Ultrarapid train stimulation versus conventional programmed electrical stimulation for induction of ventricular arrhythmias in patients with coronary artery disease.

Conventional programmed electrical stimulation (PES) of the ventricle is useful for establishing inducibility or noninducibility of clinical ventricular arrhythmias (VA) but is complex and time consuming. The present study was designed to compare a standard PES protocol with an alternative method using ultrarapid train stimulation in patients with VA and coronary artery disease (CAD). A prospective, randomized, crossover design was used. During each session in the electrophysiology laboratory, patients were studied using both the trains and PES protocols in randomized order. In 82 matched pairs of comparisons in 50 patients, results were concordant in 85% (p < 0.0001). There were no differences related to type of clinical arrhythmia or to the presence of antiarrhythmic drugs. There were no significant differences in the induction of nonclinical arrhythmias with the two methods (p < 0.0001 for concordance). There were no significant differences related to the cycle length of the trains (10, 20, or 30 ms, equivalent to 100, 50, or 33 Hz). The number of drive-extrastimuli sequences and the time required to complete the trains protocol was significantly shorter (p < 0.0001) using trains versus PES. Ultrarapid train stimulation provides results in CAD patients that are comparable with those of conventional PES protocols. There is a significant savings in time, adding practical value to intrinsic electrophysiologic interest. Trains may be useful when multiple inductions are desirable, for example, in the setting of antitachycardia pacing parameters in an implantable defibrillator (ICD), during ICD implantation, or in other circumstances where the main question is inducibility of ventricular arrhythmias.

Occult T wave alternans in long QT syndrome.

T wave alternans that is visually apparent on the ECG is a known risk factor for sudden death in idiopathic long QT syndrome (LQTS). To determine if occult and visually undetectable forms of T wave alternans are also present in LQTS, we measured T wave alternans from a 16-year-old girl with LQTS during exercise using spectral analysis methods and a recording system designed to minimize exercise-related noise. While there was no alternans at rest, statistically significant, yet visually inapparent T wave alternans were measured both during exercise and recovery. Using identical recording techniques, no significant T wave alternans was detected from the subject's mother, who had a prolonged QT interval but was not experiencing arrhythmias, nor from five healthy volunteers with normal QT intervals. This report suggests that electrocardiographically occult, yet prognostically important forms of T wave alternans may be present in patients with LQTS.

Suppression of ventricular output by noise in the atrial channel in a dual chamber pacemaker.

In a pacemaker dependent, 60-year-old man with complete heart block, programming high (5.0 V and 1.0 ms) atrial output and 5.0 volt and 0.5 ms ventricular output while in the DDD mode of a pulse generator, resulted in loss of ventricular channel output with resulting asystole, while the simultaneous, pulse generator produced ECG interpretation channel falsely indicated continuing ventricular channel output. Ventricular pacing was promptly restored by programming to the emergency VVI mode. At later operation the atrial lead was determined to be defective, with a low impedance, while the ventricular lead was intact (lead impedance telemetry was not available). The manufacturer has acknowledged a pulse generator design anomaly that may occur in the setting of a low atrial impedance and issued a Health Safety Alert.

Direct and telemetered lead impedance.

OBJECTIVES: We undertook this study to determine whether telemetered lead impedance measurements (LIM) can be correlated with direct LIM and to determine the stability of LIM over time when measured directly and via telemetry. METHODS: Direct LIM and telemetered LIM were measured in 91 patients; 101 leads during initial implantation and 40 leads during pulse generator replacement. Differences in direct LIM measured during initial implant and pulse generator replacement (direct-direct) were compared in 41 patients (28 atrial leads and 37 ventricular leads). The stability of telemetered LIM obtained immediately postoperatively, at 1 month and 1 year, postimplantation was assessed in 50 patients (23 atrial and 49 ventricular leads). RESULTS: In atrial leads acute direct LIM was 633.9 +/- 18.4 omega versus 575.8 +/- 18.5 omega for telemetered LIM (r = 0.58), and chronic direct LIM was 670.9 +/- 49.3 omega versus 607.0 +/- 36.3 omega for telemetered LIM (r = 0.87). In ventricular leads acute direct LIM was 747.3 +/- 16.9 omega and 684.7 +/- 16.4 omega for telemetered LIM (r = 0.69), and chronic direct LIM was 674.8 +/- 29.9 omega and 625.2 +/- 28.5 omega for telemetered LIM (r = 0.68). The mean direct-direct LIM rose 124 omega (P < 0.001) in atrial leads and 10 omega (P = NS) in ventricular leads. Telemetered LIM for atrial leads was 581.0 +/- 27.6 omega immediately postimplantation compared to 625.7 +/- 34.8 omega at 1 month and 754.1 +/- 43.0 omega at 1 year. Telemetered LIM for ventricular leads was 661.3 +/- 17.5 omega at implant, 684.6 +/- 20.7 omega at 1 month and 724.7 +/- 22.7 omega at 1 year. CONCLUSIONS: There is a good but limited correlation between direct and telemetered LIM. Mean direct LIM obtained at initial implantation is similar to that measured at pulse generator replacement. The telemetered LIM is stable over the first month postimplantation but tends to rise during the first year of follow-up and substantial changes in impedance are not uncommon in individuals with normal function. There is a tendency for LIM to rise with lead maturation. If telemetered LIM is to be followed over time, a baseline telemetered value should be obtained immediately postoperatively.