Philip R. Reid

Termination of malignant ventricular arrhythmias with an implanted automatic defibrillator in human beings.

THE development of a clinically applicable, automatic, implantable defibrillator has been described previously.1 This electronic device is designed to monitor cardiac electrical activity, to recogn...

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.

Intravenous nitroglycerin in acute myocardial infarction.

Vasodilator therapy has been shown to improve ventricular function in patients with left ventricular failure complicating acute myocardial infarction. Sublingual nitroglycerin also improves ventricular function in these patients but its effects are transient and variable. Infusion of intravenous nitroglycerin in 12 patients with acute infarction resulted in a decrease in left ventricular filling pressure from a mean of 22 ± 2 mm Hg to 12 ± 1 mm Hg (P < 0.001) associated with a 7 mm Hg decrease in mean arterial pressure (P < 0.05). Since stroke work index did not change significantly, this represents an improvement in ventricular performance and/or an alteration in ventricular compliance. All six patients in whom serial precordial mapping studies were performed showed a decrease in ∑ ST (P < 0.001). These findings suggest that intravenous nitroglycerin improved left ventricular function and decreased the extent of myocardial ischemia. Longer infusion may act to preserve borderline ischemic myocardium and thus limit infarct size.

The repetitive ventricular response in man. A predictor of sudden death.

We examined the value of cardiac pacing for assessing ventricular electrical instability and for predicting ventricular tachycardia and sudden death in 50 patients with refractory symptomatic ventricular tachycardia, 12 normal patients, and 48 survivors of a recent myocardial infarction. The repetitive ventricular response (two or more ventricular premature beats produced by a single ventricular pacing stimulus during control of heart rate with atrial pacing) was absent in all 12 normal patients but was present in 44 of the 50 patients (88 per cent) with recurrent ventricular tachycardia (P less than 0.001). Of the 48 survivors of myocardial infarction, 19 had repetitive ventricular responses. During the next 12 months 15 of these patients (79 per cent) had symptomatic ventricular tachycardia or sudden death, or both, as compared with four of 29 patients (14 per cent) who did not have repetitive ventricular responses (P less than 0.001). The repetitive ventricular response identifies patients with life-threatening ventricular instability, but it is still an investigational technic that should be used only with due precautions.

The automatic implantable defibrillator

The automatic implantable defibrillator is an electronic device programmed to monitor the cardiac rhythm continuously, to recognize ventricular fibrillation and ventricular tachyarrhythmias characterized by sinusoidal waveform, and to deliver corrective difibrillatory discharges when indicated. Three patients suffering from recurrent malignant ventricular arrhythmias refractory to medical therapy underwent permanent implantation of this device. Seven episodes of ventricular tachycardia and flutter-fibrillation were documented during the weeks following the implantations; two were induced at electrophysiologic studies and five occurred spontaneously. All were correctly identified and six were automatically reverted to normal sinus rhythm by the implanted device; one induced episode was cardioverted externally before the unit could recycle. Although many problems remain to be solved and the ultimate value of this therapeutic modality has to be determined, a new approach to prevention of sudden death in patients at high risk of developing lethal ventricular arrhythmias has become available.

Myocardial-Infarct Extension Detected by Precordial ST-Segment Mapping

Abstract Daily precordial ST-segment mapping was performed with the millimeter sum of ST-segment deviation (ΣST) in a 48-lead system (1 mv = 20 mm) to evaluate 26 normal subjects and 19 patients with acute myocardial infarction. At the time of admission, ΣST (± S.D.)for transmural infarction (men + 140 ± 84.8, and women + 95.7 ± 8.8) and nontransmural infarction (-67 ± 32) was significantly different (p<0.001) from controls (men + 30.1 ± 18.1, and women + 17 ± 11.7). ΣST approached normal values by 10.6 and 13 hospital days, respectively. Twelve of 14 patients (86 per cent) with transmural infarction had re-elevation of ΣST ( + 76 ± 49.7) 5.8 days (mean) after admission. This finding was associated with abnormal creatine phosphokinase in eight (57 per cent), suggesting infarct extension. Standard six precordial leads did not reflect re-elevation of ΣST in four of the 12 patients with infarct extension. The 86 per cent incidence of infarct extension indicates that measures designed to decrease myocardial i...

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.

Effect of intravenous nitroglycerin on collateral blood flow and infarct size in the conscious dog.

SUMMARY This study was performed to determine whether nitroglycerin (NG) can increase collateral flow to ischemic myocardium and reduce ultimate infarct size. Permanent occlusion of the mid-circumflex coronary artery was produced in 43 previously instrumented conscious dogs and within 3 minutes, 6-hour intravenous infusions were begun of saline (controls, n = 18), NG in doses to reduce mean arterial pressure by 10% but not below 90 mm Hg (n = 15), or NG followed by methoxamine (MX) to correct the NG-induced fall in blood pressure (n = 10). After sacrifice 2 days later, the occluded coronary bed was defined by postmortem coronary arteriography and masses of infarct and occluded bed were measured by planimetry of weighed rings of the left ventricle (LV). Infarct size was significantly less with NG than saline, both as a percent of LV (12.1 vs 6.4%, p < 0.05) and as a percent of occluded bed (32.0 vs 15.9%, p < 0.005). NG plus MX did not reduce infarct size more than NG alone: 6.6 vs 6.4% of LV, and 16.0 vs 15.9% of occluded bed. Masses of LV and occluded bed did not differ significantly among the three groups. Coronary blood flow (CBF), measured by 7–10-μm radioactive microspheres, increased by more than 50% throughout the occluded bed (p < 0.005) after NG, and was more than the spontaneous increase seen in controls (p < 0.05), but MX had no additional effect on CBF over NG alone. Six-hour infusions of NG therefore decreased infarct size and improved CBF, and addition of MX to reverse the systemic effects of NG did not lessen the benefit. The results suggest that under the conditions of this study, myocardial protection by NG did not depend on a decrease in myocardial oxygen demands, but rather on an increase in collateral flow resulting from a direct vasodilating action of NG on the coronary bed.

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.

Lidocaine Kinetics Predicted by Indocyanine Green Clearance

To evaluate the importance of hepatic blood flow in lidocaine kinetics, we compared indocyanine green clearance, an estimate of hepatic plasma flow, to lidocaine clearance in 26 patients, half with and half without congestive heart failure, who received a lidocaine infusion for 24 hours as clinically indicated. The results demonstrated that patients with congestive heart failure had significantly higher steady-state lidocaine levels (6.8 +/- 3.6(S.D.) vs. 2.9 +/- 0.9 microgram per milliliter, P less than 0.005) and reduced lidocaine clearance (3.8 +/- 1.4 vs. 10.9 +/- 3.1 ml per minute per kilogram, P less than 0.005) than patients without heart failure. Potentially subtherapeutic or toxic lidocaine levels were found in 10 patients. The regression line (y = 0.3 + 1.07 x) relating clearance of lidocaine to that of indocyanine green was linear (r = 0.95, P less than 0.001). Since indocyanine green clearance can be determined rapidly and noninvasively, it offers the potential of predicting lidocaine dosage requirements with avoidance of toxicity or suboptimum therapy.