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Biomedical subjects

G J Klein

Publications and source records attributed to G J Klein.

At least 19 recordsLinked to original sources
PubMed1999

Use of an extended monitoring strategy in patients with problematic syncope. Reveal Investigators.

BACKGROUND: The conventional investigation of patients who present with syncope involves short-term ECG monitoring or provocative testing with head-up tilt and electrophysiological testing. A symptom-rhythm correlation is often difficult to obtain during spontaneous syncope because of its sporadic, infrequent, and unpredictable nature. METHODS AND RESULTS: We used a prolonged monitoring strategy to determine the cause of syncope in 85 patients (age, 59+/-18 years; 44 men) with recurrent undiagnosed syncope with an implantable loop recorder capable of cardiac monitoring for up to 18 months. During a mean of 10.5+/-4.0 months of follow-up, symptoms recurred in 58 patients (68%) 71+/-79 days (2.3+/-2.6 months) after implantable loop recorder insertion. An arrhythmia was detected in 42% of patients who recorded a rhythm during recurrent symptoms, with bradycardia present in 18 and tachycardia in 3. Five of the 18 bradycardic patients and 2 additional sinus rhythm patients received a clinical diagnosis of neurally mediated syncope. Patients who experienced presyncope were much less likely to record an arrhythmia during symptoms compared with recurrence of syncope (24% versus 70%, P=0.0005). There were no adverse events associated with recurrent symptoms, and there were no sudden deaths. Inability to freeze after an event occurred in 8 patients, and pocket infection occurred in 3. CONCLUSIONS: The strategy of prolonged monitoring is effective and safe in patients with problematic syncope.

Adult↗
PubMed1999

The high cost of syncope: cost implications of a new insertable loop recorder in the investigation of recurrent syncope.

BACKGROUND: Patients with recurrent syncope frequently undergo extensive investigations that consume significant health care resources. Recent advances in long-term monitoring techniques have enhanced diagnostic yield in patients with infrequent symptoms. There is little information on the relative cost-effective profile of the investigative tools used in patients with syncope. METHODS: Two methods to determine health care costs in patients with syncope were used. In the first, health care resource utilization was determined in 24 patients with recurrent unexplained syncope and negative investigations who underwent insertion of the implantable loop recorder (ILR) during a pilot study of the feasibility of the device. The costs of investigations before, during, and after ILR implantation in each patient were calculated on the basis of median charges for an index investigation and a regression analysis of 1018 US Medicare hospital claims for syncope from 1993. Charges were converted to costs using a cost-to-charge ratio of 0.64. The second method was based on estimated costs per diagnosis and published diagnostic yields of 6 commonly applied tests in patients with syncope. A cohort simulation using theoretic models of 100 patients undergoing investigation for syncope was created to compare the diagnostic yield and cost per diagnosis of various diagnostic cascades. RESULTS: In the pilot study, the cost of investigation of syncope in the 2 years before ILR insertion was $7584 per patient. After the ILR was inserted, a diagnosis was obtained in 21 of 24 patients (diagnostic yield 88%). The cost of therapy was $2452, followed by a reduction in cost of care to $596 over 30 +/- 10 months of follow-up. In the second method, the diagnostic yield of individual tests ranged from 3% for echocardiography to 88% for the ILR. The cost per diagnosis obtained ranged from $529 for the external loop recorder to $73,260 for electrophysiologic testing in patients without structural heart disease. An approach to syncope similar to that of the ILR pilot study resulted in a cost per diagnosis of $3193 and a diagnostic yield of 98%. Performance of echocardiography in half of the patients and electrophysiologic testing only in the presence of structural heart disease reduced the cost to $2494 and retained a diagnostic yield of 98%. CONCLUSIONS: The cost of investigation of syncope is high. The ILR may reduce health care resource utilization by providing a diagnosis permitting definitive therapy. The cost per diagnosis profile of current diagnostic tests commonly used in patients with syncope is highly variable. A cost-effective approach to diagnosing this disorder can retain a high diagnostic yield with a reduction in resource utilization compared with a conventional approach.

Cost of Illness↗
PubMed1999

Sevoflurane has no effect on sinoatrial node function or on normal atrioventricular and accessory pathway conduction in Wolff-Parkinson-White syndrome during alfentanil/midazolam anesthesia.

BACKGROUND: The effects of sevoflurane on the electrophysiologic properties of the human heart are unknown. This study evaluated the effects of sevoflurane on the electrophysiologic properties of the normal atrioventricular conduction system, and on the accessory pathways in patients with Wolff-Parkinson-White syndrome, to determine its suitability as an anesthetic agent for patients undergoing ablative procedures. METHODS: Fifteen patients with Wolff-Parkinson-White syndrome undergoing elective radiofrequency catheter ablation were studied. Anesthesia was induced with alfentanil (20-50 microg/kg) and midazolam (0.15 mg/kg), and vecuronium (20 mg) and maintained with alfentanil (0.5 to 2 microg x kg(-1) x min(-1)) and midazolam (1 or 2 mg every 10-15 min, as required). An electrophysiologic study measured the effective refractory period of the right atrium, atrioventricular node, and accessory pathway; the shortest conducted cycle length of the atrioventricular node and accessory pathway during atrial pacing; the effective refractory period of the right ventricle and accessory pathway; and the shortest retrograde conducted cycle length of the accessory pathway during ventricular pacing. Parameters of sinoatrial node function included sinus node recovery time, corrected sinus node recovery time, and sinoatrial conduction time. Intraatrial conduction time and the atrial-His interval were also measured. Characteristics of induced reciprocating tachycardia, including cycle length, atrial-His, His-ventricular, and ventriculoatrial intervals, also were measured. Sevoflurane was administered to achieve an end-tidal concentration of 2% (1 minimum alveolar concentration), and the study measurements were repeated. RESULTS: Sevoflurane had no effect on the electrophysiologic parameters of conduction in the normal atrioventricular conduction system or accessory pathway, or during reciprocating tachycardia. However, sevoflurane caused a statistically significant reduction in the sinoatrial conduction time and atrial-His interval but these changes were not clinically important. All accessory pathways were successfully identified and ablated. CONCLUSIONS: Sevoflurane had no effect on the electrophysiologic nature of the normal atrioventricular or accessory pathway and no clinically important effect on sinoatrial node activity. It is therefore a suitable anesthetic agent for patients undergoing ablative procedures.

Adult↗
PubMed1999

Acute testing of the rate-smoothed pacing algorithm for ventricular rate stabilization.

We evaluated the capability of a new pacemaker-based rate-smoothing algorithm (RSA) to reduce the irregular ventricular response of AF. RSA prevents sudden decreases in rate using a modified physiological band and flywheel feature. Twelve patients (51 +/- 21 years) with hemodynamically tolerated AF of 4 months to 20 years duration were studied. Atrial and ventricular leads were connected to the external pacemaker device in the electrophysiology laboratory. Consecutive RR intervals during AF were measured at baseline and after ventricular pacing with RSA ON. Ventricular pacing with the rate smoothing algorithm reduced maximum RR intervals (1,207 +/- 299 vs 855 +/- 148 ms, P = 0.0005), with no significant change in the minimum RR interval (401 +/- 55 vs 393 +/- 74 ms, P = 0.292). A small shortening of the mean RR interval (634 +/- 153 vs 594 +/- 135 ms, P = 0.007) was seen with no change in the median RR interval (609 +/- 153 vs 595 +/- 143 ms, P = 0.388). There was a 43% reduction in RR standard deviation (145 +/- 52 vs 82 +/- 28, P = 0.0005), 49% reduction in mean absolute RR interval difference (MAD) (152 +/- 64 vs 77 +/- 34, P = 0.0005) and MAD/mean RR ratio (0.23 +/- 0.05 vs 0.13 +/- 0.04, P = 0.0005). We conclude that rate-smoothed pacing effectively reduces RR variability of AF in the acute setting.

Adult↗
PubMed1999

A cost effective approach to the investigation of syncope: relative merit of different diagnostic strategies.

OBJECTIVE: To compare the cost effectiveness of a conventional diagnostic work-up with that of several different diagnostic cascades for the investigation of undifferentiated syncope. DESIGN: A MEDLINE search established a weighted estimate of diagnostic yield for several diagnostic investigations. 'High-end' and 'low-end' cost estimates were calculated for these investigations based on figures from four representative Canadian tertiary care centres in four different provinces. Several diagnostic models were applied to a hypothetical cohort of 100 patients with undifferentiated syncope. RESULTS: The conventional diagnostic cascade resulted in a diagnosis in 85% of patients, at a cost per diagnosis of $467 to $959. The optimal model increased the diagnostic yield to 98.9%, at a cost of $460 to $1043 per diagnosed patient. CONCLUSION: A combination of new technology and selective use of investigations has the potential to raise diagnostic yield without appreciably increasing cost per diagnosis.

Algorithms↗
PubMed1998

Final results from a pilot study with an implantable loop recorder to determine the etiology of syncope in patients with negative noninvasive and invasive testing.

Twenty-four patients with recurrent unexplained syncope and negative tilt and electrophysiologic testing underwent implantation of the implantable loop recorder, with recurrence of syncope in 21 patients 5.1+/-4.8 months after device implantation. Eighteen of the 21 had a treatable diagnosis, with arrhythmias in 11. Treatment resulted in resolution of syncope in most patients during long-term follow-up.

Adult↗
PubMed1998

Correlation of waiting time with adverse events in patients admitted for nonelective permanent pacemaker implantation.

OBJECTIVE: To determine the effect of a dedicated permanent pacemaker implantation procedure room on waiting time and waiting time-related morbidity. DESIGN: Retrospective chart review. SETTING: Two tertiary care teaching hospitals in southern Ontario; one with a dedicated procedure room (centre B) and one without (centre A). PATIENTS: Two hundred and fourteen consecutive patients who required permanent pacing urgently or emergently. METHODS: Charts were examined retrospectively at centre A (131 patients) and centre B (83 patients) to determine the waiting time for and the number of preoperative adverse events in nonelective permanent pacemaker implantation. RESULTS: Patients in centre A waited a mean of 4.5 +/- 3.0 days while patients in centre B waited a mean of 1.9 +/- 1.6 days (P = 0.0001). Centre A patients experienced a total of 57 adverse events that were likely or possibly related to the waiting period, while patients at centre B experienced eight such events (P < 0.0001). Thirty-three per cent of the centre A patients experienced at least one adverse event, while 8% of centre B patients experienced at least one adverse event (P < 0.00001). Of the centre A patients who waited for more than six days (26 patients), 58% had at least one adverse event, compared with 26% of those who waited less than six days (105 patients, P = 0.0009). CONCLUSIONS: Delays in implanting nonelective permanent pacemakers are strongly associated with an increase in adverse events. Measures to shorten the waiting time are likely to result in a reduction in morbidity in conjunction with a beneficial impact on health care resource utilization.

Humans↗
PubMed1997

Progressive anterior ablation in the coronary sinus region: evidence to support the presence of a 'slow pathway' input in normal patients?

BACKGROUND: AV node modification is an emerging approach to rate control in patients with medically refractory atrial fibrillation. The mechanism of benefit of this procedure is not completely understood. METHODS AND RESULTS: Twenty-two patients (age, 65+/-11 years; 16 women) with medically refractory paroxysmal atrial fibrillation referred for complete AV node ablation underwent serial ablations beginning at the level of the coronary sinus os progressing in a superior and anterior direction toward the His bundle. Serial atrial extrastimulus testing was performed to determine the effect of the progressive posteroseptal ablation in the region of the coronary sinus on the AV node antegrade refractory curve. Two of 22 patients had antegrade dual AV node pathways before ablation. Three patterns of response to serial ablation were noted. In 10 patients (45%), loss of the terminal portion of the AV node antegrade refractory curve occurred without evidence of fast pathway injury. In 7 patients (32%) the curve was shifted upward and to the left, consistent with nonspecific AV node damage. In 5 patients (23%), no effect could be attained before induction of complete AV block at superior and anterior ablation sites. Clinical variables and site of ablation did not predict response to serial ablations. CONCLUSIONS: These data suggest that the mechanism of benefit of AV node modification in this population may be through elimination of "slow pathway" tissue in half of patients and nonspecific injury in the remainder. Modification without complete AV block may not be possible in a minority of patients, as the response to progressive ablation appears to be "all or none" conduction.

Aged↗
PubMed1997

Hysteresis of the RT interval with exercise: a new marker for the long-QT syndrome?

BACKGROUND: The diagnosis of the long-QT syndrome (LQTS) may be difficult to establish in patients with normal or borderline prolongation of the QT interval. Noninvasive markers are needed to identify patients with LQTS. METHODS AND RESULTS: Fourteen patients with known LQTS, 9 unaffected family members, and 40 control subjects underwent modified Bruce protocol exercise testing. The RT interval (peak of R wave to peak of T wave) and rate-corrected RT interval (RTc) were measured during exercise and recovery. The RT interval at 1 minute into recovery was subtracted from the RT interval at a similar heart rate during exercise (deltaRT). The RTc shortened by 61 milliseconds (ms) in the LQTS patients compared with 23 to 26 ms in the other two groups (P=.003 by ANOVA). The RT interval shortened in a linear fashion in all patients but demonstrated persistent shortening during recovery in the LQTS patients. This was manifested as a hysteresis loop in the curve relating the RT interval to cycle length. The hysteresis loop was present in 13 of 14 LQTS patients and only 4 of 40 control subjects. DeltaRT >25 ms had a sensitivity of 73%, a specificity of 92%, a positive predictive value of 79%, and a negative predictive value of 90% for LQTS. CONCLUSIONS: Hysteresis of the RT interval with exercise may be useful for the diagnosis of LQTS.

Adolescent↗
PubMed1997

Safety of slow pathway ablation in patients with atrioventricular node reentrant tachycardia and a long fast pathway effective refractory period.

Radiofrequency catheter ablation is an accepted primary therapy for atrioventricular (AV) node reentrant tachycardia (AVNRT). There is concern that slow pathway ablation in patients with a long anterograde fast pathway effective refractory period (ERP) may potentially impair subsequent node conduction. Eighteen patients (14 women; age 53 +/- 20 years) with symptomatic AVNRT, whose fast pathway ERP at baseline was > or = 500 ms, underwent slow pathway ablation. Their outcome was compared with 24 consecutive control patients (17 women; age 42 +/- 17 years) who underwent ablation for AVNRT whose fast pathway ERP at baseline was <500 ms (controls). Slow pathway ablation was successful in 16 patients (90%). One patient had inadvertent fast pathway ablation. In a second patient the slow pathway could not be ablated because of recurrent transient AV block. Ablation was successful in all patients in the control group. Transient AV block related to current application occurred in 4 patients (22%) versus 1 control (4%) (p = 0.07). After ablation, the AV node refractory period increased in patients (368 +/- 68 to 428 +/- 92 ms, p = 0.02) and in controls (282 +/- 35 to 336 +/- 55 ms, p <0.0001), but the fast pathway ERP shortened in both groups (patients: 558 +/- 63 to 428 +/- 92 ms, p = 0.003; controls: 356 +/- 53 to 336 +/- 55 ms, p = 0.05). Furthermore, the slope of the regression line relating to shortening of the fast pathway ERP to the baseline ERP was markedly steeper in patients compared with controls (1.9 vs 0.4, p <0.0001). The shortening of the fast pathway ERP was greater in patients compared with controls (122 +/- 130 vs 21 +/- 50 ms, p = 0.001). During a mean follow-up of 18 +/- 11 months, 1 patient with severe coronary artery disease died suddenly 2 years after ablation. There was no recurrence of clinical tachycardia, and none of the patients developed symptoms of bradycardia or required permanent pacing. Thus, slow pathway ablation in patients with AVNRT and a long fast pathway ERP is safe and effective.

Adult↗
PubMed1997

Recurrent syncope. Experience with an implantable loop recorder.

The cause of recurrent syncope is often difficult to determine when initial laboratory investigations are negative. Advances in implantable monitoring technology permit long-term monitoring of the electrocardiogram in patients with recurrent undiagnosed syncope. A pilot device implanted in the left pectoral region established the cardiac rhythm during syncope in all 20 of 24 patients who developed syncope during follow-up. The cause was arrhythmic in 10 and nonarrhythmic in 10. Therapy resulted in resolution of symptoms in 17 of 20 patients. The implantable loop recorder is a promising diagnostic tool for investigation of syncope.

Electrophysiology↗
PubMed1997

Current role of pharmacologic therapy for patients with paroxysmal supraventricular tachycardia.

Intravenous antiarrhythmic drugs will continue to have an important role in the acute management of SVT. Long-term antiarrhythmic drug therapy is often effective in preventing or reducing frequency and severity of arrhythmic episodes. The cost, adverse effects, and inconvenience of long-term drug therapy will result in the increasing use of curative ablation for most individuals with problematic SVT.

Adenosine↗
PubMed1997

A methodology for specifying PET VOI's using multimodality techniques.

Volume-of-interest (VOI) extraction for radionuclide and anatomical measurements requires correct identification and delineation of the anatomical feature being studied. We have developed a toolset for specifying three-dimensional (3-D) VOI's on a multislice positron emission tomography (PET) dataset. The software is particularly suited for specifying cerebral cortex VOI's which represent a particular gyrus or deep brain structure. A registered 3-D magnetic resonance image (MRI) dataset is used to provide high-resolution anatomical information, both as oblique two-dimensional (2-D) sections and as volume renderings of a segmented cortical surface. VOI's are specified indirectly in two dimensions by drawing a stack of 2-D regions on the MRI data. The regions are tiled together to form closed triangular mesh surface models, which are subsequently transformed into the observation space of the PET scanner. Quantification by this method allows calculation of radionuclide activity in the VOI's, as well as their statistical uncertainties and correlations. The methodology for this type of analysis and validation results are presented.

Brain↗
PubMed1997

Comparison of single-biphasic versus sequential-biphasic shocks on defibrillation threshold in pigs.

Current generation implantable cardioverter defibrillators use monophasic, biphasic, or sequential pulse shocks, most of which truncate after a given time, dumping the remaining charge on the capacitor through an internal resistor. We hypothesized that having an additional current pathway, and delivering the majority of the remaining charge on a single capacitor to the two pathways using additional shock phases, would improve defibrillation efficacy. This hypothesis was tested by comparing DFTs using a simulated single capacitor, single-biphasic shock (two 5-ms pulses separated by 0.2 ms), delivered to coupled pairs of electrodes, to those using a sequential-biphasic shock (four 5-ms pulses separated by 0.2 ms) delivered to separate opposing electrodes, delivered from the same electrodes for both waveforms. In eight open-chest anesthetized pigs, four mesh electrodes (Medtronic TX-7, 6.5 cm2), were sutured on the epicardium of the anterior and posterior surfaces of each ventricle. Shocks were delivered from a 200-microF capacitor bank. Triplicate DFTs were obtained using each waveform in a randomized crossover design. Initial leading edge voltage (mean +/- SEM: 420 +/- 33 V vs 497 +/- 34 V; P < 0.05), initial peak current (4.8 +/- 0.4 A vs 13 +/- 1.1 A; P < 0.001), and delivered energy (16.9 +/- 2.6 J vs 30.4 +/- 5.3 J; P < 0.05) at the DFT were all significantly lower using sequential-biphasic shocks than those using single-biphasic shocks, respectively. We conclude that for direct heart defibrillation, it is worthwhile to combine sequential capability to biphasic shocks and deliver the remaining charge on the capacitor to the two different pathways.

Animals↗
PubMed1997

Maturation of the sensed electrogram amplitude over time in a new subcutaneous implantable loop recorder.

The cause of recurrent syncope may be difficult to determine if the diagnosis is not established from initial noninvasive and invasive testing. Eighteen patients with recurrent syncope and negative tilt table and electrophysiological testing underwent implantation of a left pectoral subcutaneous loop recorder. This device "freezes" the preceding 7.5 or 15 minute rhythm strip after magnet application after spontaneous syncope. Baseline and follow-up electrograms were routinely recorded, and patients were followed until syncope recurred. Three patients had syncope within 1 month of implantation and were excluded from this report. Implantation electrogram amplitude was 250 +/- 124 microV and increased to 291 +/- 114 microV at 2-3 months, and increased further to 353 +/- 167 microV at 4-6 months (P < 0.001, ANOVA). Syncope recurred in 14 of the 15 patients. An arrhythmic basis for syncope was established (n = 7) or excluded (n = 7) in every patient who had recurrent syncope. All syncopal episodes were associated with diagnostic sensed electrograms. The increase in sensed electrogram amplitude over time suggests a maturation of the device-tissue interface. These results support the long-term viability of this implantable monitoring technique.

Arrhythmias, Cardiac↗
PubMed1997

The effect of variable retrograde penetration on dual AV nodal pathways: observations before and after slow pathway ablation LDD.

Retrograde VA conduction is usually over the fast pathway and rarely over the slow pathway in patients with dual AV nodal pathways. It is unknown whether this apparent unidirectional conduction of the slow pathway is due to the lack of its retrograde conducting ability or the result of concealment. The effect of variable retrograde AV nodal penetration on antegrade AV nodal conduction was determined in patients with typical AV nodal reentrant tachycardia before and after the slow pathway ablation. Variable retrograde penetration was produced by delivering a ventricular extrastimulus simultaneously with (VE-0), 50 ms after (VE-50), or 100 ms after (VE-100) the last basic atrial stimulus, while atrial extrastimuli were used to determine changes of anterograde AV nodal effective refractory period (ERP) and A-H interval. The AV nodal functions measured without the ventricular extrastimuli served as the baseline. Although the mean slow pathway ERP was not significantly different among the different stimulation protocols, a significant shortening of the slow pathway conduction time (A-H from 348 +/- 60 to 324 +/- 119 ms, P < 0.05) was observed with upper level retrograde penetration of the AV node (VE-0). This facilitating effect became a prolonging effect when the retrograde penetration level moved to the lower level (VE-100, A-H from 324 +/- 119 to 366 +/- 122 ms, P < 0.05). The fast pathway ERP shortened with an upper level penetration (VE-0) but tended to prolong with a lower level retrograde-penetration (VE-100) both before and after the slow pathway ablation (preablation, from 348 +/- 143 of the baseline to 302 +/- 114 to 360 +/- 143 ms, P < 0.05; postablation, from 314 +/- 101 of the baseline to 274 +/- 118 to 361 +/- 143 ms, P < 0.05). The mean A2-H2 interval of the slow pathway was significantly shorter than the baseline (350 +/- 44 ms) with VE-0 (249 +/- 48 ms, P < 0.05) and VE-50 stimulation (285 +/- 82 ms, P < 0.05) but not with VE-100 stimulation (330 +/- 83 ms, P = NS). Before slow pathway ablation, the A2-H2 interval of the fast pathway at equal coupling intervals was shorter than the baseline (165 +/- 53 ms) with VE-0 (144 +/- 47 ms, P < 0.01) and VE-50 stimulation (152 +/- 43 ms, P < 0.05) but tended to be longer with VE-100 stimulation (175 +/- 47 ms, P = NS). After slow pathway ablation, the mean A2-H2 interval at the same coupling interval was shorter than the baseline (173 +/- 39 ms) with VE-0 (139 +/- 35 ms, P < 0.05), VE-50 (153 +/- 32 ms, P = 0.05) but tended to be longer with VE-100 stimulation (178 +/- 49 ms, P = NS). We conclude that: (1) concealed retrograde conduction can be demonstrated in both the slow and the fast AV nodal pathways; and (2) concealed retrograde conduction may either shorten or prolong anterograde refractoriness and conduction time, depending on the level of retrograde penetration.

Adult↗