Notes: Introduction: The crista terminalis (CT) has been shown to be a barrier to transverse conduction during typical atrial flutter (AFL). However, some studies have demonstrated the presence of functional block in the sinus venosa region but not at the CT. The aim of this study was to define these regions of block in the right atrium using a three-dimensional noncontact mapping system. Methods and Results: In 39 AFL patients (33 men and six women, mean age 56 ± 13 years), a noncontact multielectrode array was used to reconstruct electrograms in the right atrium. Isochronal and isopotential propagation mapping was performed during AFL and during pacing from the coronary sinus ostium and the low lateral wall (cycle length from 600 to 240 msec) in sinus rhythm after creation of isthmus block. A single line of block along the CT area was found in 18 patients (46%). Two lines of block were found in 21 patients (54%), with the first line located along the CT area. The second was located in the sinus venosa region in 20 patients (51%) and in the lateral wall in 1 patient (3%). In all patients, the block in the lower part of the CT was observed during AFL (60%) and during pacing at all cycle lengths (48%–62%). The length and proportion of block were inversely proportional to pacing cycle length. Conclusion: Double lines of block were frequently observed in patients with AFL, and both lines may form the posterior boundaries of the AFL circuit. Block was fixed in the lower part of the CT and was functional in the upper part of the CT. (J Cardiovasc Electrophysiol, Vol. 14, pp. ***-***, October 2003)

Notes: A QRS width greater than 120 ms is assumed to be a marker of inter- and intraventricular asynchrony in severe heart failure (HF) patients. Color Doppler tissue velocity imaging (c-TVI) with a time resolution of 10 ms was used to study regional left ventricular (LV) longitudinal systolic contraction pattern in HF patients with left and right bundle branch block (LBBB and RBBB) and in patients with normal QRS width. We studied 12 women and 23 men with severe HF, with a mean age of 66 ± 11 years in New York Heart Association functional Class 2.9 ± 0.6. Twenty patients had LBBB and 10 of those were accepted for cardiac resynchronization therapy by biventricular pacing (CRT). Ten patients had normal QRS width, and five had RBBB. In the echocardiographic apical four chamber view, regional peak LV tissue velocities and regional LV time differences of peak tissue velocities were compared at basal and mid-LV segments. There were no significant differences in regional mean peak tissue velocities among the patient groups. In patients with LBBB accepted for CRT, the LV lateral free-wall movement at basal LV was 29 ms delayed during main systole, almost significantly different from LBBB patients not accepted for CRT (P = 0.075). Even in HF patients with normal QRS width or RBBB, significant asynchronous longitudinal LV contraction was observed. Conclusions: For the detection of regional longitudinal LV contraction asynchrony in patients with severe HF, supplementary methods to the surface ECG, such as c-TVI, are strongly recommended. (PACE 2004; 27:460–467)

Notes: FAERESTRAND, S., et al.: Alternate Pacing Sites for Patients with Tricuspid Valve Prostheses. The objective of this study was to pace via a coronary vein to avoid interfering with the tricuspid valve prosthesis function. Pacing leads were inserted into the posterior cardiac vein in a 68-year-old woman (patient 1), and in the great cardiac vein and the right auricle in a 32-year-old woman (patient 2). In patient 1 the stimulation threshold was 1.8 V at implant and stabilized at 3.0 V at the 24-month follow-up. In patient 2 the ventricular pacing threshold was 1.2 V at implant and stabilized at 0.7 V at the 24-month follow-up. The cardiac output at rest increased 43% during atrioventricular synchronous pacing compared to ventricular pacing. Long-term stable ventricular pacing via the coronary venous system was obtained.

Notes: With the aid of an algorithm for automatic pacing threshold (T) measurement in the atrium and ventricle, downloadable into implanted Thera pacemakers (Medtronic Inc.), we studied T evolution during lead maturation, T variation during activities of daily living, and various types of beat-to-beat T variations in three tined bipolar leads: 5.6-mm2 steroid-eluting (Medtronic Inc. models 4524 atrial-J [n = 8] and 4024 ventricular [n = 8]), 1.2-mm2 steroid-eluting (Medtronic Inc. models 5534 atrial-J [n = 9] and 5034 ventricular [n = 9]), and 8-mm2 without steroid (Intermedics models 432–04 atrial-J [n = 7] and 430–10 ventricular [n = 7]). The leads were implanted in 24 consecutive patients with intact AV conduction (required by the algorithm) and followed for up to 13–25 months after implantation. Since the algorithm determined pulse width Ts at different amplitudes that, depending upon T level, could range from 0.5 to 5.0 V, we invented a methodology for conversion of pulse width Ts into voltage Ts at 0.5 ms, to pool and present T data on a universal scale. Frequent, high resolution T measurements revealed details on the lead maturation process that we divided into three stages: initial T subsiding, first wave of T peaking, and a new, quicker or slower, T rise. Although there were notable differences in duration and magnitude of T peaking on the individual basis, differences between the three lead types and between the atrium and ventricle were demonstrable. The 1.2-mm2 leads exhibited less T peaking than their predecessors 5.6-mm2 leads and excellent positional stability, whereas 8-mm2 leads demonstrated the most intensive T peaking and highest mean chronic T values. T changes during activities of daily living showed some tendencies—higher T during night and lower T during exercise —yet with a number of exceptions. The overall magnitude of daily T fluctuations was 〈 0.2 V in all but one lead, and 50% daily voltage safety margin would be sufficient. A 100% voltage safety margin may be inadequate for a 1-year period during the chronic phase (after 6 months of implantation). A scheme for calculation of pulse width safety margins equivalent to voltage safety margins is given. Some leads can exhibit very large beat-to-beat T variations before, during, and after T peaking, and prospective algorithms for automatic T measurement should verify T values through more than 1–2 captured beats to obviate a great underestimation of the T providing consistent capture. T dependence upon pacing rate was negligible. Consistent-capture hysteresis may, in conjunction with lead instability, be as much as 0.25 V. Therefore, it is better to use an incremental approach from below to T level during automatic T measurements.

Notes: Pacing threshold is affected by many factors. A pacing system able to confirm capture at each beat and automatically adjust its output close to the actual pacing threshold is highly desirable. This study evaluates the safety and efficacy of the Autocapture function of the Pacesetter Microny SR+. One hundred thirteen patients were recruited from 16 centers in 7 European countries and followed up for 1 year. All pacemakers were implanted with Pacesetter's low polarization, bipolar leads. The key feature of Autocapture is the immediate delivery of a 4.5 V safety backup pulse 62.5 ms after any ineffective ongoing low output pulse. Holter recordings confirmed total reliability of this feature without any exit block. The measured evoked response (ER) signal was stable over time. Acute and chronic pacing thresholds measured by VARIO and Autocapture tests correlated (r 〉 0.79) over the period of the study. The incidence of backup pulses was 1.1% during pacing. With Autocapture programmed ON, the overall total current consumption was 4.1 μA for VVI and 5.0 μA for VVIR pacing. Tbis study proved that the Autocapture safely and reliably regulates the pacemaker's output according to the prevailing threshold thus providing maximum patient safety and prolonging service life.

Notes: The aim of the study was to investigate pacing impedance (PI) behavior in ambulatory patients. Eighteen atrial and 18 ventricular tined steroid eluting leads with 1.2-mm2 and 5.6-mm2 electrodes were implanted in 20 patients. At 9–27 months after implantation PI was measured automatically by means of additional algorithms downloaded via telemetry links into implanted Thera® pulse generators. PI was determined based on the voltage drop on the output capacitor during the 5 V-1 ms pacing impulse, at the programmable sampling rates from 1 second to 30 minutes. The study examined in particular: (1) PI trends and variations associated with different breathing patterns, body postures, provocative maneuvers, bike exercise, and during 24 hours; (2) impact of pacing rate and AV-delay on PI; (3) correlation between PI variability and pacing threshold, lead configuration, absolute PI value, age, gender, disease, and cardiac chamber. The most important findings were: (1) large PI variations of up to 450 Ω were observed in properly functioning leads, (2) PI variability exhibited a weak negative correlation with pacing thresholds as if electrode positional stability was not a major factor underlying PI variations, (3) unipolar and bipolar PI variations were equivalent to each other (correlation factor = 0.93) implying that PI was mostly dependent on the circumstances around the lead tip.

Notes: We have developed an algorithmic method for automatic determination of stimulation thresholds in both cardiac chambers in patients with intact atrioventricular (AV) conduction. The algorithm utilizes ventricular sensing, may be used with any type of pacing leads, and may be downloaded via telemetry links into already implanted dual-chamber Thera® pacemakers. Thresholds are determined with 0.5 V amplitude and 0.06 ms pulse-width resolution in unipolar, bipolar, or both lead configurations, with a programmable sampling interval from 2 minutes to 48 hours. Measured values are stored in the pacemaker memory for later retrieval and do not influence permanent output settings. The algorithm was intended to gather information on continuous behavior of stimulation thresholds, which is important in the formation of strategies for programming pacemaker outputs. Clinical performance of the algorithm was evaluated in eight patients who received bipolar tined steroid-eluting leads and were observed for a mean of 5.1 months. Patient safety was not compromised by the algorithm, except for the possibility of pacing during the physiologic refractory period. Methods for discrimination of incorrect data points were developed and incorrect values were discarded. Fine resolution threshold measurements collected during this study indicated that: (1) there were great differences in magnitude of threshold peaking in different patients; (2) the initial intensive threshold peaking was usually followed by another less intensive but longer-lasting wave of threshold peaking; (3) the pattern of tissue reaction in the atrium appeared different from that in the ventricle; and (4) threshold peaking in the bipolar lead configuration was greater than in the unipolar configuration. The algorithm proved to be useful in studying ambulatory thresholds.

Notes: A new generation of tined steroid-eluding leads featuring 1.2-mm2 distal electrodes (CapSure® Z, Medtronic Inc., Minneapolis MN, USA) has the potential to reduce battery current drain and enhance pulse generator longevity by means of high pacing impedance and low pacing threshold. Forty patients aged 50–87 years (mean 72.4 years) were implanted with 33 ventricular (models 4033 and 5034) and 30 atrial-J (models 4533 and 5534) leads with 1.2-mm2 electrodes. Low pacing outputs, mainly in the range from 1 V/0.20 ms to 1.6 V/0.36 ms with ≥ 3:1 pulse width safety margins (PWSM) applied, were instituted at 3–6 months of implantation and adjusted at subsequent follow-up controls according to changes in thresholds. Cumulative follow-up period of low outputs was 1,512 months (24 months per lead, range 9–36 months), which involved 3.43 follow-up controls per lead (range 2–5). During follow-up, pulse width thresholds (PWTs) at the used amplitudes did not change in 55.5% of the leads; PWTs increased by ≤ 100% in 36.5%, by 101%–200% in 1.6%, and by 〉 200% in 6.3% of the leads. Changes in PWT that would apparently exceed 3:1 PWSM over a 1-year period occurred in one atrial lead where even the nominal 3.5 V/0.4-ms output would not be effective and in one ventricular lead in the aftermath of an acute myocardial infarction (300% PWT rise at 1.6 V). Based on the present observations, pacemaker dependent patients require ≥ 4:1 PWSM and other patients ≥ 3:1 PWSM with output pulse widths ≤ 0.60 ms and annual pacemaker clinic visits. Calculated battery current drain and anticipated longevity associated with a variety of pacing outputs and impedances are provided, compared, and discussed. Correlation between acute and chronic pacing impedances and pacing thresholds was weak, implying that a systematic intraoperative pacing site optimization cannot contribute significantly to the extension of average battery longevity.

Notes: A VDD pacing system with bipolar single-pass leads, were implanted in 36 consecutive patients (average age 72 ± 2years) with high degree atrioventricular block and normal sinus node function. At implant the atrial signal amplitude was 2.6 ± 0.2mV measured by a pacing system analyser (PSA), 1.8 ± 0.1mV measured peak-to-peak from the telemetered calibrated electrogram, and 1.3 ± 0.1mV measured from the sensing threshold. At one month follow-up the peak-to-peak amplitudes (mV) of the telemetered atrial electrograms were not significantly different measured continuously during resting supine with quiet breathing (1.4 ± 0.1), sitting (1.6 ± 0.2). standing (1.5 ± 0.1), arm swinging (1.4 ± 0.2), hyperventilation (1.3 ± 0.1), Vaisalva manoeuvre (1.4 ± 0.1), and treadmill exercise (1.9 ± 0.6). The telemetered atrial electrogram amplitude and the atrial sensing threshold varied between 1.2 ± 0.09mV and 1.8 ± 0.1mV, and between 0.95 ± 0.07mV and 1.3 ± 0.01mV, respectively at 0.5, 1, 3, 6 and 12 months follow-up, but the changes were statistically nonsignificant. The Event Summary showed sensing of 98% to 99% of the atrial events at the different follow-up periods.