Lawrence S.C. Griffith

Thallium-201 myocardial perfusion imaging at rest and during exercise. Comparative sensitivity to electrocardiography in coronary artery disease.

SUMMARYThe sensitivity of myocardial perfusion imaging (MPI) using thallium-201 injected both at rest and during peak exercise was compared to simultaneously recorded 12 lead electrocardiography (ECG) for the detection of transient ischemia in 20 normal subjects and 63 patients with coronary artery disease (CAD). No significant perfusion defects or ECG changes were seen on either the rest or exercise studies in any of the normal subjects. Fifty-six percent of patients with CAD developed new perfusion defects with exercise compared to 38% who developed ischemic ST-segment depression (P < 0.02). However, when chest pain and/or ST depression were considered indices of ischemia, the sensitivity of exercise testing and thallium-201 MPI was similar. The increased sensitivity of MPI compared to ST-segment depression on the ECG was due to patients with baseline ECG abnormalities and those who failed to achieve 85% of predicted maximum heart rate with exercise.Analysis of the exercise results according to the extent of coronary artery disease revealed a progressive increase in both positive ECGs and MPI with the number of vessels involved. In patients with single vessel disease the MPI was more sensitive than the ECG (P <0.02).The combination of the rest and exercise ECG, MPI and chest pain during exercise failed to identify 11% of patients with CAD.Exercise thallium-201 MPI is a useful adjunct to conventional exercise testing particularly when evaluating patients with abnormal resting ECGs, those who develop ventricular conduction defects or arrhythmias during exercise, and those who fail to achieve their predicted heart rate because of fatigue or breathlessness.

Mortality in Patients with Implanted Automatic Defibrillators

Fifty-two patients who survived several arrhythmic cardiac arrests had implantation of an automatic defibrillator along with additional cardiovascular surgery as indicated. The mean follow-up was 14.4 months and the longest was 3 years. In the hospital, the implanted devices identified and reverted 82 episodes of spontaneous and 81 of 99 episodes of induced malignant tachyarrhythmias. There were 62 automatic resuscitations in 17 patients outside the hospital. Twelve patients died; four of the deaths were not witnessed. These deaths represent a 22.9% total and 8.5% sudden-death 1-year mortality rate. Because the expected 1-year mortality in patients without the automatic defibrillator was calculated to be 48%, there was an estimated 52% decrease in anticipated total deaths. The automatic implantable defibrillator can identify and correct potentially lethal ventricular tachyarrhythmias, leading to a substantial increase in 1-year survival in properly selected high-risk patients.

Analysis of left ventricular function from multiple gated acquisition cardiac blood pool imaging. Comparison to contrast angiography.

Global ventricular function was evaluated by both multiple gated cardiac blood pool scans (MUGA) and contrast ventriculograms in a group of 17 patients with suspected coronary artery disease. The contrast ventriculograms were analyzed frame by frame to generate a volume versus time curve for each patient, while the tracer data were analyzed by two methods: 1) the standard method, in which the left ventricle is identified on the end-diastolic frame and the background corrected activity under the region of interest obtained from the entire cardiac cycle, and displayed as a time versus activity curve; and 2) by a semi-automatic method in which the computer applies a threshold detection program to define the ventricular borders, and activity in the chamber at each point in the cardiac cycle is defined after background correction. The tracer data in each patient were analyzed independently by four observers. The tracer data correlated with the contrast data on a point by point basis r = 0.87 for the standard method, and 0.93 for the semi-automatic technique. An F test of variance revealed the semi-automatic method superior to the standard approach (P < 0.05).

Predictors of first discharge and subsequent survival in patients with automatic implantable cardioverter-defibrillators.

BackgroundTwo hundred eighteen patients were evaluated in a two-phase approach (time to first appropriate discharge, survival after discharge) to identify factors that may be related to maximal benefit derived from use of an automatic implantable cardioverter-defibrillator (AICD). Methods and ResultsOne hundred ninety-seven patients survived implantation of AICD, with or without concomitant cardiac surgery. One hundred five patients had an AICD discharge associated with syncope, presyncope, documented sustained ventricular tachycardia or fibrillation, or sleep at 9.1 ± 11.1 months after implantation. Patients survived 23.8 ± 18.0 months after AICD discharge. Left ventricular dysfunction (p =0.008 for ejection fraction less than 25%) was associated with earlier AICD discharge and shortened survival after AICD discharge (p =0.008 for ejection fraction less than 25%;p=0.01 for New York Heart Association functional class III and IV). B-Blocker administration (p =0.006) and coronary bypass surgery (p =0.06) were associated with later AICD discharge. Coronary bypass surgery (p =0.035) but not P-blockers was associated with more prolonged survival after AICD discharge. ConclusionsThese data suggest that a relatively easy algorithm can be applied to predict which patient will benefit most from AICD implantation.

Value and limitations of segmental analysis of stress thallium myocardial imaging for localization of coronary artery disease.

This study was done to determine the value of thallium-201 myocardial scintigraphic imaging (MSI) for identifying disease in the individual coronary arteries. Segmental analysis of rest and stress MSI was performed in 133 patients with arteriographically proved coronary artery disease (CAD). Certain scintigraphic segments were highly specific (97-100%) for the three major coronary arteries: anterior wall and septum for the left anterior descending (LAD) coronary artery; the inferior wall for the right coronary artery (RCA); and the proximal lateral wall for the circumflex (LCX) artery. Perfusion defects located in the anterolateral wall in the anterior view were highly specific for proximal disease in the LAD involving the major diagonal branches, but this was not true for “septal” defects. The apical segments were not specific for any of the three major vessels. Although MSI was abnormal in 89% of these patients with CAD, it was less sensitive for identifying individual vessel disease: 63% for LAD, 50% for RCA and 21% for LCX disease (narrowings > 50%). Sensitivity increased with the severity of stenosis, but even for 100% occlusions was only 87% for LAD, 58% for RCA and 38% for LCX. Sensitivity diminished as the number of vessels involved increased: with single-vessel disease, 80% of LAD, 54% of RCA and 33% of LCX lesions were detected, but in patients with triple-vessel disease, only 50% of LAD, 50% of RCA and 16% of LCX lesions were identified. Thus, although segmental analysis of MSI can identify disease in the individual coronary arteries with high specificity, only moderate sensitivity is achieved, reflecting the tendency of MSI to identify only the most severely ischemic area among several that may be present in a heart. Perfusion scintigrams display relative distributions rather than absolute values for myocardial blood flow.

Unstable angina pectoris: Morbidity and mortality in 57 consecutive patients evaluated angiographically

Fifty-seven consecutive patients presenting with unstable angina pectoris or so-called pre-infarction angina were prospectively evaluated by clinical and angiographic studies. One patient died during angiography and another died of acute myocardial infarction 11/2 hours after cardiac catheterization. Forty-five patients had significant obstruction in two or three coronary arteries. The average left ventricular ejection fraction was 59 percent. Of 15 patients treated medically, 10 were potential candidates for surgery. One of these 10 died during hospitalization and 9 survived. The nine survivors were followed up for an average of 10 months; six reported symptomatic improvement, and one had an uncomplicated myocardial infarction 6 months after study. Aortocoronary saphenous vein bypass was performed in 40 patients, of whom 9 died during hospitalization and 31 survived operation. Of the 31 survivors, 1 had an uncomplicated myocardial infarction 9 months postoperatively; there were no late deaths in this group during a follow-up period averaging 16.7 months. Thirty of the 31 survivors reported marked symptomatic improvement, and 21 of these survivors were pain-free.

Influence of coronary collateral vessels on the results of thallium-201 myocardial stress imaging

Abstract Although collateral vessels are commonly seen in patients with coronary disease, their functional significance has been debated. In this study segmental analysis of thallium-201 perfusion scintigrams obtained at rest and after exercise was made in 124 patients with angiographically proved coronary artery disease to determine whether collateral vessels could provide protection front myocardial ischemia during stress. All 15 coronary arteries that were completely occluded and had no collateral vessels showed a corresponding stress perfusion abnormality, but only 65 of 92 occluded arteries with angiographically visualized collateral vessels showed a corresponding stress defect (P

Clinical evaluation of the internal automatic cardioverter-defibrillator in survivors of sudden cardiac death

An R-wave synchronous implantable automatic cardioverter-defibrillator (IACD) was evaluated in 12 patients with repeated episodes of cardiac arrest who remained refractory to medical and surgical therapy. Seven men and 5 women, average age 61 years, surgically received a complete IACD system. Coronary artery disease was found in 11 and the prolonged Q-T syndrome in 1. The average ejection fraction was 34%, and 6 patients had severe congestive heart failure (New York Heart Association class III or IV). The IACD is a completely implantable unit consisting of 2 bipolar lead systems. One system uses a lead in the superior vena cava and on the left ventricular apex through which the cardioverting pulse is delivered. The second system employs a close bipolar lead implanted in the ventricle for sensing rate. After the onset of ventricular tachycardia or fibrillation, the IACD automatically delivers approximately 25 J. Postoperative electrophysiologic study in 10 and spontaneous ventricular tachycardia in 1 patient demonstrated appropriate IACD function and successful conversion in all with an average of 18 +/- 4 seconds. The induced arrhythmias were ventricular tachycardia (160 to 300 beats/min) in 9 and ventricular fibrillation in 1. These data demonstrate that ventricular tachycardia, not ventricular fibrillation, was the predominant rhythm induced during programmed ventricular stimulation in these survivors of cardiac arrest and that the IACD effectively responded to a wide range of ventricular tachycardia rates as well as ventricular fibrillation. Use of the IACD offers an effective means of therapy for some patients who otherwise may not have survived.

The Automatic Implantable Cardioverter-Defibrillator

The automatic implantable cardioverter‐defibrillator is an electronic device designed to monitor the heart continuously, to identify malignant ventricular tachyarrhythmias, and then to deliver effective countershock to restore normal rhythm. There are two defibrillating electrodes which are also used for waveform analysis; one is located in the superior vena cava, the other is placed over the cardiac apex. A third bipolar right ventricular electrode serves for rate counting and R‐wave synchronization. When ventricular fibrillation occurs, a 25 joule pulse is delivered; when ventricular tachycardia faster than a preset rate is detected, the discharge is R‐wave synchronized. The device can recycle three times if required. Special batteries can deliver over 100 shocks or provide a 3‐year monitoring life. Implantation of the device is made either through a thoracotomy or by a subxiphoid approach. Thus far, the device has been implanted in 160 patients with a follow‐up of 42 months. Acceleration of ventricular tachycardia to a faster rhythm or to ventricular fibrillation occurred only rarely and is dealt with most successfully through recycling. Actuarial analysis of the initial 52 patients has indicated 22.9% one‐year total mortality, a 52% decrease from the 48% mortality that would be expected in the same group of patients without the device: the mortality attributed to arrhythmias was only 8.5%. In conclusion, the automatic cardioverter‐defibrillator can reliably identify and correct potentially lethal ventricular tachyarrhythmias, leading to a substantial increase in survival in properly selected high‐risk patients.

Ambulatory electrocardiographic recordings at the time of fatal cardiac arrest

The relation between arrhythmias at cardiac arrest and the outcome of arrest is poorly understood. The Holter monitor tracings of 13 patients were reviewed after they sustained an in-hospital cardiac arrest during ambulatory electrocardiographic monitoring. All had a prior cardiac arrest or cardiac syncope. Twelve patients had ventricular tachycardia (VT) as their initial arrest arrhythmia and 1 patient had bradycardia followed by ventricular fibrillation (VF). VT degenerated to VF in 10 of 12 patients after a mean interval of 96 +/- 31 seconds (+/- standard error of the mean). The number of VT runs increased significantly during the hour immediately preceding arrest (p = 0.004). Despite prompt resuscitation efforts in 12 patients, only 6 survived. The 6 survivors and 6 nonsurvivors were not different with regard to age, ejection fraction, extent of coronary artery narrowing and time to first defibrillation. However, degeneration to VF within 30 seconds of arrest (5 of 6 nonsurvivors and 1 of 6 survivors, p = 0.04) and a slower rate of VT at the onset of arrest (166 beats/min in nonsurvivors and 227 beats/min in survivors, p = 0.02) were associated with unsuccessful resuscitation.