Biomedical subjects
David G Benditt
Publications and source records attributed to David G Benditt.
Comparison of automatic and patient-activated arrhythmia recordings by implantable loop recorders in the evaluation of syncope.
The implantable loop recorder (ILR) has become an important tool for evaluating patients with recurrent syncope. Second generation ILRs have the ability to record events either automatically (auto activated) or by manual activation (patient activated). In an attempt to evaluate the relative utility of the auto-activation feature, this study stratified ILR events based on a grading system designed to classify detected arrhythmias in terms of the likelihood that they provide a diagnostic basis for syncope. Data from 50 patients (27 men, mean age 64 +/- 22 years) who underwent ILR implantation for investigation of recurrent syncope were assessed. The arrhythmia syncope grading system used 5 levels, ranging from grade 0 (rhythm recorded during syncope) to grade IV (rhythm unlikely to provide a diagnostic basis for syncope). Thirty-six patients (72%) demonstrated > or =1 auto-activated or patient-activated recording during a follow-up of 14.3 +/- 7.9 months. Of the total of 529 recordings, 223 (194 after auto activation [86.9%]) from 30 patients showed a rhythm abnormality. Auto activation was more effective for documenting arrhythmias that were recorded during syncope or those with highest probability of providing a syncope diagnosis (grade 0 or I arrhythmias: auto activated, 19 patients, patient activated, 3 patients). Times from ILR implantation to first grade 0 and grade I arrhythmias were 13.4 and 7.8 months, respectively. The ILR auto-activation feature proved effective in providing a high probability basis for syncope (196 arrhythmia recordings [87.1%] in 27 patients) and enhanced the diagnostic effectiveness of the device compared with patient activation alone (29 arrhythmia recordings [12.9%] in 6 patients).
Adrenal/renal contribution to circulating norepinephrine in posturally induced neurally mediated reflex syncope.
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Syncope: is a diagnosis a diagnosis?
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Implantable diagnostic monitoring devices for evaluation of syncope, and tachy- and brady-arrhythmias.
Symptoms arising from cardiac arrhythmias are often transient. Consequently, defining the responsible rhythm disturbance remains a challenge. However, absent a confident diagnosis of the arrhythmic basis for the symptoms, it is not possible to develop an effective treatment strategy. The implantable loop recorder (ILR) has become a valuable element in the evaluation of patients with suspected intermittent arrhythmia related symptoms. In this regard, clinical studies have not only demonstrated its superior effectiveness compared to other monitoring modalities, but even suggest that it may be cost-effective for the ILR to be used at an earlier stage of the evaluation strategy.
Improved survival of cardiac transplantation candidates with implantable cardioverter defibrillator therapy: role of beta-blocker or amiodarone treatment.
INTRODUCTION: Survival in patients awaiting cardiac transplantation is poor due to the severity of left ventricular dysfunction and the susceptibility to ventricular arrhythmia. The potential role of implantable cardioverter defibrillators (ICDs) in this group of patients has been the subject of increasing interest. The aims of this study were to ascertain whether ICDs improve the survival rate of patients on the waiting list for cardiac transplantation and whether any improvement is independent of concomitant beta-blocker or amiodarone therapy. METHODS AND RESULTS: Data comprised findings from 310 consecutive patients at a single center who were evaluated and deemed suitable for cardiac transplantation and placed on the waiting list. Kaplan-Meier actuarial approach was used for survival analysis. Survival analysis censored patients at time of transplantation or death. Of the 310 patients, 111 (35.8%) underwent successful cardiac transplantation and 164 (52.9%) died while waiting; 35 patients remain on the waiting list. Fifty-nine (19%) patients had ICD placement for ventricular arrhythmias prior to or after being listed. Twenty-nine (49.1%) ICD patients survived until cardiac transplantation, 13 (22%) patients died, and 17 (28.8%) remain on the waiting list. Among non-ICD patients, 82 (32.7%) received transplants, 151 (60.2%) died, and 18 (7.2%) remain on the waiting list. Survival rates at 6 months and 1, 2, 3, and 4 years were better for all ICD patients compared to non-ICD patients (log-rank x2, P = 0.0001). By multivariate analysis, ICD therapy and beta-blocker treatment were the strongest predictors of survival. Further, ICD treatment was associated with improved survival independent of concomitant treatment with beta-blocker or amiodarone. Among ICD and non-ICD patients treated with a beta-blocker or amiodarone, survivals at the 1 and 4 years were 93% vs 69% and 57% vs 32%, respectively (log-rank x2, P = 0.003). CONCLUSION: ICD therapy is associated with improved survival in high-risk cardiac transplant candidates, and ICD benefit appears to be independent of concomitant treatment.
Feasibility and effects of transcutaneous phrenic nerve stimulation combined with an inspiratory impedance threshold in a pig model of hemorrhagic shock.
OBJECTIVE: Intrathoracic pressure changes are of particular importance under hypovolemic conditions, especially when central venous blood pressure is critically low. Accordingly, the purpose of this study was to assess the feasibility of transcutaneous phrenic nerve stimulation, used in conjunction with an inspiratory impedance threshold, on hemodynamic variables during hemorrhagic shock. DESIGN: Prospective, randomized laboratory investigation using a porcine model for measurement of hemodynamic variables, left and right ventricular diameter, and transmitral, transpulmonary, and transaortic blood flow employing transesophageal echo-Doppler technique. SETTING: University hospital laboratory. SUBJECTS: Thirteen female pigs weighing 28-36 kg. INTERVENTIONS: The anesthetized pigs were subjected to profound hemorrhagic shock by withdrawal of 55% of estimated blood volume over 20 mins. After a 10-min recovery period, the diaphragm was stimulated with a prototype transcutaneous phrenic nerve stimulator at a rate of ten per minute while the airway was intermittently occluded with an inspiratory threshold valve between positive pressure ventilations. Hemodynamic variables were monitored for 30 mins. MEASUREMENTS AND MAIN RESULTS: Phrenic nerve stimulation in combination with the inspiratory threshold valve significantly (p <.001) improved right and left ventricular diameter compared with hypovolemic shock values by 34 +/- 2.5% and 20 +/- 2.5%, respectively. Moreover, phrenic nerve stimulation together with the inspiratory threshold valve also increased transaortic, transpulmonary, and transmitral valve blood flow by 48 +/- 6.6%, 67 +/- 13.3, and 43 +/- 8.2%, respectively (p <.001 for comparisons within group). Mean +/- sem coronary perfusion and systolic aortic blood pressures were also significantly (p <.001) higher compared with values before stimulation (30 +/- 2 vs. 20 +/- 2 mm Hg, and 37 +/- 2 vs. 32 +/- 3 mm Hg, respectively). CONCLUSIONS: This feasibility study suggests that phrenic nerve stimulation with the inspiratory threshold valve may improve cardiac preload and, subsequently, key hemodynamic variables in porcine model of severe hemorrhagic shock.
Efficacy of biphasic waveform cardioversion for atrial fibrillation and atrial flutter compared with conventional monophasic waveforms.
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Cardiology patient page. Fainting.
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Sudden death in patients with implantable cardioverter defibrillators: the importance of post-shock electromechanical dissociation.
OBJECTIVES: The purpose of this study was to determine the mechanisms of sudden death (SD) in patients with ventricular tachyarrhythmias (ventricular tachycardia/ventricular fibrillation [VT/VF]) treated with an implantable cardioverter defibrillator (ICD). BACKGROUND: Despite ICD therapy, some patients with VT/VF still die suddenly. Optimal ICD use requires determination of the mechanisms of these residual SDs. METHODS: We reviewed 320 patient deaths during trials of Medtronic transvenous ICD systems (Medtronic Inc., Minneapolis, Minnesota). Sudden deaths were further categorized according to mechanism. Post-shock electromechanical dissociation (EMD) describes a scenario where VT/VF was appropriately detected and treated by an ICD shock that restored a physiologic rhythm, but death still occurred immediately by EMD. RESULTS: A mode of death could be ascribed for 317 patients-90 (28%) were sudden, 156 (49%) were non-sudden cardiac, and 71 (22%) were noncardiac. A mechanism of SD was proposed for 68 patients-20 (29%) had post-shock EMD, 17 (25%) had VT/VF uncorrected by shocks, 11 (16%) had primary electromechanical dissociation, 9 (13%) had incessant VT/VF, 5 (7%) had VT/VF after their ICD was deactivated or removed, and 6 (9%) had single instances of various other terminal events. Only New York Heart Association functional class independently predicted SD by post-shock EMD. CONCLUSIONS: The most common mechanism of SD in patients with an ICD is VT/VF treated with an appropriate shock followed by EMD. As this mechanism accounted for 29% of the SDs to which a cause could be ascribed, this mechanism of SD warrants further investigation.
Trans-aortic His bundle ablation with permanent ventricular pacing via the coronary sinus in L-transposition of great arteries with classic Fontan procedure.
We report findings in a patient with 1-transposition of great arteries with single ventricle and classic Fontan procedure who required both His bundle ablation for palliation of refractory atrial tachycardia and placement of a transvenous dual-chamber atrio-ventricular permanent pacemaker for hemodynamic support. A method for retrograde trans-aortic His bundle ablation in this congenital anomaly and subsequent placement of permanent dual chamber pacemaker using the right atrium and coronary sinus as an access to the ventricle is described.