Transient appearance of Q waves in coronary disease during exercise electrocardiography: consideration of mechanisms and clinical importance

Transient abnormal Q waves during exercise electrocardiography

Myocardial ischaemia during exercise electrocardiography is usually manifested by ST segment depression or elevation. Transient abnormal Q waves are rare, as Q waves indicate an old myocardial infarction. The case of a patient with exercise induced transient abnormal Q waves is reported. The potential mechanisms involved in the development of such an abnormality and its clinical implications are discussed.

Q wave and Non-Q wave myocardial infarction after thrombolysis

OBJECTIVES

We studied the clinical outcome of Q wave and non-Q wave infarction after thrombolytic therapy.

BACKGROUND

Controversy exists over the clinical significance of Q waves after thrombolysis.

METHODS

We studied postthrombolytic angiographic results and short- and long-term clinical outcome in 150 patients with acute myocardial infarction classified as Q wave and non-Q wave on the 24-h and discharge electrocardiograms (ECGs). The results from the two groups were then compared.

RESULTS

Eighty percent of patients had a Q wave and 20% a non-Q wave infarction on the 24-h ECG. The latter patients had lower peak creatine kinase (CK) levels (p < 0.001), but the two groups did not differ significantly otherwise. In 18 patients with a Q wave infarction on the 24-h ECG, pathologic Q waves disappeared. However, in seven patients with a non-Q wave infarction on the 24-h ECG, pathologic Q waves appeared throughout the hospital period. Q wave regression was associated with lower peak CK levels (p < 0.001) and an improvement in left ventricular ejection fraction (p < 0.01). Thus, only 72% of patients had a Q wave and 28% a non-Q wave infarction on the discharge ECG. Patients with a non-Q wave infarction on the discharge ECG had higher patency of the infarct-related artery (p < 0.04), lower mean peak CK levels (p < 0.0001), a higher ejection fraction (p = 0.001) and a lower incidence of heart failure (p = 0.06) than patients with a Q wave infarction on the discharge ECG. Although the 2-year incidence of reinfarction and revascularization was higher in patients with a non-Q wave infarction on the discharge ECG (p < 0.05), 2-year mortality was lower (p = 0.08).

CONCLUSIONS

Although the early postthrombolytic distinction between Q wave and non-Q wave infarction conveys no significant information, during the hospital period, non-Q wave infarction is associated with a smaller infarct area, improved left ventricular function and lower mortality.

Transient "pathological" Q-waves occurring during exercise testing: assessment of their clinical significance in a presentation of a series of patients

Exercise-induced Q-waves were encountered in four Caucasian males presenting to the Cardiac Clinic, Tygerberg Hospital, with chest pain suggestive of angina pectoris. This phenomenon occurred in four out of a total of 1943 patients undergoing treadmill stress testing (Bruce Protocol) during a two-year period, giving an incidence of 0.21 percent of this ECG response. Two of the four patients (cases 1 and 2) were documented to have coronary atherosclerosis by selective coronary arteriography. One of these patients may well have been experiencing coronary vasospasm. One of the remaining two patients was a teenager whose exercise response was probably normal, whilst the last patient could have had ischemic heart disease (IHD). This most interesting and rare response to exercise (stress) testing is discussed, emphasis being placed on its incidence, mechanism and clinical significance in IHD and other conditions in clinical practice. Awareness of the occasional transient nature of "pathological" Q-waves, whether these occur at rest or during exercise, has an important bearing on such acute therapeutic interventions as intracoronary thrombolysis and percutaneous transluminal coronary angioplasty.

Transient Q waves followed by left anterior fascicular block during exercise

A 45 year old white man developed transient abnormal Q waves and ST segment elevation preceding left anterior fascicular block during exercise stress testing. The simultaneous disappearance of Q waves and fascicular block suggested that the abnormal Q waves were determined by an early septal conduction defect.

Myocardial infarction and thrombolysis. Electrocardiographic short term and long term results using precordial mapping

In a consecutive series of 56 patients with acute myocardial infarction, ST segment depression and elevation in the electrocardiographic limb leads I, II, and III were summated for each patient before and immediately after intracoronary streptokinase infusion and the results compared with the angiographic findings. Forty three patients had angiographically confirmed reperfusion of an initially occluded vessel and showed a significant decrease in summated ST shift. The ST segment changes in the limb leads virtually returned to normal in all 43 patients, and in most, inverted T waves developed. Thrombolysis was unsuccessful in 10 patients, and the infarct related coronary artery was already patent in three. When these two groups are combined, all 13 patients without reperfusion showed no significant change in summated ST segment shift. During percutaneous transluminal angioplasty inflation of the balloon in the vessel that was previously occluded simulated reocclusion and was followed by new ST elevation if the artery supplied viable myocardium. In a further consecutive study of 54 patients with anterior myocardial infarction, the precordial R waves and Q waves were studied over the four to six months following infarction using a standardised 48 electrode mapping system. All patients underwent a repeat angiogram after four to six months. In 36 patients the infarct related vessel was patent. They showed a significant mean increase in summated precordial R wave amplitude and a reduction in the mean number of precordial leads without R waves. In 18 patients with unsuccessful thrombolysis or reocclusion there was a further reduction in mean summated R wave amplitude and an increased number of precordial leads not showing R waves. Precordial R wave mapping seems to be a valuable non-invasive method of assessing the salvage of myocardium after reperfusion and the damage caused by reocclusion. Loss of R waves in the acute phase of myocardial infarction does not necessarily mean an irreversibly damaged myocardium.

Electrocardiographic changes after streptokinase-induced recanalization in patients with acute left anterior descending artery obstruction

ECG changes were assessed in 15 patients in whom intracoronary streptokinase recanalized a totally occluded left anterior descending artery during acute myocardial infarction. These results were compared retrospectively with those in 22 comparable conventionally treated patients who underwent catheterization during the acute stage of infarction. Before angiography no significant differences were found in the sum of ST elevation (sigma ST increase V1-V6), the sum of R waves (sigma RV1-V6), or the number of Q waves (nQV1-V6) in leads V1 through V6. sigma ST increase V1-V6 was significantly lower in the streptokinase group than in control patients at all times after angiography. sigma RV1-V6 declined and nQV1-V6 increased in both groups during the first 12 hr, but there was no further change in the control group, whereas in the streptokinase group a significant increase in sigma RV1-V6 and decrease in nQV1-V6 followed. There was a significant correlation between long-term electrocardiographic (sigma RV1-V6; nQV1-V6) and angiographic findings (ejection fraction, akinetic segment length). Thus, the Q wave regression and increase in sigma RV1-V6 after streptokinase suggest, in accordance with angiographic findings, that jeopardized myocardium was salvaged by reperfusion.