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Biomedical subjects

M Block

Publications and source records attributed to M Block.

At least 19 recordsLinked to original sources
PubMed1995

Radiofrequency catheter ablation of sustained ventricular tachycardia in idiopathic dilated cardiomyopathy.

BACKGROUND: The feasibility of radiofrequency (RF) catheter ablation for the treatment of sustained ventricular tachycardia (VT) in patients with coronary artery disease and remote myocardial infarction has recently been demonstrated. At present, therapeutic options for VT in patients with idiopathic dilated cardiomyopathy (DCM) include antiarrhythmic drugs and implantable cardioverter/defibrillators (ICD). The purpose of the present study was to investigate the feasibility of RF catheter ablation in patients with idiopathic DCM who could not be adequately treated by conventional treatment modalities because of incessant or frequent, recurrent VT. METHODS AND RESULTS: RF current application for ablation of 9 VTs (mean cycle length, 402 +/- 78 ms) was attempted in 8 patients with idiopathic DCM (4 men, 4 women; mean age, 54 +/- 6 years; mean left ventricular ejection fraction, 30 +/- 9%). Inclusion criteria for ablation were incessant VT (n = 4) or frequent, recurrent VT reproducibly inducible with programmed electrical stimulation (n = 5). Three patients had suffered aborted sudden cardiac death, and 2 had experienced syncope. Two patients were artificially ventilated and catecholamine dependent for hemodynamic reasons at the time of attempted ablation. Potential target sites for RF current application were identified by detailed endocardial mapping during sinus rhythm, activation and entrainment mapping during VT, and pace mapping. After 7 +/- 5 RF pulses (range, 2 to 18 pulses; median, 6 pulses) applied with 32 +/- 7 W for 39 +/- 9 seconds, 6 of the 9 target VTs (67%) were rendered noninducible (4 of 4 incessant VTs and 2 of 5 chronic recurrent VTs). In 6 patients, VTs with ECG morphologies other than the target VTs were inducible after RF catheter ablation. Seven patients were on antiarrhythmic drugs during the ablation procedure and during the follow-up period of 8 +/- 5 months (range, 2 to 17 months). One patient received an ICD before RF ablation, 4 patients after RF ablation, and 1 patient after ablation of an incessant VT and before attempted ablation of frequent, recurrent VTs. One patient underwent heart transplantation 5 months after ablation in end-stage heart failure. There were no acute complications during the mapping and ablation procedure. During the follow-up period, 1 patient had been resuscitated from ventricular fibrillation 6 weeks after ablation and finally died of congestive heart failure 2 weeks later. No further episodes of incessant VT occurred in the patients who had undergone RF current application for ablation of incessant VT. A complete prevention of VT could be achieved in 2 of 8 patients, whereas in 5 patients, VT episodes were stored in the ICD devices during follow-up. CONCLUSIONS: The results of the present study indicate that RF current application for ablation of VT in a select group of patients with idiopathic DCM is feasible. The efficacy of RF ablation may be high in patients presenting with incessant VT, whereas the success rate seems to be only moderate in patients with chronic recurrent VT. In all patients, additional treatment options, including antiarrhythmic drugs, ICDs, and/or heart transplantation, were applied after RF ablation, indicating that RF ablation for this indication may be an adjunctive and not a curative treatment option.

Anti-Arrhythmia Agents↗
PubMed1995

Optimizing defibrillation through improved waveforms.

Defibrillation of the heart is achieved if an electrical current depolarizes the majority of the unsynchronized fibrillating myocardial cells. The applied current or the corresponding voltage described as a function of time is called the waveform. In pacing, to stimulate myocardial cells close to the electrode, a relatively low voltage is needed for a relatively brief duration. However, in defibrillation, approximately a 100-fold higher voltage is needed and achieved by the use of capacitors. The exponential voltage decay of a capacitor during its discharge determines the basic waveform for defibrillation. In an attempt to lower the energy needed for defibrillation, the steepness of the decay (different capacitances), the duration (fixed duration waveforms) or tilt (fixed tilt waveforms), or the initial polarity can be changed. Additionally, the polarity of the electrodes can be reversed during the discharge of the capacitor once (biphasic waveform) or twice (triphasic waveform). If two capacitors and defibrillation pathways are available, bidirectional defibrillation pulses can be delivered sequentially. In humans, the original standard waveform used with endocardial leads was a single monophasic pulse delivered by a 125-microF capacitor using the endocardial right ventricular electrode as cathode. It is now known that a reversal of the initial polarity and a reversal of polarity during capacitor discharge may significantly lower the energy needed for defibrillation, thereby preventing formerly frequent failures of defibrillation with endocardial lead systems. The use of sequential pulses showed no or only slight reductions of energy requirements and was abandoned due to the additional electrode needed. The use of a smaller capacitance (60-90 microF reduced maximum energy output but generally did not reduce energy requirements for defibrillation. However, with more efficient electrodes, smaller capacitances that will help to reduce the size of the defibrillator might be used. Thus, today defibrillation is optimized with respect to energy, capacitor size, and ease of implantation if an approximately 90-microF capacitor is used to deliver a biphasic pulse via a bipolar lead system using the right ventricular electrode as anode.

Animals↗
PubMed1995

Erroneous discharge of an implantable cardioverter defibrillator caused by an electric razor.

We report an unusual case of the erroneous discharge of a third-generation multiprogrammable implantable cardioverter defibrillator in a 64-year-old patient with a history of recurrent ventricular tachycardias caused by electromagnetic interference while shaving with an electric razor. Electromagnetic interference was related to a defect in the electrode's insulation and could not be provoked in an intact electrode.

Defibrillators, Implantable↗
PubMed1995

Internal defibrillation with smaller capacitors: a prospective randomized cross-over comparison of defibrillation efficacy obtained with 90-microF and 125-microF capacitors in humans.

INTRODUCTION: The size of current implantable cardioverter defibrillators (ICD) is still large in comparison to pacemakers and thus not convenient for pectoral implantation. One way to reduce ICD size is to defibrillate with smaller capacitors. A trade-off exists, however, since smaller capacitors may generate a lower maximum energy output. METHODS AND RESULTS: In a prospective randomized cross-over study, the step-down defibrillation threshold (DFT) of an experimental 90-microF biphasic waveform was compared to a standard 125-microF biphasic waveform. The 90-microF capacitor delivered the same energy faster and with a higher peak voltage but provided only a maximum energy output of 20 instead of 34 J. DFTs were determined intraoperatively in 30 patients randomized to receive either an endocardial (n = 15) or an endocardial-subcutaneous array (n = 15) defibrillation lead system. Independent of the lead system used, energy requirements did not differ at DFT for the experimental and the standard waveforms (10.3 +/- 4.1 and 9.5 +/- 4.9 J, respectively), but peak voltages were higher for the experimental waveform than for the standard waveform (411 +/- 80 and 325 +/- 81 V, respectively). For the experimental waveform the DFT w as 10 J or less using an endocardial lead-alone system in 10 (67%) of 15 patients and in 12 (80%) of 15 patients using an endocardial-subcutaneous array lead system. CONCLUSIONS: A shorter duration waveform delivered by smaller capacitors does not increase defibrillation energy requirements and might reduce device size. However, the smaller capacitance reduces the maximum energy output. If a 10-J safety margin between DFT and maximum energy output of the ICD is required, only a subgroup of patients will benefit from 90-microF ICDs with DFTs feasible using current defibrillation lead systems.

Adolescent↗
PubMed1995

Benefits of treatment with implantable cardioverter-defibrillators in patients with stable ventricular tachycardia without cardiac arrest.

BACKGROUND: The availability of implantable cardioverter-defibrillators (ICD) that are capable of antitachycardia pacing may lead to an increased use of ICDs in patients with haemodynamically tolerated ventricular tachycardia without a history of cardiac arrest. The frequency of potentially life-threatening fast ventricular tachycardias (cycle length < 250 ms) was investigated in patients who had a third generation ICD with endocardial leads implanted because they had haemodynamically tolerated ventricular tachycardia without a history of cardiac arrest. METHODS: Between January 1990 and October 1993, 50 patients (age (mean (SD)) 60 (11); ejection fraction 39 (16)%; 82% with coronary artery disease and 8% with dilated cardiomyopathy) with haemodynamically tolerated ventricular tachycardia (cycle length (mean (SD)) 348 (60) ms; range 250-500 ms) and without a history of cardiac arrest were treated with third generation ICDs that were capable of antitachycardia pacing. Fast ventricular tachycardia had been induced in 14 (28%) during baseline electrophysiological study. The benefit of ICD treatment was estimated as the difference between total mortality and the occurrence of fast ventricular tachycardia that would have been fatal if it had not been terminated. RESULTS: During follow up of 17 (12) months, 33 patients (66%) had a total of 3861 episodes of ventricular tachycardia. 91% of these episodes were terminated by antitachycardia pacing. 11 patients (22%) had episodes of potentially life-threatening fast ventricular tachycardia and 3 of these also had inducible fast ventricular tachycardia. One patient died suddenly 27 months after implantation. The difference between survival without fast ventricular tachycardia and total mortality was 9%, 12%, 27%, and 27% at 6, 12, 18, and 24 months, respectively. CONCLUSIONS: About a fifth of patients who had been given an ICD to treat haemodynamically tolerated ventricular tachycardia and who had no history of cardiac arrest experienced fast ventricular tachycardia during follow up requiring immediate cardioversion. Prospective studies are needed to investigate whether the prognosis of patients with a history of haemodynamically tolerated ventricular tachycardia without cardiac arrest is improved by ICD therapy.

Cardiomyopathy, Dilated↗
PubMed1995

Control of gill filament blood flow by serotonin in the rainbow trout, Oncorhynchus mykiss.

The effects of exogenously applied serotonin [5-hydroxytryptamine (5-HT)] on the distal arterial vasculature of gill filaments were observed using an epi-illumination microscope equipped with a water-immersion objective and connected to a video camera. In addition, ventral aortic flow (Q) and celiac artery pressure (PCA) were measured. Intra-arterial injection of serotonin (100 nmol/kg) completely stopped the blood flow in the distal part of the filaments and caused a rapid decrease of PCA. Repeatedly, the flow reduction was found to coincide with a constriction of the distal portion of the efferent filamental vasculature. Because there was no concomitant reduction in Q, it is concluded that a redistribution of blood to more proximal parts of the filaments occurred. After treatment with the serotonergic receptor antagonist methysergide, the vasoconstrictor effect of serotonin on the filamental vasculature was eliminated, while a decrease in PCA was still observed. The results demonstrate a specific site(s) for the serotonergic vasoconstriction in the distal portion of the filament.

Animals↗
PubMed1995

[In vitro validation of intravascular ultrasound, computerized and magnetic resonance tomography in diagnosis of atherosclerotic vascular segments in comparison with direct magnification radiography].

The depiction of atherosclerotic vessel abnormalities is a prerequisite for percutaneous interventional therapy and long-term observations of peripheral artery disease. The aim of this in-vitro study was to determine the potentials and limitations of 12.5 and 20 MHz intravascular ultrasound, computed tomography and magnetic resonance (MR) imaging in comparison to direct magnification radiography for the localization and quantification of peripheral vessel wall calcifications. Forty-three postmortem, human iliac segments were examined by intravascular ultrasound (12.5 and 20 MHz), computed tomography and magnetic resonance tomography (gradient echo-and spin echo-technique). For comparative analysis, each segment was divided into eight sectors of 45 degrees each; using all five methods, the presence of calcified wall areas was examined in each sector, and luminal area (42 segments) and plaque area (32 isolated plaques) were quantitatively estimated. In the sonograms, the circumferential extension of the boundary between intima and media was measured. 122 of 344 sectors showed regional vessel wall calcifications. Sensitivity of 20 MHz intravascular ultrasound was 73% versus 59% with the 12.5 probe, specificity was 97% with 20 MHz, 96% with 12.5 MHz. Sensitivity of both 12.5 and 20 MHz intravascular ultrasound was higher with increased thickness of the calcified structures. 20 MHz ultrasound identified the intima-media boundary averaging 146.8 degrees of the vessel circumference; the corresponding value of 131.8 degree with 12.5 MHz did not differ significantly. Computed tomography detected calcifications with a sensitivity of 88%, specificity was 88%. With MR imaging, sensitivity of the gradient echo-technique was 94% versus a sensitivity of 86% with spin echo-technique. Quantification of luminal and plaque areas showed that luminal area was precisely estimated only by 20 MHz ultrasound (no significant difference to direct magnification radiography), whereas all other techniques showed significant overestimation. Plaque areas were markedly overestimated by computed tomography and MR imaging, too. In an in vitro set-up, intravascular ultrasound, MR tomography and computed tomography do not allow an authentic depiction of peripheral vessel wall architecture. Limited resolution, subintimal shadowing and and distortion are the main limitations of these new techniques so that details of regional vessel wall calcifications cannot be presented thoroughly. Relevant over-estimation of luminal and plaque areas must be considered.

Arteriosclerosis↗
PubMed1994

The role of implantable cardioverter defibrillators in dilated cardiomyopathy.

Depending on the severity of the disease, patients with dilative cardiomyopathy (DCM) have a poor prognosis. No definite data are available to show that complex ventricular ectopy, the presence of ventricular late potentials, or programmed electrical stimulation in patients without symptoms with DCM identify patients at risk of sudden cardiac death. Although poor left ventricular function seems to be the most potent predictor of total cardiac death, the prediction of sudden death in patients without symptoms with DCM is poor. Studies with either class I antiarrhythmic drugs or amiodarone have not yet demonstrated a reduction in total mortality rates or sudden death. The usefulness of an implantable cardioverter defibrillator (ICD) in patients without symptoms with DCM is currently under investigation. The usefulness of serial electropharmacologic testing for patients with documented sustained ventricular tachycardia or ventricular fibrillation and DCM is still controversial. Because most patients with DCM and VT or out-of-hospital cardiac arrest have either no inducible ventricular tachyarrhythmia at baseline or the reproducibility of ventricular tachycardia/ventricular fibrillation induction is poor, implantation of an ICD should be considered in most of these patients. The indication for implantation of an ICD should be made on clinical judgment of the patient's functional status and other prognosis-limiting factors, such as rapid progression of heart failure, end-stage heart failure, and age.

Anti-Arrhythmia Agents↗
PubMed1994

Implantable cardioverter defibrillator therapy in patients with arrhythmogenic right ventricular cardiomyopathy, long QT syndrome, or no structural heart disease.

Recent technical developments in implantable cardioverter defibrillator (ICD) systems and reduced operative mortality and morbidity rates associated with ICD implantation have expanded the indications for ICD treatment of ventricular tachyarrhythmias. This review summarizes data regarding ICD therapy in patients with arrhythmogenic right ventricular cardiomyopathy, long QT syndrome, and idiopathic ventricular fibrillation and presents preliminary concepts for identification of patients who will benefit more from ICD therapy than from pharmacologic and other nonpharmacologic approaches. Recent studies suggest that ICD therapy may improve long-term prognosis by reliably terminating recurrences of life-threatening arrhythmias. Appropriate ICD therapies during mean follow-up periods of 12 to 36 months occurred in 30% of patients with idiopathic ventricular fibrillation to 50% of patients with arrhythmogenic right ventricular cardiomyopathy and long QT syndrome. At present no strict recommendations can be given for ICD implantation in these patients. However, at least in cardiac arrest survivors in whom the clinical arrhythmia is not reproducibly inducible during electrophysiologic study, ICD therapy appears to be superior to other treatment options with regard to long-term survival and thus should be considered as a first-line treatment. We are hopeful that continued study of long-term follow-up with and without ICD treatment and improved risk stratification will lead to better criteria for selection of treatment options.

Adult↗
PubMed1994

Single-incision implantation of cardioverter defibrillators using nonthoracotomy lead systems.

This study describes the placement of a newly designed implantable cardioverter defibrillator in a subpectoral device pocket using the incision for venous access in 16 patients undergoing implantation of an implantable cardioverter defibrillator with a nonthoracotomy lead system. The endocardial lead system consisted of a right atrial/superior vena cava defibrillation spring electrode and a right ventricular bipolar sensing/defibrillation electrode, inserted by cephalic venotomy or by puncturing of the subclavian vein. As a result of intraoperative testing using biphasic shocks the defibrillation threshold (DFT) had to be less than 24 J, otherwise an additional subcutaneous patch electrode was placed in the lateral chest wall near the cardiac apex through another incision. All patients received a nonthoracotomy lead system in combination with a subpectoral device placement. In 11 of 16 patients the endocardial leads alone were sufficient (DFT, 13.4 +/- 7.0 J), 5 of 16 patients (31%) required an additional subcutaneous patch electrode to achieve proper device function (DFT, 14.6 +/- 9.0 J). The operation lasted 93 +/- 20 minutes. This was a significant (p < 0.05) lower time consumption than standard nonthoracotomy approach combined with abdominal device placement (120 +/- 50 minutes). There were no postoperative complications. During follow-up period (average, 4 months), none of the patients reported major local symptoms, especially no device migration occurred. This approach, in contrast to an abdominal device placement, avoids another incision and subcutaneous tunneling of leads. In 11 of 16 patients defibrillator implantation by a single incision in the deltoideopectoral groove was possible.

Aged↗
PubMed1994

Nonthoracotomy defibrillator implantation: a single-center experience with 200 patients.

Nonthoracotomy leads for defibrillator implantation and biphasic shocking devices are under investigation. Implantation success and mortality and morbidity of the procedure determine the operative course. Lead-associated complications, late infection, and freedom of sudden cardiac death characterize the follow-up period with respect to the implanted device. From October 1989 to March 1993 in 200 patients, 205 (including five infections caused by reimplantations) transvenous or transvenous-subcutaneous lead systems were tested. Mean ejection fraction was 0.40 +/- 0.16. In 62.5% (125/200) coronary artery disease and in 19% (38/200) cardiomyopathy was the underlying disease (59 patients with prior cardiac operations). Leads were implanted with defibrillation thresholds less than 25 J in 195 patients, whereas 10 patients received intrathoracal patches. Since biphasic shocks became available, no nonthoracotomy lead system has failed in the last 115 consecutive patients. Perioperative mortality in the nonthoracotomy group was 1% (2/195). In 6.2% (12/193) of the surviving patients, perioperative complications occurred. Major problems were bleeding from the device or patch pocket (n = 6) and early infection (n = 2). During the follow-up of 20 +/- 10 months, lead-associated complications (dislocation, lead fracture, insulation defect, loss of sensing) occurred in 9 patients and in 5 patients late infection appeared. Within the follow-up period no patient died suddenly, and 134 patients received therapeutic interventions by the device. Defibrillator implantation using nonthoracotomy leads, especially combined with biphasic shocking devices, is applicable in almost every patient. During the operative course and follow-up, the defibrillator-associated morbidity and mortality is at the same level as or lower than when using patch lead systems.

Adolescent↗
PubMed1994

Role of programmed ventricular stimulation in patients with idiopathic dilated cardiomyopathy and documented sustained ventricular tachyarrhythmias: inducibility and prognostic value in 102 patients.

The role of programmed ventricular stimulation (PVS) in patients at high risk of sudden death related to idiopathic dilated cardiomyopathy (DCM) is still controversial. The possible reason is that most study series have been too small or that only a few patients had documented sustained ventricular tachyarrhythmias. This study therefore, looked at PVS performed in 102 patients with DCM and documented sustained ventricular tachycardia (VT; n = 63) or ventricular fibrillation (VF; n = 39). Sustained VT was induced in 27 of 63 patients (43%) with documented sustained VT and in 14 of 39 patients (36%) with documented VF (ns). VF was induced in nine patients (14%) with a history of sustained VT and in seven (18%) with a history of VF (ns). At a mean follow-up of 32 +/- 15 months, sudden death occurred in 14 (14%) patients, a rate similar in both patients with documented VT and VF (ns). Incidence of sudden death at 36 months was 6% in patients with inducible sustained VT/VF compared to 29% in patients without inducible VT/VF (P < 0.05). A favourable drug regimen (response to drug and no intolerable side effects) was obtained by serial drug testing in 25 of all 102 patients (25%). A cardioverter defibrillator (ICD) was implanted in 32 patients, in 63% of whom discharges were observed during 18 +/- 11 months of follow-up; only one patient (3%) died suddenly. Thus, in patients with DCM, there was no relationship between documented and inducible ventricular tachyarrhythmias, and initiation of sustained VT or VF had little prognostic value for the prediction of subsequent sudden death. Wherever antiarrhythmic drug therapy was of limited value, implantation of an ICD may improve the prognosis of these high risk patients.

Anti-Arrhythmia Agents↗
PubMed1994

Transvenous-subcutaneous defibrillation leads: effect of transvenous electrode polarity on defibrillation threshold.

INTRODUCTION: The defibrillation threshold (DFT) of a transvenous-subcutaneous electrode configuration is sometimes unacceptably high. To obtain a DFT with a sufficient safety margin, the defibrillation field can be modified by repositioning the electrodes or more easily by a change of electrode polarity. In a prospective randomized cross-over study, the effect of transvenous electrode polarity on DFT was evaluated. METHODS AND RESULTS: In 21 patients receiving transvenous-subcutaneous defibrillation leads, the DFT was determined intraoperatively for two electrode configurations. Two monophasic defibrillation pulses were delivered in sequential mode between either the right ventricular (RV) electrode as common cathode and the superior vena cava (SVC) and subcutaneous electrodes as anodes (configuration I) or the SVC electrode as common cathode and the RV and subcutaneous electrodes as anodes (configuration II). In each patient, both electrode configurations were used alternately with declining energies (25, 15, 10, 5, 2 J) until failure of defibrillation occurred. The DFT did not differ between both configurations (18.3 +/- 8.2 J vs 18.9 +/- 8.9 J; P = 0.72). Eleven patients had the same DFT with both electrode configurations, 5 patients a lower DFT with the RV electrode as cathode, and 5 patients a lower DFT with the SVC as cathode. Four patients had a sufficiently low DFT (< or = 25 J) with only 1 of the 2 configurations. CONCLUSION: A change of electrode polarity of transvenous-subcutaneous defibrillation electrodes may result in effective defibrillation if the first electrode polarity tested fails to defibrillate. In general, neither the RV electrode nor the SVC electrode is superior if used as a common cathode in combination with a subcutaneous anodal chest patch.

Adult↗
PubMed1994

A prospective randomized cross-over comparison of mono- and biphasic defibrillation using nonthoracotomy lead configurations in humans.

INTRODUCTION: For current implantable defibrillators, the nonthoracotomy approach to implantation fails in a substantial number of patients. In a prospective randomized cross-over study the defibrillation efficacy of a standard monophasic and a new biphasic waveform was compared for different lead configurations. METHODS AND RESULTS: Intraoperatively, in 79 patients receiving nonthoracotomy defibrillation leads, the defibrillation threshold was determined in the initial lead configuration for the mono- and biphasic waveform. In each patient, both waveforms were used alternately with declining energies (20, 15, 10, 5 J) until failure of defibrillation occurred. Three different initial lead configurations were tested in different, consecutive, nonrandomized patients using a bipolar endocardial defibrillation lead alone (A; n = 36) or in combination with a subcutaneous defibrillation patch (B; n = 24) or array (C; n = 19) lead. The lowest successful defibrillation energy with the biphasic waveform was less than, equal to, or higher than with the monophasic waveform in 64%, 28%, and 8% of patients, respectively, and on average significantly lower with the biphasic waveform for all three lead configurations (A: 11.3 +/- 4.4 J vs 14.5 +/- 4.5 J; B: 9.7 +/- 4.7 J vs 15.1 +/- 4.5 J; C: 7.9 +/- 4.5 J vs 12.4 +/- 4.9 J). Defibrillation efficacy at 20 J was significantly improved by the biphasic waveform (91% vs 76%). CONCLUSION: In combination with nonthoracotomy defibrillation leads, the biphasic waveform of a new implantable cardioverter defibrillator showed superior defibrillation efficacy in comparison to the standard monophasic waveform. Defibrillation thresholds were improved for lead systems with and without a subcutaneous patch or array lead.

Adult↗
PubMed1994

Dynamics of mitral regurgitant flow and orifice area. Physiologic application of the proximal flow convergence method: clinical data and experimental testing.

BACKGROUND: The proximal flow convergence method, a quantitative color Doppler flow technique, has been validated recently for calculating regurgitant flow and orifice area. We investigated the potential of the method as a tool to study different pathophysiological mechanisms of mitral valve incompetence by assessing the time course of regurgitant flow and orifice area and analyzed the implications for quantification of mitral regurgitation. METHODS AND RESULTS: Fifty-six consecutive patients with mitral regurgitation of different etiologies were studied. The instantaneous regurgitant flow rate Q(t) was computed from color M-mode recordings of the proximal flow convergence region and divided by the corresponding orifice velocity V(t) to obtain the instantaneous orifice area A(t). Regurgitant stroke volume (RSV) was obtained by integrating Q(t). Mean regurgitant flow rate Qm was calculated by RSV divided by regurgitation time. Peak-to-mean regurgitant flow rates Qp/Qm and orifice areas Ap/Am were calculated to assess the phasic character of Q(t) and A(t). In the first 24 patients (group 1), computation of Qm and RSV from the color Doppler recordings was compared with the conventional pulsed Doppler method (r = .94, SEE = 29.4 mL/s and r = .95, SEE = 9.7 mL) as well as with angiography (rs = .93 and rs = .94, P < .001). The temporal variation of Q(t) and A(t) was studied in the next 32 patients (group 2): In functional regurgitation in dilated cardiomyopathy (n = 12), there was a constant decrease in A(t) throughout systole with an increase during left ventricular relaxation; Ap/Am was 5.49 +/- 3.17. In mitral valve prolapse (n = 6), A(t) was small in early systole, increasing substantially in midsystole, and decreasing mildly during left ventricular relaxation; Ap/Am was 2.48 +/- 0.26. In rheumatic mitral regurgitation (n = 14), a roughly constant regurgitant orifice area during most of systole was found in 4 patients. In the other patients there was significant variation of A (t) and the time of its maximum; Ap/Am was 1.81 +/- 0.56. ANOVA demonstrated that the differences in Ap/Am were related to the etiology of mitral regurgitation (P < .0001). To verify that the calculated variation in regurgitant orifice area during the cardiac cycle reflects an actual variation, the ability of the method to predict a constant orifice area throughout systole was tested experimentally in a canine model of mitral regurgitation. Five flow stages were produced by implanting fixed grommet orifices of different sizes into the anterior mitral leaflet. A constant regurgitant orifice area was correctly predicted throughout systole with a mean percent error of -1.8 +/- 4% (from -6.9% to +5.8%); the standard deviation of the individual curves calculated at 10% intervals during systole averaged 13.3% (from 3.6% to 19.6%). In addition, functional mitral regurgitation caused by ventricular dysfunction was produced pharmacologically in five dogs, and the color M-mode recordings of the proximal flow convergence region were obtained with the transducer placed directly on the heart instead of the chest, thus ruling out a significant effect of translational motion on the observed flow pattern. The pattern of regurgitant flow variation was identical to that observed in patients. CONCLUSIONS: The proximal flow convergence method demonstrates that regurgitant flow and orifice area vary throughout systole in distinct patterns characteristic of the underlying mechanism of mitral incompetence. Therefore, in addition to the potential of the method as a tool to quantify mitral regurgitation, it allows analysis of the pathophysiology of regurgitation in the individual patient, which may be helpful in clinical decision making. Calculating mitral regurgitant flow rate and volume from the time-varying proximal flow field (ie, without assuming a constant orifice area that would produce overestimation in individual patients) provides excellent agreement with independent te

Adult↗
PubMed1994

[Pectoral cardioverter-defibrillator implantation combined with transvenous bipolar defibrillation electrodes].

Ultimately, implantable cardioverter-defibrillators (ICD) will one day be implantable like present pacemakers. However, due to the size of the pulse generator and the low defibrillation efficacy of monophasic shocks, only a few selected patients have been implanted transvenously-pectorally. Therefore, we have prospectively investigated whether a transvenous-pectoral approach is in general feasible with a new downsized ICD capable of delivering biphasic shocks. Out of 33 patients, 76% received a bipolar transvenous defibrillation lead system. In the first 13 consecutive patients, a randomized crossover study showed that this high efficacy was above all achieved by a superior defibrillation efficacy of the biphasic waveform in comparison to the monophasic waveform (69% vs. 23%; p = 0.03). Not a single patient could be defibrillated exclusively with the monophasic waveform. In a further 15 consecutive patients, a crossover study showed that a position of the transvenous anode within the Vena anonyma instead of the Vena cava superior is, in general, not superior (87% vs. 80%; p = 0.67). Only one patient could be exclusively defibrillated with the V. anonyma position. Intraoperatively, no complications occurred and all but one patient received a pectoral implantation of the pulse generator. Postoperatively, in five patients local complications related to the ICD system were seen; two needed a surgical revision. In two patients movements of the left shoulder joint were temporarily restricted. Thus, in the majority of patients a new downsized ICD capable of biphasic shocks can be implanted transvenously-pectorally like a pacemaker.

Adult↗