Donald A. Underwood

Electrocardiographic Diagnosis of Evolving Acute Myocardial Infarction in the Presence of Left Bundle-Branch Block

BACKGROUND The presence of left bundle-branch block on the electrocardiogram may conceal the changes of acute myocardial infarction, which can delay both its recognition and treatment. We tested electrocardiographic criteria for the diagnosis of acute infarction in the presence of left bundle-branch block. METHODS The base-line electrocardiograms of patients enrolled in the GUSTO-1 (Global Utilization of Streptokinase and Tissue Plasminogen Activator for Occluded Coronary Arteries) trial who had left bundle-branch block and acute myocardial infarction confirmed by enzyme studies were blindly compared with the electrocardiograms of control patients who had chronic coronary artery disease and left bundle-branch block. The electrocardiographic criteria for the diagnosis of infarction were then tested in an independent sample of patients presenting with acute chest pain and left bundle-branch block. RESULTS Of 26,003 North American patients, 131 (0.5 percent) with acute myocardial infarction had left bundle-branch block. The three electrocardiographic criteria with independent value in the diagnosis of acute infarction in these patients were an ST-segment elevation of 1 mm or more that was concordant with (in the same direction as) the QRS complex; ST-segment depression of 1 mm or more in lead V1, V2, or V3; and ST-segment elevation of 5 mm or more that was disconcordant with (in the opposite direction from) the QRS complex. We used these three criteria in a multivariate model to develop a scoring system (0 to 10), which allowed a highly specific diagnosis of acute myocardial infarction to be made. CONCLUSIONS We developed and validated a clinical prediction rule based on a set of electrocardiographic criteria for the diagnosis of acute myocardial infarction in patients with chest pain and left bundle-branch block. The use of these criteria, which are based on simple ST-segment changes, may help identify patients with acute myocardial infarction, who can then receive appropriate treatment.

Ineffectiveness of dipyridamole spect thallium imaging as a screening technique for coronary artery disease in patients with end-stage renal failure

The efficacy of dipyridamole single photon emission computed tomography (SPECT) thallium as a screening test for coronary artery disease (CAD), was studied in 45 patients with end-stage renal failure undergoing evaluation for renal transplantation. Coronary arteriography, dipyridamole SPECT thallium imaging and clinical follow-up were performed in all patients. Nineteen patients (42%) had an obstruction of 50% or more in at least one coronary artery. Fourteen patients had a positive thallium scan, but 7 of these were false-positives (sensitivity 37%, specificity 73%). The sensitivity was considerably lower than that quoted for non-ESRF patients in the literature, and significantly lower than a control group of 19 patients without ESRF having comparable severity and distribution of CAD. Five of the 6 patients who died of cardiac causes over a mean follow-up period of 25 months had normal thallium imaging, but all had significant coronary artery disease at cardiac catheterization. Dipyridamole SPECT thallium imaging has not proved a useful screening test for angiographically significant CAD, and does not predict cardiac prognosis in this population.

Acute Myocardial Infarction and Complete Bundle Branch Block at Hospital Admission: Clinical Characteristics and Outcome in the Thrombolytic Era

OBJECTIVES We sought to assess the outcome of patients with acute myocardial infarction (MI) and bundle branch block in the thrombolytic era. BACKGROUND Studies of patients with acute MI and bundle branch block have reported high mortality rates and poor overall prognosis. METHODS The North American population with acute MI and bundle branch block enrolled in the Global Utilization of Streptokinase and t-PA [tissue-type plasminogen activator] for Occluded Coronary Arteries (GUSTO-I) trial was matched by age and Killip class with an equal number of GUSTO-I patients without conduction defects. RESULTS Of all 26,003 North American patients in GUSTO-I, 420 (1.6%) had left (n = 131) or right (n = 289) bundle branch block. These patients had higher 30-day mortality rates than matched control subjects (18% vs. 11%, p = 0.003, odds ratio [OR] 1.8) and were more likely to experience cardiogenic shock (19% vs. 11%, p = 0.008, OR 1.78) or atrioventricular block/asystole (30% vs. 19%, p < 0.012, OR 1.57) and to require ventricular pacing (18% vs. 11%, p = 0.006, OR 1.73). Bundle branch block also carried an independent 53% higher risk for 30-day mortality. Thirty-day mortality rates for patients with complete, partial and no reversion of the bundle branch block were 8%, 12% and 20%, respectively (two-tailed chi-square test for trend 5.61, p = 0.02, OR 0.34 for complete reversion, OR 0.55 for partial reversion). CONCLUSIONS Bundle branch block at hospital admission in patients with acute MI predicts in-hospital complications and poor short-term survival.

Electrocardiographic manifestations of right ventricular infarction

RVI is a frequent occurrence in the setting of an acute inferoposterior myocardial infarction and its early recognition has important therapeutic and prognostic implications. Because of this, diverse invasive and noninvasive diagnostic techniques have been investigated to identify patients with RVI. Electrocardiography is the most available, simple, and objective of these techniques. Numerous ECG signs of RVI have been described and some of them, especially ST segment elevation and patterns of necrosis (QS, QR) in the right precordial leads (V3R to V5R), have a very high sensitivity, specificity, and positive predictive value for the detection of RVI. ST segment elevation in lead V4R is also helpful in identifying the occluded coronary artery in patients with acute myocardial infarction, which could have great importance in their management. Hence, a 12-lead ECG with the right precordial leads (V3R to V6R) should be a routine part of the initial evaluation of patients with clinical suspicion of acute inferior myocardial infarction. This article reviews the value, limitations, and pathogenesis of the ECG manifestations of RVI.

Myocardial infarction and normal coronary arteriography: A 10 year clinical and risk analysis of 74 patients

Myocardial infarction with normal coronary arteries was identified in 74 patients with a mean age of 43 years (range 19 to 66). A mean follow-up period of 10.5 years after documented myocardial infarction and 8.6 years after cardiac catheterization was obtained. The survival rate was 85% (n = 63). There were no statistical differences in age or clinical risk factor prevalence between survivors and nonsurvivors. Moderate (55%) to severe (27%) left ventricular impairment was more common in nonsurvivors. Nine of 11 deaths were cardiovascular, 6 were sudden and 8 occurred in patients with moderate to severe global left ventricular impairment. Seventy-six percent of survivors were asymptomatic and 86% were fully active at follow-up. Two survivors and three nonsurvivors experienced a second myocardial infarction. The clinical risk factors of the study group (Group I) were compared by age, sex and year of catheterization with risk factors in two matched groups. Group II consisted of 74 patients with coronary occlusive disease and myocardial infarction and Group III consisted of 148 patients with normal arteriograms. Group I differed from Group II in having fewer clinical risk factors (p = 0.01 to less than 0.0001). Cigarette smoking did not differ significantly between Group I (72%) and Group II (69%) but was less common in Group III (45%) (p less than 0.001). Hormone therapy or the peripartum state was more common in women in Group I (34%) than in women in Group III (14%) (p = 0.03).(ABSTRACT TRUNCATED AT 250 WORDS)

Diagnostic accuracy of the resting electrocardiogram in detection and estimation of left atrial enlargement: an echocardiographic correlation in 551 patients.

The identification of LA enlargement may have important clinical implications. Previous correlations of ECG P wave morphologies associated with LA enlargement and echocardiography have been limited by the use of small numbers of patients and by the employment of M-mode echocardiography without the benefit of two-dimensional guidance. The purpose of this study was to further examine the sensitivity and specificity of various P wave morphologies (P wave greater than or equal to 110 msec, notched P greater than or equal to 40 msec, and PTFV1 greater than or equal to 40 msec.mm) for the diagnosis of LA enlargement and to determine if these waveforms may be predictive of LA size. ECGs and surface echocardiograms obtained within 1 week of each other were evaluated in 551 patients (140 normal and 411 study subjects). The various P wave morphologies were found to be poorly sensitive (30% to 60%) but very specific (90%) for LA enlargement. Combinations of P wave morphologies did not improve sensitivity or specificity. ECG features did give an estimate of the degree of LA enlargement. When PTFV1 is greater than or equal to 40 msec.mm, 95% of patients had LA size greater than or equal to 40 mm; and when this parameter was greater than or equal to 60 msec.mm, 75% had LA size greater than or equal to 60 mm. These criteria for LA enlargement on the ECG are specific and predictive of the degree of LA enlargement measured by echocardiography.

Left ventricular hypertrophy: An overlooked cardiovascular risk factor

Left ventricular hypertrophy (LVH) is common in hypertensive patients, and it increases the risk of myocardial infarction, stroke, and death. Recent evidence indicates it is a modifiable risk factor that is not entirely dependent on blood pressure control. The authors review its pathogenesis, diagnosis, and treatment. Antihypertensive treatment that causes left ventricular hypertrophy to regress also decreases rates of cardiovascular morbidity and death, independently of how much the blood pressure is lowered.

The incidence of scintigraphically viable and nonviable tissue by rubidium-82 and fluorine-18-fluorodeoxyglucose positron emission tomographic imaging in patients with prior infarction and left ventricular dysfunction

BackgroundAlthough reversible perfusion defects, perfusion-metabolism mismatch and match patterns are important for differentiating viable from nonviable myocardium, the frequency of these scintigraphic patterns has not been reported. The study objective was to establish the incidence of these scintigraphic patterns to estimate the clinical need for metabolic positron emission tomography for evaluating tissue viability in patients with prior myocardial infarction (MI).Methods and Results82Rb perfusion images were interpreted to identify reversible or irreversible defects, followed by determination of their 18F-fluorodeoxyglucose (18F-FDG) uptake pattern. In 155 patients with prior MI, analysis of 613 abnormal segments showed reversible perfusion defects in 13%. The 87% irreversible defects, 18% showed perfusion-metabolism mismatch, whereas 69% showed the match pattern. Reversible perfusion defects and perfusion-metabolism mismatches were noted in 20% (31/155) and 29% (45/155) of patients, respectively, whereas the match pattern was noted in 51% (79/155) of patients.ConclusionIrreversible perfusion defects were common in our patients with prior MI, and distinction between viable and nonviable tissue was not possible by perfusion imaging alone. The identification of hibernating myocardium was possible only with the additional 18F-FDG imaging in about one third of patients. This indicates a significant clinical demand for 18F-FDG imaging that identifies patients who will benefit from revascularization.

Signal‐Averaged ECG Parameters in Cardiac Normals Using Frank Lead System and Fourier Transform Filter and Gender Specific Differences: A Multicenter Study

There is only limited data on normal reference values for signal‐averaged electrocardiograms (SAECGs) using Frank leads and fast Fourier transform filter (FFT). Furthermore, the influence of gender on reference values and their relation to body characteristics was only the subject of a few studies on small series of normals. One hundred eigbty‐five cardiac normals (85 women and 100 men) were examined in this multi‐center study. The obtained SAECG values (mean ± standard deviation) are as follows: filtered QRS duration (FQRSD) = 108.6 ± 7.5 msec; low amplitude signal duration < 40 μV (LASD) = 30.4 ± 8.4 msec; and root mean square voltage in the terminal 40 msec (RMSV) = 43.5 ± 20.6 μV. Between men and women, significant differences were found in FQRSD (111.7 ± 6.5 vs 105.0 ± 7.0 msec, P < 0.001) and in RMSV (38.6 ± 17.4 vs 49.4 ± 22.7 μM, P < 0.001). No difference was observed for LASD. After normalizing the three SAECG parameters for body characteristics, FQRSD normalized for height was the only variable where gender differences were eliminated. For FQRSD and LASD the 90th percentile and for RMSV the 10th percentile are proposed as cut‐off values. Only for the 90th percentile of FQRSD a clear difference between men and women was observed. The following gender specific normal values for SAECG, at 40‐Hz high pass filtering, using Frank leads and an FFT filter are proposed: for males, FQRSD < 122 msec; for females, FQRSD < 115 msec; for both genders, LASD < 41 msec and RMSV > 20 μV.

Establishment of signal-averaged electrocardiographic criteria with Frank XYZ leads and spectral filter used alone and in combination with ejection fraction to predict inducible ventricular tachycardia in coronary artery disease

Signal-averaged electrocardiographic criteria are reported for corrected Frank XYZ leads and a spectral filter. The new criteria were used alone and in combination with ejection fraction to predict inducibility of ventricular tachycardia (VT) at electrophysiologic testing. Signal-averaged electrocardiographic criteria were developed in 87 control subjects and validated in 182 patients (aged 63 +/- 10 years) with coronary artery disease and QRS duration less than 118 ms. Patients underwent electrophysiologic testing in which up to 3 extra-stimuli were used during 2 paced drives from 2 right ventricular sites. A positive finding was monomorphic VT lasting 30 seconds or needing intervention. An ejection fraction less than 40% was considered abnormal. Signal-averaged electrocardiographic variables that best characterized control subjects and separated patients with and without inducible VT were filtered QRS duration less than 120 ms, low-amplitude signal duration less than 38 ms and root-mean-square voltage greater than 20 muv. With these criteria, signal-averaged electrocardiographic and ejection fraction sensitivities were 87 and 45%, respectively, and specificities were 65 and 77%, respectively. Combining signal-averaged electrocardiography with ejection fraction improved the predictive accuracy. In conclusion, diagnostic criteria for signal-averaged electrocardiography with use of Frank XYZ leads and a spectral filter produced results similar to those reported for use of bipolar XYZ leads and a Butterworth filter. Signal-averaged electrocardiography was a better predictor of VT than was ejection fraction.