Myrvin H. Ellestad

Chronotropic Incompetence The Implications of Heart Rate Response to Exercise (Compensatory Parasympathetic Hyperactivity

The report in this issue by Lauer et al1 provides more fascinating data on the possible predictive value of a reduced response of the sinus node to exercise. They exploited the opportunity to study this important response in 1575 healthy participants in the Framingham Offspring Study who had exercise tests on entry in the 1970s. The mortality and morbidity of the men in this study were extracted from the Framingham follow-up data as well as during follow-up examinations 8, 12, and 16 years after their entry. These investigators correlated the mortality and incident coronary disease with the subject’s ability or failure to reach 85% of maximum predicted heart rate, actual increase in heart rate from rest to maximum, and a ratio of heart rate to metabolic reserve achieved by stage 2 of the Bruce exercise protocol. This ratio compensates for the differences in age and physical fitness and provides a chronotropic index. During a mean follow-up of 7.7 years, the inability to achieve the target heart rate in 21% of the subjects was correlated with total mortality and with the incidence of coronary disease including myocardial infarction. Similar correlations occurred with a reduced heart rate increase with exercise and with the chronotropic response index calculated as previously mentioned. The data suffer from the fact that exercise was arbitrarily terminated at 85% of age-predicted heart rate, a highly artificial value that had considerable adherence in the 1970s. However, previous work suggests that if their patients had been exercised to a symptom-limited end point, the correlations with coronary events would have been even stronger. The reason the magnitude of the increase in heart rate during an exercise test would be predictive of subsequent events and mortality is an intriguing one. Lauer and colleagues’1 report reaches the same …

Inability of the Submaximal Treadmill Stress Test to Predict the Location of Coronary Disease

Two hundred patients had submaximal treadmill stress tests (STSTs) and selective coronary arteriography performed within 2 months of each other. An attempt was made to assess the predictability of disease isolated to any given coronary vessel by performance on the treadmill. This was not possible for disease isolated to the right coronary, the left anterior descending, the circumflex branch of the left coronary, or a combination of right coronary and circumflex arteries. Eleven patients had disease in the left main coronary artery; all had associated disease of some other branch as well. One of these patients had a negative submaximal treadmill stress test but was unable to reach 90% of his maximum predicted heart rate. The remaining 10 patients had positive STSTs. Patients with 26-50% narrowing of any branch had treadmill results similar to those with 51-75% narrowing. There was a large number of patients with single-vessel disease in the study and most of the negative STSTs occurred in this group. Nevertheless, within this group no one vessel gave a higher incidence of positive STSTs than any other. It is concluded that (1) a positive STST is more likely to be associated with increased severity and extent of coronary artery disease; (2) a negative STST is more likely to be found in disease limited to a single vessel; and (3) within the latter group, the STST is of no value in predicting the specific coronary artery involved.

Coronary artery bypass surgery morbidity.

A retrospective analysis was undertaken of 365 consecutive patients, 75 women and 290 men with a mean age of 59.9 +/- 9.7 years, who had coronary artery bypass surgery during 1981. Complications classified as major were: mediastinal hemorrhage, pericardial tamponade, wound dehiscence, sternal osteomyelitis, myocardial infarction, bacterial endocarditis, dissecting aneurysm and diabetes insipidus. Complications classified as minor were: atrial fibrillation, postpericardiotomy syndrome, cellulitis, thrombophlebitis and phrenic nerve palsy. There were 48 patients (13%) with 52 major complications. Age more than 60 years, cardiopulmonary bypass time longer than 150 minutes, aortic cross-clamp time longer than 100 minutes, number of grafts greater than five and presence of diabetes mellitus were significantly associated with major complications. Complications tended to occur more frequently in women, obese patients and those with emergency operation or ejection fraction less than 30%, but the associations were not statistically significant. Physicians referring patients for coronary artery surgery should be cognizant of the incidence of morbidity along with the other risks and benefits when considering coronary artery bypass surgery.

Coronary sinus pacing clinical follow-up.

Coronary sinus pacing is a safe and effective means of pacing from the atrium. In 66 patients with an average follow-up of 14 months, there was a 14% failure rate. There were transient problems in 14% which were subsequently corrected. There was a 6% death rate which was not pacemaker related. Successful atrial pacing with thresholds up to 6.0 mA is feasible. Atrial pacing was successful in 18 of 19 patients with varying degrees of atrioventricular block. Our experience with a new electrode has been very satisfactory.

Identification of septal ischemia during exercise by Q-wave analysis: Correlation with coronary angiography

Septal Q-wave amplitudes were studied in lead CM5 to evaluate its utility in predicting segmental coronary artery pathoanatomy. Q-wave amplitudes were measured in 41 patients with coronary artery disease (CAD) before and immediately after treadmill exercise. All patients studied had either significant single-vessel CAD (greater than 70% diameter reduction) or normal coronary anatomy; 13 had left anterior descending (LAD) CAD, 8 had right coronary occlusions, 8 had left circumflex (LC) CAD, and 12 had angiographically normal coronary arteries. Septal Q-wave amplitude measurements at rest and during peak exercise were recorded in 0.5 mm increments and classified as increasing in 20 patients, decreasing in 8, and no change in 13 with exercise. All 13 patients with isolated LAD narrowing had either no change (5 patients) or a decrease (8 patients) in the septal Q wave with exercise. Statistical analysis revealed 62% sensitivity and 100% specificity for single LAD narrowing if a decreasing Q wave was noted with exercise. Patients with isolated right or LC CAD or normal coronary anatomy had mixed septal Q-wave responses to exercise. Only patients with LAD narrowing had reductions in Q-wave amplitude with treadmill exercise. This finding suggests that low Q-wave voltage and its failure to increase after exercise imply abnormal septal activation, reflecting loss of contraction associated with ischemia from LAD narrowing.

Efficacy of three-channel ambulatory electrocardiographic monitoring for the detection of myocardial ischemia

The recognition of silent myocardial ischemia (SMI) has been demonstrated to have important clinical relevance. Two-channel ambulatory (Holter) electrocardiographic recording is a commonly utilized method for detecting transient electrocardiographic ST segment changes representative of SMI. It has been suggested that the analysis of two channels alone may not adequately detect SMI. We therefore evaluated the diagnostic yield of three channels using a three-channel electrocardiographic monitoring device in 46 consecutive patients (age 61 +/- 9 years) undergoing percutaneous transluminal coronary angioplasty of an isolated single-vessel stenosis. Modified bipolar chest leads V2, V5, and AVF (CM-V2, CM-V5, and CS-AVF) were utilized for analysis. The percent detection of ST segment changes from various combinations of two-lead recordings were compared to the total three leads, and an absolute transient ST segment shift (STSS) of greater than or equal to 1 mm during balloon inflation was considered as evidence of myocardial ischemia. One patient was excluded because of the need for ventricular pacing during balloon inflation. A total of 33 of 45 patients had STSS in all three leads (percent detection = 73%), while 32 (71%) had STSS in the two-lead grouping with the highest diagnostic yield (CM-V2/CM-V5; p = ns). Of the various two-lead combinations studied, leads CM-V2 and CM-V5 provided the best lead set overall for the detection of ischemic STSS. Three-channel ambulatory electrocardiographic recording only marginally improves upon the detection of ischemia when compared with standard (CM-V2/CM-V5 or CM-V5/CS-AVF) two-channel ambulatory electrocardiographic recordings.

Transient central diabetes insipidus after aortocoronary bypass operations

Three cases of transient central diabetes insipidus after cardiopulmonary bypass are presented. All 3 patients responded promptly to administration of vasopressin, and were completely recovered from polyuria 10 days after cardiac surgery. It is postulated that transient diabetes insipidus after cardiac operation occurred in some patients who had preexisting selective osmoreceptor dysfunction when cardiac standstill during extracorporeal circulation alters the left atrial nonosmotic receptor function, resulting in suppression of antidiuretic hormone release.

A basic approach to the interpretation of the exercise test

For primary care physicians, exercise testing is a cost-effective tool to evaluate patients presenting with symptoms. It helps to stratify those with probable coronary artery disease into a high-risk group needing referral and a low-risk group that can be observed. Each of the five main responses--the presence of myocardial ischemia, the heart rate and blood pressure response, the symptoms, any dysrhythmias, and the maximal aerobic capacity--should be mentioned in the final report. A suggested format for the exercise test report is shown in Table 4. Using the tools of pretest and post-test probability, the severity of disease, and the exercise treadmill scores greatly aids the primary care physician in the management of the patient evaluated with an exercise test.

Usefulness of P-Wave Duration to Identify Myocardial Ischemia During Exercise Testing

It is well recognized that ST-segment depression is due to subendocardial ischemia secondary to an increase in left ventricular end-diastolic pressure. The increase in left ventricular end-diastolic pressure is associated with increased left atrial pressure, resulting in left atrial wall distension that contributes to increasing P-wave duration (PWD). The objective of this study was to determine if PWD measured in leads II and V(5) during maximum exercise stress testing could be a reliable predictor of myocardial ischemia. Patients with suspected coronary disease underwent maximum exercise stress testing with myocardial perfusion imaging. PWD was measured using leads II and V(5) at rest and after exercise, with electrocardiographic complexes magnified 4 times (100 mm/s, 40 mm/mV). The change in PWD was calculated as Delta = PWD(recovery) - PWD(rest). DeltaPWD and ST-segment changes were related to the absence or presence of ischemia (localized reversible perfusion abnormalities) on myocardial perfusion imaging scans. DeltaPWD had sensitivity of 72%, specificity of 82%, negative predictive power (NPP) of 90%, and positive predictive power of 57%. ST-segment change had sensitivity of 34%, specificity of 87%, NPP of 80%, and positive predictive power of 47%. When DeltaPWD and ST changes were combined, sensitivity increased to 79% and NPP increased to 91%. In conclusion, DeltaPWD outperformed ST-segment changes in predicting myocardial ischemia on myocardial perfusion imaging scans. Furthermore, when DeltaPWD and ST-segment changes were combined, sensitivity and NPP were also significantly increased. In this study population, measuring DeltaPWD substantially increased the diagnostic value of maximum exercise stress testing.

Enhanced recognition of ischemia by three variable analysis of the exercise stress test

BACKGROUND ECG ST-segment deviations have been the standard measure of coronary artery disease (CAD) during the exercise stress test (EST). Our past research has shown other ECG variables to be significant in EST. This study evaluates the benefit of routinely combining these variables in the detection of CAD. METHODS Sequential patients (n = 439) with suspected CAD referred for EST had their cases reviewed. Clinical and ECG variables were associated with myocardial perfusion imaging (MPI) scintigrams used to detect ischemia during maximum EST. RESULTS An increase in P-wave duration was the most sensitive predictor of ischemia with a sensitivity of 64.3%, a specificity of 86.5%, and a positive predictive power (PPP) of 57.8%. ST elevation ≥ 1 mm in lead AVR had a sensitivity of 53.1%, a specificity of 78.3%, and a PPP of 41.3%. ST depression ≥ 1 mm in leads V₄-V₆ had a sensitivity of 11.2%, a specificity of 94.7%, and a PPP of 37.9%. When these variables were combined, specificity and PPP increased to 100% (p < 0.001). CONCLUSIONS EST evaluation solely by ST deviation fails to identify a significant portion of ischemic cases. Combinations of ΔPWD, ST elevation in AVR, and ST depression improved the identification of ischemia.