Right atrial pacing soon after myocardial infarction

Simultaneous transesophageal two-dimensional echocardiography and atrial pacing for detecting coronary artery disease

This study describes a new technique for assessing wall motion abnormalities, combining transesophageal echocardiography (TEE) and transesophageal atrial pacing in 71 patients. Stable capture was reached in 70 patients (99%). In 3 patients (4%) pacing was discontinued prematurely because of discomfort. TEE during pacing was performed in 52 patients with and in 18 patients without coronary artery disease (CAD). In 43 of 52 patients with CAD, regional wall motion abnormalities occurred (sensitivity 83%). No wall motion abnormalities occurred in 17 of 18 patients without CAD (specificity 94%, positive predictive value 98%). Wall motion abnormalities related to another vascular region were observed in 17 of 22 patients with previous myocardial infarction (sensitivity 77%, specificity 100%, positive predictive value 100%). Simultaneous 12-lead electrocardiography during atrial pacing was performed in 57 patients and yielded positive results in 21 of 40 patients with (sensitivity 52%) and in 3 of 17 patients without (specificity 82%, positive predictive value 88%) CAD. Exercise stress testing was performed in 66 patients. Twenty-four of 48 patients with CAD had a positive exercise electrocardiogram (sensitivity 50%); a false-positive exercise electrocardiogram was observed in 3 of 18 patients (specificity 83%, positive predictive value 89%). It is concluded that TEE during transesophageal atrial pacing is a feasible and promising alternative technique for the assessment of CAD, with a higher sensitivity than simultaneous 12-lead and exercise electrocardiography.

Utility of stress echocardiography for postinfarct prognosis

Although high-risk patients following myocardial infarct are usually identified in the acute stage by clinical assessment and determination of left ventricular function at rest, a significant percentage of infarct patients with increased risks, i.e., presence of residual myocardial ischemia, remain undetected at discharge. Since the yield of adequate images for interpretation stress echocardiograms has been significantly improved with digital technology, stress echocardiography has become a truly practical technique to identify these patients. Presence of remote asynergy, i.e., asynergy not directly adjacent to the infarcted area and supposed to be related to another vascular region, directly following cessation of dynamic exercise appears to be highly related to multivessel disease and an unfavorable follow-up period. Treadmill electrocardiographic findings, however, appeared to be of limited value in this respect. Furthermore, the echocardiographic ejection fraction was also a poor predictor. The versatility of the technique, lack of injections, or radiation hazard, and the relatively low cost will undoubtedly increase the application of stress echocardiography for postinfarct stratification.

The importance of stress-induced cardiac wall motion abnormalities in the evaluation of drug intervention

Stress-induced wall motion abnormalities are a sensitive marker of myocardial ischaemia. Stress echocardiography has recently been the subject of increasing interest because of its improved feasibility and compatibility with new and effective alternative stresses. Transoesophageal atrial pacing (TAP) with 2-dimensional echocardiography (2-D echo) is a recently developed echo-cardiographic stress procedure that has been shown to be reliable and effective in both the diagnosis and evaluation of stress-induced myocardial ischaemia. TAP with 2-D echo was performed after treatment with placebo and intravenous gallopamil 0.03 mg/kg in 12 patients with stable, reproducible angina of effort. Compared with placebo, gallopamil treatment increased the time to 1 mm ST-segment depression (6.6 vs 5.3 minutes; p less than 0.05) and improved the ventricular wall motion score at a heart rate of 130 beats/min (17 vs 15; p less than 0.01) and 150 beats/min (13 vs 11; p = 0.07). Three patients who developed angina after placebo administration were symptom-free after gallopamil. Thus, gallopamil exerts a beneficial effect on atrial pacing-induced ischaemia, by increasing the pacing time to the ischaemic threshold and reducing the extent of dysfunctional myocardium during ischaemia.

Prediction of cardiac events after uncomplicated myocardial infarction by cross-sectional echocardiography during transesophageal atrial pacing

Atrial pacing can safely be utilized shortly after myocardial infarction. To evaluate the prognostic value of wall motion abnormalities induced by such pacing 83 consecutive patients with recent uncomplicated myocardial infarction underwent transthoracic cross-sectional echocardiography during transesophageal atrial pacing and upright bicycle exercise stress test. Patients were followed-up for 14 +/- 5 months. During the atrial pacing and the echocardiography, patients were defined at high risk if abnormalities of wall motion were detected in left ventricular regions remote from the infarcted area. Then, during the exercise stress test, high risk patients were those with ST segment depression greater than or equal to 1 mm. On the other hand, patients were considered to be at low risk if they had no abnormalities of wall motion during atrial pacing in remote regions or, in the case of the stress test, if they did not develop ST depression greater than or equal to 1 mm. Of the 83 patients, 21 had major cardiac events during the period of follow-up. Cardiac events occurred in 15/23 (65%) and 5/60 (8%, P less than 0.001) patients assigned to the groups adjudged to be at high and low risk, respectively, on the basis of echocardiographic results. Exercise testing was less reliable in identifying patients at risk of future cardiac events. Major events occurred in only 6 of the 19 patients with a positive stress test (32%, P less than 0.05 vs positive stress echocardiography) and in 14 of the 64 patients with a negative exercise stress test (22%, P = NS vs positive exercise stress test, P less than 0.05 vs negative atrial pacing echocardiography).

The prognostic value of right atrial pacing after acute myocardial infarction

We performed right atrial pacing in 90 consecutive patients 10 to 30 days (mean 16.8 days) after acute myocardial infarction. Right atrial pacing was normal in 28 patients, depression of the ST segment occurred in 27 patients, systolic blood pressure fell below control values in 20 patients and, in 15 patients, right atrial pacing was non-diagnostic. Follow-up was from 12 to 28 months (mean = 17.3). Global mortality was 11.1%, with none of the patients with normal tests dying, 11% of those with ST depression, 30% of those with induced hypotension (P less than 0.01) and 7.1% of those in whom pacing was non-diagnostic. Patients with high clinical risk at discharge in Peel Class III-IV, showed 41.2% mortality during the period of follow-up. None of those had shown normal responses to pacing, but those dying included 50% of the patients with ST depression and 66.7% of those in whom right atrial pacing induced hypotension. Development of new angina during the period of follow-up was more frequent among the patients with ST depression (33.3%) (P less than 0.001). Thus, our results showed that right atrial pacing was useful in predicting mortality after acute myocardial infarction. In patients at high risk, we observed that a fall of systolic blood pressure was the best predictor of mortality.

Residual left ventricular function and prognosis of patients with asymmetric septal hypertrophy recovering from acute myocardial infarction

The prognosis of patients recovering from acute myocardial infarction (MI) depends mainly on their residual left ventricular (LV) function. In patients with asymmetric septal hypertrophy (ASH) who are recovering from MI, a larger functioning myocardial mass may remain. However, the frequency of ASH in these patients has not yet been described. Predischarge echocardiography, radionuclide ventriculography, and treadmill stress tests were performed in 403 consecutive patients who had recovered from acute MI. Eighty-eight patients (22%) had ASH with septal thickness greater than or equal to 1.3, and 32 (8%) had septal thickness greater than or equal to 1.5 cm. One hundred thirty-six patients who had recovered from a first MI and had no ASH served as control subjects. Left ventricular ejection fraction (LVEF) in the group with ASH was significantly higher than in control subjects (61% vs 50%; p = 0.0001). LV end-diastolic diameter (LVD(d] and E point septal separation (EPSS) were smaller in the group with ASH (4.9 cm and 5.4 mm) than in the control group (5.5 cm and 10.5 mm). The frequency of positive treadmill test results, angina pectoris, recurrent MI, heart failure, and death during a 22-month follow-up period was similar in both groups. Fifty subjects in the control group were matched with 50 patients from the group with ASH on the basis of maximal level of creatine phosphokinase, location of infarct, and presence or absence of hypertension, and the difference between the two groups was even more marked (LVEF 48% vs 61%, respectively; p = 0.0004).(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of coronary artery disease in the patient unable to exercise: alternatives to exercise stress testing

Exercise stress testing is a well-established method for the diagnostic, prognostic, and functional assessment of patients with known or suspected CAD. A variety of alternative tests have been described in patients unable to perform leg exercise. Atrial pacing and dipyridamole imaging have been evaluated most extensively, and results compare favorably with those of exercise testing for diagnosing the presence of CAD. Both tests may be used to assess prognosis after myocardial infarction, and dipyridamole imaging may be useful in patients undergoing preoperative evaluation. The use of the cold pressor test and isometric handgrip exercise have also been described. However, the value of both tests is limited by a relatively low sensitivity for detecting the presence of CAD. Other testing modalities--arm ergometry, intravenous infusion of beta-adrenergic agonists, and transthoracic pacing--show promise but require further assessment to confirm their value.

Risk of myocardium adjacent to infarcted myocardium: electrocardiographic, metabolic and scintigraphic evidence within the first week of acute myocardial infarction

Atrial pacing was carried out within 5 days of an uncomplicated acute myocardial infarction (AMI) in 28 patients to detect the existence of a menaced area. A positive pacing response (at least 1.0 mm of ST-segment shift) was observed in 23 patients (82%, group I), whereas pacing results were negative in 5 (18%, group II). Pacing-induced electrocardiographic changes involved the leads affected by AMI in patients with transmural necrosis. A well-defined thallium-201 redistribution, mostly localized near or within the AMI site, was present in 10 patients from group I (43%), in 1 from group II (20%), and in 1 of 12 comparable patients (8%) in whom pacing was not performed. During pacing, abnormal lactate metabolism was observed in 11 of 17 patients from group I (65%) and in 0 of 5 from group II (0%). A 90% or greater coronary stenosis of at least 1 artery was found in 19 of 23 patients from group I (83%) and in 1 of 5 from group II (20%); 2- to 3-vessel disease (more than 70% diameter stenosis) was present in 14 patients from group I (61%) and 1 from group II (20%). During a 15-month follow-up (range 9 to 25), effort angina developed in 9 patients from group I (39%) and in none from group II. No deaths or reinfarctions occurred in either group. Thus, very early after a first AMI, most patients have a jeopardized periinfarction area that is usually associated with a critical coronary stenosis and that heralds effort angina in a significant proportion of them.

Reciprocal electrocardiographic changes in acute myocardial infarction

If reciprocal electrocardiographic changes during acute myocardial infarction (AMI) are a result of ischemia of the wall opposite the AMI, a stress test is expected to induce similar changes in the corresponding electrocardiographic leads. Right atrial pacing was used as a myocardial stress method in 137 consecutive patients recovering from a transmural AMI, and the appearance of pacing-provoked ischemia before hospital discharge was correlated to the presence of absence of ST depression in the opposite wall during the initial 48 hours. Of the 137 patients, 83 (61%) had reciprocal changes; they were more common in inferior (87%) than in anterior (37%) AMI (p less than 0.01). Of 54 patients without reciprocal changes, only 5 (9%) had ST depression during predischarge pacing; however, of the 83 patients with reciprocal changes, 41 had pacing-induced ischemia (p less than 0.01) and 42 did not, indicating that in half of this group the reciprocal changes represent ischemia of the opposite wall. In the other half of the group, without ST depression during pacing, these changes may be a "mirror image" phenomenon. Follow-up showed that angina pectoris, positive treadmill test response 6 months later, or recurrent AMI all consequences of impaired myocardial blood supply, were significantly more frequent in patients with reciprocal changes. This group could be further separated according to the results of right atrial pacing, because angina pectoris or recurrent AMI were infrequent among those with reciprocal changes and negative pacing responses, but was frequent among those with reciprocal changes and positive pacing responses.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of clinical variables and variables derived from a limited predischarge exercise test as predictors of early and late mortality after myocardial infarction

An exercise test limited to 5 METS or 70% of age-predicted maximal heart rate was performed 1 day before hospital discharge by 225 survivors of acute myocardial infarction, all of whom were subsequently followed up for at least 5 years. The mortality rate was 11.1% during the first year, but averaged only 2.9% per year from the second to fifth year. Over the entire follow-up period, the five variables that predicted mortality by multivariate analysis were QRS score, an exercise-induced ST segment shift, previous infarction, failure to achieve target heart rate or work load and ventricular arrhythmia during the exercise test. Because mortality differed markedly before and after 1 year, Cox regression analyses were performed separately for both of these periods. The factors that were predictive of mortality during the first year were an exercise-induced ST shift (p less than 0.0001, relative risk 7.8), failure to increase systolic blood pressure by 10 mm Hg or more during exercise (p = 0.0039, relative risk 4.3) and angina in hospital 48 hours or longer after admission (p = 0.0046, relative risk 3.4). None of these three variables was predictive of mortality after 1 year. Previous infarction (p = 0.0007), QRS score (p = 0.0042) and ventricular arrhythmia during the exercise test (p = 0.016) were predictive of mortality after the first year. Thus, clinical and exercise test variables are complementary predictors of mortality after myocardial infarction. An abnormal ST segment response during an early limited exercise test and angina in the hospital are common strong predictors of mortality to 1 year, but not thereafter. Late mortality correlates with markers of poor left ventricular function.

The pacing stress test: a reexamination of the relation between coronary artery disease and pacing-induced electrocardiographic changes

Electrocardiographic (ECG) changes during graded pacing-induced tachycardia have been considered unreliable as a test for the presence of coronary artery disease (CAD) because of poor sensitivity and specificity. As a result, atrial pacing has not been widely used as an alternative to exercise testing. However, the limited value of the pacing stress test may be related to technical aspects, such as the duration of pacing and ECG monitoring. To study this problem, 22 patients undergoing coronary cineangiography underwent standard exercise stress testing and graded tachycardia induced by atrial pacing. A 12-lead ECG recorder was used for both tests. Pacing tachycardia was terminated when 85% of maximal predicted heart rate had been achieved or when significant ischemic chest pain accompanied by diagnostic ECG changes occurred. The ECG was considered positive if at least 1 mm of horizontal or downsloping ST-segment depression was present. Six patients with normal or minimally diseased coronary arteries were compared to 16 patients with significant CAD. Of the patients without significant CAD, 5 (83%) had a negative electrocardiogram during both exercise and pacing. Of 16 patients with CAD, the electrocardiogram was positive for ischemia in 10 patients (63%) during exercise, in 15 (94%) during atrial pacing and in 12 (80%) after pacing. When the presence or absence of ECG changes was compared between the exercise and the pacing tests, there was a concordance of 90% (Fisher p less than 0.0015). Two patients without significant CAD (33%) had chest pain during both exercise and pacing. Among patients with CAD, 7 (44%) had chest pain during exercise and 8 (50%) had chest pain during atrial pacing.(ABSTRACT TRUNCATED AT 250 WORDS)

The pacing stress test: thallium-201 myocardial imaging after atrial pacing. Diagnostic value in detecting coronary artery disease compared with exercise testing

Many patients suspected of having coronary artery disease are unable to undergo adequate exercise testing. An alternate stress, pacing tachycardia, has been shown to produce electrocardiographic changes that are as sensitive and specific as those observed during exercise testing. To compare thallium-201 imaging after atrial pacing stress with thallium imaging after exercise stress, 22 patients undergoing cardiac catheterization were studied with both standard exercise thallium imaging and pacing thallium imaging. Positive ischemic electrocardiographic changes (greater than 1 mm ST segment depression) were noted in 11 of 16 patients with coronary artery disease during exercise, and in 15 of the 16 patients during atrial pacing. One of six patients with normal or trivial coronary artery disease had a positive electrocardiogram with each test. Exercise thallium imaging was positive in 13 of 16 patients with coronary artery disease compared with 15 of 16 patients during atrial pacing. Three of six patients without coronary artery disease had a positive scan with exercise testing, and two of these same patients developed a positive scan with atrial pacing. Of those patients with coronary artery disease and an abnormal scan, 85% showed redistribution with exercise testing compared with 87% during atrial pacing. Segment by segment comparison of thallium imaging after either atrial pacing or exercise showed that there was a good correlation of the location and severity of the thallium defects (r = 0.83, p = 0.0001, Spearman rank correlation). It is concluded that the location and presence of both fixed and transient thallium defects after atrial pacing are closely correlated with the findings after exercise testing.(ABSTRACT TRUNCATED AT 250 WORDS)

Early right atrial pacing after myocardial infarction. I. Comparison with early treadmill testing

Right atrial (RA) pacing and modified treadmill testing (TT) were performed in 111 patients recovering from acute myocardial infarction (MI) before hospital discharge to determine whether ischemic responses are more common with RA pacing than with TT and whether the prognosis could be better determined by the results of 1 test compared with the other. Patients with predischarge congestive heart failure, chest pain, physical disability or age older than 70 years were excluded. Ischemic responses were significantly more frequent during RA pacing than during TT (41% vs 34%, p = 0.02). The results of the 2 tests were concordant in 102 patients (92%): Both were positive in 37 and both negative in 65. In 8 patients, results of RA pacing were positive and results of TT were negative; only 1 patient had positive TT and negative RA pacing responses. The higher percentage of positive responses during RA pacing than during TT can be attributed to the significantly higher pressure-rate product achieved during pacing (18,773 vs 16,831 mm Hg/min, p less than 0.001). The ischemic threshold, defined as the pressure-rate product at which an ischemic change was first noted in a particular patient, was almost identical in both tests. During a mean follow-up period of 16 months, 10 patients had recurrent MI; 8 had positive predischarge RA pacing but only 5 had positive TT responses (p = 0.008). Six patients died; in 3 RA pacing responses were positive and in 2 TT responses were positive.(ABSTRACT TRUNCATED AT 250 WORDS)

Early right atrial pacing after myocardial infarction. II. Results in 77 patients with predischarge angina pectoris, congestive heart failure, or age older than 70 years

Seventy-seven consecutive postinfarction patients who had either predischarge angina pectoris or congestive heart failure, or who were older than 70 years of age, underwent right atrial (RA) pacing before hospital discharge. In 60% of these patients, ischemic changes developed during RA pacing; this high yield of positive response indicates advanced coronary arterial disease. During a mean follow-up of 15 months, these patients had a high mortality rate (18%) and a reinfarction rate of 9%. RA pacing separated this a priori high-risk group into lower- and higher-risk subsets. Of the 46 patients with a positive RA pacing response, 6 had reinfarction, while none of the 31 patients with a negative RA pacing response had reinfarction (p = 0.04); 10 of the 14 cardiac deaths were among the patients who had positive RA pacing responses at discharge (p = not significant). Thus, of the 20 major cardiac events, 16 occurred among those with positive RA pacing responses (p less than 0.05). Predischarge clinical symptoms, however, were not good predictors of subsequent major cardiac events. We conclude that RA pacing can be safely performed even in high-risk and elderly patients and a positive response can identify those who have a poorer prognosis. Therefore, for postinfarction patients who, according to the prevailing criteria, are excluded from treadmill testing, we advocate the use of RA pacing.

Peri-infarction zone at risk during the first 5 days after an acute transmural myocardial infarction: electrocardiographic evidence

An atrial pacing test was performed daily during the initial 5 days after a first myocardial infarction (MI) in 33 patients in Killip class I or II, to assess the presence of areas at risk of ischemia. Pacing caused a transient ST-segment shift of 1 mm or more in 26 patients (79%) (positive test, Group I) in the first 3.6 +/- 1.1 days after infarction, whereas no ST-segment change developed during pacing in 7 patients (negative test, Group II). Pacing-induced electrocardiographic changes were always localized in the leads involved by the MI. Right and left ventricular filling pressures were higher in Group I than in Group II (8 +/- 4 vs 5 +/- 3 mm Hg, p less than 0.05, and 16 +/- 7 vs 12 +/- 7 mm Hg, p less than 0.02, respectively). Both groups had similar increases in peak enzyme values and a similar mortality rate (2 of 26 vs 1 of 7 at an average follow-up of 16 months). The reinfarction rate was higher in Group II (3 of 7 vs 1 of 26). In 7 patients similar to the 33 patients studied, metabolic studies revealed lactate abnormalities during pacing in 4 of the 6 patients with positive test results and unchanged metabolism in the patient with a negative test result. Thus a jeopardized peri-infarction area appears to exist in most patients soon after an uncomplicated MI. Its presence is often associated with silent heart failure, but it is probably unrelated to peak enzyme increase or to prognosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of right atrial pacing soon after myocardial infarction with treadmill testing 6 months later

Seventy-four patients recovering from acute myocardial infarction underwent right atrial pacing before hospital discharge, and treadmill exercise testing 6 months later. The early right atrial pacing test was positive in 32 patients (43 percent) and the late treadmill test was positive in 32 patients (42 percent). The results of the two tests were concordant in 77 percent of the patients, 23 with an ischemic response and 34 with a normal response on both tests. In nine patients a positive right atrial pacing test was followed by a negative treadmill test, and in eight patients a negative pacing test was followed by a positive treadmill test. A positive right atrial pacing test at hospital discharge had an 81.0 percent predictive accuracy for a positive late treadmill test; chest pain, congestive heart failure or increased cardiothoracic ratio at discharge had a predictive value of only 52.9, 42.8 and 42.8 percent, respectively. Both the early right atrial pacing test and the late treadmill test were positive in a significantly higher proportion of patients with inferior or subendocardial infarction than of patients with anterior myocardial infarction. During early right atrial pacing the mean maximal heart rate achieved was higher than that during late treadmill testing (148 versus 133 beats/min) and the mean systolic blood pressure was lower (137 versus 162 mm Hg), but the pressure-rate product was similar on the two tests (20,282 versus 21,455 mm Hg/min). This finding may explain the similar frequency of ischemic responses to the two tests. These results indicate that the response to right atrial pacing soon after myocardial infarction is a good predictor for the presence or absence of an ischemic response to treadmill testing 6 months later. Thus, early right atrial pacing at the time of hospital discharge may be used to determine the pace of rehabilitation and short-term prognosis.