Computer analysis of exercise-induced changes in QRS duration in patients with angina pectoris and in normal subjects

Heart rate and QRS duration as biomarkers predict the immediate outcome from pulseless electrical activity

INTRODUCTION

Pulseless electrical activity (PEA) is commonly observed in in-hospital cardiac arrest (IHCA). Universally available ECG characteristics such as QRS duration (QRSd) and heart rate (HR) may develop differently in patients who obtain ROSC or not. The aim of this study was to assess prospectively how QRSd and HR as biomarkers predict the immediate outcome of patients with PEA.

METHOD

We investigated 327 episodes of IHCA in 298 patients at two US and one Norwegian hospital. We assessed the ECG in 559 segments of PEA nested within episodes, measuring QRSd and HR during pauses of compressions, and noted the clinical state that immediately followed PEA. We investigated the development of HR, QRSd, and transitions to ROSC or no-ROSC (VF/VT, asystole or death) in a joint longitudinal and competing risks statistical model.

RESULTS

Higher HR, and a rising HR, reflect a higher transition intensity ("hazard") to ROSC (p < 0.001), but HR was not associated with the transition intensity to no-ROSC. A lower QRSd and a shrinking QRSd reflect an increased transition intensity to ROSC (p = 0.023) and a reduced transition intensity to no-ROSC (p = 0.002).

CONCLUSION

HR and QRSd convey information of the immediateoutcome during resuscitation from PEA. These universally available and promising biomarkers may guide the emergency team in tailoring individual treatment.

Relation between QRS duration and atrial synchronicity in patients with systolic heart failure

OBJECTIVES

The association of QRS duration (QRSd) with ventricular dyssynchrony is well-known in systolic heart failure (HF). However, there are no data regarding the relationship between QRSd and atrial dyssynchrony in patients with HF. We aimed to investigate the association of QRSd with intra-atrial and inter-atrial dyssynchrony in patients with systolic HF by using color tissue Doppler imaging (TDI).

METHODS

The study consisted of 70 systolic HF patients and 35 healthy controls. According to QRSd, HF patients were categorized into 2 subgroups as narrow QRS (n = 35) and wide QRS (n = 35) groups. Time intervals between the onset of P-wave and the onset of A-wave on color TDI from the right atrium (P-RA), inter-atrial septum (P-IAS) and left atrium (P-LA) were measured. Atrial dyssynchrony was defined as differences between P-RA and P-IAS (RA dyssynchrony), between P-LA and P-IAS (LA dyssynchrony) and between P-RA and P-LA (inter-atrial dyssynchrony).

RESULTS

In patients with either HF groups, we observed significant impairment in intra-atrial and inter-atrial synchronicity compared with the controls (P < 0.001). Moreover, LA, RA and inter-atrial synchrony were found to be significantly impaired in the wide QRS group compared to narrow QRS group. There was also a positive and strong correlation between atrial and ventricular dyssynchrony parameters. In stepwise multivariate analysis, QRSd was found to be the independent predictor of intra-atrial and inter-atrial dyssynchrony in systolic HF.

CONCLUSION

Among patients with systolic HF, prolonged QRSd is associated with impaired intra-atrial and inter-atrial synchrony. Atrial and ventricular dyssynchrony parameters were well-correlated with each other.

QRS prolongation on the signal-averaged electrocardiogram versus ST-segment changes on the 12-lead electrocardiogram: which is the most sensitive electrocardiographic marker of myocardial ischemia?

BACKGROUND

ST-segment changes and QRS prolongation are electrocardiographic (ECG) markers of myocardial ischemia.

HYPOTHESIS

This study was undertaken to investigate the appearance of QRS duration changes with or without concomitant ST-segment changes during a typical anginal episode.

METHODS

For this purpose, 126 patients underwent 12-lead surface ECG and signal-averaged electrocardiogram (SAECG) during typical anginal pain as well as at the time the patient was asymptomatic. In both periods, QRS duration and ST-segment changes were evaluated. All patients underwent cardiac catheterization.

RESULTS

Of the 126 patients, 108 (86%) had coronary artery disease (CAD), whereas the remaining 18 (14%) patients had normal coronary arteriograms. During typical anginal pain, 75 of the 108 (70%) patients with CAD and 2 of the 18 (11%) patients with normal coronary arteriograms developed QRS prolongation, whereas 60 of the 108 (56%) patients with CAD and 2 of the 18 (11%) patients with normal coronary vessels developed ST-segment changes. Thus, the sensitivities of QRS prolongation measured by SAECG and of ST-segment changes on the surface ECG for the detection of myocardial ischemia were found to be 70 and 56%, respectively, (p < 0.01), whereas the specificities were both found to be 89% (p = NS).

CONCLUSIONS

During typical anginal pain, QRS prolongation on the SAECG is more sensitive than are ST-segment changes on the ECG for the detection of myocardial ischemia.

Changes during exercise of ECG intervals related to increased risk for ventricular arrhythmia in repaired tetralogy of Fallot and their relationship to right ventricular size and function

PURPOSE

Our study aimed to assess pro-arrhythmogenic electrocardiographic changes during maximal physical exercise in patients operated for Tetralogy of Fallot (TOF).

METHODS

TOF patients prospectively underwent: 1) bicycle ergometry, 2) cardiac MRI, and 3) 24-hour Holter. ECG data was analyzed at rest, at 60% of peak exercise and at peak exercise. R-R duration, QRS-, QT- and JT-duration and dispersions were assessed. Changes of ECG parameters during exercise were calculated and correlated to RV volume, RVEF, RV wall-mass, PR-percentage and VO(2max). Exercise ECG data from healthy controls were used as reference.

RESULTS

Thirty-one patients (mean age at repair (SD) 0.8 (0.5) years, age at study 16 (5) years) and 25 controls (age 12 (2) years) were included. With exercise mean QTc and JTc dispersions increased in patients (p<0.001), but not in controls. At peak exercise JTc dispersion was larger in patients (p<0.01). QTc did not change with exercise in patients (p=0.14) and decreased in controls (p<0.05). At all levels of exercise mean QTc, QRS and QRS dispersion were larger in patients (all p<0.001). Significant associations were found for; 1) a larger increase of JTc dispersion with a higher PR-percentage, a larger RV volume, a larger RV wall-mass, 2) a larger QTc increase with a larger RV volume and worse RVEF.

CONCLUSION

During physical exercise inhomogeneity of repolarisation, known to predispose for re-entry ventricular arrhythmia, increases in repaired TOF. Larger inhomogeneity is found with more severe PR.

Detection of coronary artery stenosis after successful percutaneous coronary intervention by dipyridamole stress portable type signal-averaged electrocardiography: a prospective study

In our previous studies, using portable type signalaveraged electrocardiography (portable SAECG) with dipyridamole stress we reported that patients with coronary artery disease were identified at the bedside with high sensitivity and specificity. In this study we prospectively investigated whether coronary artery stenosis after successful percutaneous coronary intervention (PCI) could be detected. Standard 12-lead QRS wave SAECG was performed before and after dipyridamole stress at the bedside in 61 patients 8.0 +/- 9.4 months after successful PCI for myocardial infarction or angina pectoris (46 males and 15 females, mean age 66 +/- 12 years). The filtered QRS duration (fQRSd) before and after dipyridamole stress was determined by the multiphasic oscillation method at each lead of the standard 12 leads, and the maximal value of changes in fQRSd (MAX DeltafQRSd) among the 12 leads was determined. The positive test was defined as MAX DeltafQRSd > or =5 ms, and negative as MAX DeltafQRSd <5 ms based on our previous studies. Then selective coronary arteriography was performed. In the positive group (n = 24), 21 patients had stenosis (> or =50%) of the coronary artery and 3 did not. In the negative group (n = 37), 8 patients had stenosis and 29 did not. The sensitivity, specificity, positive predictive accuracy, and negative predictive accuracy for the detection of coronary artery stenosis by SAECG were 72%, 91%, 88%, and 78%, respectively. Dipyridamole stress portable SAECG is useful to detect patients with coronary artery stenosis after successful PCI.

Portable-type signal-averaged electrocardiography with dipyridamole to detect patients with coronary artery disease

BACKGROUND

In a retrospective study portable-type signal-averaged electrocardiography (SAECG) with dipyridamole stress was found to identify patients with coronary artery disease (CAD) at their bedside with high sensitivity and specificity, so the utility of this method was prospectively investigated in the present study.

METHODS AND RESULTS

Standard 12-lead QRS wave SAECG was performed before and after dipyridamole stress at the bedside in 71 patients with chest pain (43 males, mean age 63 +/-9 years). The filtered QRS duration (fQRSd) before and after dipyridamole stress was determined by multiphasic oscillation method for each of the standard 12 leads, and the maximal value of changes in fQRSd (MAX DeltafQRSd) among the 12 leads was determined. The positive test was defined as MAX DeltafQRSd >or=5 ms, and negative as MAX DeltafQRSd <5 ms based on the previous study. Selective coronary arteriography was performed next. In the positive group (n=31), 25 patients had significant stenosis of the coronary artery and 6 did not. In the negative group (n=40), 5 patients had significant stenosis and 35 did not. The sensitivity, specificity, positive predictive accuracy and negative predictive accuracy for CAD detection by SAECG was 83%, 85%, 81% and 88%, respectively.

CONCLUSIONS

Dipyridamole-stress portable SAECG is useful for detecting CAD at the patient's bedside with high sensitivity and specificity.

The value of changes in QRS width and in ST-T segment during exercise test in hypertrophic cardiomyopathy for identification of associated coronary artery disease

OBJECTIVES

Non-invasive methods cannot reliably predict the presence of coronary artery disease (CAD) in hypertrophic cardiomyopathy (HCM). This study aims to define the accuracy of QRS width changes versus standard ST-T criteria for recognition of associated ischemic CAD in patients with HCM undergoing exercise testing (ET).

METHODS

A retrospective study including patients with HCM. HCM was defined by left ventricular hypertrophy (LVH) of unknown etiology of at least 15 mm. Coronary angiography was performed as a gold standard for definition of CAD (> or =70% obstruction in at least one major artery). QRS width duration was measured at peak ET by a computerized method employing an optical scanner. No changes in QRS width or shortening during ET were considered normal; QRS width prolongation of more than 3 ms was defined as abnormal.

RESULTS

68 patients (56/12 M/F) aged 60+/-12 y were studied. During ET, abnormal QRS response was found in 40 (58.8%) and Ischemic ST-T changes in 52 (76.5%) patients. CAD in at least one artery was diagnosed in 31 patients (45.5%). The sensitivity of QRS width versus ST-T changes during ET for associated CAD was 82% and 28%, respectively. Specificity was 75% and 48%, respectively. Positive and negative predictive values were 88%; 68% for QRS width and 67%; 59% for ST-T changes respectively.

CONCLUSIONS

In patients with HCM undergoing ET, the association with CAD was more accurately predicted by an increase in QRS complex width than by standard criteria of ST-T segment changes. Thus, its use should be encouraged, especially in patients with HCM.

Portable type signal-averaged electrocardiography with dipyridamole: a new and convenient method to detect patients with coronary artery disease and ischemia

BACKGROUND

Whether or not patients with coronary artery disease (CAD) could be easily detected at the bedside using dipyridamole stress was investigated using a portable type signal-averaged electrocardiography (portable SAECG).

METHODS AND RESULTS

The standard 12-lead QRS wave SAECG was performed at the bedside before and after dipyridamole stress in 30 patients with angiographically significant stenotic lesions, who had positive myocardial ischemia in the dipyridamole-thallium myocardial perfusion imaging (CAD group), and 33 patients with no significant stenotic lesions, who had negative imaging (control group). The filtered QRS duration (fQRSd) before and after dipyridamole stress was determined by the vector magnitude method and the difference (DeltafQRSd) was obtained. Furthermore, the DeltafQRSd was obtained using the multiphasic oscillation method, as well at the same standard 12-lead, and the maximal value of changes in fQRSd (MAX DeltafQRSd) between the 12 leads was determined. The DeltafQRSd was similar between 2 groups (p = 0.11). The MAX DeltafQRSd associated was significantly greater in the CAD group (p < 0.0001). When a cut-off value of MAX DeltafQRSd > or = 5 ms was used for the detection of CAD, the sensitivity and specificity were 97 and 94%, respectively.

CONCLUSION

The portable dipyridamole-stress SAECG easily detect CAD and myocardial ischemia at the bedside.

Rate-dependent QRS prolongation during exercise testing associated with hyperkalemia

The present case showed gradual increase of QRS duration from 100 ms up to 180 msec during an ergometer exercise test along with the heart rate increase. After exercise, QRS duration shortened and normalized. Laboratory test showed hyperkalemia (K = 8.0 mEq/l). T1 myocardial scintigraphy revealed exercise-induced transient ischemia in posterolateral region of left ventricle. Coronary angiography showed significant stenosis in the distal portion of left circumflex coronary artery. The increase of QRS duration was possibly due to the combination of hyperkalemia and the effect of mexiletine. The rate dependent blocking effect on sodium channel of mexiletine might be intensified under hyperkalemia.

QRS prolongation: a sensitive marker of ischemia during percutaneous transluminal coronary angioplasty

The purpose of this study is to measure QRS duration changes in the human model of ischemia during percutaneous transluminal coronary angioplasty (PTCA) and compare these results to the commonly used ischemia markers, chest pain, and classical ST-T changes. Using a computerized method, QRS duration was measured in 51 patients undergoing elective PTCA. Three milliseconds (msec) or more prolongation of the QRS at peak inflation was considered to be an ischemic response. The results were compared to chest pain and ST-T changes and were analyzed for inflation site within individual coronary arteries. Forty-two patients had a pathological prolongation of the QRS during PTCA. Thirty-two patients developed chest pain, while 19 had ischemic ST-T changes. QRS duration was more prolonged in PTCA to proximal or middle segments of major arteries or their large branches, while it was less prolonged in distal segments or smaller branches. Using our method, QRS prolongation was an ischemia marker in most patients during PTCA and was more sensitive than chest pain or ST-T changes. QRS duration was more prolonged with occlusion of proximal and middle segments of major arteries. Cathet. Cardiovasc. Intervent. 50:177-183, 2000.

Exercise-induced QRS prolongation in patients with mild coronary artery disease: computer analysis of the digitized multilead ECGs

Although exercise-induced QRS prolongation has been reported as a possible marker for inducible ischemia, subtleness of the prolongation makes it unidentifiable from standard, chart-recorded electrocardiograms (ECGs). To overcome such a limitation, we measured the QRS width using high-resolution ECGs and examined the diagnostic value of the exercise-induced QRS prolongation in patients before and after percutaneous transluminal coronary angioplasty (PTCA). In 16 patients with single- (n = 12) or double-vessel disease (n = 4), treadmill exercise ECG tests were performed before and after PTCA, while continuously recording 8-lead ECGs at 500 Hz. The onset of the QRS complexes was defined by the earliest deflection, and the end was defined as the latest deflection among 8 leads with the use of algebraic sum of the absolute voltage and their time derivatives (dV/dt) from all 8 leads. We compared QRS complexes before and 1 minute after exercise. Before PTCA, exercise prolonged the QRS width in all but 3 patients (unchanged in 2, decreased in 1) (84 +/- 7 to 87 +/- 8 ms, P < .005). After PTCA, it decreased in 4, was unchanged in 5, and increased in 7 (83 +/- 7 to 83 +/- 6 ms, not significant). PTCA shortened postexercise QRS width in all but 3 (unchanged in 2, increased in 1: 83 +/- 6 to 87 +/- 8 ms, P < .001). High-resolution ECGs enabled us to measure subtle QRS prolongation induced by mild ischemia. Because the QRS prolongation and ST-segment changes would reflect different aspects of myocardial ischemia, incorporating this measure into ST segment criteria might significantly improve the diagnostic accuracy for coronary artery disease.

The potential for inappropriate ventricular tachycardia confirmation using the Intracardiac Electrogram (EGM) Width Criterion

The "Intracardiac Electrogram (EGM) Width Criterion," the first digital signal processing feature used in an implantable cardioverter defibrillator (ICD), is a detection enhancement algorithm that intends to improve ventricular tachycardia (VT) detection specificity by rejecting inappropriately detected supraventricular tachyarrhythmias. The algorithm may be activated after setting the optimal EGM source, slew, and width thresholds based on EGM width testing during sinus rhythm. This study evaluates the accuracy of the EGM width measurements during exercise testing. Twenty-one patients with Medtronic Micro Jewel II Model 7223 ICDs underwent treadmill exercise testing. EGM width testing was repeatedly performed during exercise and recovery to detect potential inappropriate measurements. In seven (33%) patients the EGM Width Criterion inappropriately confirmed VT detection. Eleven patients had inappropriately wide EGM width measurements, but did not satisfy the EGM Width Criterion. The causes of wide EGM width measurements were an actual increase in EGM width and/or inappropriate detection of the baseline irregularities as EGM onset or offset points. Based on our observations, we recommend to test the EGM Width Criterion during exercise testing for optimal ICD programming.

Ischemia detection in women: the diagnostic value of exercise QRS duration changes

AIM

To compare the diagnostic accuracy of exercise electrocardiographic (ECG) ST-T changes and QRS duration changes as a means of ischemia detection in a female population.

METHODS AND RESULTS

A total of 101 women from a pool of 318 referred for ECG stress testing underwent standard testing using ST-T criteria with the additional measurement of QRS duration before and at peak exercise using a new computerized optic scanner for precise QRS duration measurement. The diagnostic accuracy of the test was determined using planar thallium stress testing as a "gold standard." For the overall population, the sensitivity of ST-T criteria was 47% with a specificity of 58%. The sensitivity of QRS duration changes was 91% with a specificity of 89%. For Group 1 (age 27-50) the sensitivity of the ST-T criteria was 40% with a specificity of 58%. The sensitivity of the QRS duration changes was 80% with a specificity of 83%. For Group 2 (age 51-83), the sensitivity of the ST-T criteria was 43% with a specificity of 56%. The sensitivity of the QRS duration changes was 94% with a specificity of 90%.

CONCLUSION

In our female population exercise, QRS duration changes using our computerized method were better markers of ischemia than standard ST-T criteria.

Abnormal ventricular activation and repolarisation during dobutamine stress echocardiography in coronary artery disease

OBJECTIVE

To assess possible ECG changes caused by dobutamine stress and their relation to wall motion disturbances in patients with coronary artery disease.

DESIGN

Prospective recording and analysis of 12 lead ECG at rest and during each stage of dobutamine stress echocardiography, and correlation with wall motion changes.

SETTING

A tertiary referral centre for cardiac disease equipped with non-invasive facilities for pharmacological stress tests.

SUBJECTS

27 patients, mean (SD) age 60 (8) years, with documented evidence of coronary artery disease in whom dobutamine stress echo was clinically indicated, and 17 controls of similar age.

RESULTS

In controls, all ECG intervals shortened with increasing heart rate but in the patient group only PR and QT intervals shortened while QRS duration broadened and QTc interval prolonged progressively. In the 27 patients, 16 developed chest pain, 15 with reduced left ventricular long axis systolic excursion (p < 0.001), and all showed reduced peak lengthening rate; ST segment shift appeared in 16, 13 of whom developed chest pain, but did not correlate with reduction of either systolic long axis excursion or peak lengthening rate; QRS duration broadened in 20, 16 with reduction of long axis excursion (p < 0.02) which was more often seen at the septum (p < 0.005); QTc interval prolonged in 19, all of whom had associated reduction of peak long axis lengthening rate (p < 0.02).

CONCLUSIONS

QRS duration and QTc interval both normally shorten with dobutamine stress, while in coronary artery disease they both lengthen: changes in QRS duration correlate with systolic and QTc interval with diastolic left ventricular wall motion disturbances. ST segment shift also occurred in most patients, but without consistent correlation with wall motion abnormalities. It was thus less discriminating than the other two abnormalities in this respect.

Ischemia detection after myocardial infarction: diagnostic value of exercise-induced QRS duration changes evaluated by a new computerized method

A new computerized optical scanner was used to measure QRS complex duration during exercise stress testing, both pre- and postdischarge, as a means of ischemia detection after acute myocardial infarction. Thallium stress testing was used as a standard of comparison. Each patient underwent predischarge exercise testing (while receiving anti-ischemic drug therapy) and a postdischarge test 1 month later (without anti-ischemic drug therapy), as well as thallium stress testing within 4 months of infarction. In the population of 68 patients, 42 of the predischarge tests and 43 of the postdischarge tests showed an ischemic response of QRS prolongation. When compared with thallium testing for QRS prolongation criteria, the sensitivity was 95% with a specificity of 77% predischarge and 89% with a specificity of 65% postdischarge. According to ST-T criteria, only 12 of 68 patients were positive for ischemia predischarge; this number increased to 29 postdischarge (predischarge sensitivity 24% and specificity 90%, with postdischarge sensitivity 68% and specificity 87%), when compared with thallium testing. Measuring QRS duration during exercise increased the sensitivity of detection of ischemic patients over that of ST-T criteria by 71% predischarge and 21% postdischarge, with a 22-23% loss of specificity, and was apparently not influenced by anti-ischemic drug therapy.

QRS prolongation as an indicator of risk of ischemia-related ventricular tachycardia and fibrillation induced by exercise

The majority of patients with serious ventricular arrhythmias induced by exercise have ischemic heart disease. These arrhythmias, however, develop only in a minority of the patients with coronary artery disease. The aim of this study was to investigate whether patients with ventricular tachycardia or fibrillation produced by exercise-induced ischemia exhibit any premonitory electrocardiographic indicators of arrhythmia propensity and whether arrhythmia suppression by myocardial revascularization abolished these changes. High-quality exercise electrocardiograms (50 mm/sec) from 30 case patients with ventricular tachycardia and fibrillation produced by exercise-induced ischemia were studied before and after surgical revascularization. These results were compared with those obtained from 30 control patients matched for age, sex, heart disease, and preoperative exercise capacity. The resting and peak exercise electrocardiograms were examined separately in a blinded manner with respect to QRS duration, ST-segment depression, and JT intervals. Patients with bundle branch block patterns were excluded. The QRS duration at rest was similar in case and control patients preoperatively and increased significantly with exercise in both groups. However, the QRS prolongation was larger in the case group, in which it was 11 +/- 3 msec compared with 4 +/- 2 msec in the control group (p = 0.043). QRS prolongation > or = 15 msec predicted ischemia-related ventricular arrhythmias in 73% of the patients. After surgical revascularization, there was no QRS prolongation with exercise in either group. In both groups, the QRS prolongation was associated with significant ST-segment depression, which was larger in the case patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Exercise-induced QRS duration changes in patients with coronary artery disease-appearing "walkthrough" angina

Two patients with coronary artery disease appearing as "walkthrough" angina underwent a treadmill exercise test. During the exercise, the patients appeared to have anginal pain associated with ST-segment depression and increased QRS duration. As the patients continued walking, anginal pain disappeared and a concomitant lessening in ST-segment depression and QRS prolongation was observed. Thus, the fact that the onset of angina was associated with ST-segment depression and prolonged QRS duration, while the disappearance of angina was associated with a decrease in ST-segment depression and QRS prolongation, is indicative of the effect of exercise-induced myocardial ischemia on QRS duration.

Exercise-induced QRS prolongation in patients with coronary artery disease: a marker of myocardial ischemia

The objective of this study was to investigate the effect of myocardial ischemia on the QRS duration in patients with coronary artery disease since acute myocardial ischemia decreases conduction velocity through the ischemic myocardium and may produce QRS prolongation on the surface electrocardiogram. One hundred fifty patients who underwent cardiac catheterization and exercise radionuclide ventriculography within 1 month of each other were studied. Forty patients had normal coronary arteries and 110 had coronary artery disease. QRS duration decreased with exercise in patients with normal coronary arteries (-3.0 msec, confidence limits -6.2 to 0.2), but increased in patients with coronary artery disease; exercise-induced QRS prolongation was directly related to the number of diseased vessels (4.8 msec in patients with one, 7.8 msec in patients with two, and 13.3 msec in patients with three-vessel disease, p < 0.001). Likewise, QRS duration decreased with exercise in patients without exercise-induced segmental contraction abnormalities (-1.8 msec, confidence limits -3.7 to 0.1), but increased in patients with segmental contraction abnormalities (6.7 msec in patients with one, 13.5 msec in patients with two, and 21 msec in patients with three segmental contraction abnormalities, p < 0.0001). Exercise-induced QRS prolongation was better related to the number of segmental contraction abnormalities than to the number of diseased vessels (p < 0.01). It was concluded that exercise produces QRS prolongation in patients with coronary artery disease in direct relation to the number of diseased vessels and to exercise-induced segmental contraction abnormalities.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in the QRS segment during exercise: effects of acute beta-blockade with propranolol

Changes in the QRS complex during exercise may provide information with respect to ischaemic heart disease. The intention with present investigation was to shed light on mechanisms behind QRS changes and to study the possibly confounding effects of beta-blockade on such alterations with exercise. Placebo or propranolol respectively was infused in randomized and double-blinded order in seven young healthy men before a maximum exercise test. Advanced computerized vectorcardiography and impedance cardiography was recorded continuously together with blood pressures and blood samples. The Y-lead magnitude increased significantly with propranolol infusion (P < 0.05), but it tended to decrease in the Z-lead (P < 0.07). While the serum potassium concentrations increased (P < 0.0005), the spatial QRS magnitude tended to decrease irrespective of treatment (P < 0.07). These changes correlated with changes in QR-duration (adj r2 > 0.58). With exercise, the mean spatial QRS magnitude decreased with similar amounts irrespective of treatment. However, propranolol made the magnitude decrease earlier (P < 0.01). No effect of treatment was detected on the decrease in QRS-duration. Immediately after exercise, the QRS complex continued to change as during exercise in the placebo investigations, but did not with propranolol (P < 0.05). These different patterns were most obvious in the first half of the QRS complex in the Y-lead. It is concluded that acute beta-blockade modifies QRS alterations both during and after exercise in healthy subjects. This indicates that such drugs may have confounding effects in evaluations of the diagnostic value of QRS alterations.

Exercise-induced S-wave prolongation in left anterior descending coronary artery stenosis

Myocardial ischemia may decrease conduction velocity and produce QRS prolongation in the surface electrocardiogram. In cases with normal intraventricular conduction, areas of the myocardium contributing to the development of the S wave receive blood from all 3 major coronary arteries, whereas in left anterior hemiblock or right bundle branch block, most of the blood supply to the areas of the myocardium contributing to the development of the S wave is from the left anterior descending (LAD) coronary artery. To test the hypothesis that the S wave will be prolonged with exercise only in patients with LAD coronary artery stenosis and left anterior hemiblock or right bundle branch block, 88 patients with normal intraventricular conduction, 66 with left anterior hemiblock and 36 with right bundle branch block were studied. Sixty-four, 32 and 21 patients had LAD, right and left circumflex coronary artery stenoses, respectively. In patients with normal coronary arteries, S-wave duration decreased with exercise regardless of the status of ventricular conduction. In patients with coronary artery disease and normal intraventricular conduction, the S wave was prolonged slightly with exercise, but in those with left anterior hemiblock and right bundle branch block, it was prolonged significantly (12.5 +/- 6 and 10.4 ms, respectively) only in those with LAD, but not in those with circumflex or right coronary artery stenosis. S-wave prolongation in patients with LAD coronary artery stenosis and left anterior hemiblock or right bundle branch block most likely is related to exercise-induced ischemia in the areas of the myocardium contributing to the development of the S wave.

Ischaemic heart disease and the changes in the QRS and ST segments during exercise: a pilot study with a novel vectorcardiographic system

In order to find new ischaemic parameters, the spatial changes of the Frank vectorcardiogram were continuously analysed with a new, highly precise vectorcardiographic method during, and immediately after a maximal exercise test. This was done in 18 young healthy males, and 18 patients with scintigraphic reversible ischaemia. During exercise, different patterns between the groups were noted for the changes in the mean QRS magnitude in the Y-lead (P less than 0.005), the QRS-integral (P less than 0.05), and the QRS-duration (P less than 0.05). Immediately after exercise, several QRS parameters in the normal group continued to change according to the same pattern as during exercise (P less than 0.05), which was in contrast with the patterns of the ischaemic group (P less than 0.01). The spatial ST difference at J+20 ms discriminated well between the groups, especially when corrected for QRS-magnitudes at rest and heart rate (P less than 0.0005). In short, this pilot study supports previous findings in that changes in amplitude and duration of the QRS complex during exercise discriminated between healthy young males and patients with ischaemic heart disease. Moreover, rapid discriminating changes were seen in the QRS segment during cessation of exercise. These changes deserve attention since they may be of importance for the conflicting results on the diagnostic value of QRS changes during exercise.

An off-line digital system for reproducible interpretation of the exercise ECG

Exercise electrocardiograms of 20 patients were analyzed using a customized software exercise electrocardiographic program and compared to measurements made by two cardiologists performing independent interpretations. The computerized program requires identification of the PQ junction, J point, and tracing of the ST-segment in three consecutive beats. The proportion of variance for J point, and ST 80 measurements was 0.93 and 0.90, respectively, when the same electrocardiogram was processed twice and analyzed by two separate cardiologists. The same 20 exercise electrocardiograms were analyzed by two other experienced cardiologists without computerized measurements. The proportion of variance was less at 0.73 and 0.76 for the J point and ST 80 measurements, respectively. The average amount of time required for the cardiologist to over read the computerized measurements was 2.7 +/- 1.5 minutes per ECG as compared to 20.7 +/- 11 minutes for the cardiologists who did not have computer-assisted measurements (p less than 0.0001). Thus, off-line computerized exercise electrocardiographic interpretation is highly reproducible, accurate, time-sparing for cardiologist over read function, and suitable for use in large-scale clinical trials.

Use dependence of amiodarone during the sinus tachycardia of exercise in coronary artery disease

The QRS duration at rest and during exercise was studied in 19 patients with coronary artery disease before and after oral amiodarone therapy to determine if this drug produces detectable rate-dependent conduction slowing during physiologic increases in heart rate. QRS duration did not change significantly during exercise in the absence of the drug. However, after amiodarone, QRS duration at rest increased from 99 to 114 ms (p less than 0.001), and increased further from 114 to 127 ms (p less than 0.001) during the 45 beats/min mean increase in heart rate produced by exercise. The magnitude of this effect was related to the resting QRS duration. After amiodarone therapy, the QRS increased during exercise by only 6% in 8 patients with QRS less than 110 ms, while in 12 patients with QRS greater than or equal to 110 ms, the QRS increased by 15% (p less than 0.05). Rate-dependent conduction slowing occurs during the sinus tachycardia of exercise in patients treated with amiodarone, presumbably due to use-dependent sodium channel blockade. This result is most pronounced in patients with abnormal ventricular conduction at rest.