W. Stafford

Abnormal Forearm Vascular Responses During Dynamic Leg Exercise in Patients With Vasovagal Syncope

BACKGROUND We have reported previously that in some patients with normal hearts who present with exercise syncope, abnormal forearm vasodilation is seen during leg exercise and tilt table tests are positive. This suggests that exercise syncope may be a variant of vasovagal syncope. In this study we tested the hypothesis that there is loss of the normal forearm vasoconstrictor response during dynamic leg exercise in an unselected population of patients with classic vasovagal syncope. METHODS AND RESULTS We evaluated forearm vascular responses during maximal semierect cycle exercise in 28 consecutive patients with vasovagal syncope and compared them with 30 age-matched control subjects. We also evaluated blood pressure responses during erect treadmill exercise (Bruce protocol). While forearm vascular resistance at rest was similar in the patients with vasovagal syncope and the control group, forearm vascular resistance was markedly lower in the patients than in control subjects at peak exercise (85 +/- 54 versus 149 +/- 94 units, P = .002). Forearm vascular resistance fell by 3 +/- 48% during exercise in patients versus an increase of 135 +/- 103% in control subjects (P < .0001). Systolic blood pressure during erect exercise was lower in patients versus control subjects (155 +/- 32 versus 188 +/- 17 mm Hg, P < .0001). Six of the vasovagal patients complained of exercise syncope or presyncope on specific inquiry, and 4 of these 6 exhibited exercise hypotension during erect treadmill exercise testing. CONCLUSIONS Patients with vasovagal syncope exhibit a failure of the normal vasoconstrictor response in the forearm during dynamic leg exercise. Exercise syncope and presyncope are not uncommon in unselected patients with classic vasovagal syncope, as is exercise hypotension.

Mechanism of exercise hypotension in patients with ischemic heart disease. Role of neurocardiogenically mediated vasodilation.

BackgroundExercise-induced hypotension in patients with coronary artery disease (CAD) has been considered to be due to an inability to achieve an adequate increase in cardiac output to match the demands of exercise. We investigated 10 consecutive patients (9 men and 1 woman; age, 38 to 71 years; mean, 52 years) with angiographically documented CAD and exercise-induced hypotension (EIH) (BPPeak < BPRest). Ten approximately age- and sex-matched patients with documented CAD and normal exercise blood pressure response (NBP) served as control subjects. Methods and ResultsNine patients with EIH and all 10 control subjects underwent forearm plethysmography and radionuclide ventriculography (RNV) during semierect cycle exercise. Forearm vascular resistance (FVR) fell by 35 ± 21% in exercise-induced hypotension patients versus an increase of 78 ± 65% in patients with an NBP response (P < .0001). Left ventricular ejection fraction increased by 5.1 ± 7.5% in the group with EIH versus a fall of 4.1 ± 6.2% in the control group (P = .004). Cardiac output at peak exercise (RNV) increased by 2.2 ± 0.89-fold in the group with EIH versus 1.49 ± 0.47-fold in the control group (P = .04). The tenth patient in the group with EIH underwent invasive hemodynamic evaluation during erect exercise. Systolic blood pressure fell (136/80Rest to 50/40Peak) and cardiac output (Fick) tripled, whereas calculated systemic vascular resistance decreased by a factor of 10. Successful angioplasty to an isolated circumflex lesion resulted in resolution of symptoms and abnormal hemodynamic responses during exercise. ConclusionsAbnormal vasodilation associated with a normal or even increased rather than decreased cardiac output response appears to be an important mechanism underlying EIH in some patients with CAD. In the present study, this appears to have been the dominant mechanism in 8 and contributory in 2 of the consecutive patients studied.

Experience with a dual chamber implantable defibrillator.

KÜHLKAMP, V., et al.: Experience with a Dual Chamber Implantable Defibrillator. An implantable defibrillator with dual chamber pacing may have advantages for pacing, sensing, and detection of bradyand tachyarrhythmias. This study evaluates the safety and performance of a dual chamber implantable cardioverter defibrillator that incorporates an algorithm to discriminate supraventricular from ventricular arrhythmias. The 300 patients in this study had the device implanted for the following indications: ventricular tachycardia (47%), sudden cardiac death survivorship (51%), and prophylactic implants (2%). Patients received dual chamber pacing for accepted bradyarrhythmic (51.7%) or investigational indications. During a mean follow‐up period of 1.7 months a total of 1,092 arrhythmia episodes in 96 patients were fully documented in the device memory: 66 patients experienced a total of 796 ventricular tachyarrhythmia episodes and 42 experienced a total of 296 supraventricular episodes. The device appropriately detected 100% of sustained ventricular tachyarrhythmias while reducing the inappropriate detection of supraventricular tachyarrhythmias by 72% compared to single chamber rate only detection. The positive predictive value was 90.5% for ventricular tachyarrhythmia detection in episodes that exceeded the tachycardia detection rate. Adverse events observed in at least 2% of the patients were incisional pain (22%), inappropriate ventricular detection (7%), atrial lead dislodgement (4%), atrial oversensing/undersensing (3%), hematoma (3%), incessant ventricular tachyarrhythmia (2%), and pneumothorax (2%). There were 13 deaths, none of which were attributed to device failure. The Gem DR is safe and effective for the detection and treatment of ventricular tachyarrhythmias. The dual chamber detection algorithm appropriately recognized supraventricular tachycardia with rapid ventricular rates 72% of the time while maintaining 100% detection of sustained ventricular tachyarrhythmias.

Wolff‐Parkinson‐White Syndrome Associated with a Coronary Sinus Diverticulum: Ablative Surgical Approach

This report concerns a patient with drug refractory supraventricular tachycardia due to the Wolff‐Parkinson‐White syndrome in association with a coronary sinus diverticulum. Division of the anomalous bypass tract was initially performed by an endocardial approach together with circumferential dissection of the neck of the diverticulum. This procedure failed to ablate the bypass tract that was only successfully divided when the superficial wall of the diverticulum was excised. This case illustrates the dose association that exists between an anomalous atrioventricular bypass tract and a coronary sinus diverticulum, and the importance of dividing the superficial wall of the diverticulum as an integral part of the ablative procedure.

Reassessment of Radiation Risks from Electrophysiology Procedures Compared to Coronary Angiography

BACKGROUND Electrophysiology (EP) procedures have been reported to carry a significantly greater radiation risk than that of coronary angiography (CA). This is largely due to numerous reports linking severe deterministic radiation effects to long procedure and fluoroscopy times (FTs). This study documents low radiation doses achieved by strategies involving operator training and education as well as equipment and technique optimisation to reduce radiation risks. METHODS Records relating to 732 diagnostic EP and 1744 therapeutic EP procedures performed between January 2002 and December 2007 were analysed. Data from 1458 diagnostic only CA procedures performed in 2006 was used for comparison. For each procedure type, FT, number of digital frames acquired and estimated effective dose (E) were compared. RESULTS Although the FT for CA procedures is significantly less than for therapeutic EP procedures (FT for diagnostic EP being similar), EP procedures generally are associated with lower E, the exception being procedures for atrial fibrillation (AF). CONCLUSION Through the application of a comprehensive exposure minimisation strategy, the radiation risk to patients undergoing diagnostic and, therapeutic EP procedures (except AF ablation procedures) is significantly less than that faced by patients undergoing CA. E, however, is heavily dependent on procedure type and as such care must be taken in undertaking generalised comparisons for audit and benchmarking purposes.

Effect of Purine Restriction on Serum and Urine Urate in Normal Subjects

We sought to determine in individual patients with gout the contribution which the diet was making to the serum urate concentration and the urine urate excretion. In order to interpret the results, we needed to know the findings in healthy subjects studied under similar conditions. Previous studies in 22 normal male subjects in USA (1) had shown an upper limit of urinary urate excretion on a purine-free diet of 575 mg (3.4 mmol) per 24 hours. The serum urate concentration and urine urate excretion reached a nadir after 5 days purine restriction, with a mean fall in the serum urate concentration of 1 mg/100 ml (0.06 mmol/1). Accordingly, we planned to compare the serum urate concentration and the mean 24 hour urinary urate excretion on a normal diet with values obtained after 5 days of a low purine diet. The resulting change would reflect the contribution by the purines in the normal Australian diet to the serum and the urine urate. The values during purine restriction would also provide information concerning the normal range for the 24 hour urinary urate excretion on a low purine food diet.

Reversible ischaemia in hypertrophic cardiomyopathy.

Atypical and typical chest pains are common symptoms in patients with hypertrophic cardiomyopathy. Some of these chest pains seem to be caused by ischaemia. It is difficult to objectively demonstrate ischaemia in hypertrophic cardiomyopathy. The first line treatment for chest pain considered to be ischaemic in patients with hypertrophic cardiomyopathy is the use of either a beta blocker or calcium blocker. Septal myectomy can be effective in patients with symptoms refractory to conventional treatment but is associated with significant morbidity and mortality. Recently dual chamber pacing has been advocated in such patients. In some cases dual chamber pacing alleviates chest pain in hypertrophic cardiomyopathy by an anti-ischaemic action, presumably by reducing the left ventricular outflow tract gradient and perhaps by causing an associated decrease in left ventricular outflow tract gradient and perhaps by causing an associated decrease in left ventricular end diastolic pressure.

Radiation risk reduction in cardiac electrophysiology through use of a gridless imaging technique.

AIMS It has been previously demonstrated that use of appropriate frame rates coupled with minimal use of high-dose digital acquisition can limit radiation risk to patients undergoing diagnostic and therapeutic electrophysiology (EP). Imaging without the anti-scatter grid has been proposed as a means of achieving further radiation reduction. We evaluate application of a gridless imaging technique to deliver further reductions in radiation risk to both patients and personnel. METHODS AND RESULTS Radiation and clinical data for EP procedures performed for 16 months from March 2012 were monitored. The period was divided into three phases: Phase 1 (March 2012-June 2012) provided a performance baseline (radiation output modelling and procedural risk adjustment calibration), Phase 2 (July 2012-September 2012) confirmation of performance with the grid, and Phase 3 (September 2012-June 2013) gridless imaging period. Statistical process control (SPC) charts were used to monitor for changes in radiation use and clinical outcomes (procedural success). Imaging without the grid halved the levels of radiation delivered in undertaking EP procedures. Although there was a perceptible impact on image quality with the grid removed. Review of the SPC chart monitoring procedural outcomes did not identify any discernable adverse impact on success rates. Selected use of the gridless technique is recommended with re-introduction of the grid in larger patients or during aspects of the procedure where image quality is important (e.g. transeptal punctures). CONCLUSION Use of a gridless imaging technique can contribute to a significant reduction in radiation risk to both patients and operators during cardiac EP procedures.

Neural Networks in Cardiac Electrophysiological Signal Classification

The aim of this work was to develop a method by which intra-cardiac electrograms could be classified. A new algorithm for training this particular network has been established and applied to the task of finding the onset times of intra-cardiac electrograms. The algorithm is based on adding a choice function to the combination function of each neuron. The choice function enables the network to consider delays in each of its synapses. The gradient of error is then calculated with respect to the weights and delays. A synaptic delay-based artificial neural network was implemented using MATLAB and used to detect the onset times of the atrial, His and ventricular electrograms from the His catheter recordings. Results from a subset of a clinical, 12-channel electrophysiology study demonstrated the ability of the network to successfully identify peak potentials and onset times. Errors in detection of onset times were in the range of 1–2 ms. This method, which does not utilise traditional windowing and/or thresholding operations, can be effectively used to detect temporal patterns in a range of electrophysiological and biological signals.