular end diastolic and end systolic pressures, epicardial and endocardial circumference, and wall stress. Only changes in diastolic wall stress correlated with changes in ventricular refractoriness (r = 0.69, p = 0.027). CONCLUSIONS: Left ventricular dilatation results in shortening of ventricular refractoriness in the isolated, ejecting rabbit heart. Regional changes in refractoriness are best correlated with changes in wall stress.

Acute Disease↗

PubMed1993

Influence of a third extrastimulus in defining effective drug therapy during serial electrophysiological testing.

Many electrophysiology laboratories use three extrastimuli in all patients with ventricular tachyarrhythmias during antiarrhythmic drug testing, regardless of the mode of arrhythmia induction in the baseline state. The purpose of this study was to compare this pacing protocol (full protocol) with a protocol in which three extrastimuli were only used during drug tests, if they were required in the baseline state for arrhythmia induction (limited protocol). There were 181 electrophysiology tests performed on 69 patients with ventricular tachyarrhythmias that were retrospectively analyzed. In all studies the full protocol was used, but the results of stimulation were also analyzed assuming the limited protocol had been used. In the baseline state, sustained ventricular tachyarrhythmias were reproducibly inducible with one or two extrastimuli in 38 (55%) patients. Of these patients, six (16%) achieved a drug efficacy prediction using the full protocol versus 15 (39%) patients using the limited protocol (P < 0.001). In all 69 patients, the drug response rate increased from 25% to 38% (P < 0.01) using the limited protocol.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗

PubMed1993

Palpitations occur frequently following radiofrequency catheter ablation for supraventricular tachycardia, but do not predict pathway recurrence.

Radiofrequency ablation of extranodal pathways is an effective treatment for supraventricular tachycardia, but late recurrences of pathway conduction do occur. To determine if recurrence of palpitations following ablation predicts pathway recurrence, we interviewed 77 patients who were at least 4 weeks status-post successful ablation of an accessory pathway (43 overt, 11 concealed) or slow pathway (23) for AV nodal reentrant tachycardia. Palpitations were reported by 45 (58%) patients postablation, and 28 (36%) patients reported palpitations lasting > or = 10 seconds and/or felt their symptoms represented recurrent tachycardia (major palpitations). Repeat electrophysiological testing was performed 3 months postablation in 53 patients, including 34 patients with palpitations (22 with major symptoms). Eight (10%) patients had recurrent pathway conduction demonstrated on repeat testing: two had no symptoms prior to restudy and six had major symptoms. One patient had major symptoms, but was found to have inducible atrial tachycardia and not pathway recurrence on restudy. Thus, 15 (68%) of 22 patients with major symptoms who were restudied had no pathway recurrence or inducible arrhythmia to explain their symptoms. Of the 24 patients not restudied, none has had documented recurrent tachycardia or overt pathway conduction by electrocardiogram over a mean follow-up of 335 +/- 138 (range 132-616) days. Thus, palpitations, including palpitations reminiscent of preablation symptoms, are common following radiofrequency ablation and often do not predict pathway recurrence. Repeat electrophysiological testing is frequently required to document long-term success of radiofrequency ablation for supraventricular tachycardia in patients with recurrence of major symptoms.

Adult↗

PubMed1993

Interaction of hypokalemia and ventricular dilatation in isolated rabbit hearts.

Potassium depletion has been implicated in the genesis of ventricular arrhythmias, especially in patients with congestive heart failure, but the nature of this interaction is unknown. We studied the electrophysiological effects of varying concentrations of extracellular K+ in 24 isolated, retrogradely perfused rabbit hearts. The left ventricular cavity was dilated with a fluid-filled balloon. Left ventricular effective refractory period decreased significantly (from 119 +/- 3 to 105 +/- 3 ms) with ventricular dilatation but was not influenced by K+ concentration. Conduction velocity was not changed by dilatation but was decreased by hypokalemia (81 +/- 2 cm/s, K+ = 4.9 mM; 75 +/- 2 cm/s, K+ = 3.5 mM; 70 +/- 2 cm/s, K+ = 2.5 mM; P < 0.05). No ventricular arrhythmias were induced in undilated hearts at a K+ concentration of 4.9 mM. Induced ventricular fibrillation was more frequent (38%; P < 0.01) in the dilated heart and increased markedly (92%; P < 0.01) with coexisting hypokalemia. The incidence of induced fibrillation was highly correlated with the wavelength of the ventricular impulse (wavelength = refractory period x conduction velocity). Thus dilatation and hypokalemia have very different electrophysiological effects that can interact synergistically to predispose the heart to reentrant arrhythmias in this model.

Animals↗

PubMed1992

Effect of pacing drive cycle length on induction of sustained monomorphic ventricular tachycardia.

To assess the effect of pacing drive cycle length on induction of sustained monomorphic ventricular tachycardia, 40 patients were prospectively studied in the drug-free state. Ventricular extrastimuli were sequentially delivered at the same coupling interval at each of three drive cycle lengths (600, 500, and 400 ms) before the coupling interval was shortened and the process repeated. This protocol was continued until sustained monomorphic ventricular tachycardia was induced at all three drive cycle lengths or until pacing was completed through three extrastimuli. Of the 27 patients in whom sustained monomorphic ventricular tachycardia was induced, tachycardia was induced at all 3 drive cycle lengths in 12 (44%), only 2 drive cycle lengths in 11 (41%), and only 1 drive cycle length in 4 (15%) patients. Although the yield of inducible ventricular tachycardia increased with each additional extrastimulus, this yield increased even further with the use of multiple drive cycle lengths. In 10 of 11 patients, failure to induce ventricular tachycardia at any drive cycle length was not due to failure to achieve at that drive cycle length the critical extrastimulus coupling interval required to induce tachycardia at other drive cycle lengths. Induction of sustained monomorphic ventricular tachycardia is often drive cycle length specific, and failure to induce tachycardia cannot be explained by failure to achieve critically short coupling intervals. Pacing at multiple drive cycle lengths increases the yield of induced ventricular tachycardia.

Cardiac Pacing, Artificial↗

PubMed1992

Effect of acute ventricular dilatation on fibrillation thresholds in the isolated rabbit heart.

We examined the effects of ventricular dilatation on epicardial refractoriness and ventricular fibrillation threshold (VFT) in the isolated, retrograde-perfused rabbit heart. Ventricular size was modified by acutely changing the volume of a fluid-filled balloon secured within either the left or right ventricle. Left ventricular dilatation (to an end-diastolic pressure of 30-38 mmHg) significantly decreased left ventricular effective refractory period (ERP) and myocardial wavelength (calculated as ERP x conduction velocity). Left VFT (determined by scanning the vulnerable period with a train of pulses) decreased from 6.4 +/- 0.9 to 4.4 +/- 0.5 mA; P < 0.01) with left but not right ventricular dilatation. Right ventricular dilatation was associated with a decrease in the right ventricular ERP and myocardial wavelength, and right VFT decreased from 13.6 +/- 1.8 to 4.1 +/- 0.3 mA (P < 0.01). Changes in VFT correlated with the decrease in local refractoriness and shortening of local excitation wavelength.

Animals↗

PubMed1991

Atrioventricular nodal reentrant tachycardia initiated by catecholamine-induced ventricular tachycardia. A case report.

The authors describe a patient who experienced recurrent wide-complex and narrow-complex tachycardias during exercise. Electrophysiologic testing in the resting state revealed dual atrioventricular (AV) nodal pathways. AV nodal reentrant tachycardia was inducible by ventricular premature stimulation but was always nonsustained, terminating with block in the anterograde slow pathway. During isoproterenol infusion, runs of ventricular tachycardia occurred frequently, and spontaneously initiated sustained AV nodal reentrant tachycardia. Exercise testing also provoked ventricular tachycardia and sustained AV nodal reentrant tachycardia. The patient was effectively treated with a combination of atenolol and verapamil. This case is an unusual example of a catecholamine-induced arrhythmia, possibly due to triggered activity (exercise-induced ventricular tachycardia), initiating an arrhythmia due to reentry (AV nodal reentrant tachycardia).

Catecholamines↗

PubMed1991

Electrophysiologic effects of verapamil metabolites in the isolated heart.

The electrophysiologic effects of the metabolites of verapamil are unknown and may contribute to the observed differences between intravenous and oral verapamil. We examined the electrophysiologic effects of verapamil and its metabolites (norverapamil, N-dealkylverapamil (D617), and N-dealkylnorverapamil (D620)) at estimated, free therapeutic concentrations, in the retrogradely perfused, isolated rabbit heart. Verapamil at 5 and 10 ng/ml significantly prolonged anterograde (11 and 27%, respectively) and retrograde (10 and 25%, respectively) atrioventricular (AV) nodal block cycle lengths. Anterograde and retrograde AV nodal conduction times and refractory periods were also prolonged. Norverapamil at 100 ng/ml had qualitatively similar effects equivalent to 20-50% that observed with verapamil at 10 ng/ml. D620 had small but statistically significant effects on some AV nodal parameters. D617 had no effect. The combination of verapamil plus its principal metabolite, norverapamil, had additive effects. None of the compounds had any measurable effect on atrial conduction, His-Purkinje conduction, or atrial refractoriness. Ventricular refractoriness was significantly prolonged only by norverapamil. In conclusion, some of the metabolites of verapamil have important electrophysiologic AV nodal effects and may contribute to the clinical effects observed during chronic oral verapamil dosing.

Animals↗

PubMed1990

Effects of upright posture on atrioventricular accessory pathway conduction.

The electrophysiologic effects of 45 degrees head-up tilt were studied in 19 patients with atrioventricular accessory pathways. Upright posture enhanced both anterograde and retrograde accessory pathway conduction when compared to the supine position: the anterograde block cycle length decreased from 374 +/- 52 ms (mean +/- standard error) (supine) to 303 +/- 33 ms (tilt) (p less than 0.05); anterograde effective refractory period decreased from 286 +/- 17 to 249 +/- 10 ms (p less than 0.05); retrograde block cycle length shortened from 331 +/- 36 to 291 +/- 35 ms (p less than 0.05); retrograde effective refractory period decreased from 312 +/- 26 ms to 274 +/- 15 ms (p less than 0.05). During induced atrial fibrillation the mean RR interval and the shortest RR interval between preexcited beats decreased approximately 10% with head-up tilt. During orthodromic reciprocating tachycardia, tachycardia cycle length shortened 15%. Tachycardia rate during electrophysiologic study in the head-up position more closely approximated the rate of clinical tachycardia than did the rate in the supine position. Head-up tilt significantly enhances anterograde and retrograde accessory pathway conduction, increases the rate of arrhythmias using an accessory pathway and may be clinically useful in the assessment of patients with an accessory pathway.

Adult↗

PubMed1990

Flow of non-Newtonian blood analog fluids in rigid curved and straight artery models.

The influence of non-Newtonian rheology on wall shear rate in steady and oscillatory flow through rigid curved and straight artery models was studied experimentally. Wall shear rates measured by flush mounted hot film anemometry under nearly identical flow conditions are reported for the following four fluids: aqueous glycerin (Newtonian), aqueous polyacrylamide (shear thinning, highly elastic), aqueous Xanthan gum (shear thinning, moderately elastic), and bovine blood. For steady flow conditions there was little difference at any measurement site in the wall shear rate levels measured for the four fluids. However, large differences were apparent for oscillatory flows, particularly at the inner curvature 180 degrees from the entrance of the curved artery model. At that position the peak wall shear rate for polyacrylamide was 5-6 times higher than for glycerin and 2-3 times higher than for bovine blood. It is concluded that polyacylamide is too elastic to provide a good model of blood flow under oscillatory conditions, particularly when there is wall shear reversal. Xanthan gum and glycerin are better analog fluids, but neither is entirely satisfactory.

Acrylic Resins↗

PubMed1990

Electrocardiographic abnormalities in patients with myotonic dystrophy.

In examining the incidence and progression of electrocardiographic abnormalities in 45 patients with myotonic dystrophy, 26 (58%) of whom at entry had at least 1 electrocardiographic abnormality, we found conduction abnormalities in 17 (38%). In 21 patients (47%), new abnormalities developed during follow-up (mean, 4.6 years). The overall incidence of electrocardiographic abnormalities increased to 78%, and the incidence of conduction defects increased to 62%. Second-degree or complete atrioventricular block did not develop in any of the patients. Pseudoinfarction patterns were common at entry and during follow-up and were not correlated with evidence of clinical coronary artery disease. There was no correlation between the presence of electrocardiographic abnormalities and apparent disease severity.

Adolescent↗

PubMed1989

Effects of flecainide on defibrillation thresholds in the anesthetized dog.

The effects of flecainide on defibrillation thresholds in 21 open chest, anesthetized dogs were studied. Defibrillation was accomplished using nontruncated exponential pulses delivered through two epicardial patches. Multiple shocks of varying energy were administered after 10 s of ventricular fibrillation in random order. The percent success was plotted against the energy delivered for each dog. A sigmoidal curve was fit to the data and the energy associated with 50% success (E50) calculated. Flecainide (n = 16) or saline solution (n = 5) was then infused and E50 again determined. Flecainide infusion produced mean (+/- standard error of the mean) plasma levels of 610 +/- 111 ng/ml. Defibrillation thresholds were obtainable in 10 of 16 dogs that received flecainide infusion. Flecainide infusion increased E50 by 75% (from 6.5 +/- 1.9 to 11.4 +/- 2.6 J) (P less than 0.05). Infusion of saline solution did not significantly affect defibrillation energy. Of 16 dogs that received flecainide infusion, 12 had one or more complications: 6 had ventricular fibrillation resistant to defibrillation, 6 developed severe hypotension after successful defibrillation and 5 had spontaneous ventricular fibrillation after successful defibrillation. These effects were not seen in any control dogs. Flecainide infusion significantly increases defibrillation threshold and has important adverse arrhythmic and hemodynamic effects in this experimental preparation.

Animals↗

PubMed1989

Effects of ventricular fibrillation and defibrillation on pacing threshold in the anesthetized dog.

The effects of transthoracic and internal defibrillation on the bipolar ventricular pacing threshold in 20 anesthetized dogs were examined. Ventricular pacing was accomplished with a computer-controlled, constant voltage pacemaker that permitted rapid determination of pacing threshold. Defibrillation at various energy levels was administered during ventricular pacing and after ventricular fibrillation of 5, 15, 30, 45, 60 or 120 s duration in the 20 dogs. Defibrillation during pacing or within 15 s after initiation of ventricular fibrillation did not significantly increase threshold, regardless of defibrillation energy or mode of delivery. Defibrillation after ventricular fibrillation lasting greater than or equal to 30 s increased (p less than 0.05) threshold determined 6 s after defibrillation. The increase in threshold (in volts) determined 6 s after defibrillation was an exponential function of fibrillation duration (30 s = 0.30 +/- 0.09 V; 45 s = 0.53 +/- 0.13 V; 60 s = 2.24 +/- 1.05 V), but was independent of defibrillation energy or mode of delivery. Threshold returned to control values 15 to 30 s after defibrillation. Cardiopulmonary bypass to maintain coronary perfusion prevented the increase in pacing threshold even after ventricular fibrillation of up to 2 min duration. Pacing threshold is not increased by transthoracic or internal defibrillation, but is increased by ventricular fibrillation of sufficient duration to create substantial myocardial hypoxemia.

Anesthesia↗

PubMed1989

Bradycardia-dependent block and fatigue phenomenon of the His-Purkinje system manifested during upright tilt.

Atrioventricular (AV) block occurring in the His-Purkinje system may occur sporadically and can be difficult to document. In this article, we describe two patients with spontaneous episodes of AV block, in whom the use of upright tilt during electrophysiological testing led to a diagnosis of His-Purkinje disease. In both cases, testing in the supine position only uncovered mild or no abnormalities of infra-nodal conduction. In the first case, high grade block distal to the His occurred and the mechanism appeared to be bradycardia-dependent block. In this case, increased sympathetic tone due to upright tilt may have enhanced the slope of phase 4 depolarization in abnormal His-Purkinje cells, leading to block. In the second case, high grade block distal to the His was seen with upright tilt and the mechanism of block appeared to be fatigue phenomenon in the His-Purkinje system. These cases emphasize the elusive nature and varied mechanisms of His-Purkinje block and illustrate the utility of electrophysiological testing in the upright position in patients with suspected conduction system disease.

Adult↗

PubMed1988

Effects of upright posture on atrioventricular nodal reentry and dual atrioventricular nodal pathways.

The electrophysiologic effects of upright posture (45 degrees upright tilt) were studied in 17 patients with dual atrioventricular (AV) nodal pathways, AV nodal reentry or both. Discontinuous AV nodal conduction curves were observed in 16 patients while supine, but in only 11 patients while upright. Fast pathway refractoriness was shortened: the anterograde fast pathway effective refractory period decreased from 360 +/- 22 to 275 +/- 14 ms (mean +/- standard error of the mean), the anterograde fast pathway block cycle length shortened from 448 +/- 28 to 348 +/- 20 ms and the retrograde fast pathway block cycle length shortened from 425 +/- 29 to 338 +/- 24 ms (all p less than 0.01). The anterograde slow pathway block cycle length shortened from 378 +/- 29 to 316 +/- 17 ms (p less than 0.05). AV nodal reentrant tachycardia was induced in 5 patients while supine (2 sustained, 3 nonsustained) and in 6 patients while upright (4 sustained, 2 nonsustained). Tachycardia cycle length shortened during upright posture, from 413 +/- 30 to 345 +/- 22 ms (p less than 0.01), primarily due to shortened anterograde slow pathway conduction time, from 322 +/- 23 to 268 +/- 20 ms (p less than 0.05). Upright posture thus enhances conduction in patients with dual AV nodal pathways, facilitating AV nodal reentry. Electrophysiologic testing in the upright position may yield additional clinical important information in patients with dual AV nodal pathways.

Atrioventricular Node↗

PubMed1988

Intermittent preexcitation: marked enhancement of anterograde conduction in the atrioventricular accessory pathway with isoproterenol.

A 29-year-old man presented with intermittent preexcitation and exertional syncope. Electrophysiological evaluation in the control state demonstrated a single, left posterior free-wall atrioventricular accessory pathway. The anterograde and retrograde effective refractory periods and block cycle lengths were long in the control state. No tachycardias were induced during programmed electrical stimulation. After intravenous administration of isoproterenol, anterograde conduction of the accessory pathway was markedly enhanced (block cycle length shortened 45% to less than 240 ms) and rapid antidromic reciprocating tachycardia (CL = 250 ms) associated with syncope was observed. Following successful surgical dissection of the accessory pathway the patient has been without tachycardia or exertional symptoms. We conclude that, under the influence of exercise or emotion, patients with intermittent preexcitation may be at risk for serious arrhythmias.

Adult↗