Reverse remodelling of systolic left ventricular contraction pattern by long term cardiac resynchronisation therapy: colour Doppler shows resynchronisation.

OBJECTIVE: To quantify long term effects of cardiac resynchronisation therapy (CRT) by biventricular pacing in patients with heart failure (HF). METHODS: Regional changes in left ventricular (LV) contraction patterns effected by CRT in 19 patients with HF (12 with ischaemia; mean (SD) age 66 (9) years) with bundle branch block were examined by colour Doppler tissue velocity imaging (c-TVI). Time differences during main systolic tissue velocity peak (SYS) were compared in the basal and mid LV interventricular septum and in the corresponding LV free wall segments. RESULTS: From baseline to long term (9.8 (3.0) months) CRT, ejection fraction increased from 21.8 (5.4)% to 30.8 (7.6)%, LV end diastolic diameter decreased from 7.6 (0.9) cm to 7.1 (0.8) cm, and end systolic diameter decreased from 6.4 (1.2) cm to 6.0 (1.2) cm (p < 0.05). LV peak tissue velocities were unchanged during follow up. At baseline, SYS in LV free wall was typically delayed by an average of 29 ms in the basal LV site and by 18 ms in the mid LV site. The regional movements of the LV free wall and interventricular septum were separated by an average of only 14 ms and -4 ms (p < 0.05) at the basal site and by -21 ms and -16 ms at the mid LV site during short term and long term CRT, respectively. CONCLUSIONS: The improved haemodynamic functions observed during CRT may be explained by a significant resynchronisation of the regional LV movement pattern during long term follow up.

Immediate control of life-threatening digoxin intoxication in a child by use of digoxin-specific antibody fragments (Fab).

Digoxin-immune antibody fragments (Fab) for treatment of digitalis intoxication was introduced in 1976. Many reports have been published concerning this therapy for children, but few have focused on its immediate reversal of cardiac as well as extracardiac life-threatening manifestations of digoxin toxicity. We present a case of life-threatening digitalis intoxication in a child with postoperative renal insufficiency, after a Sennings procedure for transposition of the great arteries. Digoxin administration according to the nationally recommended dosage and intervals unexpectedly resulted in serum levels in the toxic range. Severe cardiac arrhythmias, haemodynamic instability and a rapid-increasing serum potassium level resulted. This report demonstrates how administration of Fab according to the manufacturer's dosage recommendation reversed the tachyarrhythmia immediately and re-established a normal level of serum potassium within minutes.

Colour tissue velocity imaging can show resynchronisation of longitudinal left ventricular contraction pattern by biventricular pacing in patients with severe heart failure.

OBJECTIVE: To quantify ventricular resynchronisation by biventricular pacing using colour tissue Doppler velocity imaging (c-TVI). DESIGN AND PATIENTS: c-TVI shows regional tissue velocity profiles with a very high time resolution (10 ms). Eighteen patients were studied from an apical four chamber view at baseline and after a one month follow up of biventricular pacing. Regional left ventricular peak tissue velocities and regional time differences during the cardiac cycle were compared in the basal and mid interventricular septal segments of the left ventricle, and in the corresponding segments in the left ventricular free wall. RESULTS: From baseline to follow up, mean peak tissue velocities changed only during isovolumic contraction in the basal interventricular septum and the left ventricular free wall. At baseline the peak main systolic tissue velocities in the left ventricular free wall were typically delayed by an average of 42 ms in the basal left ventricular site and by 14 ms in the mid left ventricular site compared with the corresponding sites in the interventricular septum. After resynchronisation by biventricular pacing those regional movements were separated by an average of only 7 ms at the basal site, but there was still a 21 ms earlier movement of the left ventricular free wall in the mid left ventricular site. The diastolic movement pattern remained unchanged from baseline to follow up. CONCLUSIONS: c-TVI showed a significant asynchronous regional longitudinal movement of basal left ventricular sites at baseline. A change to a more synchronous longitudinal left ventricular movement pattern during biventricular pacing was demonstrated.

Acute resumption of conduction in the cavotricuspid isthmus after catheter ablation in patients with common atrial flutter. Real-time evaluation and long-term follow-up.

AIMS: Cavotricuspid isthmus conduction (CIC) is closely associated with the maintenance and recurrence of common atrial flutter (AFL). This study systematically sought to assess the prevalence and characteristics of acute CIC recovery during AFL ablation and to define its predictors and its relationship with the results of long-term follow-up. METHODS AND RESULTS: A total of 124 consecutive patients (105 men, 19 women, mean age 58 +/- 11 years) who underwent successful AFL ablation were included. The procedure endpoint was defined as complete bi-directional CIC block. During an observation period of 30 min, the incidence of CIC restoration was 34.% in patients and 39.8% in applications. It increased with increasing block time and decreased over time during the observation period. Block time in successful burns followed by persistent block was shorter than in those followed by CIC resumption (12 +/- 6 vs 33 +/- 12 s, P<0.0001). A negative correlation between block time and resumption time was found (r = - 0.57, P<0.001). Patients with permanent pacemakers had a higher incidence of acute CIC resumption than those without pacemakers (5/7 vs 29/117, P = 0.007). The AFL recurrence rate was 4.8% during a mean follow-up period of 21 +/- 8 months. Our results suggest that acute CIC resumption may be a potential risk for clinical AFL recurrence during long-term follow-up. CONCLUSIONS: Acute CIC resumption in common AFL ablation varies in terms of incidence and time course. Block time has a predictive value for acute CIC recovery. Observation time can be shortened if block time is short. With longer block time, it is essential to observe for a longer period in order to minimize CIC resumption.

[Biventricular pacemaker treatment of patients with severe heart failure]. / Biventrikulaer pacemakerbehandling av pasienter med alvorlig hjertesvikt.

BACKGROUND: Biventricular pacing using a pacemaker lead located epicardially on the left ventricle, introduced via the coronary sinus to a coronary vein, and one pacemaker lead located endocardially at the apex of the right ventricle can resynchronize the contraction of the left ventricle. Approximately 30-50% of patients with severe heart failure have left bundle branch block indicating asynchronous contraction of the left ventricle. These patients can have a significant haemodynamic benefit from biventricular pacing. MATERIAL AND METHODS: The methods for implanting the leads are described. Biventricular pacemakers were implanted in five patients. RESULTS: Acceptable low thresholds for pacing the left ventricle were achieved. Resynchronization of the contraction of the left ventricle was demonstrated by using colour tissue Doppler measurements. The mechanisms for the haemodynamic benefit of biventricular pacing are discussed on the basis of our data. The first patient has been followed for 12 months. He has a lasting improvement in functional capacity from class IV to class II, marked reduction of the left ventricular size, and improvement of the left ventricular ejection fraction from 15% to 38%. INTERPRETATION: The results are promising for patients who, because of lack of donor hearts and age criteria, often cannot be offered heart, transplantation.

[Atrial flutter--diagnosis and therapeutic possibilities]. / Atrieflutter--diagnostikk og behandlingsmuligheter.

BACKGROUND: Atrial flutter and atrial fibrillation are among the most common heart rhythm disturbances in the population, with an assumed prevalence of 1-2%. About 40,000-60,000 Norwegians endure such rhythm disorders, with an increasing occurrence in the elderly population. MATERIAL AND METHODS: Surface ECG remains the corner-stone for the clinical diagnosis. We describe the various mechanisms, clinical presentation, and diagnosis based on modern invasive electrophysiological methods of atrial flutter. RESULTS: The available therapeutic modalities for conversion during episodes and prophylaxis with drugs, various pacing techniques, DC conversion and surgical therapy are discussed. INTERPRETATION: Radiofrequency catheter ablation is the only available method to cure the patient in a gentle manner.

[Radiofrequency catheter ablation of atrial flutter]. / Radiofrekvenskateterablasjon av atrieflutter.

BACKGROUND: The anatomical structure of atrial flutter is now well recognized, and treatment with radiofrequency catheter ablation (RFA) is established. Several recording and ablation techniques can be applied. MATERIAL AND METHODS: An increasing number of patients have been treated with RFA at the Arrhythmia Centre at Haukeland University Hospital over the last six years. During the two-year period 1999 and 2000, a total of 108 procedures were performed for atrial flutter in a total of 84 patients. A total of 543 RFA procedures for various forms of re-entry tachycardias were performed during the same period; hence, atrial flutter comprised about 20% of RFA procedures. Altogether 71 men and 14 women with a mean age of 57 +/- 12 years were treated. The mean history of atrial flutter had a duration of nine years, maximum 43 years with several hospital admissions, drug trials, overdrive pacing and DC conversion until they were ultimately cured with RFA. RESULTS: The success rate during first time treatment was 96.5%. No serious complications were observed. INTERPRETATION: RFA should be the treatment of first choice in patients with recurrent or incessant atrial flutter.

RV function in stable and unstable VT: is there a need for hemodynamic monitoring in future defibrillators?

During electrophysiological investigation of 22 patients with VT or aborted sudden cardiac death, arterial and RV pressures were measured. The time courses of mean arterial pressure (MAP), RV pulse pressure (RVPP), RV pulse pressure integral (RVPPI), and maximum right ventricular dP/dt (RV dP/dtmax) were followed during the first 15 seconds after VT induction. Compared to basal (preinduction) conditions, the RVPPI decreased by 41+/-10% (mean +/- SD) after 10-15 seconds of VT in 11 patients with stable VT and by 75+/-8% in 11 patients with unstable VT (MAP < 60 mmHg 15 s after VT onset). RVPP decreased by 13+/-11% after 10-15 seconds of VT in the stable VT group and by 50+/-16% in the unstable VT group. For RV dP/dtmax, these decreases were 4+/-22% in the stable VT group and 37+/-24% in the unstable VT group. There was a good correlation between percent decrease in MAP and percent decrease in RVPPI, RVPP, and RV dP/dtmax at 5-10 seconds (r = 0.86, 0.81, and 0.73, respectively) and 10-15 seconds (r = 0.84, 0.82, and 0.69, respectively) after VT onset. There was hardly any overlap of distributions of the individual values with the RVPPI parameter between the two VT groups. Comparing and correlating the percent decrease in mean arterial pressure with the RVPPI, RVPP, and RV dP/dtmax during induced VT, RVPPI demonstrated the most significant and specific changes in discriminating stable from unstable rhythms. However, by comparing RVPPI and RVPP using the area under the receiver operating characteristic curves, there was no significant statistical difference between the two parameters. By integrating rate criteria, electrogram signal analysis, and RVPPI or RVPP as a hemodynamic criterion, detection and treatment algorithms could improve the performance of future implantable defibrillators and avoiding shocks in VTs that can be terminated by antitachycardia pacing.

A typical P-wave morphology in incessant atrial tachycardia originating from the right upper pulmonary vein.

Automatic atrial tachycardias often originate from the ostia of the pulmonary veins. P-wave morphology during tachycardia may indicate from which pulmonary vein the tachycardia originates. Two patients with pulmonary vein tachycardias demonstrating atypical P-wave morphology were investigated. One of the patients had a tachycardia with two different cycle lengths. P-wave morphology was evaluated in 12-lead ECGs from two patients with incessant atrial tachycardia, during tachycardia and sinus rhythm. Their tachycardias were successfully ablated at the mouth of the right upper pulmonary vein. Previous studies have demonstrated a positive or negative P-wave configuration in lead aVL originating from this area and a change from a biphasic P-wave in V1 during sinus rhythm to a positive P-wave configuration during tachycardia. Neither of our two patients had such a change in lead V1. One our patients had two tachycardias with different cycle lengths originating from the same area. It is concluded that if an atrial tachycardia with P-wave morphology resembling that of sinus rhythm cannot be located to the right atrium, its origin may be the right upper pulmonary vein.

Pacing threshold trends and variability in modern tined leads assessed using high resolution automatic measurements: conversion of pulse width into voltage thresholds.

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.

Automatic adjustment of pacemaker stimulation output correlated with continuously monitored capture thresholds: a multicenter study. European Microny Study Group.

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 microA for VVI and 5.0 microA for VVIR pacing. This 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.

Pacing impedance variability in tined steroid eluting leads.

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 omega 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.

An algorithm for automatic measurement of stimulation thresholds: clinical performance and preliminary results.

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.

Atrial synchronous ventricular pacing with a single lead: reliability of atrial sensing during physical activities, and long-term stability of atrial sensing.

A VDD pacing system with bipolar single-pass leads, were implanted in 36 consecutive patients (average age 72 +/- 2 years) with high degree atrioventricular block and normal sinus node function. At implant the atrial signal amplitude was 2.6 +/- 0.2 mV measured by a pacing system analyser (PSA), 1.8 +/- 0.1 mV measured peak-to-peak from the telemetered calibrated electrogram, and 1.3 +/- 0.1 mV 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), Valsalva 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 +/- 0.09 mV and 1.8 +/- 0.1 mV, and between 0.95 +/- 0.07 mV and 1.3 +/- 0.01 mV, respectively at 0.5, 1, 3, 6 and 12 months follow-up, but the changes were statistically non-significant. The Event Summary showed sensing of 98% to 99% of the atrial events at the different follow-up periods.

Clinical use of low output settings in 1.2-mm2 steroid eluting electrodes: three years of experience.

A new generation of tined steroid-eluting 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 > or = 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 < or = 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 > or = 4:1 PWSM and other patients > or = 3:1 PWSM with output pulse widths < or = 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.

Clinical performance of steroid-eluting pacing leads with 1.2-mm2 electrodes.

To raise pacing impedance and reduce battery current drain, new tined steroid-eluting leads were developed with 1.2-mm2 hemispherical electrodes, instead of conventional 5-8 mm2. Twenty-two unipolar J-shaped atrial leads and 25 unipolar ventricular leads (models 4533 and 4033, respectively) were implanted in 33 consecutive patients and followed for a mean of 25 months (range 18-29). Handling characteristics of atrial leads were found favorable. The leads slipped easily into the right atrial appendage and were easy to position. Handling characteristics of ventricular leads were satisfying, but more efforts had to be applied to cross the tricuspid valve. Special care was taken to avoid perforation of the myocardium due to the small lead tip. Following implantation, four ventricular and one atrial lead exhibited instability of pacing thresholds that resolved spontaneously within 1-3 days of implantation. Except for this, no lead malfunctioned. The reoperation rate was zero. The mean electrogram amplitudes of 15 mV (ventricle) and 4 mV (atrium), and the mean chronic pacing threshold of 0.085 ms at 1.6 V (app. 0.43 V at 0.5 ms) were comparable with the best values seen in the literature on passive fixation leads. The rest of the electrophysiological parameters were enhanced: mean pacing impedances were 984 omega (acute) and 900 Q (chronic), mean slew rates 3.26 V/s (ventricle) and 1.75 V/s (atrium), mean acute voltage threshold at 0.5 ms was 0.25 V, mean current and energy thresholds calculated at 0.5 ms were 260 microA and 32 nJ (acute) and 478 microA and 103 nJ (chronic). The electrical characteristics of these leads provide for increased pacemaker longevity in combination with substantial safety margins for pacing and sensing.

Clinical evaluation of a thin bipolar pacing lead.

The main disadvantages of bipolar pacing leads have traditionally been related to their relative thickness and stiffness compared to unipolar leads. In a new "drawn filled tube" plus "coated wire" technology, each conductor strand is composed of MP35N tubing filled with silver core and coated with a thin ETFE polymer insulation material. This and parallel winding of single anode and cathode conductors into a single bifilar coil resulted in a bipolar lead (ThinLine, Intermedics) with a body diameter and flexibility similar to unipolar leads. The lead is tined, polyurethane, with the cathode and the anode made of iridium-oxide-coated titanium (IROX). The slotted 8-mm2 cathode tip is coated with polyethylene glycol, a blood soluble material. We present the clinical evaluation results from four pacemaker clinics, where 47 leads (23 atrial-J model 432-04 and 24 ventricular model 430-10) were implanted in 25 patients and followed for up to 2 years. The lead handling characteristics were found to be very satisfactory. Electrical parameters of the leads were measured at implant and noninvasively on postoperative days 1, 2, 21, 42, and months 3, 6, 12, and 24. Mean chronic pulse width thresholds at 2.5 V were 0.14 +/- 0.05 ms in the atrium and 0.10 +/- 0.02 ms in the ventricle, pacing impedances 443 +/- 104 omega and 520 +/- 241 omega, while median electrogram amplitudes were > or = 3.5 mV and > or = 7 mV, respectively. Pacing impedances and thresholds were found to be slightly but statistically significantly higher in unipolar than in bipolar configuration--the findings are explainable by the lead construction. One of 47 leads failed 3 weeks after implant; the conductors were short circuited due to an error during the manufacturing process. We conclude that the new lead thus far has demonstrated appropriate mechanical and electrical characteristics.