The Ventricular Paced QT Interval-The Effects of Rate and Exercise (original) (raw)
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Relationship Between QT Interval Duration and Electrical Induction of Ventricular Tachycardia
Pacing and Clinical Electrophysiology, 1991
tricular Tachycardia. The relation of inducible ventricular tachycardia (VT] to QT intervai duration of ventricular paced rhythm has not been evaluated. To clarify this relation we measured corrected QT interval duration (QTc j during sinus rhythm and QT interval duration during ventricuiar paced rhythm (QT-VJ in patients with coronary artery disease without (non-VT group = group B] and with inducible VT (VT group = group A). Duration of QT-V was greater in the VT group (n = 20] compared with non-VT group (n = 20] during ventricular pacing at cycle lengths of 600 ms (424 ± 26 vs 396 ±19 ms, P < 0.01], of 500 ms (407 ± 20 vs 383 ± 21 ms, P < 0.01], and of 400 ms (390 ± 21 vs 362 ± 17 ms, P < 0.001]. During sinus rhythm the mean values of QTc were similar in both groups (408 ± 25 vs 413 ± 20 ms, NS]. During ventricular stimulation the percentage of patients with values of QT-V exceeding 380 ms was 35% in non-VT group and 95% in VT group (P < O.OlJ at cycle length of 500 ms and 5% versus 60%, respectively, (P < O.Olj, at cycle length of 400 ms. Thus, a trend toward longer QT values o/ventricuiar paced rhythm exists in patients with inducibie VT. (PACE, VoJ. 14, February, Part II1991] QT interval, programmed ventricular stimulation, ventricuiar tachycardia Address for reprints: Prof. A. Dabrowski,
Journal of the American College of Cardiology, 2000
The study was done to determine whether variables of QT dispersion from the 12-lead electrocardiogram (ECG) are dependent on heart rate. BACKGROUND The dispersion of the QT interval is under evaluation as a risk marker in patients at risk for ventricular arrhythmias. Assuming that a similar rate correction is necessary as for the QT interval itself, investigators have frequently reported QTc-dispersion values utilizing the Bazett formula. It is not known whether there is a physiologic basis for such a rate correction in the human heart.
Assessment of QT interval in ventricular paced rhythm: Derivation of a novel formula
Journal of Electrocardiology, 2019
The objective of the study was to determine the optimal formula to estimate QT interval adjusting for QRS prolongation during right ventricular (RV) pacing. Methods: This observational study included individuals (n=43) with a newly implanted permanent ventricular pacemaker, who had a narrow QRS complex before pacemaker insertion. QT interval with RV pacing was related to QT interval before pacemaker implantation. The validation cohort (n=442) had permanent RV pacing in DDD mode. Results: A new QTc formula was derived utilizing the constants from the relationship between the spline heart rate QT correction (QTcRBK) before and after pacing; specifically, QTcRBK PACED = QTcRBK x 0.86. The JT interval from paced complexes was highly heart rate (HR) dependent and was not accurate for QT assessment. Previous, QTc formula for paced complexes were not highly correlated with QT before pacing unless a robust HR correction is added. Formulae subtracting a fixed amount from QTc PACED markedly overestimated QTc before pacing. Conclusion: We proposed a new, simple formula for QT estimation in RV pacing. JT interval in paced complexes is highly HR dependent and is not accurate for QT assessment. The new spline approach for HR correction for the QT, once incorporated into some previously proposed formulae, blunts HR dependency and improves prediction of QT before pacing. QTcRBK PACED *0.86 and QTcRBK PACED-(QRS*0.5) demonstrated the best balance of relatively strong correlation to QTc before pacing and accurate QTc prolongation identification. Abnormal QT for QTcRBK PACED *0.86 as defined by the 97.5 th and 99 th percentile are 469 and 479 ms respectively.
Pacing and Clinical Electrophysiology, 1988
KOCOVIC, D., ET AL.: Association between stimulated QT interval and ventricular rhythm disturbances: influence of autonomic nervous system. To examine the association between ventricular rhythm disturbances and changes in the pacemaker-induced stimulated T interval (STIM-T intervai), we compared findings from monitoring 0/ two patient groups. The first group consisted 0/ 15 patients with QTX microprocessor pacemakers and the second group consisted of 198 patients with documented ventricular rhythm disturbances and coronary artery disease (CAD). In the first group, which was free of ventricuiar rhythm disturbances and manifest coronary artery disease, the STIM-T interval was measured every 4 hours over a 36-hour period at/our pacemaker frequency settings (70, 80, 90, and 100} in order to observe the circadian variation 0/ the STIM-T intervai as a function of changes in autonomic nervous system (ANS) tone. The second group was comprised of patients with CAD and over 30 VES/hrs (Lown grade classification 1-5], and taking no antiarrhythmic medication. These patients were followed using 24-hour Holter monitoring over a minimum of 23 hours and with less than 5% artifact/recording. Information regarding mean hourly heart rate, total number of VES, VES pairs, VT runs, and ischemic episodes in this group was compared with changes in the STIM-T interval in the first group. The STIM-T interval was found to be shorter during the day and longer at night ai all heart rate settings. The total frequency of VES, of VES pairs, VT runs, and ischemic episodes in the second group varies in a similar circadian fashion. The greatest total number of VES, of VES pairs, VT runs, and ischemic episodes was recorded in the waking hours, at the same time when the STIM-T interval is the shortest, while this number was signi/icantly iower during sleep, when the STIM-T interval of the first group is the longest. This coincidence of circadian variation pattern between STIM-T intervai in group I, and ventricular arrhythmias and ischemic episodes in group II, suggests that alterations in ANS tone reflected in the STIM-T interval may be an important factor in the occurrence of these untoward events. fPACE, Vol. 11, November Part II 1988} circadian variations, autonomic tone, rhythm disturbances, QT interval
Pacing and Clinical Electrophysiology, 1985
FANANAPAZIR, L., ET AL.: Reliability of the evoked response in determining the paced ventricular rate and performance of the QT or rate responsive (TX) pacemaker. The TX pacemaker uses a conventiona] (ransvenous electrode to sense T-waves of paced ventricular compiexes and it adapis (he pacing rate to varying physioiogica/ demands by responding lo changes in the QT or, more correctly, Ihe stimulus arti/acI-to-T-wave (stimuJus-TJ interval. This pacing system was assessed in 13 patients. The relation between heart rate and s(imuJus-T interval and the e^ecl 0/ programming on the performance of this pacemaker were studied on several occasions in each patient. Treadmill exercise per/ormance during TX pacing mode was compared with atrial synchronized ventricular (VAT) and asynchronous ventricular demand (VOO and WI-70 beats per minute) pacing modes. T-wave sensing problems arose in three patients. In one. this was overcome by reducing the pulse amplitude from 5.0 to 2.5 V. In another patienl, spontaneous recovery of T-wave sensing occurred 5 months after pacemaker implantation. T-wave sensing deteriorated with the passage 0/ time in most patients. Satisfactory rate response as assessed by treadmill exercise testing and Holter monitoring was achieved in 12 patients through adjustments 0/ two programmable parameters: the slope that defines the alteration in heart rate in response to a millisecond change in stimuIus-T interval and the "sensing window" that is the interval during which T-waves can be sensed and a rate response is possibie. Exercise per/ormance was significantly better during rate responsive pacing (TX) mode as compared with WI pacing but was comparable to that during VAT pacing. The resting heart rate/stimulus-T interval can be described by the following linear regression equation; stimulus-T interval ^ 466 -1.68 X paced-rate, r^ = -0.62. This relation, however, was subject to wide inter-and intra-patient variation. Consequently, given identical programmed parameters and exercise protocol, the chronotropic response differed significantly from patient to patient and in the same patient from one occasion to another. Our results show that a physiologically beneficial chronotropic response can be achieved in most patients. However, reprogramming, based on results of exercise tests and Holter monitoring, may be necessary to adjust for changes in T-wave sensing and the heart rate/stimuIus-T interval relation and, thus to ensure that the pacemaker continues to function optimally.
Effect of ventricular function on the exercise hemodynamics of variable rate pacing
Journal of the American College of Cardiology, 1988
When implantable pacemakers were introduced in 1959, their primary function was to prolong life. As pacemakers became more sophisticated, improving the quality of life became an imp&ant goal as well. Studies (I-7) have cornlimted that the use of dual chamber pacing. which provides rate variability and alrioventricular (AV) synchrony. in. creases exercise time and work capacity and provides important benefits for selected patients. However, in patients who have sinus node disease with an inadequate increase in atrial rate during exercise or other times of metabolic need, dual chamber pacing provides AV synchrony ht not rate variability. In patients with chronic atrial fibrillation dual &amber pacing is less effective and may deliver an inapprcpriatc rate. In addition, the added costs and problems associated with dual chamber pacemakers have limited their use (8). t'wthermore. a variety of studies (9-l I) have shown that during exercise. an increase in heart rate is ttmre intxxtant than AV synchrony. ihex factors have led to the development of single chamber pacemakers with sensors that detect the need for heart rate changes by tracking variables other than atrial function (12-191. Clinical investigators (12-21) using these new devices have reported beneficial effects in selected patients. However, the exact characteristics of patients likely to benefit from these pacemakers have not been precisely defmcd. Patients who have chronotropic incompetcnce or at&l flbritlation with high degree AV block tindications foor a variable mtc pacemaker1 may be more likely to have underlying heart disease with coexisting left ventricular