Transient alterations of the QRS complex and ST segment during percutaneous transluminal balloon angioplasty of the right and left circumflex coronary arteries

Right ventricle injury in RCA occlusion: Exploration using precordial bipolar leads and surrogate vectorcardiograms

BACKGROUND

Precordial Bipolar Leads (PBL) provide new electrocardiographic information derived from standard 12‑lead ECG recordings.

OBJECTIVES

To explore the usefulness of PBL in patients with acute right coronary artery (RCA) occlusion.

METHODS

Sixteen patients undergoing elective percutaneous transluminal coronary angioplasty (PTCA) were studied before and after RCA occlusion and their data were processed with new methods based on PBL.

RESULTS

The findings were: 1. In PBL V2-V1, strong systolic currents of injury moving in the left to right direction coexist with those directed towards leads II, III and aVF. 2. Changes in the time of the peaks of the QRS waves do not alter the duration of the QRS. 3. The QRS loops of the surrogate VCG generated show that, during ischemia, the time changes in the peak of the QRS waves displayed in one axis are the consequence of an increase in the amplitude of the waves observed in the perpendicular axis. 4. The use of two simultaneous dimensions (transverse and frontal planes) facilitates the location of the J-point. 5. In the surrogate VCGs of this group of patients, J-point and ST segment shifts produced an image that reminded the Greek letter omega (Ω). 6. The QRS wave changes, in time and amplitude, explained the rotational changes and the ischemic distortions of the surrogate VCG loops.

CONCLUSIONS

Computerized processing of ECG data appears to provide new and valuable diagnostic data in patients with acute RCA occlusion. The loops revealed important information related to systolic currents of injury. Because these methods use routine 12‑lead ECG data, the procedure is based only in software applications.

Apparent electrocardiogram left ventricular hypertrophy during tachycardia

The electrocardiographic transient display of left ventricular hypertrophy (LVH), during rapid heart rates, in the setting of sinus/supraventricular tachycardias and atrial fibrillation, is illustrated via 3 case reports. This common occurrence is expressed by an increase in the S-waves in leads V2-V5, during tachycardias, rendering a false positive diagnosis of LVH by the frequently employed Cornell voltage LVH criteria. This tachycardia-mediated apparent LVH, is unrelated to the occasionally encountered stable, and unrelated to tachycardia, "false positive diagnosis of LVH", which could in reality occasionally reflect altered electrical properties of myocardium that could create a functional substrate for developing arrhythmias. The importance of awareness of this insight by all health professionals is immeasurable, considering that a false positive diagnosis of LVH has major consequences in the management, prognostication, resort to expensive unnecessary testing, and stress to the patients and their families.

Attenuation of ST-segment elevation after ischemic conditioning maneuvers reflects cardioprotection online

Ischemic conditioning maneuvers, when induced either locally in the heart or remotely from the heart, reduce infarct size. However, infarct size reduction can be assessed no earlier than hours after established reperfusion. ST-segment elevation and its attenuation might reflect cardioprotection by ischemic conditioning online. Pigs were subjected to regional myocardial ischemia/reperfusion (1 h/3 h). Ischemic conditioning was induced prior to ischemia either locally (preconditioning; IPC; n = 15) or remotely (remote preconditioning; RIPC; n = 21), remotely during ischemia (remote perconditioning; RPER; n = 18), or locally at reperfusion (postconditioning; POCO; n = 9). Pigs without conditioning served as controls (PLA; n = 29). Area at risk and infarct size were measured postmortem, and ST-segment elevation was analyzed in a V2-like electrocardiogram lead. Ischemic conditioning reduced infarct size (PLA 42 ± 11% of area at risk; IPC 18 ± 10%; RIPC 22 ± 12%; RPER 23 ± 12%, POCO 22 ± 11%). With PLA, ST-segment elevation was increased at 5 min ischemia, sustained until 55 min ischemia and further increased at 10 min reperfusion. IPC and RIPC did not impact on ST-segment elevation at 5 min ischemia, but attenuated ST-segment elevation at 55 min ischemia. With RPER, ST-segment elevation was not different from that with PLA at 5 min, but attenuated at 55 min ischemia. POCO abolished the further increase of ST-segment elevation with reperfusion. Cardioprotection by ischemic conditioning is robustly reflected by attenuation of ST-segment elevation online.

The 4th Report of the Working Group on ECG diagnosis of Left Ventricular Hypertrophy

The 4th Report provides a brief review of publications focused on the electrocardiographic diagnosis of left ventricular hypertrophy published during the period of 2010 to 2016 by the members of the Working Group on ECG diagnosis of Left Ventricular Hypertrophy. The Working Group recommended that ECG research and clinical attention be redirected from the estimation of LVM to the identification of electrical remodeling, to better understanding the sequence of events connecting electrical remodeling to outcomes. The need for a re-definition of terms and for a new paradigm is also stressed.

A Simple Numerical Body Surface Mapping Parameter Signifies Successful Percutaneous Coronary Artery Intervention

BACKGROUND

In coronary artery disease (CAD), body surface potential mapping (BSPM) may reveal minor electrical potential changes appearing in the depolarization phase even if pathological changes are absent on the conventional 12-lead ECG. We hypothesized that a simple BSPM parameter, Max/Min signifies successful percutaneous coronary intervention (PCI).

METHODS

Ninety-two adult Caucasian patients with stable CAD and positive exercise test underwent coronary angiography. Seventy patients (age, 59 ± 8; 46 males) were revascularized by PCI (left anterior descending [LAD] in 38, right [RCA] in 17 and left circumflex [LCX] coronary artery in 15). Control groups contained 22 patients (age, 60 ± 8; 14 males) without intervention and 35 healthy subjects (age, 58 ± 2; 15 males). Left ventricular ejection fraction (LVEF, transthoracic echocardiography) and Max/Min BSPM parameter (63-lead Montreal system) were evaluated before and 4-40 days following coronary angiography. Max/Min was defined by the ratio of the highest maximum to the deepest minimum potential of all leads recorded by BSPM.

RESULTS

Before PCI, Max/Min value of patients with LAD lesion (0.83 [0.74; 0.93]) was significantly lower while that with RCA lesion (1.63 [1.35; 1.99]) was significantly higher than that of healthy group (1.01 [0.970; 1.13]) (P < 0.05) and LVEF was significantly lower in LAD lesion (46.50% [43.00; 51.00]) than in the healthy group (55.00% [50.00; 58.75]) (P < 0.01). Max/Min value significantly increased from 0.83 [0.74; 0.93] to 0.92 [0.82; 0.99] (P < 0.01) following LAD PCI while significantly decreased from 1.63 [1.35; 1.98] to 1.35 [1.21; 1.43] (P < 0.01) post-RCA PCI. It did not vary significantly, however, either following LCX PCI or without intervention. LVEF significantly increased (from 46.50% [43.00; 51.00] to 49.00% [46.00; 51.00]) only after LAD PCI.

CONCLUSION

Max/Min parameter is suitable to follow patients after LAD and RCA PCI.

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.

Discriminating Between Right Coronary Artery and Circumflex Artery Occlusion by Using a Noninvasive 18-Lead Electrocardiogram

• Background Differentiating occlusion of the circumflex branch of the left coronary artery (also called the circumflex artery) from occlusion of the right coronary artery is often difficult because either may be associated with a pattern of acute inferior myocardial infarction on the electrocardiogram.

• Objectives To determine if an inexpensive 18-lead electrocardiogram can provide useful information in differentiating sites of coronary occlusion.

• Methods Continuous 18-lead electrocardiograms, including standard 12-lead, right ventricular, and posterior leads, were recorded in 38 and 50 subjects undergoing percutaneous coronary interventions in the right coronary artery and the circumflex artery, respectively.

• ResultsST-segment elevation in the posterior leads was twice as frequent during occlusion of the circumflex artery as during right coronary occlusion (P &lt; .001). ST-segment elevation in the right ventricular leads and inferior leads occurred more often during occlusion of the right coronary artery than during occlusion of the circumflex artery. ST-segment depression in lead aVL is highly suggestive of right coronary occlusion, whereas ST-segment elevation in posterior leads without depression of the ST segment in lead aVL is highly sensitive and specific for occlusion of the circumflex artery.

• Conclusions ST-segment changes in the 18-lead electrocardiogram can be used to differentiate between occlusions of the circumflex artery and occlusions of the right coronary artery. Knowing which vessel is occluded before percutaneous coronary intervention can help in planning the procedure and recognizing when patients are at high risk for disturbances in conduction at the atrioventricular node.

Real-Time Detection and Alerting for Acute ST-Segment Elevation Myocardial Ischemia Using an Implantable, High-Fidelity, Intracardiac Electrogram Monitoring System With Long-Range Telemetry in an Ambulatory Porcine Model

OBJECTIVES

The purpose of this study was to evaluate feasibility of using real-time, high-fidelity, intracardiac electrogram monitoring from a permanently implantable ischemia detection system (IIDS), with long-range telemetry capability to detect ST-segment shifts associated with acute or subacute coronary occlusion in a porcine model.

BACKGROUND

Early identification of coronary occlusion with ST-segment elevation could profoundly accelerate the timing of revascularization and improve clinical outcomes.

METHODS

This paper reports the first investigation using real-time, high-fidelity, intracardiac electrogram monitoring from a permanently IIDS, with long-range telemetry capability. This IIDS was tested in an ambulatory porcine model, with acute coronary occlusion precipitated by stent thrombosis. Two overlapping copper stents were implanted in the left anterior descending (n = 3), the circumflex (n = 3), or the right coronary artery (n = 2) of juvenile farm pigs. Monitoring was carried using telemetry from the IIDS.

RESULTS

All stented pigs had acute ST-segment elevation event(s) triggering the alerting thresholds of the IIDS. All triggered events were confirmed to be caused by thrombosis of the copper stent(s), and well correlated to infarct age and location. Four of the 8 pigs died from ventricular fibrillation, recorded by the IIDS at a mean time of 70 +/- 121 h after ST-segment alert. The sensitivity and specificity of alerting for ST-segment shift, associated with thrombotic coronary occlusion, were 100% and 100%, respectively.

CONCLUSIONS

This study demonstrates the ability of an implantable ischemia detection system to detect ST-segment elevation from coronary occlusion in a porcine model of ST-segment elevation myocardial infarction. ST-segment elevation was sufficient to trigger alerting thresholds in all 3 epicardial coronary distributions. Such a system, with real-time alerting capability, could advance the time frame of reperfusion therapy and potentially prevent, rather than interrupt, acute myocardial infarction in patients with coronary artery disease.

Transient giant R-wave, right axis deviation, and intraventricular conduction delay during exercise treadmill testing: a case report

A 53 year old man complained of chest pain during an exercise treadmill test. Electrocardiogram revealed transient giant R-wave, right-axis deviation, intraventricular conduction delay, and ST-segment elevation in the inferolateral leads. Subsequent coronary angiography showed an 80% lesion in mid part of a nondominant left circumflex artery, whereas the other coronary arteries had mild atherosclerosis only. Percutaneous coronary intervention and stenting was performed on the left circumflex artery lesion. A follow-up exercise thallium scan 3 months later still showed an intermediate-sized, mild reversible perfusion defect in the inferior and lateral wall but the giant R-wave ECG pattern was not inducible anymore. Restudy coronary angiography showed no in-stent restenosis, but there was disease progression in the midpart of the right coronary artery. The initial electrocardiographic pattern is typical of the "giant R-wave syndrome." Severe coronary spasm superimposed on the underlying mild atherosclerotic lesion of the right coronary artery is hypothesized to be the cause of the initial event. Ad hoc direct stenting was performed on the right coronary artery lesion. The patient remained symptom-free with a normal thallium scan 9 months later.

Exercise-triggered transient R-wave enhancement and ST-segment elevation in II, III, and aVF ECG leads: a testament to the “Plasticity” of the QRS complex during ischemia

We describe a patient with coronary artery disease who showed transiently augmented R-waves in his electrocardiogram (ECG) during the course of an exercise treadmill test (ETT), an ECG pattern occasionally associated with the hyperacute phase of myocardial infarction and variant angina. This change in the R-waves was noted in II, III, and aVF ECG leads and was associated with ST-segment elevation; both changed gradually and were normalized during the recovery period. Cardiac enzymes after ETT were negative, and arteriography revealed 3-vessel coronary artery disease, with a completely occluded right coronary artery. The ventriculogram showed very mild hypokinesis of the inferior left ventricular wall, while the global ejection fraction was 75%. These ECG changes, noted previously during ETT in precordial ECG leads, are herein reported to occur also in II, III, and aVF ECG leads. The generation of these ECG changes, which hinges upon a late unopposed depolarization occurring in the course and at the site of severe ischemic injury, constitutes a transient focal ventricular conduction abnormality.

Electrocardiographic diagnosis of the coronary artery culprit site in ischemic heart disease

The diagnostic accuracy of using electrocardiographic findings to identify affected vessels in cases of myocardial infarction and angina pectoris treated by percutaneous transluminal coronary angioplasty was assessed. From the anterior wall leads, ST segment elevation in leads I and aV(L) showed diagnostic accuracy (sensitivity, specificity and positive predictive value) in identifying proximal lesions of the left anterior descending coronary artery of 89%, 58% and 62%, and the diagnostic accuracy of the QS wave in V(1) was 62%, 83% and 72%, respectively. For the posterior wall leads, the corresponding values for the diagnosis of affected vessels based on R/S>1 in V(1) for the left circumflex coronary artery were 50%, 89% and 60%, respectively. The inferior wall leads with ST segment elevation in leads II, III and aV(F), and ST segment depression in aV(L), showed diagnostic accuracy for the right coronary artery of 90%, 90% and 92%, respectively. Bifurcation of the first diagonal branch, dominance of the posterior descending branch, the normal subtypes of the coronary artery and the occurrence of spontaneous recanalization may have influenced the accuracy of diagnosis. Adding a high lateral wall lead one intercostal space above V(4) and a posterior wall lead located one intercostal space below V(6) appeared to increase the diagnostic accuracy of detecting the coronary artery lesions responsible for myocardial ischemia.

Giant R-waves in a patient with an acute inferior myocardial infarction

We describe a case of a male patient with "giant" R-waves (GRWs) in association with an acute inferior myocardial infarction (MI). Such electrocardiogram (ECG) pattern has been associated heretofore with the hyperacute phase of an anterior MI, and unstable, and variant angina, although it is found in illustrations of many previous publications in conjunction with inferior MI. The GRWs, along with ST-segment elevations, were noted transiently in the inferior ECG leads, early in the clinical course of our patient. Subsequent evolution of the ECG revealed classic appearances for an inferior MI. Cardiac enzymes, and thallium-201 myocardial perfusion scintigraphy revealed evidence for inferiorly-located myocardial necrosis. Coronary arteriography showed stenosis of the right coronary artery, for which the patient underwent an uneventful angioplasty and "stenting" of the culprit vessel. The pathophysiology of the syndrome of GRWs is briefly discussed.

Use of intracoronary electrocardiography for detecting ST-T, QTc, and U wave changes during coronary balloon angioplasty

Intracoronary electrocardiography (IC-ECG) is a more sensitive method than surface ECG to detect electrical changes during percutaneous transluminal coronary angioplasty (PTCA). It also provides direct monitoring of ST-T segment, QTc intervals, and U-wave genesis during balloon inflation. These changes are reflective of myocardial ischemia. The authors studied the effect of transient myocardial ischemia on ST-T segment, QTc intervals, and U-wave appearance by comparing standard and perfusion balloon angioplasty. PTCA of left anterior descending artery was performed in 14 patients using the standard balloons and in 11 patients using the perfusion balloons. Patients with perfusion balloon angioplasty had less ST-T elevation (0.15 +/- 0.05 mV versus 1.04 +/- 0.19 mV, P < 0.001), less QTc-shortening intervals (0.01 +/- 0.02 seconds versus -0.05 +/- 0.04 seconds, P < 0.001), and less positive U waves (two versus nine). The authors concluded that balloon angioplasty with perfusion balloons is associated with less ischemia as reflected by ST-T, QTc-shortening intervals, and U-wave changes. There was more positive U-wave appearance with the standard balloon angioplasty, which implies more ischemia. In addition, QTc-shortening intervals are associated with the development of U waves during standard balloon angioplasty. These findings suggest that IC-ECG is a sensitive tool in detecting myocardial ischemia. IC-ECG may also help to clarify the nature of chest pain during PTCA in some patients. Like QT dispersion (QTd), QTc-shortening intervals and new U waves can have prognostic implications and additional studies are needed to define this role.

Changes in high-frequency QRS components are more sensitive than ST-segment deviation for detecting acute coronary artery occlusion

OBJECTIVES

This study describes changes in high-frequency QRS components (HF-QRS) during percutaneous transluminal coronary angioplasty (PTCA) and compares the ability of these changes in HF-QRS and ST-segment deviation in the standard 12-lead electrocardiogram (ECG) to detect acute coronary artery occlusion.

BACKGROUND

Previous studies have shown decreased HF-QRS in the frequency range of 150-250 Hz during acute myocardial ischemia. It would be important to know whether the high-frequency analysis could add information to that available from the ST segments in the standard ECG.

METHODS

The study population consisted of 52 patients undergoing prolonged balloon occlusion during PTCA. Signal-averaged electrocardiograms (SAECG) were recorded prior to and during the balloon inflation. The HF-QRS were determined within a bandwidth of 150-250 Hz in the preinflation and inflation SAECGs. The ST-segment deviation during inflation was determined in the standard frequency range.

RESULTS

The sensitivity for detecting acute coronary artery occlusion was 88% using the high-frequency method. In 71% of the patients there was ST elevation during inflation. If both ST elevation and depression were considered, the sensitivity was 79%. The sensitivity was significantly higher using the high-frequency method, p<0.002, compared with the assessment of ST elevation.

CONCLUSIONS

Acute coronary artery occlusion is detected with higher sensitivity using high-frequency QRS analysis compared with conventional assessment of ST segments. This result suggests that analysis of HF-QRS could provide an adjunctive tool with high sensitivity for detecting acute myocardial ischemia.

Electrocardiographic changes during prolonged coronary artery occlusion in man: comparison of standard and high-frequency recordings

Detection of acute myocardial ischaemia using electrocardiographic methods is generally based on assessment of the ST segments in the standard 12-lead electrocardiogram (ECG). Several studies have also shown changes in high-frequency QRS components during acute ischaemia. The purpose of the present study was to determine the changes in high-frequency QRS components during prolonged percutaneous transluminal coronary angioplasty (PTCA) and to compare these changes with ST-segment deviations in the standard 12-lead ECG. The study population consisted of 19 patients receiving prolonged PTCA. Standard and high-resolution signal-averaged ECGs were recorded before and during balloon inflation. The high-resolution recordings were performed using bipolar X, Y and Z leads. The QRS complexes in the high-resolution signal-averaged ECGs were analysed within a bandwidth of 150-250 Hz. During inflation, significant reductions in high-frequency QRS components were observed (12-72%). Changes in the high-frequency QRS components were seen in four of the patients without ST-segments deviation in the standard ECG. The correlation between the ST-segment deviation and the reduction in high-frequency QRS components was weak (r = 0.27). Acute coronary artery occlusion produces changes in high-frequency QRS components, even in the absence of ST-segment deviation in the standard ECG. Further studies need to be carried out to evaluate whether analysis of high-frequency QRS components could provide a method for detecting myocardial ischaemia and give additional information to that available in the ST segment in the standard ECG.

QRS changes during percutaneous transluminal coronary angioplasty and their possible mechanisms

OBJECTIVES

The purpose of the study was to describe the configuration, and investigate the mechanisms, of QRS changes occurring during percutaneous transluminal coronary angioplasty (PTCA).

BACKGROUND

QRS changes during PTCA have been attributed to both a passive ST segment shift and conduction disturbances (peri-ischemic block). The direct relation between ST segment shift and QRS changes, however, has not been established, and the definition of conduction disturbances remains to be clarified.

METHODS

Twelve-lead electrocardiograms (ECGs) were recorded before PTCA, at the end of 2 min of PTCA and after return to baseline values in 29 patients (left anterior descending coronary artery [LAD] in 13 patients, right coronary artery [RCA] in 14 and left circumflex coronary artery in 2). Electrocardiographic complexes before and during PTCA were superimposed to determine the amplitudes of initial, terminal and total QRS deflection; the relations of QRS changes to baseline (TP segment) and ST segment shift; and the duration of QRS and corrected QT intervals. RESULTS. 1) The direction of the initial QRS deflection was unchanged, but changes of its amplitude occurred. 2) Terminal QRS deflection changed in all patients with a ST segment shift > 17% of the R amplitude, and the correlation between the decrease in the S amplitude and ST segment shift was significant (r = 0.9, p < 0.01) in patients with LAD PTCA. Correlation between changes in total QRS amplitude and ST segment shift in patients with RCA PTCA was weaker (r = 0.54, p = 0.056). 3) Transient conduction disturbance manifested by QRS widening in selected leads occurred in 2 of 29 patients. CONCLUSIONS. 1) Changes in terminal QRS deflection during PTCA are proportional to the magnitude of the ST segment shift. 2) Conduction disturbances manifested by increased QRS duration occurred infrequently. We suggest that the term peri-ischemic block be applied only to changes in QRS configuration associated with QRS widening.

QRST changes during and after percutaneous transluminal coronary angioplasty

This study reports preliminary results on 45 patients who underwent percutaneous transluminal coronary angioplasty (PTCA); 120-lead data (including the 12-lead standard electrocardiogram [ECG]) were recorded before, during, and after balloon inflation. Twenty-one patients underwent PTCA for left anterior descending coronary disease, 13 for right coronary artery disease, and 10 for left circumflex; 1 patient had combined left anterior descending and right coronary artery disease. In each patient, voltage data recorded during the various phases of the procedure were compared with the patient's own baseline data. In 18 patients, 120 leads were also recorded 24 hours after PTCA. In this study, the usefulness of the standard 12-lead ECG was investigated in locating the coronary artery being occluded, in elucidating the mechanisms of the QRS changes, and in identifying changes occurring 24 hours after completion of the procedure. Results indicate that the observation of ST elevation in the 12-lead ECG may lead to ambiguous interpretation. Also, limiting observation to ST-T patterns alone instead of including QRS changes further hampers correct identification of the involved vessel. QRS modifications during inflation are interpreted as conduction disturbances, although other mechanisms are evoked: study of surface maps may contribute to the understanding of these mechanisms. Changes present 24 hours later are visible in the standard leads, but again, in the absence of the thoracic potential distribution, these are difficult to interpret. These changes were different from those observed after cessation of inflation at the end of the procedure. It is hypothesized that next-day changes may reflect reperfusion injury and/or represent myocardial stunning. Presence of injury and reversibility of changes require further investigation. Also, biochemical markers such as creatine kinase-MB mass, creatine kinase-MB activity, myoglobin, and troponin-T may help elucidate the significance of these findings.

The "giant R waves" ECG pattern of hyperacute phase of myocardial infarction. A case report

The author describes a rarely appreciated electrocardiographic (ECG) pattern of the hyperacute phase of myocardial infarction, characterized by the transient development of very tall R waves merging with maximally elevated ST-segments, and the reduction of the depth, or complete disappearance of S waves. Similar ECG findings are frequently recorded in epicardial and precordial tracings in the animal laboratory, immediately following experimental occlusion of a coronary artery. In patients with acute myocardial infarction, the "giant R waves" ECG pattern is seen very early in the clinical course. Often the ECG appearances described above are missed either because patients suffering a myocardial infarction do not present to the hospital shortly after the inception of symptoms, or are attributed to conduction abnormalities of the classic variety or to ventricular tachycardia. The incidence of the giant R waves ECG pattern in the setting of clinical acute myocardial infarction is not known. Also its pathophysiologic, clinical, and prognostic correlates remain to be defined by appropriately designed research protocols.

QT interval shortening and ST elevation in intracoronary ECG during PTCA

Percutaneous transluminal coronary angioplasty (PTCA) can provide a unique model of transient and reversible myocardial ischemia. The aim of this study was to assess the serial changes in QT interval during elective PTCA-induced transient ischemia. The serial changes in QT interval before, during, and after PTCA of the left anterior descending artery (LAD) were measured in patients who showed ST elevation in intracoronary electrocardiogram. Twelve consecutive patients who showed ST-segment elevation during PTCA-induced ischemia anterior precordial leads of the electrocardiogram (ECG) were enrolled in the present study. Target lesions for PTCA were all in the LAD. There were six patients with angina pectoris, two with non-Q-wave infarction, and four with Q-wave myocardial infarction. During balloon inflation, QTc interval shortened in both intracoronary ECG (ic-ECG) (0.472 +/- 0.013 vs 0.436 +/- 0.014) and surface ECG (0.462 +/- 0.012 vs 0.438 +/- 0.011). However, a significant shortening of the QT interval was more rapidly observed in the ic-ECG (20 s) than in the surface ECG (40 s). We conclude that the QT interval in both ic-ECG and surface ECG becomes shortened in PTCA-induced myocardial ischemia, and that the ic-ECG might be a good probe for detecting survived viable myocardium in the infarcted zone.

Differentiation between left circumflex and right coronary artery occlusions: studies on ST-segment deviation during percutaneous transluminal coronary angioplasty

To distinguish between acute occlusion of the right coronary artery (RCA) and the left circumflex artery (LCx) by electrocardiography, we studied ST-segment deviation during balloon inflation in percutaneous transluminal angioplasty. The composite electrocardiographic criteria based on ST-segment deviations increased the diagnostic specificity: that is, the finding of inferior infarction (ST-segment elevation in leads II, III, aVF) without lateral infarction (ST-segment elevation in leads V5,6) was highly suggestive of RCA occlusion (sensitivity and specificity: 35 of 43 cases, 81.4%; and 33 of 36 cases, 91.7%), whereas ST-segment elevation in leads V5,6 (LCx: 23 of 36 cases; 63.9%, RCA: 5 of 43 cases; 11.6%) or isolated ST-segment depression in leads V2-4 (LCx: 9 of 36 cases; 25.0%, RCA: none of 43 cases) was highly suggestive of LCx occlusion. These results indicate that the composite electrocardiographic criteria were useful in predicting the artery involved in acute myocardial infarction, although any single criterion was not sensitive or specific enough to differentiate right from left circumflex coronary artery occlusion.