Arrhythmias and acute myocardial infarction.

The most common arrhythmias associated with inferior-wall and anterior-wall myocardial infarction are bradycardia and supraventricular and ventricular tachycardia. Optimal treatment approaches are based on the pathophysiology of the infarct and the presence of contributing medical factors (eg, congestive heart failure, metabolic disorders). Temporary or permanent pacemaker therapy is helpful in some patients. Sudden death due to arrhythmia after myocardial infarction may be predicted and avoided in certain situations.

Late potentials on signal-averaged electrocardiograms and patency of the infarct-related artery in survivors of acute myocardial infarction.

This study evaluated the relation between patency of the infarct-related artery and the presence of late potentials on the signal-averaged electrocardiogram (ECG) in 124 consecutive patients (98 men, 26 women; mean age 59 years) with acute myocardial infarction receiving thrombolytic therapy, acute percutaneous transluminal coronary angioplasty or standard care. All patients were studied by coronary angiography, measurement of ejection fraction and signal-averaged ECG. The infarct-related artery was closed in 51 patients and open in 73. Among patients with no prior myocardial infarction undergoing early attempted reperfusion therapy, a patent artery was associated with a decreased incidence of late potentials (20% versus 71%; no significant difference in ejection fraction). In the 48 patients receiving thrombolytic agents within 4 h of symptom onset, the incidence of late potentials was 24% and 83% among patients with an open or closed artery, respectively (p less than 0.04). The most powerful predictors of late potentials were the presence of a closed infarct-related artery, followed by prior infarction and patient age. Among patients receiving thrombolytic agents within 4 h of symptom onset, the only variable that was predictive of the presence of late potentials was a closed infarct-related artery. These data imply that reperfusion of an infarct-related artery has a beneficial effect on the electrophysiologic substrate for serious ventricular arrhythmias that is independent of change in left ventricular ejection fraction as an index of infarct size. These findings might explain, in part, the low late mortality rate in survivors of myocardial infarction with documented reperfusion of the infarct-related artery.

The divergent recovery of ST-segment depression and radionuclide angiographic indicators of myocardial ischemia.

This study evaluated the recovery after exercise of both ST-segment depression on the exercise electrocardiogram (electrical evidence of ischemia) and exercise-induced abnormalities in wall motion or ejection fraction as detected by radionuclide angiography. The study group of 31 patients was selected to undergo prolonged electrocardiographic and radionuclide imaging after exercise because they had persistent ST-segment depression greater than 3 minutes after exercise and radionuclide angiographic evidence of ischemia at peak exercise. In 27 (87%) of the 31 patients, radionuclide evidence of ischemia recovered more quickly than the electrocardiogram. Only 15 of the 31 patients had exercise-induced radionuclide abnormalities after exercise. Compared with the 16 patients without such findings of ischemia after exercise, these 15 patients had a worse wall motion score at peak exercise (5.3 vs 3.9; p less than 0.01) and a smaller increase in systolic blood pressure with exercise (p less than 0.05) and after exercise (p less than 0.01). Radionuclide angiographic evidence of ischemia recovers more quickly after exercise than ST-segment depression. When there is radionuclide evidence of ischemia after exercise, it is associated with more severe ischemia during exercise.

Influence of ventricular function and presence or absence of coronary artery disease on results of electrophysiologic testing for asymptomatic nonsustained ventricular tachycardia.

One hundred ten patients with asymptomatic nonsustained ventricular tachycardia (VT) were evaluated prospectively to assess the value of electrophysiologic testing. This testing consisted of up to 3 extrastimuli delivered during 3 drive cycle lengths from 2 right ventricular sites. A positive study was defined as monomorphic VT lasting 30 seconds or requiring cardioversion. Patients with a positive study were treated, and serial drug testing was done. An event during follow-up was sustained VT or cardiac arrest. The mean follow-up was 15 months. Of 57 patients with an ejection fraction greater than or equal to 40%, 6 had a positive electrophysiologic test with 1 event and 51 had a negative test with 1 event. Twenty-eight patients had an ejection fraction less than 40% and coronary artery disease: 14 had a positive test with 1 event, and 14 had a negative test with 3 events. Twenty-five patients had an ejection fraction less than 40% and no coronary artery disease: 1 had a positive test with no events, and 24 had a negative test with 8 events. Only ejection fraction and congestive heart failure class were found to be independent predictors of outcome. Patients with an ejection fraction greater than 40% had low inducibility (11%), had few events (3.5%) and did not require electrophysiologic testing. In patients with an ejection fraction less than 40% and coronary artery disease, inducibility was high (50%) and a negative study was of no value. Patients with an ejection fraction less than 40% and no coronary artery disease had low inducibility (4%), had frequent events (33%) and did not benefit from electrophysiologic testing.

Improving the predictive ability of the signal-averaged electrocardiogram with a linear logistic model incorporating clinical variables.

To improve the predictive accuracy of the signal-averaged electrocardiogram, we created a linear logistic model for predicting ventricular tachycardia during electrophysiologic testing. This signal-averaged electrocardiographic model was created from data obtained from 214 patients undergoing electrophysiologic testing (70 had ventricular tachycardia during electrophysiologic testing) by using stepwise logistic regression to rank eight clinical and nine signal-averaged electrocardiographic variables. The best predictors were ejection fraction, history of infarction, ventricular ectopic pairs or nonsustained ventricular tachycardia on Holter monitoring, QRS duration after 25-Hz filtering, and root mean square voltage of the terminal 40 msec of the QRS complex after 40- and 80-Hz filtering. Cross validation (a statistical technique that can be used to accurately evaluate how a predictive model will perform on a prospective patient population) was used to validate the model. After cross validation, the model's sensitivity was 91% and specificity was 59% for predicting ventricular tachycardia during electrophysiologic testing. This model compared favorably with established 25-Hz late-potential criteria (QRS duration of more than 110 msec and root mean square voltage of less than 25 microV of the terminal 40 msec of the QRS complex; sensitivity, 64%; specificity, 85%) and with established 40-Hz late-potential criteria (QRS duration of more than 114 msec or root mean square voltage of less than 20 microV of the terminal 40 msec of the QRS complex or duration of the low-amplitude signal less than 40 microV at the terminal QRS complex that is greater than 38 msec; sensitivity, 84%; specificity, 54%).(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical application of the signal-averaged electrocardiogram and "late potentials".

The signal-averaged ECG has proven to be a valuable tool for identifying patients at risk of ventricular arrhythmias. This computerized method of analyzing standard ECGs identifies microvolt-level late potentials that represent delayed conduction through diseased myocardium. This diseased myocardium is a potential substrate for reentrant ventricular arrhythmias. In select patient groups, the signal-averaged ECG predicts electrophysiologic testing results. Problems remain and continued development is needed to evaluate patients with conduction system disease, the patient without coronary artery disease but at risk of sudden death, and proper general application of the technique.

Signal-averaged electrocardiography: a new noninvasive test to identify patients at risk for ventricular arrhythmias.

Signal-averaged electrocardiography (ECG) is a new noninvasive test for identifying patients at risk for ventricular arrhythmias. This computerized method of analyzing standard ECGs identifies particular microvolt-level signals called late potentials. Late potentials have been correlated with clinical ventricular tachycardia, are predictive of ventricular tachycardia inducibility at the time of electrophysiologic testing, and are predictive of arrhythmic events after myocardial infarction. In this review, we describe late potentials, the method of obtaining and processing the signal-averaged ECG, and clinical studies in various patient groups that have assessed the predictive value of the signal-averaged ECG for identification of patients at risk for subsequent ventricular arrhythmias.

The effect of residual noise on the reproducibility of the signal-averaged electrocardiogram.

Signal averaging reduces noise in the surface ECG, allowing late potential identification. However, late potentials may vary within a patient from study to study. In a population with stable biopotentials, this work evaluated how residual noise (RN) affects signal-averaged ECG (SA-ECG) reproducibility.

Severe isolated tricuspid insufficiency in coronary artery disease.

We describe 3 patients who presented with severe cardiac disability as a result of tricuspid insufficiency, in the setting of severe coronary disease. Pertinent physical findings were signs of right heart failure, a tricuspid regurgitant murmur, and absence of left heart failure. Echocardiography and subsequent cardiac catheterization demonstrated significant tricuspid insufficiency, dilated right ventricle, impairment of right ventricular function, and preserved left ventricular function. Two patients were treated successfully with DeVega annuloplasty. Symptomatic tricuspid insufficiency can be seen in the setting of coronary artery disease and, when left ventricular function is well preserved, surgical correction is feasible.

DDD pacing: clinical considerations.

DDD pacemakers offer a physiologic form of pacing for selected patients by incorporating atrioventricular synchrony over a wide range of atrial rates. Selection of a patient for DDD pacing necessitates a thorough knowledge of the individual functions of the DDD pacemaker, the limitations of DDD pacing, and the patient's own electrical and physiologic needs. Continuing developments in cardiac pacing include further reduction of the possibility of pacemaker-mediated tachycardia, increased matching to metabolic needs, and advancement of telemetric technology and electrophysiologic testing.

Results of triple valve replacement in 91 patients: perioperative mortality and long-term follow-up.

Between 1961 and 1984, 91 patients underwent simultaneous triple valve replacement at the Mayo Clinic. Of the 273 prosthetic valves used, 77% were Starr-Edwards. Perioperative (30 day) mortality was 24% to 27% between 1962 and 1974 and 7% between 1975 and 1983 (p = .17). In patients with NYHA class IV symptoms, perioperative mortality was 44%, and in those with milder symptoms, it was 8% (p less than .0001). The median follow-up was 7.5 years (range, 6 weeks to 20 years). Cumulative survival, which was calculated taking into consideration perioperative mortality, was 64% at 1 year, 55% at 5 years, 40% at 10 years, and 25% at 15 years. Multivariate analysis identified preoperative functional class and age as predictors of late survival. Among causes of late mortality were sudden death in 32.5%, congestive heart failure in 15%, thromboembolism in 12.5%, prosthetic valve dysfunction in 7.5%, and infective endocarditis in 5%. Late complications included systemic emboli in 42% (embolic rate, 12.3 events per 100 patient-years), bleeding in 22%, myocardial infarction in 16%, and infective endocarditis in 6%. Eight patients required reoperation for prosthetic valve dysfunction, and 12 patients had permanent pacemakers. Of the 29 patients still alive, 79% are in NYHA class I or II. In summary, perioperative mortality after triple valve replacement appears to be declining; long-term survival in 30 day survivors is similar to that after single valve replacement and excellent symptomatic improvement can be obtained, although morbidity is high.