Sum-Kin Leung

Automatic Optimization of Resting and Exercise Atrioventricular Interval Using a Peak Endocardial Acceleration Sensor: Validation with Doppler Echocardiography and Direct Cardiac Output Measurements

Peak endocardial acceleration (PEA) measured by an implantable acceleration sensor inside the tip of a pacing lead reflects ventricular filling and myocardial contractility. The contribution of the plateau phase of PEA as an indicator of optimal ventricular filling, hence of the appropriate atrioventricular interval (AVI) at rest and during exercise, was studied in 12 patients (age 69 ± 6 years) with complete AV block and a PEA sensing DDDR pacemakers (Living 1 Plus, Sorin Biomedica). At a mean resting heart rate of 79 ± 15 beats/min, the mean AVI optimized by PEA versus Doppler echocardiography (echo) were identical (142 ± 37 vs 146 ± 26 ms, P = 0.59). During submaximal exercise at a mean heart rate of 134 ± 6 beats/min, AVI optimized by PEA was 135 ± 37 ms. Cardiac output at rest, measured by the CO2 rebreathing method, was comparable with AVI determined by echo versus PEA (4.3 ± 2.9 and 3.7 ± 2.4 L/min, respectively), and increased to the same extent (8.0 ± 3.9 vs 8.3 ± 5.2 L/min) during sub‐maximal exercise. In patients with AV block, AVI automatically set by PEA was comparable with AVI manually optimized by Doppler echocardiography and was associated with comparable exercise induced hemodynamic changes.

Comparative evaluation of acute and long-term clinical performance of two single lead atrial synchronous ventricular (VDD) pacemakers : diagonally arranged bipolar versus closely spaced bipolar ring electrodes

Floating P wave sensing can be derived from bipolar atrial electrodes with different electrode configurations, although the relative clinical efficacy of these methods of atrial sensing has not been studied. We evaluated 32 sex and age matched patients with advanced AV block who received A V synchronous pacers using either a single lead with diagonally arranged bipole (Unity VDDR, Model 292, Intermedics Inc.) or closely spaced bipolar complete ring electrodes (Them VDD, Model 8948, Medtronic Inc.). The total surface area of the atrial electrodes were 17.2 and 25 mm2, and the highest programmable atrial sensitivities were 0.1 and 0.25 mV, respectively. Atrial electrogram amplitude and sensing threshold were evaluated at implant and at each follow‐up clinic visit (1, 3, and 6 months), Stability of atrial sensing was assessed during physical maneuvers, treadmill exercise test, and Holier recording. Atrial electrogram amplitude at implantation was higher in the Them VDD (2.08 ± 0.79 vs 1,45 ± 0.59 mV in Unity VDDR; P < 0.05), but the value of atrial sensing threshold was lower during follow‐up than Unity VDDR. P wave undersensing was additionally observed with both pacemakers during physical maneuvers and exercise testing (6%‐19% of patients). Two and four patients had atrial undersensing on Holter in the Unity VDDR and Them VDD, respectively, and the percentage P wave undersensing were 0.88%± 2.41% versus 3.63%± 8.16%, respectively. Reprogramming of the atrial sensitivity in the Unity VDDR and the use of investigational software allowing 0.18 mV atrial sensitivity to be programmed in the Them VDD substantially reduced the percentage of P wave undersensing on Holter to 0.46%± 1.67% and 0.10%± 0.24%, respectively. Beginning at discharge with a programmed atrial sensitivity level at least twice the sensing margin, the mean atrial sensitivity level was reprogrammed from 0.29 to 0.26 mV for Unity VDDR and 0.33 to 0.24 mV for Them VDD at 6 months. There was no incidence of atrial oversensing. Despite differences in atrial amplitudes at implantation between the diagonally arranged bipole and closely spaced full ring single lead systems, the clinical performances of atrial sensing were similar at an appropriately high atrial sensitivities. The absence of atrial oversensing suggests that single pass VDD pacemakers should probably be programmed at the highest available atrial sensitivity to ensure adequate P wave sensing as guided by physical maneuvers and Holter recording to minimize the need of subsequent reprogramming.

PROGRAMMED ATRIAL SENSITIVITY : A CRITICAL DETERMINANT IN ATRIAL FIBRILLATION DETECTION AND OPTIMAL AUTOMATIC MODE SWITCHING

Automatic mode switching (AMS) prevents tracking of paroxysmal atria] fibrillation (AF) in dual chamber pacing. The correct detection of AF can be affected by the programmed atrial sensitivity (AS). We prospectively studied the relationship between AS, AF under‐sensing, an d AMS, using unfiltered bipolar in tracardiac atrial electrogram s recorded from 17 patients during sinus rhythm (SR) and in AF. Overall, 780 rhythms were recorded and replayed onto three dual chamber pacemaker models using different AMS algorithms (Thera DR 7940, Marathon DDDB 294–09, and Meta DDDH 1254), and the ventricular responses were measured. AS was randomly programmed in steps from the highest available AS to half of the mean atrial P wave amplitude (PWA), and the percentage of appropriate AMS responses (defined as a ventricular pacing rate at the expected AMS mode) were recorded. AMS efficacy was related to the programmed AS settings in an exponential manner. At low AS settings, a higher percentage of tests were associated with absence of, or with intermittent AMS and tracking of AF, whereas at higher AS, oversensing of noise during SR occurred. An optimal AS measured approximately 1.3 mV, representing about one‐third of the PWA measured during SR, although oversensing of SR and undersensing of AF continued to occur in 14% of tests and time, respectively, due to the high variation in PWA during AF. Thus, a fixed AS cannot eliminate AF undersensing without inviting noise oversensing, suggesting the need for automatic adjustments of AS, or the use of a rate‐limiting algorithm to prevent rate oscillation during intermittent AF sensing. In conclusion, AMS functions of existing pacemakers were significantly limited by the undersensing of AF and oversensing of noise. Proper adjustment of the AS is important to enable effective AMS during AF.

Automatic mode switching of implantable pacemakers: I. Principles of instrumentation, clinical, and hemodynamic considerations.

LAU, C.‐P., et al.: Automatic Mode Switching of Implantable Pacemakers: I. Principles of Instrumentation, Clinical, and Hemodynamic Considerations. Automatic mode switching (AMS) is now a programmable function in most contemporary dual chamber pacemakers. Atrial tachyarrhythmias are detected when the sensed atrial rate exceeds a “rate‐cutoff,”“running average,”“sensor‐based physiological” rate, or using “complex” detection algorithms. AMS algorithms differ in their atrial tachyarrhythmia detection method, sensitivity, and specificity and, thus, respond differently to atrial tachyarrhythmia in terms of speed to the AMS onset, rate stability of the response, and speed to resynchronize to sinus rhythm. AMS is hemodynamically beneficial, and most patients with atrial tachyarrhythmias are symptomatically better with an AMS algorithm in their pacemakers. New diagnostic capabilities of pacemaker especially stored electrograms not only allow programming of the AMS function, but enable quantification of atrial fibrillation burden that facilitate clinical management of patients with implantable devices who have concomitant atrial tachyarrhythmia.

Automatic mode switching of implantable pacemakers: II. Clinical performance of current algorithms and their programming.

LAU, C.‐P., et al.: Automatic Mode Switching of Implantable Pacemakers: II. Clinical Performance of Current Algorithms and Their Programming. While the hemodynamic and clinical significance of automatic mode switching (AMS) in patients with pacemakers has been demonstrated, the clinical behavior of AMS algorithms differ widely according to the manufacturers and pacemaker models. In general, a “rate‐cutoff” detection method of atrial tachyarrhythmias provides a rapid AMS onset and resynchronization to sinus rhythm at the termination of atrial tachyarrhythmias, but may cause intermittent oscillations between the atrial tracking and AMS mode. This can be minimized with a “counter” of total number of high rate events before the AMS occurs. The use of a “running average” algorithm results in more stable rate control during AMS by reducing the incidence of oscillations, but at the expense of delayed AMS onset and resynchronization to sinus rhythm. Algorithms may be combined to fine tune the AMS response and to avoid rapid fluctuation in pacing rate. Appropriate programming of atrial sensitivity, and the avoidance of ventriculoatrial cross‐talk are essential for optimal AMS performance.

Single lead DDD system: a comparative evaluation of unipolar, bipolar, and overlapping biphasic stimulation and the effects of right atrial floating electrode location on atrial pacing and sensing thresholds

Single lead DDD pacing using unipolar or bipolar stimulation is limited by high atrial threshold. Overlapping biphasic (OLBI) waveform stimulation via atrial floating ring electrodes may preferentially enhance atrial pacing and avoid diaphragmatic pacing. Single lead DDD pacing with OLBI atrial pacing was studied in 12 patients (6 men and 6 women; mean age 74 ± 7 years) with complete heart block. At implantation, atrial bipolar rings (area 27 mm2, separation 10 mm) were positioned at radiological defined high, mid, and low right atrial (RA) levels, and P wave amplitude and atrial and diaphragmatic pacing thresholds were determined in each position using unipolar, bipolar, and OLBI stimulation in random order. Although statistically insignificant, both the maximum and minimum sensed P wave amplitudes tended to be lower in the low RA position. Independent of the stimulation modes, minimum atrial pacing threshold occurred in the mid‐RA. At mid‐RA. the atrial pacing threshold was significantly lower with OLBI pacing compared with either unipolar or bipolar mode (3.9 ± 2.2 V vs 6.7 ± 3.5 V and 6.9 ± 3.5 V, P < 0.05). Although the diaphragmatic thresholds were similar, OLBI pacing modes in the mid‐RA and final location significantly improved the Safety margin for avoidance of diaphragmatic pacing compared with unipolar mode. There was no correlation between atrial pacing and sensing threshold. At predischarge testing, all but one patient who developed atrial fibrillation had satisfactory atrial capture and a stable atrial pacing threshold (day 0: 2.6 ± 1.1 V vs day 2: 3.2 ± 1.3V, P = NS). However, diaphragmatic pacing occurred in four of 11 (36%) patients, especially in the upright position (sitting and standing). Our preliminary clinical results suggest that OLBI pacing via atrial floating ring electrodes can reduce the atrial pacing threshold. To optimize atrial pacing and sensing, the bipolar electrodes should be located at the mid‐RA level first, although the high RA is an alternative. Despite significant improvements in the safety margin for diaphragmatic pacing with OLBI pacing, diaphragmatic stimulation remains a clinical problem.

A Cephalic Vein Cutdown and Venography Technique to Facilitate Pacemaker and Defibrillator Lead Implantation

TSE, H.–F., et al.: A Cephalic Vein Cutdown and Venography Technique to Facilitate Pacemaker and Defibrillator Lead Implantation. The aim of this study was to assess the feasibility of a cephalic vein cutdown and venography technique for implantation of a pacemaker or ICD and to determine the causes of failure of cephalic vein cutdown. In consecutive patients who underwent pacemaker or ICD implants, a modified cephalic vein guidewire technique was performed. This technique was attempted in 289 pacemaker implants and 26 ICD implants (155 men, 160 women; mean age 74 ± 10 years). The success rate for implantation of a single chamber and a dual chamber device by using this technique alone was 84% (54/64) and 74% (185/251), respectively (P = 0.10). In an additional 7% of patients with dual chamber implant, the cephalic vein can be used for passage of the ventricular lead. A cephalic venogram was required in 82 patients and facilitated the passage of the guidewire in 62 (79%) of them. No complication related to vascular access was observed with this technique. This technique failed in 54 (17%) of 315 patients due to (1) failure of cephalic vein isolation (48%), (2) venous stenosis (24%), or (3) venous torturosity or anomalies (28%). There were no significant differences in the patients age, sex, type of device, and the fluoroscopic time for lead placement between patients with or without successful lead placement using this technique (all P > 0.05). In conclusion, a simple modification of the cephalic vein guidewire technique together with venography has facilitated the placement of leads during pacemaker and ICD implant. This technique is safe and applicable in the majority of patients and avoids the risk of subclavian puncture.

Quantitative Comparison of Rate Response and Oxygen Uptake Kinetics Between Different Sensor Modes in Multisensor Rate Adaptive Pacing

Although multisensor pacing may mitigate the inadequacy of rate adaptation in a single sensor system, the clinical role of multisensor driven rate adaptive pacing remains unclear. The cardiopulmonary performance of six patients (mean age 63.5 ± 10 years) who had undergone the implant of combined QT and activity VVIR (Topaz®) pacemakers was assessed during submaximal and maximal treadmill exercise with the rate response sensor randomly programmed to either single sensor mode. QT and activity (ACT), or dual sensor mode, with equal contribution of QT and ACT (QT = ACT). The rate of response, the proportionality, oxygen kinetics, and maximal exercise performance of the various sensor modes during exercise were measured and compared. The ACT sensor mode “overpaced” and the QT and QT = ACT sensor modes “underpaced” during the first three quartiles of exercise (P < 0.05). The ACT sensor mode also gave the fastest rate of response with the shortest delay (13 ± 1.5 sec vs 145 ± 58 sec and 41 ± 17 sec, P < 0.05), time to 50% rate response (39 ±2.7 sec vs 275 ± 48 sec and 203 ± 40 sec, P < 0.05), and time to 90% of rate response (107 ± 21 sec vs 375 ± 34 sec and 347 ± 34 sec, P < 0.05) and a smaller oxygen debt (0.87 ± 0.16 L vs 1.10 ± 0.2 L and 1.07 ± 0.18 L, P < 0.05) compared to the QTand QT = ACT sensor modes, respectively. These differences were most significant at low exercise workloads. Thus, different sensor combinations resuh in different rate response profiles and oxygen delivery, especially during low level exercise. However, the observed oxygen kinetics difference was workload dependent, and its clinical relevance remains to be tested. Despite the marked difference in exercise rate profile and oxygen kinetics, there was no difference in the maximal oxygen uptake, anaerobic threshold, and exercise duration between the various sensor modes during maximal exercise.

DEVELOPMENTS IN SENSOR-DRIVEN PACING

This article reviews the recent major developments in the field of rate adaptive pacing. Including, the improved instrumentation of existing sensors, the use of multiple sensors to enhance sensor specificity or sensitivity, and the automation of sensor calibration. The physiologic benefits and programming of rate adaptive pacing are reviewed.

New Integrated Sensor Pacemaker: Comparison of Rate Responses Between an Integrated Minute Ventilation and Activity Sensor and Single Sensor Modes During Exercise and Daily Activities and Nonphysiological Interference

A dual sensor DDDR pacemaker (DX2 Model 7970, Medtronic Inc.) has integrated the rate response of minute ventilation (MV) and activity (ACT) sensors. False rate acceleration by the ACT (constrained upper rate) and MV (cross‐checked by ACT) is reduced. We examined the rate response profile and rate kinetics of the automatically optimized integrated sensor by comparing with the projected rate response of ACT and MV sensors alone in nine patients. After 1 month of sensor optimization using rate profile optimization (RPO), patients underwent maximal and submaximal treadmill exercises and performed activities of daily living (ADL). The integrated sensor mode gave a faster speed of rate response with a shorter delay time, time to 50% rate response and time to 90% of rate response compared to the MV sensor during hall walk (0.37 ± 0.08, 0.7 ± 0.09, 1.43 ± 0.19 vs 1.11 ± 0.1, 1.75 ± 0.14, 2.91 ± 0.17 min; P < 0.05), The average maximal sensor rates were significantly more proportional for the integrated sensor mode compared with either the ACT or MV mode. There was no significant difference in both the maximal pacing rate among the three sensor modes during maximal exercise and the rate decay during recovery. During interference studies by arm swinging (30–40 swings/min) and external tapping of the pacemakers (2 taps/s), there was only a moderate increase in pacing rate by 13 ± 9, 16 ± 5 beats/min. Hence, the new integrated sensor with the automatic rate profile optimization algorithm resulted in improved rate response profiles during submaximal exercise and ADL compared to the individual sensor response, and the sensor blending and cross‐checking algorithm made the pacemaker relatively immune to false triggering of both the ACT and MV sensors.