Myocardial ischemia in patients awaiting coronary artery bypass grafting

Continuous 12-lead electrocardiographic monitoring in an emergency department chest pain unit: an assessment of potential clinical effect

STUDY OBJECTIVES

Continuous 12-lead serial ECG monitoring has been proposed to assist in the evaluation of patients with acute coronary syndrome and nondiagnostic ECG in an emergency department chest pain unit. However, the ability of serial ECG to detect acute coronary syndrome and its benefit in addition to a standard protocol has not been established. We evaluate the ability of continuous 12-lead ECG to detect acute coronary syndrome, assess the incremental benefit of the serial ECG in association with a set protocol in an ED chest pain unit, and evaluate whether serial ECG changes could be considered as prognostic factors.

METHODS

Patients who met Agency for Health Care Policy and Research guidelines for intermediate risk for short-term cardiovascular event unstable angina were prospectively studied in the chest pain unit. Patients were monitored with the Mortara Instruments ELI 100 STM continuous 12-lead ECG system with ST-segment analysis. ST-segment changes of greater than 100 microV in 2 or more contiguous leads or greater than 200 microV in 1 lead were considered positive. Data were compared with serial serum cardiac markers, cardiac function study results, angiographic results, and 30-day outcome results.

RESULTS

One hundred nineteen patients had serial ECG applied. The median duration of monitoring was 4.2 hours. Forty patients were given a diagnosis of acute coronary syndrome. Chest pain unit protocol detected 52 patients, and 23 were given a diagnosis of acute coronary syndrome (sensitivity 58%; specificity 63%). Sixteen patients had ST-segment changes of greater than 100 microV or greater than 200 microV, and 9 were given a diagnosis of acute coronary syndrome. The addition of the serial ECG to the chest pain unit protocol increased the sensitivity to 65% and decreased the specificity to 58%. Two patients with ST-segment changes but none without ST-segment changes had an adverse cardiac event, yielding a sensitivity of 100% and a specificity of 88%.

CONCLUSION

Serial ECG is of limited value in the diagnostic evaluation of intermediate-risk patients managed in the chest pain unit with a standard protocol. However, when ST-segment changes are present, they indicate an increased likelihood for an adverse cardiac event.

Prophylactic value of preincision intra-aortic balloon pump: analysis of a statewide experience

OBJECTIVE

The objective of this study was to determine whether preincision use of an intra-aortic balloon pump improves survival and shortens postoperative length of stay in hemodynamically stable, high-risk patients undergoing coronary artery bypass grafting.

METHODS

A post hoc analysis of the Alabama CABG Cooperative Project database was performed by using propensity scores to model the likelihood of receiving a prophylactic preincision intra-aortic balloon pump. Every patient receiving a prophylactic preincision balloon pump was matched with another patient of similar propensity score who did not receive one. We then compared outcomes for matched pairs.

RESULTS

There were 7581 patients of whom 592 received a prophylactic preincision balloon pump. Patients with preoperative renal insufficiency, heart failure, or left main coronary artery disease, or who had undergone previous bypass grafting were significantly more likely to receive a prophylactic preincision balloon pump. By using propensity scores, we matched 550 patients who received a prophylactic preincision balloon pump with 550 who did not. Survival did not significantly differ by whether a prophylactic preincision balloon pump was used. However, surviving patients who received a preincision balloon pump had a significantly shorter postbypass length of stay (7 +/- 7.3 days) than did matched patients not receiving a balloon pump (8 +/- 6.2 days; P <.05).

CONCLUSIONS

No survival advantage was found for use of a prophylactic intra-aortic balloon pump in hemodynamically stable, high-risk patients undergoing bypass grafting, as opposed to placing a balloon pump on an "as needed" basis during or after the operation. However, the patients receiving the balloon pump had improved convalescence as shown by significantly shorter length of stay.

Choice of anesthesia and intraoperative monitoring for lower extremity revascularization

The prevalence of significant coronary artery disease re-enforces the importance of careful preoperative and intraoperative management in patients undergoing lower extremity revascularization. This article presents a practical approach toward the evaluation of anesthetic risk and the proper use of anesthetic agents and monitoring devices to minimize morbidity. The role of general and regional anesthetic agents is discussed, and complications of both techniques are presented.

Improved detection of silent cardiac ischemia with a 12-lead portable microprocessor-driven real-time electrocardiographic monitor

OBJECTIVE

To compare a microprocessor-driven real-time 12-lead electrocardiographic monitoring device with Holter monitoring for detection of ischemia.

DESIGN

Electrocardiographic monitoring was conducted in 110 patients at bed rest or undergoing surgical procedures.

MATERIAL AND METHODS

In three groups of patients, simultaneous monitoring with a 12-lead real-time device and a 2-channel Holter system was performed to detect ischemic episodes. The differences in the number of ischemic events and the total time of ischemia revealed by the two devices were analyzed statistically.

RESULTS

In patients with coronary artery disease, more ischemic ST-segment shifts were detected by the 12-lead device than by Holter monitoring (44 versus 16 events; P < 0.05). Total time of ischemia was also greater with the 12-lead device (879 versus 273 minutes; P < 0.05). Ischemia was detected by both techniques in 6 patients, only by the 12-lead device in 12, and only by Holter monitoring in 1. Neither device detected ischemia in control subjects. The 12-lead device had an advantage in detecting inferior ischemia, and it identified an additional 13 patients with unstable angina who had changes in T-wave polarity but did not exhibit ST-segment shifts.

CONCLUSION

The 12-lead real-time electrocardiographic monitoring device is superior to Holter monitoring in detecting and facilitating real-time identification of myocardial ischemia in patients at bed rest.

Nitrates in silent ischemia

In recent years it has become clear that episodes of transient myocardial ischemia commonly occur in patients with coronary artery disease in the absence of chest pain or angina equivalent. These episodes of "silent myocardial ischemia" are particularly well documented during continuous ambulatory electrocardiographic monitoring in daily life. Evidence suggests that these episodes represent true ischemia, and appear to be a marker of unfavorable outcome. While the pathophysiology is not completely understood, it appears as though the mechanisms of angina and silent ischemia are the same. Both forms of ischemia respond to conventional antianginal medication. While long-acting nitrates are effective in reducing or preventing myocardial ischemia, because of their propensity to cause tolerance they should be used intermittently and in association with either beta-blockers or calcium antagonists. Nitrates are safe and comparatively inexpensive, and will continue to play an important role in the treatment and prevention of angina. However, in the light of current knowledge, there is no specific indication for the treatment of silent ischemia by nitrates.

Patients' responses to postponement of coronary artery bypass graft surgery

The purpose of this study was to determine the thoughts and feelings of patients (n = 24) awaiting coronary artery bypass graft (CABG) surgery and, in particular, the thoughts and feeling of those patients (n = 17) whose surgical procedure was postponed. On average these patients waited four additional days before the surgery could be performed. Patients reported that the most difficult part of CABG surgery was the wait itself. Those whose CABG surgery was postponed expressed anger and disappointment, had additional tests, procedures and medication, extended hospital stays and increased costs.

Continuous 12-lead electrocardiograph monitoring in the emergency department

Many patients presenting to the emergency department with suspected acute myocardial infarction have an initial electrocardiogram (ECG) non-diagnostic for acute injury or ischemia. Continuous ST segment monitoring devices have been used by physicians in the past to diagnose ischemia in the ambulatory outpatient population and to identify coronary occlusion in postthrombolytic and postsurgical patients. We report three patients with suspected acute myocardial infarction who underwent real-time continuous 12-lead ST segment monitoring with frequent serial ECGs on a microprocessor-controlled device during their initial emergency department evaluation. Continuous 12-lead ECG monitoring revealed significant changes on the ECG in all three cases presented, with a resultant change in emergency department therapy. Interestingly, all of these patients had significant ECG changes in the absence of recurrence of chest pain. We believe real-time continuous 12-lead ST segment monitoring with frequent serial ECGs can identify patients with an initially nondiagnostic or atypical ECG who may benefit from early interventional therapy.

Intravenous nifedipine for prevention of myocardial ischaemia after coronary revascularization

We sought to determine the pharmacokinetic and pharmacodynamic behaviour of a continuous infusion of nifedipine given for prevention of myocardial ischaemia following coronary artery bypass graft (CABG) surgery. Patients scheduled for elective CABG, who had good left ventricular function, were included. Only normotensive patients who did not require treatment with vasoactive drugs and were bleeding less than 100 ml.hr-1 following surgery were included. The patients were randomly distributed into two groups: a control group not receiving any treatment and a treated group receiving a bolus (3 micrograms.kg-1.min-1 for 5 min) and maintenance (0.2 micrograms.kg-1.min-1) infusion of nifedipine, starting upon arrival in the recovery room and continuing for four hours. Patients given nifedipine were compared with control patients in order to determine the effects of nifedipine on haemodynamic function and on the postoperative incidence of hypotension, hypertension, myocardial ischaemia and infarction. Continuous 2-lead Holter monitoring was used to detect myocardial ischaemia. Infarction was diagnosed by 12-lead ECGs and by assessment of the MB-isoenzyme creatine kinase. The infusion of nifedipine rapidly achieved and maintained plasma concentrations between 30 and 40 ng.ml-1. The pharmacokinetic studies revealed a systemic clearance of nifedipine of 0.371 +/- 0.101 L.hr-1.kg-1, an apparent volume of distribution of 0.764 +/- 0.288 L.kg-1 and an elimination half-life of 1.4 +/- 0.6 hr. No correlation was found between plasma concentration of nifedipine and mean arterial pressure (MAP). The incidence of postoperative hypotension (MAP < 70 mmHg) and hypertension (MAP > 100 mmHg) was comparable between the groups. All haemodynamic variables were similar in both groups during the study period. Of 23 patients who received nifedipine, none showed evidence of ischaemia within six hours of starting the infusion. During the same period, five of 24 patients in the control group had ST-segment deviation suggestive of myocardial ischaemia (P = 0.05, Fisher's exact test). Three patients in the control group and none in the nifedipine group suffered perioperative myocardial infarction (P = NS). In conclusion, the continuous infusion of nifedipine used in this study is safe and reduces the incidence of myocardial ischaemia in normotensive patients with good left ventricular function following CABG. Further studies of larger number of patients are required to determine the role of calcium entry blockers following coronary artery surgery.

Can we really justify the treatment of silent ischemia in 1992? No!

Since the advent of ambulatory ST-segment monitoring, it has been established that silent ischemia is common in patients with various coronary artery disease syndromes, and such silent episodes represent up to 80% of all ischemic episodes. It appears to be associated with an adverse prognosis when compared with similarly characterized patients without silent ischemia during daily life. Silent ischemia does not, however, bother the patients, by virtue of the fact that it is silent, and therefore treatment of such ischemia must be justified by an improved outlook for the patient, rather than symptom relief. There is no direct evidence to date that silent ischemia is associated with acute myocardial infarction or sudden cardiac death in a cause-and-effect relationship, or that reduction or eradication of silent ischemia will lead to an improved prognosis for the patient; indeed, we have been unable to demonstrate any significant improvement in outlook when using the various antianginal/antiischemic agents at our disposal. Until we can demonstrate a benefit to the patient by detecting and treating silent ischemia, we should not waste large resources attempting to eradicate something whose significance we do not understand.

Early postoperative myocardial morbidity in patients with coronary artery disease undergoing major non-cardiac surgery: correlation with perioperative ischaemia

As a part of a study assessing early postoperative myocardial morbidity in 50 patients with active coronary artery disease undergoing major non-cardiac surgery, the ECG was monitored continuously for 24 hr after the onset of anaesthesia, using a frequency modulated (FM) Holter monitor. Concurrent automated blood pressure and pulse were measured non-invasively at three-minute intervals during anaesthesia and subsequently at five-minute intervals. Thirty patients were monitored with two-site ECG recordings, from modified V1 and V5 (Group A). Twenty patients had seventeen-site ECG monitoring, multiplexing a four by four array of precordial electrodes onto one channel of the frequency modulated recorder (Group B). Tapes were analyzed for noise, supraventricular and ventricular dysrythmias, runs of tachy- and bradycardia, and ST segment changes. These data were correlated with serial standard 12-lead ECGs and CK-MB assay in the 72 hr after surgery. Seven tapes from Group A could not be analyzed. Change (greater than 1 mm) on ST monitoring from both Groups A (14/23), B (14/20), correlated with serial 12-lead ECG and/or CK-MB changes. The majority of first ST change 19/28 (70%) occurred after anaesthesia. In 14/28 (50%) ST change occurred during episodes of tachycardia and elevated blood pressure (greater than 20% above baseline). Nine patients (9/23) in Group A had no ST change; however, six had serial 12-lead ECG and/or CK-MB changes. Six patients (6/20) in Group B had no ST changes, and none of these patients had any change of serial 12-lead ECGs or CK-MB assay. No patient complained of chest pain during the Holter monitoring period. Continual monitoring of heart rate and blood pressure and accurate ST monitoring are essential to detect and treat perioperative myocardial ischemia. A multiple-lead precordial system is substantially more sensitive than traditional two-lead ECG holter monitoring in detecting myocardial ischaemia.

Perioperative myocardial ischemia in patients undergoing noncardiac surgery--I: Incidence and severity during the 4 day perioperative period. The Study of Perioperative Ischemia (SPI) Research Group

To determine the incidence and characteristics of perioperative myocardial ischemia, the electrocardiographic (ECG) changes consistent with ischemia during the 4 day perioperative period were documented and characterized in 100 patients with or at risk for coronary artery disease undergoing noncardiac surgery. Using continuous two channel ECG monitoring (leads CC5 and CM5), the frequency and severity of ECG ischemic episodes defined by ST segment depression greater than or equal to 1 mm or elevation greater than or equal to 2 mm during the preoperative (up to 2 days), intraoperative and early postoperative (first 2 days) periods were compared. Preoperatively, 28 patients (28%) exhibited 105 episodes of ischemia; intraoperatively, 27 patients exhibited 39 episodes and postoperatively, 42 patients exhibited 187 episodes. There was no difference between the pre- and intraoperative episode characteristics. However, postoperative ischemic episodes were the most severe. The mean ST change was 1.5, 2 and 2.6 mm for pre-, intra- and postoperative episodes, respectively (p less than 0.0001 postoperative versus pre- or intraoperative); duration of ischemic episodes was 69, 45 and 207 min, respectively (p less than 0.005 postoperative versus preoperative, p less than 0.001 versus intraoperative) and area under the ST curve was 88, 74 and 383 mm.min (p less than 0.009 postoperative versus preoperative, p less than 0.005 versus intraoperative). Ninety-four percent of all postoperative ischemic episodes were silent; 80% of all episodes occurred without acute change (+/- 20% of control) in heart rate and 77% of intraoperative episodes occurred without acute change in blood pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Characteristics of electrocardiographic ischemia in high-risk patients undergoing surgery. Study of Perioperative Ischemia (SPI) Research Group

Perioperative cardiac morbidity remains a significant problem in both cardiac and noncardiac surgical patients. The role of perioperative myocardial ischemia appears to be important and is under active investigation. In a series of studies in 200 high-risk patients undergoing noncardiac surgery or coronary artery bypass graft (CABG) surgery, we measured the pre-, intra-, and post-operative electrocardiographic (ECG) ischemic patterns using either continuous 2-lead ambulatory (Holter) monitoring or continuous 12-lead (modified treadmill) monitoring. Electrocardiographic ischemic episodes were defined as reversible ST-segment changes lasting at least 1 min and involving a shift from baseline (adjusted for positional changes) of greater than or equal to 0.1 mV of ST depression (with slope less than or equal to 0) at J + 60 ms or 0.2 mV of ST elevation at the J-point. During the 2-day period preceding surgery, ECG ischemic changes were common, clinically silent, and usually independent of changes in myocardial oxygen demand. Intraoperatively, using continuous 12-lead ECG, we found a 25% incidence of ischemia, for which modified leads V5, V4, and II were the most sensitive. Most ECG ischemic episodes were supply-dependent, not demand-dependent. Comparing the pattern of intraoperative ischemia with the chronic ambulatory preoperative pattern, we found that, under conditions of strict hemodynamic control, intraoperative ischemia apparently recapitulated the preoperative pattern, and that the stresses of anesthesia and surgery contributed less than previously thought. The highest incidence of ischemia occurred postoperatively, ranging between 30% and 60%, in both cardiac and noncardiac surgical patients.(ABSTRACT TRUNCATED AT 250 WORDS)