QT/QS2 ratio as an index of autonomic tone changes

Electrocardiogram to Determine Mitral and Aortic Valve Opening and Closure

PURPOSE

Knowledge of the timing of cardiac valve opening and closing is important in cardiac physiology. The relationship between valve motion and electrocardiogram (ECG) is often assumed, however is not clearly defined. Here we investigate the accuracy of cardiac valve timing estimated using only the ECG, compared to Doppler echocardiography (DE) flow imaging as the gold standard.

METHODS

DE was obtained in 37 patients with simultaneous ECG recording. ECG was digitally processed and identifiable features (QRS, T, P waves) were examined as potential reference points to determine opening and closure of aortic and mitral valves, as compared to DE outflow and inflow measurement. Timing offset of the cardiac valves opening and closure between ECG features and DE was measured from derivation set (n = 19). The obtained mean offset in combination with the ECG features model was then evaluated on a validation set (n = 18). Using the same approach, additional measurement was also done for the right sided valves.

RESULTS

From the derivation set, we found a fixed offset of 22 ± 9 ms, 2 ± 13 ms, 90 ± 26 ms, and - 2 ± - 27 ms when comparing S to aortic valve opening, Tend to aortic valve closure, Tend to mitral valve opening, and R to mitral valve closure respectively. Application of this model to the validation set showed good estimation of aortic and mitral valve opening and closure timing value, with low model absolute error (median of the mean absolute error of the four events = 19 ms compared to the gold standard DE measurement). For the right-sided (tricuspid and pulmonic) valves in our patient set, there was considerably higher median of the mean absolute error of 42 ms for the model.

CONCLUSION

ECG features can be used to estimate aortic and mitral valve timings with good accuracy as compared to DE, allowing useful hemodynamic information to be derived from this easily available test.

The effect of mild dynamic exercise on the electromechanical systole of heart in non-athlete, healthy first year medical students of Bengal as a predictive biomarker of arrhythmia

Introduction and Aim: Measurement of Systolic Time Intervals (STIs) is a non-invasive and convenient way of assessing left ventricular electro-mechanical activity. In this study, we assessed effect of mild dynamic exercise on QT, QS2, QT/QS2 ratio, QS2-Index among healthy young first year students at a government medical college of West Bengal, India and compared the same among girls and boys.   Materials and Methods: IX-TA-220 multichannel recorder was used to record Electrocardiogram, Phonocardiogram and Carotid pulse tracing among 180 subjects before and after 1 minute of mild exercise with Harvard's Step of 30 cm height with metronome rhythm of 120 beats per minute. Results were analyzed by Microsoft Excel and comparison of each parameter between boys and girls were done using SPSS software in two hemodynamic states. P-value <0.05 was taken as statistically significant.   Results: Post exercise mean QT and QS2 shortened and their ratio QT/QS2 increased. There was a statistically significant difference between pre-exercise and post-exercise mean QT, QT/QS2 ratio, QS2 index and significant differences were observed between mean values of the boys and girls.   Conclusion: With hemodynamic changes as in exercise, due to sympathetic stimulation & catecholamine release, both QT andQS2 should reduce as all the phases of systole shorten but if QT does not reduce in comparison to QS2 it may lead to arrhythmia in future. Hence QT/QS2 can be a useful pro-arrhythmic biomarker and may complement ECG and Echocardiography in borderline cases.

Arrhythmogenic mechanisms of acute obstructive respiratory events in a porcine model of drug-induced long QT

BACKGROUND

Obstructive sleep apnea is associated with increased risk of sudden cardiac death.

OBJECTIVE

The purpose of this study was to elucidate changes in ventricular repolarization and electromechanical interaction during obstructive respiratory events simulated by intermittent negative upper airway pressure (INAP) in pigs. We also investigated the effect of a reduced repolarization reserve in drug-induced long QT (LQT) following INAP-induced changes in ventricular repolarization.

METHODS

In sedated spontaneously breathing pigs, 75 seconds of INAP was applied by a negative pressure device connected to the endotracheal tube. Ventricular electromechanical coupling was determined by the electromechanical window (EMW) before (pre-INAP), during (INAP), and after INAP (post-INAP). Incidence rates of premature ventricular contractions (PVCs) were measured respectively. A drug-induced LQT was modeled by treating the pigs with the hERG1 blocker dofetilide (DOF).

RESULTS

Whereas QT interval increased during and decreased after INAP (pre-INAP: 273 ± 5 ms; INAP 281 ± 6 ms; post-INAP 254 ± 9 ms), EMW shortened progressively throughout INAP and post-INAP periods (pre-INAP 81 ± 4 ms; post-INAP 44 ± 7 ms). DOF shortened EMW at baseline. Throughout INAP, EMW decreased in a comparable fashion as before DOF (pre-INAP/+DOF 61 ± 7 ms; post-INAP/+DOF 14 ± 9 ms) but resulted in shorter absolute EMW levels. Short EMW levels were associated with increased occurrence of PVCs (pre-INAP 7 ± 2 ms vs post-INAP 26 ± 6 ms; P = .02), which were potentiated in DOF pigs (pre-INAP/+DOF 5 ± 2 ms vs post-INAP/+DOF 40 ± 8 ms; P = .006). Administration of atenolol prevented post-INAP EMW shortening and decreased occurrence of PVCs.

CONCLUSION

Transient dissociation of ventricular electromechanical coupling during simulated obstructive respiratory events creates a dynamic ventricular arrhythmogenic substrate, which is sympathetically mediated and aggravated by drug-induced LQT.

Exercise worsening of electromechanical disturbances: A predictor of arrhythmia in long QT syndrome

Background

Electromechanical (EM) coupling heterogeneity is significant in long QT syndrome (LQTS), particularly in symptomatic patients; EM window (EMW) has been proposed as an indicator of interaction and a better predictor of arrhythmia than QTc.

Hypothesis

To investigate the dynamic response of EMW to exercise in LQTS and its predictive value of arrhythmia.

Methods

Forty‐seven LQTS carriers (45 ± 15 years, 20 with arrhythmic events), and 35 controls underwent exercise echocardiogram. EMW was measured as the time difference between aortic valve closure on Doppler and the end of QT interval on the superimposed electrocardiogram (ECG). Measurements were obtained at rest, peak exercise (PE) and 4 minutes into recovery.

Results

Patients did not differ in age, gender, heart rate, or left ventricular ejection fraction but had a negative resting EMW compared with controls (−42 ± 22 vs 17 ± 5 ms, P < 0.0001). EMW became more negative at PE (−89 ± 43 vs 16 ± 7 ms, P = 0.0001) and recovery (−65 ± 39 vs 16 ± 6 ms, P = 0.001) in patients, particularly the symptomatic, but remained unchanged in controls. PE EMW was a stronger predictor of arrhythmic events than QTc (AUC:0.765 vs 0.569, P < 0.001). B‐blockers did not affect EMW at rest but was less negative at PE (BB: −66 ± 21 vs no‐BB: −113 ± 25 ms, P < 0.001). LQT1 patients had worse PE EMW negativity than LQT2.

Conclusion

LQTS patients have significantly negative EMW, which worsens with exercise. These changes are more pronounced in patients with documented arrhythmic events and decrease with B‐blocker therapy. Thus, EMW assessment during exercise may help improve risk stratification and management of LQTS patients.

Characteristics of electromechanical window in anesthetized rabbit models of short QT and long QT syndromes

The current regulatory guidelines recommend the use of QT interval to assess the risk of arrhythmogenic potential of new chemical entities. Recently, the electromechanical window (EMW), the difference in duration between electrical and mechanical systole, has been proposed as markers for drug-induced torsades de pointes (TdP); however, data of EMW in short QT model are not available. This study aimed to characterize the EMW as a marker for drug-induced ventricular arrhythmias in anesthetized rabbit model of long QT syndrome type 2 (LQT2) and short QT syndrome (SQTS) infused with reference compounds known to lengthen or shorten QT intervals. After rabbits were anesthetized with isoflurane, body surface electrocardiograms and left ventricular pressure were recorded. The LQT2 was produced by intravenous infusion with dofetilide (n = 6), quinidine (n = 6) and sotalol (n = 6) whereas the SQTS was induced by intravenous escalating concentrations of nicorandil (n = 7), pinacidil (n = 5) and cromakalim (n = 5). The EMW in anesthetized rabbits ranged from 1.3 to 53.3 msec. All three drugs known to lengthen QT intervals prolonged QT and QTcF interval while the EMW was markedly decreased to negative values. Pinacidil significantly produced QT and QTcF shortening and significantly abbreviated the EMW (p < 0.05). This study demonstrated that the EMW is associated with QT intervals (p < 0.001). It is negative in the presence of QT-prolonging drugs while it is more positive in the presence of QT-shortening drugs. The results suggest that the EMW in anesthetized rabbits can be used in drug safety evaluation in addition to the QT interval.

Role of abnormal repolarization in the mechanism of cardiac arrhythmia

In cardiac patients, life-threatening tachyarrhythmia is often precipitated by abnormal changes in ventricular repolarization and refractoriness. Repolarization abnormalities typically evolve as a consequence of impaired function of outward K⁺ currents in cardiac myocytes, which may be caused by genetic defects or result from various acquired pathophysiological conditions, including electrical remodelling in cardiac disease, ion channel modulation by clinically used pharmacological agents, and systemic electrolyte disorders seen in heart failure, such as hypokalaemia. Cardiac electrical instability attributed to abnormal repolarization relies on the complex interplay between a provocative arrhythmic trigger and vulnerable arrhythmic substrate, with a central role played by the excessive prolongation of ventricular action potential duration, impaired intracellular Ca²⁺ handling, and slowed impulse conduction. This review outlines the electrical activity of ventricular myocytes in normal conditions and cardiac disease, describes classical electrophysiological mechanisms of cardiac arrhythmia, and provides an update on repolarization-related surrogates currently used to assess arrhythmic propensity, including spatial dispersion of repolarization, activation-repolarization coupling, electrical restitution, TRIaD (triangulation, reverse use dependence, instability, and dispersion), and the electromechanical window. This is followed by a discussion of the mechanisms that account for the dependence of arrhythmic vulnerability on the location of the ventricular pacing site. Finally, the review clarifies the electrophysiological basis for cardiac arrhythmia produced by hypokalaemia, and gives insight into the clinical importance and pathophysiology of drug-induced arrhythmia, with particular focus on class Ia (quinidine, procainamide) and Ic (flecainide) Na⁺ channel blockers, and class III antiarrhythmic agents that block the delayed rectifier K⁺ channel (dofetilide).

Impact of hypokalemia on electromechanical window, excitation wavelength and repolarization gradients in guinea-pig and rabbit hearts

Normal hearts exhibit a positive time difference between the end of ventricular contraction and the end of QT interval, which is referred to as the electromechanical (EM) window. Drug-induced prolongation of repolarization may lead to the negative EM window, which was proposed to be a novel proarrhythmic marker. This study examined whether abnormal changes in the EM window may account for arrhythmogenic effects produced by hypokalemia. Left ventricular pressure, electrocardiogram, and epicardial monophasic action potentials were recorded in perfused hearts from guinea-pig and rabbit. Hypokalemia (2.5 mM K(+)) was found to prolong repolarization, reduce the EM window, and promote tachyarrhythmia. Nevertheless, during both regular pacing and extrasystolic excitation, the increased QT interval invariably remained shorter than the duration of mechanical systole, thus yielding positive EM window values. Hypokalemia-induced arrhythmogenicity was associated with slowed ventricular conduction, and shortened effective refractory periods, which translated to a reduced excitation wavelength index. Hypokalemia also evoked non-uniform prolongation of action potential duration in distinct epicardial regions, which resulted in increased spatial variability in the repolarization time. These findings suggest that arrhythmogenic effects of hypokalemia are not accounted for by the negative EM window, and are rather attributed to abnormal changes in ventricular conduction times, refractoriness, excitation wavelength, and spatial repolarization gradients.

The electro-mechanical window in anaesthetized guinea pigs: a new marker in screening for Torsade de Pointes risk

BACKGROUND AND PURPOSE

QT prolongation is commonly used as a surrogate marker for Torsade de Pointes (TdP) risk of non-cardiovascular drugs. However, use of this indirect marker often leads to misinterpretation of the realistic TdP risk, as tested compounds may cause QT prolongation without evoking TdP in humans. A negative electro-mechanical (E-M) window has recently been proposed as an alternative risk marker for TdP in a canine LQT1 model. Here, we evaluated the E-M window in anaesthetized guinea pigs as a screening marker for TdP in humans.

EXPERIMENTAL APPROACH

The effects of various reference drugs and changes in body temperature on the E-M window were assessed in instrumented guinea pigs. The E-M window was defined as the delay between the duration of the electrical (QT interval) and mechanical (QLVP(end) ) systole.

KEY RESULTS

Drugs with known TdP liability (quinidine, haloperidol, domperidone, terfenadine, thioridazine and dofetilide), but not those with no TdP risk in humans (salbutamol and diltiazem) consistently decreased the E-M window. Interestingly, drugs with known clinical QT prolongation, but with low risk for TdP (amiodarone, moxifloxacin and ciprofloxacin) did not decrease the E-M window. Furthermore, the E-M window was minimally affected by changes in heart rate or body temperature.

CONCLUSIONS AND IMPLICATIONS

A decreased E-M window was consistently observed with drugs already known to have high TdP risk, but not with drugs with low or no TdP risk. These results suggest that the E-M window in anaesthetized guinea pigs is a risk marker for TdP in humans.

Methodological innovations expand the safety pharmacology horizon

Almost uniquely in pharmacology, drug safety assessment is driven by the need for elaboration and validation of methods for detecting drug actions. This is the 9th consecutive year that the Journal of Pharmacological and Toxicological Methods (JPTM) has published themed issues arising from the annual meeting of the Safety Pharmacology Society (SPS). The SPS is now past its 10th year as a distinct (from pharmacology to toxicology) discipline that integrates safety pharmacologists from industry with those in academia and the various global regulatory authorities. The themes of the 2011 meeting were (i) the bridging of safety assessment of a new chemical entity (NCE) between all the parties involved, (ii) applied technologies and (iii) translation. This issue of JPTM reflects these themes. The content is informed by the regulatory guidance documents (S7A and S7B) that apply prior to first in human (FIH) studies, which emphasize the importance of seeking model validation. The manuscripts encompass a broad spectrum of safety pharmacology topics including application of state-of-the-art techniques for study conduct and data processing and evaluation. This includes some exciting novel integrated core battery study designs, refinements in hemodynamic assessment, arrhythmia analysis algorithms, and additionally an overview of safety immunopharmacology, and a brief survey discussing similarities and differences in business models that pharmaceutical companies employ in safety pharmacology, together with SPS recommendations on 'best practice' for the conduct of a non-clinical cardiovascular assessment of a NCE.

The Electro-Mechanical window: a risk marker for Torsade de Pointes in a canine model of drug induced arrhythmias

BACKGROUND AND PURPOSE

In cardiovascular pharmacology, electrical and mechanical events can be distinguished, and the phrase 'electro-mechanical window' (EMw) describes the temporal difference between these events. We studied whether changes in EMw have potential predictive value for the occurrence of arrhythmias in fentanyl/etomidate-anaesthetized beagle (FEAB) dogs.

EXPERIMENTAL APPROACH

The EMw was calculated as differences between the QT interval and QLVP(end) in FEAB dogs during atrial pacing, treatment with isoprenaline or atropine, body temperature changes and induction of Torsade de Pointes (TdP) in an LQT1 model.

KEY RESULTS

The electrical systole (QT interval) was shorter than the duration of the mechanical event (QLVP(end) ), providing a positive EMw. Atrial pacing, atropine or body temperature changes had no major effects on EMw, despite large changes in QT duration. However, β-adrenoceptor stimulation (with isoprenaline) decreased the EMw (from 90 to 5 ms) and in combination with HMR1556, a blocker of the slowly activating potassium current (I(Ks) ), induced a large negative EMw (-109ms) and TdP. Prevention of TdP by atenolol or verapamil was associated with a less negative EMw (-23 to -16ms). Mexiletine, a poorly effective long QT treatment, did not affect the EMw or prevent TdP induction.

CONCLUSIONS AND IMPLICATIONS

The EMw is a marker, other than QT prolongation, of TdP risk in the FEAB model. Therefore, we suggest examining the EMw as a risk marker in cardiovascular safety studies and as a potential biomarker to improve clinical management of long QT syndrome patients, especially in patients with borderline QT prolongation.

Effect of meditation on stress-induced changes in cognitive functions

OBJECTIVES

The objective of this study was to study the effects of meditation on stress-induced changes in cognitive functions.

METHODS

The study was conducted on 32 healthy adult male student volunteers who had never practiced meditation before the study. The study consisted of practicing 20 minutes of guided meditation and administration of psychologic stress to the subjects. The psychologic stress was administered to the subjects by asking them to play a (preselected) stressful computer game. The subjects were asked to meditate either before or after the administration of psychologic stress. For the control group measurements, the subjects were asked to wait quietly for an equivalent period of meditation time.

OUTCOME MEASURES

The outcome measures were galvanic skin response (GSR), heart rate (HR), electromyography (EMG), sympathetic reactivity (QTc/QS2 ratio), cortisol, and acute psychologic stress scores. The central nervous system functions were assessed using Wechsler memory scale and visual-choice reaction time (VCRT). These parameters were measured both at the beginning and at the end of the intervention, using a pre-post experimental test design.

RESULTS

Computer game stress was associated with a significant increase in physiologic (GSR, EMG, HR, QTc/QS2) and psychologic (acute stress questionnaire scores) markers of stress. Meditation was associated with relaxation (significant decrease in GSR, EMG, QTc/QS2, and acute stress questionnaire scores). Meditation, if practiced before the stressful event, reduced the adverse effects of stress. Memory quotient significantly increased, whereas cortisol level decreased after both stress and meditation. VCRT showed no significant change.

CONCLUSIONS

Practice of meditation produced a relaxation response even in the young adult subjects who had never practiced meditation before. The practice of meditation reduced the physiologic stress responses without taking away the beneficial effect of stress, namely, improved memory scores.

Autonomic studies in hypertensive patient with unusual sexual dysfunction: response to reserpine

The authors examined a 48-year-old man with a history of hypertension (6 years) and a history of erection and ejaculation during cold exposure and confrontation with fear (20 years). Exposing the foot to cold water induced ejaculation in 10 seconds. A variety of antihypertensive medications resulted in control of hypertension, without improvement in ejaculatory dysfunction. Similarly, prazosin controlled the blood pressure, but not the episodes of ejaculation. Treatment with reserpine resulted in gradual reduction in blood pressure and an improvement in ejaculatory dysfunction.

Effects of exercise on heart rate, QT, QTc and QT/QS2 in the Romano-Ward inherited long QT syndrome

Patients with the Romano-Ward inherited long QT syndrome have an incompletely defined cardiac sympathetic system abnormality, and exhibit ventricular arrhythmias during exercise, fear and anxiety. Treadmill and bicycle exercise were used to modulate cardiac autonomic activity in 27 Romano-Ward subjects and 27 normal controls. The heart rate, and the QT, QTc and QT/QS2 (ratio of electrical to mechanical systole) intervals were compared. Subjects with long QT were compared with normals. Those with a long QT interval had the following results: similar resting heart rates; lower rates during moderate (151.6 vs 169.6 beats/min, p = 0.04) and maximal (155.9 vs 182.1 beats/min, p = less than 0.001) exercise; an abnormal QT cycle-length relationship, with failure of the QT to shorten normally with increasing heart rate; an increase in QTc versus a decrease in normals; supine rest QT/QS2 ratio of 1.12 vs 0.93, p = 0.001; and an exercise QT/QS2 that increased by 30%, from 1.12 at rest to 1.45, versus 15%, in normals, from 0.93 to 1.07, p = 0.001. The lower heart rates and excessively prolonged QT/QS2 ratios during exercise further support an abnormality of, or abnormal cardiac response to, sympathetic activity. A QT/QS2 greater than 1.0 at rest, an exercise QT/QS2 ratio greater than 1.17, and an increase in QTc during moderate exercise may be helpful diagnostic findings in patients with borderline long QTc intervals at rest.

The effects of probucol on QT/QS2 relation and systolic time intervals

The QT, QTc, QS2 intervals, pre-ejection period-left ventricular ejection time ratios and serum lipoprotein levels were measured in 8 patients with primary hypercholesterolemia before and after a 3-month therapy with probucol, 1 g/day. Both QT and QTc intervals increased significantly, whereas no significant changes were observed between the pre- and post-treatment QT/QS2 and pre-ejection period-left ventricular ejection time ratios. These results help to explain why treatment with probucol, while effecting a prolongation of the QTc interval, does not result in serious arrhythmias in man.

Effects of histamine on coronary hemodynamics in humans: role of H1 and H2 receptors

To evaluate whether histamine exerts a direct effect on coronary hemodynamics in humans, and to investigate the role played by H1 and H2 receptors in this response, intracoronary saline solution or histamine (4 micrograms) was administered in 10 patients with normal coronary arteries during diagnostic cardiac catheterization. Histamine injection was repeated after intravenous cimetidine (400 mg) and diphenhydramine (10 mg). The electrocardiogram, arterial pressure and thermodilution coronary blood flow were continuously monitored during and for 40 seconds after each injection. Immediately after histamine injection there was a significant increase in coronary blood flow (65 +/- 6%) and a decrease in coronary vascular resistance (-40 +/- 3%) (both p less than 0.001), with minor changes in the RR interval and the mean arterial pressure. H2 receptor blockade with cimetidine did not affect these changes, while H1 receptor blockade with diphenhydramine significantly reduced the histamine-induced increase in coronary blood flow and the decrease in coronary vascular resistance (26 +/- 6%, p less than 0.005 and -18 +/- 5%, p less than 0.001, respectively). Twenty to 30 seconds after histamine injection, a significant decrease in mean arterial pressure (-17 +/- 2%, p less than 0.001) and in the RR interval (-4 +/- 1%, p less than 0.01) was observed. These changes persisted after H2 receptor blockade with cimetidine, but were completely abolished after H1 receptor blockade with diphenhydramine. In each case coronary and systemic hemodynamics returned to normal within 40 seconds of the injection.(ABSTRACT TRUNCATED AT 250 WORDS)

The QT and QS2 intervals in patients with mitral leaflet prolapse

The QT interval was plotted against the R-R interval in 92 patients with mitral prolapse and 92 age- and sex-matched control subjects. Ten patients (11%) lay above the upper 95% confidence limit for the control group, and analysis of variance confirmed a small group effect (p less than 0.05). Despite this, the mean QT intervals in the two groups differed by only 7 msec and a t test showed no significant difference between the groups. The prevalence of QT prolongation was exaggerated by Bazett's rate correction formula (62%) or historical control groups published by Simonson (58%) or Ashman (70%). Simultaneous QT and QS2 intervals were measured in 67 patients with mitral prolapse. Inversion of the normal QT:QS2 relationship occurred in nine patients (13%) and was more common in the presence of severe mitral regurgitation. It was not associated with an increased prevalence of absolute QT prolongation and was therefore thought to be caused by relative shortening of the QS2 interval. In conclusion, the prevalence of QT prolongation in mitral prolapse is low (11%). The QT:QS2 ratio is unlikely to be a reliable indicator of QT prolongation in these patients.

Non-invasive evaluation of autonomic tone changes during isometric exercise in normal subjects and in patients with coronary artery disease

In order to evaluate the clinical implications of QT/QS2 ratio during manoeuvres of sympathetic stimulation we studied the effects of handgrip (75% of maximal voluntary contraction) in 18 middle-aged normal subjects and in 16 patients with previous myocardial infarction. We also evaluated the effects of propranolol (0.1 mg/kg i.v.) in all normal subjects and in 10 of the 16 patients with coronary artery disease. At rest the two groups had similar heart rate, blood pressure, QT, QS2 and QT/QS2 ratio values. A significant increase in heart rate and systolic blood pressure was recorded during handgrip both in normal subjects and in patients with coronary artery disease; QT/QS2 significantly increased in normal subjects but did not show significant variations in patients with coronary artery disease, with significant differences between the two groups at peak exercise. Handgrip-induced QT/QS2 changes showed a marked variability both in normal and diseased subjects. After propranolol, QT/QS2 showed no significant difference at peak exercise in the two groups. The variability of ratio changes was nullified by the administration of the drug. These findings suggest that handgrip-induced QT/QS2 changes might be an expression of beta-adrenergic discharge. The clinical value of handgrip-induced QT/QS2 changes in detecting patients with coronary artery disease is limited by the variability of the response of the ratio observed in the two groups.

Relation between QT and QS2 intervals during exercise and recovery. Response in patient with coronary artery disease and age-matched control subjects

We investigated the relationship between QT interval and QS2 (electromechanical systole) during exercise and recovery in patients with coronary artery disease (CAD) and exercise-induced myocardial ischemia (n = 12), and in age-matched controls (n = 20). Upright bicycle exercise was performed (50 watts/min + 20 watts/min every 2 min), recording electrocardiographic lead 2 (100 mm/sec) for QT and QS2 measurement at rest, at each step of uninterrupted exercise and every 60 sec during a 3-min recovery period. Resting data showed a QT less than QS2 finding in both groups; during exercise, QT and QS2 decreased. The values of QT and QS2, collected at each step of exercise and plotted against heart rate (HR) separately for both groups, showed a significant correlation coefficient. Comparing the regression lines of HR-QT and HR-QS2 separately for both groups, we found that both intervals decreased in parallel and the mean QT remained shorter than QS2 in both groups during exercise. The QT/QS2 ratio remained unchanged significantly during exercise and recovery in CAD. In control subjects, the ratio remained unchanged during exercise and the first min of recovery, while a significant change was detected in late (2,3 min) recovery from an adrenergic-induced effect. The mean exercise-induced response of QT-QS2 relationship includes a QT less than QS2 pattern in both groups. In CAD patients, an abnormal pattern was found in two patients during recovery by a relative prolongation of QT, suggesting the possibility of a risk factor for dangerous arrhythmias or sudden death.

Effect of acute standing and prolonged upright activity on left ventricular hemodynamics, systolic and diastolic intervals, and QT-QS2 relationship

It is generally accepted that upright posture decreases preload and afterload, which could alter left ventricular (LV) performance. It is not known if changes occurring with acute standing persist after prolonged ambulatory activity (amb-act). In seven normal subjects echocardiographic end-diastolic and end-systolic diameters, percent shortening of the internal diameter (% delta D) and end-systolic wall stress (ES-WS), radionuclide diastolic volume and ejection fraction, preejection period over left ventricular ejection time (PEP/LVET), and diastolic time and QT-QS2 were measured supine, within 1 to 2 minutes after standing and after prolonged (60 minutes) amb-act. In addition, serial measurements were performed in PEP/LVET for 105 minutes at 15-minute intervals. With acute standing, end-diastolic diameter, diastolic volume, and ES-WS decreased (p less than 0.01); heart rate and PEP/LVET increased (p less than 0.01); while % delta D and ejection fraction remained unchanged. There was an inverse correlation between change in PEP/LVET and diastolic diameter (r = -0.59), but no correlation between PEP/LVET and ES-WS. The diastolic time per beat and per minute decreased (375 +/- 115 msec from 519 +/- 176 msec [p less than 0.01] and 31.3 +/- 4.2 sec/min from 33.7 +/- 4.5 sec/min [p less than 0.01]). The QT-QS2 increased when compared to supine (-7 +/- 7.6 msec from -22 +/- 7.7 msec [p less than 0.005]), but the QT-QS2 relationship remained normal (QT less than or equal to QS2). All the dynamic changes that occurred with acute standing tended to persist during prolonged amb-act.

Prolonged electrical systole and QT greater than QS2 secondary to coronary artery disease

Dyssynchronous depolarization-repolarization in the left ventricular (LV) myocardium may produce QT greater than QS2 or long QT. In 41 patients with coronary artery disease (CAD) and LV aneurysm, 46 patients with CAD and a history of acute myocardial infarction (AMI) but no LV aneurysm, and 52 patients with CAD without previous AMI, QT and QS2 were measured simultaneously at a speed of 100 mm/s within 48 hours of cardiac catheterization. Patients receiving class I antiarrhythmic drugs were excluded. The incidence of QT greater than QS2 was significantly greater in patients with LV aneurysm (71%) than in those with previous AMI (22%) and those with CAD but no previous AMI (20%) (p less than 0.001). Likewise, the incidence of long QT corrected for heart rate was significantly greater in patients with LV aneurysm (54%) than in those with previous AMI (7%) and those with CAD and no previous AMI (6%) (p less than 0.0001). The incidence of QT greater than QS2 in another 19 patients with previous AMI who were receiving digitalis therapy was significantly greater (65%) than in those with previous AMI but not receiving digitalis therapy (22%) (p less than 0.001). The incidence of long QT corrected for heart rate and QT greater than QS2 was not statistically different between patients with previous AMI and those with CAD but no previous AMI. The QT greater than QS2 or long QT in patients with aneurysm is probably a result of dyssynchronous depolarization or repolarization within or in the border zone of the LV aneurysm.(ABSTRACT TRUNCATED AT 250 WORDS)