Influence of heart rate on exercise-induced R-wave amplitude changes in coronary patients and normal subjects

R-wave amplitude changes measured by electrocardiography during early transmural ischemia

BACKGROUND

Changes in the amplitude of the R wave (RWA) on the electrocardiogram (ECG) have been described during acute myocardial ischemia and infarction. However, this has not been well studied in a controlled setting. We hypothesized that significant increase in RWA occurs during early transmural myocardial ischemia.

METHODS

We prospectively evaluated changes in RWA in 50 patients during brief episodes of transmural ischemia induced by first balloon occlusion (mean, 38 seconds at 6-10 atmospheric pressures) during elective percutaneous coronary intervention. We recorded 12-lead ECGs at 20-second intervals before and during balloon inflation in 16 right coronary arteries, 14 left circumflex arteries, and 20 left anterior descending arteries. R wave amplitude was digitally measured in each of the 12 leads in every ECG using the ECG interval editor (General Electric HC, Menomonee Falls, WI). Intracoronary (IC) ECGs were also recorded in 4 patients. The mean of the RWA in each lead before balloon inflation was compared to the mean RWA during balloon inflation.

RESULTS

R wave amplitude significantly increased during balloon inflation from baseline in limb leads I, II, aVL, and all the precordial leads with the exception of lead V(1). The RWA increase did not reach statistical significance in leads III, aVF, and V(1). Mean RWA increase was consistent in all leads except aVR during the brief episodes of ischemia during initial balloon inflation because of the inverse polarity of this lead. The increase in RWA was seen in most patients (mean, 75%) in whom transmural ischemia was induced by first balloon inflation. Besides, the RWA showed an increase from baseline in 3 patients who had IC-lead recordings.

CONCLUSION

R wave amplitude increases significantly in precordial leads (V(2)-V(6)) and limb leads (I, II, aVL) of the surface ECG during brief episodes of transmural ischemia. The increase in RWA might be consistent with the expansion of the left ventricular cavity during ischemia and/or alterations in conduction that are intrinsic to the myocardium.

R-wave amplitude response to myocardial ischemia in hypertrophic cardiomyopathy

BACKGROUND AND PURPOSE

R-wave amplitude change during exercise has been reported to enhance diagnostic value for myocardial ischemia in coronary heart disease.

METHODS

We summed up R-wave amplitude in all the 12 leads during exercise testing and correlated the results with regional myocardial ischemia or diffuse subendocardial ischemia as detected by scintigraphy in 49 patients with hypertrophic cardiomyopathy (HCM) and 16 controls.

RESULTS

The sum of R-wave amplitude decreased during exercise in patients with HCM (mean, 12.4 mV to 11.7 mV, P < .01) as well as in controls (8.0 mV to 7.7 mV, P < .05). Percent changes in the sum of R-wave amplitude did not differ between 4 subgroups of patients with HCM: one having both regional and subendocardial ischemia, one only the former, one only the latter, and one neither of them (mean, 6.5%, 7.7%, 4.6%, and 5.1%; P = .79).

CONCLUSIONS

R-wave amplitude response to exercise failed to demonstrate myocardial ischemia in our patients with HCM.

Demonstration of the relationship between heart dimensions and QRS voltage amplitude

This study was undertaken to elucidate the still debated question of the relationship between cardiac volume and QRS voltage amplitude. The authors studied 14 healthy men, aged 24-61 years (mean age, 41.2 +/- 12.1 years). They underwent a reduction in venous return, produced by simultaneously inflating sphygmomanometric cuffs placed around the most proximal portion of each of the four limbs. In basal conditions and 5 minutes after cuff inflation, two-dimensional and M-mode echocardiograms were recorded with vectorcardiographic loops and scalar Frank leads. The reduction of the venous return to the heart induced a significant decrease of the end-diastolic left ventricular diameter (from 52.4 +/- 4.2 to 48.5 +/- 4.6 mm, P < .001), of the R wave amplitude in leads X and Y, of the sum of the R wave amplitudes in the three leads,and of the maximal vector in the frontal and horizontal planes. No significant changes in the heart rate or arterial blood pressure were observed. These results support Brody's theory concerning the relationship between cardiac blood volume and QRS voltage.

Exercise-induced changes in R wave amplitude and heart rate in normal subjects

An intermittent exercise protocol on a treadmill was used to examine six healthy subjects, and a steady protocol was applied to three of the subjects before and after short-term training. The peak blood velocity in the common carotid artery increased by 73.1% during the intermittent protocol and recovered to resting level within 3 minutes, while the heart rate (HR) remained high even 5 minutes after exercise. R wave amplitude (RWA) increased significantly from 1.40 +/- 0.39 mV at rest to 1.59 +/- 0.33 mV (P < .05) immediately after the start of walking, and decreased gradually to 1.46 +/- 0.36 mV (P < .05) during 3 minutes of walking. Thus, it decreased significantly to 1.31 +/- 0.40 mV (P < .01) during the interphase from exercise to rest, and increased again during recovery or rest periods in the intermittent protocol. The results suggest that an increase in the venous return per heart beat at the start of walking induces the increase in RWA, and that its abrupt decrease at the end of walking induces the decrease in RWA. Subjects with a higher HR response and recovery slopes have smaller abrupt changes in RWA at the interphases between rest and walking. The gradual decrease in RWA during walking may be related to a gradual increase in HR and a gradual decrease in systemic peripheral resistance, and the gradual increase in RWA after walking may be related to a gradual decrease in HR and a gradual increase in systemic peripheral resistance.

Hemodialysis changes the QRS amplitude in the electrocardiogram

We studied eight patients to determine whether changes occur in the QRS amplitude when these patients are submitted to hemodialysis. The following variables were assessed before and after each (N = 28) hemodialysis session: (1) plasma sodium and potassium concentrations, (2) QRS amplitude, (3) the heart rate and its variability, (4) ventricular volumes, ventricular mass, ejection fraction and circumferential fiber shortening, (5) arterial pressure and end systolic stress, and (6) body weight. QRS amplitude was computed as the algebraic sum of the positive and negative waves of each QRS complex of the electrocardiogram. QRS amplitude changes were compared to body weight, ventricular volumes, ventricular mass, ejection fraction, circumferential fiber shortening, plasma potassium and sodium concentrations, arterial pressure, end systolic stress, heart rate, and R-R variability. After the hemodialysis sessions we found a significant increase (P = 0.0006) in QRS amplitude and a significant decrease in body weight (P = 0.0001), end diastolic volume (P = 0.043), plasma potassium concentration (P = 0.000001), end systolic stress (P = 0.025) and systolic arterial pressure (P = 0.023). Hemodialysis did not produce significant changes in the other variables. The statistical analyses performed did not show any significant influence of any of the measured variables on the QRS amplitude change. The QRS amplitude increases after hemodialysis but the cause of this increase is still unclear.

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.

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.

New coronary artery disease index based on exercise-induced QRS changes

Exercise-induced changes in Q, R, and S wave amplitudes have been reported to detect coronary artery disease but with low specificity, low sensitivity, or both; it was hypothesized that their incorporation into a composite index (Athens QRS score) might improve specificity and sensitivity. For this purpose 246 patients were analyzed retrospectively and 160 prospectively. All patients underwent maximal exercise testing with a standard Bruce protocol and coronary arteriography as part of the diagnostic evaluation for possible or definite coronary artery disease. The Athens QRS score was decreased as the number of obstructed coronary arteries increased (normal coronary arteries = 7.85 +/- 5.23 mm, one-vessel disease = 5.2 +/- 5.3 mm, two-vessel disease = -0.85 +/- 5.4 mm, three-vessel disease = -3.5 +/- 5.8 mm; p less than 0.0001); the score was unrelated to exercise-induced ST segment depression, and negative (less than 0) scores were always associated with coronary artery disease. An Athens QRS score of 5 mm predicted coronary artery disease with sensitivity ranging from 75% to 86% and a specificity ranging from 73% to 79%, values higher than those of the Q wave (75% and 50%, respectively), R wave (65% and 55%), and S wave (70% and 10%) and of the ST segment depression (62% and 70%). It is concluded that exercise-induced changes in the QRS complex provide a useful index not only for the diagnosis but also for the assessment of severity of coronary artery disease.

Transient alterations of the QRS complex and ST segment during percutaneous transluminal balloon angioplasty of the left anterior descending coronary artery

Using continuous 3-lead electrocardiographic (ECG) recordings in 19 patients undergoing elective percutaneous transluminal coronary artery angioplasty (PTCA) of the left anterior descending (LAD) artery, this study described the dynamic changes of the ST segment and the R- and S-wave amplitudes that occur during transient myocardial ischemia. The waveforms from lead V2 were quantified at 10-second intervals during the length of the balloon inflation that produced the greatest extent of ST-segment deviation. The simultaneous changes that occurred in leads aVF and V5 were also observed, but not quantified. Measurements of R- and S-wave amplitudes were performed during maximal ischemia from both the PR- and the J-ST-segment baselines to determine which of these most nearly maintained its control position during ischemia. The results indicate that the R-wave amplitude is best determined from the PR-segment baseline (p = 0.0007), while the S wave is best determined from the J-ST-segment baseline (p = 0.03). However, only a portion of the QRS changes observed during PTCA could be accounted for by the baseline shift. There were additional QRS changes during ischemia in 11 of the patients (58%) suggestive of conduction disturbances in 3 endocardial sites: left septal, right septal and left anterosuperior. It is hypothesized that these changes may represent ischemia-induced delay in conduction ("periischemic block") previously thought to occur only with myocardial infarction.

Local conduction delay causes R-wave amplitude increase in patients with effort angina

Eighty-seven unipolar electrocardiograms distributed over the entire thorax were simulataneously recorded before and after treadmill exercise in 43 patients. Exercise-induced R-wave amplitude change (delta R) and peak R time (time from the onset of QRS to the peak of R wave), were calculated for each lead. The maximal delta R of 87 leads was designated as the max delta R. After exercise, regional delay of peak R time (greater than or equal to 10 msec) on the chest was observed in 13 patients. These patients had significantly higher max delta R than those without such regional peak R time delay (0.71 +/- 0.31mV vs. 0.33 +/- 0.20mV, p less than 0.01). In each case, the site of peak R time delay was almost the same as the site of max delta R. There was no significant difference in the peak heart rate, rise of the systolic blood pressure (delta BPs) during exercise or extent of ischemic ST depression between patients with and without peak R time delay. We concluded that ventricular condition delay plays an important role in the increase of R-wave amplitude after exercise in patients with effort angina pectoris.

R-wave amplitude changes during exercise stress testing: patients with dilative cardiomyopathy compared to patients with coronary artery disease

R-wave amplitude (RWA) depends to a large extent on the left ventricular filling volume. Changes of RWA are attributed to the Brody-effect. Exercise has been shown to induce a decrease of RWA in a healthy population and an increase in patients with coronary artery disease (CAD). No clear data exist for cardiomyopathy (CMP). Controls (n = 12), patients with CMP (n = 32) and CAD (n = 58) were compared. Alterations of RWA (Wilson lead V5) were correlated with parameters of a bicycle exercise test including resting and exercise hemodynamics and parameters of LV-function including EF, LVEDV and LVEDP. CMP compared to CAD had smaller RWA at rest (0.78 +/- 0.47 vs 1.32 +/- 0.72 mV, P less than 0.01). During comparable levels of exercise CMP (EF 35 +/- 14%) showed no significant changes of RWA. CAD (EF 57 +/- 16%) presented an increase of RWA by +0.11 +/- 0.23 mV (P less than 0.01), while controls showed a straight decline of RWA (-0.31 +/- 0.24 mV). In patients with CAD delta RWA (RWA max exercise - RWA rest) was a more sensitive parameter for detection of disease (assuming delta RWA greater than or equal to +0.1 mV, 36/58 patients) than maximal ST-segment changes (ST-segment-depression in lead V5 greater than or equal to 0.2 mV at 0.08 sec after J-point, 22/58 patients). Precordial leads V2, V4, V5 and V6 showed similar changes. This paper supports the theory that changes of wall thickness or changes in the amount of air respective to the amount of fluid in the lungs are responsible for RWA changes. These changes are clearly dependent on the severity of the disease and on left ventricular function. Therefore measurement of RWA changes during exercise may offer additional information in patients with CAD as well as in patients with CMP.

R wave of the surface and intracoronary electrogram during acute coronary artery occlusion

Increases in electrocardiographic R-wave amplitude in humans have been described with positive and negative dynamic exercise test findings, episodes of variant angina and myocardial ischemia and infarction. The role of factors other than acute reversible ischemia in the genesis of these R-wave size alterations is unclear. To evaluate the contribution of acute ischemia to changes in R-wave size in the absence of other confounding variables, electrocardiograms were recorded before and during coronary angioplasty balloon inflation. The frontal leads and V1, V2, V5 and V6 were recorded during the last 10 seconds of coronary occlusion in 20 patients and intracoronary epicardial electrograms were recorded continuously during balloon inflation in 10 patients. Inflations were 8 +/- 2 atm for 52 +/- 36 seconds. Chest pain occurred in 26 of 30 patients with balloon inflation and ST elevation occurred in 22. No significant increases in R amplitude were noted in any lead or in the sum of the R waves in all leads, including intracoronary electrograms. In contrast, R amplitude tended to decrease. The initial decrease in both surface and epicardial R amplitude was similar to the first of the biphasic changes observed in animal models. An increase in R-wave amplitude is not by itself always a marker for myocardial ischemia, but depends on severity and duration of the process.

Exercise electrocardiographic variables: a critical appraisal

To compare four recently proposed methods of analyzing the exercise electrocardiogram with the conventional analysis of ST segment depression, 303 consecutive patients without myocardial infarction who had been referred for coronary arteriography underwent stress electrocardiography and stress thallium imaging. The specificity for the prediction of a greater than 50% coronary obstruction of 0.5, 1.0, 1.5 and 2.0 mm ST segment depression measured in the conventional way was 0.59, 0.73, 0.88 and 0.94, respectively. The specificity of a thallium perfusion defect was 0.79. Sensitivities of the conventional ST depressions, thallium defect, the change in the sum of the R amplitudes and the slope adjusted for heart rate increase were calculated and compared at the cited levels of specificity. R wave changes had a significantly lower sensitivity than did the conventionally analyzed ST depression at each level of specificity. Slope-adjusted ST depression had a slightly higher sensitivity than that of conventional ST depression only at a specificity of 0.73 (0.68 versus 0.65, p = 0.07). R wave-adjusted ST depression was significantly more sensitive than conventional ST depression only at a specificity of 0.94 (0.45 versus 0.36, p = 0.01). Heart rate-adjusted ST depression was more sensitive than conventional ST depression at all of the specificities except 0.59. This pattern of superior accuracy of heart rate-adjusted ST depressions was preserved for the prediction of multivessel coronary disease. Heart rate adjustment is a simpler and more accurate modification of the conventional electrocardiographic analysis than are the other three methods studied.

Effort angina pectoris without electrocardiographic changes in coronary disease patients: correlations between scintigraphic and coronary angiographic findings

The absence of electrocardiographic changes during angina is an unusual occurrence. In 15 male patients with exercise-induced angina, the electrocardiogram failed to show the usual ischemic ST-T changes. The exercise thallium-201 myocardial imaging was employed as indicator of the ischemia and the results were correlated with coronary angiographic findings. The exercise thallium-201 myocardial imaging showed an exercise-induced reversible defect in 14 patients and a fixed defect in the remaining 1. Out of 15 patients, 13 had defects involving the infero-apical, posterior and postero-lateral segments. The coronary angiography, performed in all patients but 2, showed single-vessel coronary artery disease in 8 patients and double-vessel disease in 5. A significant circumflex or right coronary artery stenosis was found in all cases except 1; 2 patients had a coexistent left anterior descending coronary artery stenosis and 1 an isolated stenosis of this vessel. It is concluded that the myocardial scintigraphy is useful to assess the ischemic myocardial origin of chest pain in the absence of ST-T changes. The silence of the electrocardiogram might be due to the production of ischemia in not well explored areas, such as the inferior and posterior myocardial segments, and possibly to a smaller extension of ischemia.

Relation of electrocardiographic R-wave amplitude to changes in left ventricular chamber size and position in normal subjects

Although exercise-induced changes in electrocardiographic R-wave amplitude have been ascribed to changes in left ventricular (LV) size, QRS axis, heart rate and ischemia, the physiologic mechanism remains unclear. To clarify the relation between R-wave amplitude and changes in LV size and position, simultaneous 9-lead electrocardiograms and targeted M-mode echocardiograms were recorded from 15 normal subjects. Recordings were made at rest, during Valsalva maneuver and during methoxamine infusion. LV diastolic dimension increased with methoxamine and decreased with Valsalva maneuver (p less than 0.001). R-wave amplitude in leads V5 and V6 varied directly with LV dimensions (p less than 0.001). The correlation coefficient between the change in R-wave amplitude in V5 or V6 and the change in LV dimension was 0.81 (p less than 0.01). No significant changes in R-wave amplitude were seen in electrocardiographic leads I, II, III, aVR, aVL, aVF or V1. Distance from the chest wall to the LV posterior wall correlated with change in R-wave amplitude (r = 0.79, p less than 0.001). Change from supine to left lateral position moved the left ventricle closer to the lateral chest wall in association with a 41 +/- 8% increase in R-wave amplitude in V5 and V6 (p less than 0.001). In conclusion, there is a direct and a dynamic relation between R-wave amplitude and LV chamber size. Chamber size and distance from the left ventricle to leads V5 or V6 interact as major determinants of R-wave amplitude.