Seymour Gordon

Sequence of mechanical, electrocardiographic and clinical effects of repeated coronary artery occlusion in human beings: Echocardiographic observations during coronary angioplasty

The direct manipulation of coronary blood flow to induce regional myocardial ischemia has been almost entirely limited to experimental animal models. Thus, the detection of ischemia-induced left ventricular dysfunction in human subjects has been generally limited to observations made under conditions of diagnostic loading or during spontaneous clinical events. Percutaneous coronary angioplasty requires repeated interruptions of coronary blood flow for periods as long as 1 minute. The resulting appearance of or increase in ischemia-produced changes in myocardial function were detected by two-dimensional echocardiography in 18 patients undergoing angioplasty of 22 coronary stenoses. Accordingly, left ventricular contraction was studied during 52 episodes of regional coronary blood flow interruption and reperfusion in the process of inflating and deflating the angioplasty balloon. Before angioplasty, left ventricular wall motion was normal in 14 patients. There was mild anteroapical hypokinesia in two patients, anteroapical akinesia in one and mild inferior hypokinesia in one. Balloon inflations repeatedly produced new or increased wall motion abnormalities in the distribution of the instrumented coronary artery in 19 (86.4%) of the 22 procedures, but did not alter wall motion during angioplasty of one left circumflex artery lesion, one highly collateralized left anterior descending artery stenosis and one left anterior descending stenosis that had already caused severe anteroapical dyssynergy. Hypokinesia, usually rapidly progressing to dyskinesia, began 19 +/- 8 seconds (mean +/- SD) after coronary occlusion. Wall motion began to normalize 17 +/- 8 seconds after reperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Symmetric cardiac enlargement in highly trained endurance athletes: a two-dimensional echocardiographic study

Twelve highly trained male endurance athletes and 12 normally active matched control subjects were studied by two-dimensional and M-mode echocardiography to evaluate changes in the right and left heart chambers associated with intense aerobic training. Maximal oxygen uptake, a measure of cardiovascular fitness, ranged from 62.1 to 82.6 ml/kg/min in the athletes and from 33.0 to 49.3 ml/kg/min in the control subjects (p less than 0.001). The athletes had significantly greater left ventricular wall thickness (p less than 0.01), left ventricular chamber area (p less than 0.005), left atrial area (p less than 0.01), right ventricular chamber area (p less than 0.002), right ventricular wall thickness (p less than 0.05), and right atrial area (p less than 0.01). Proportionality of cardiac chamber enlargement in the athletes was shown by similar ratios of both right-to-left ventricular areas and right-to-left atrial areas in the two groups. Left ventricular contractility was not significantly different between groups. Cardiac enlargement in endurance athletes enables a greater stroke volume for the performance of sustained, intense exercise; hypertrophy of the chamber walls normalizes wall stress. These changes occur symmetrically in both right and left cardiac chambers in the endurance athlete, reflecting bilateral hemodynamic loading. The symmetry of the endurance athletes cardiac enlargement differs from most pathologic conditions which have heterogeneous effects on specific cardiac chambers.

Intracoronary streptokinase in clinical practice.

The candidacy for streptokinase (SK) infusion was studied in 95 patients displaying ECG evidence of acute or impending infarction who were catheterized within 5 hours of the onset of chest pain. Intracoronary SK was administered to 84 patients in whom occlusions of the infarct-related vessel were identified, with early recanalization having been achieved in 74 (88%). Because of completeness of studies, a data base of 72 patients was employed for further analysis. Recanalization was sustained at follow-up in 45 of 55 patients (82%). Spontaneous thrombolysis was demonstrated at follow-up in five patients (8%) initially resistant to SK, and rethrombosis occurred in 10 patients (18%). Preservation of R waves relative to Q wave depth was limited to patients with less than 90% residual stenosis. Eight of nine patients with continuing thrombolysis and patients with recanalized occlusions of the left anterior descending coronary artery displayed more impressive increases in mean (+/- SEM) ejection fraction (47% +/- 4% to 53% +/- 5% [p less than 0.05], and 47% +/- 3% to 52% +/- 5, respectively). The ejection fraction also increased significantly in 15 patients with pre-SK values of less than 50% (41% +/- 2% to 48% +/- 3%; p less than 0.05). Ventricular function deteriorated in SK failures. Reperfusion arrhythmias occurred in 28 of 62 recanalized patients (45%). Minor bleeding tendencies were displayed in 18 of 72 patients (25%). Major hemorrhages, one of which may have been fatal, occurred in four patients (5.6%). Of 84 patients, four (4.7%) died, two of whom were in cardiogenic shock when first seen. In contrast, there were 11 deaths (11.8%) in a consecutive simultaneously enrolled series of 93 control patients with similar entry criteria (p less than 0.05). Two additional SK-treated patients died, 16 and 30 days after treatment, both more than a week after surgical revascularization. It is concluded that SK recanalization is a promising new therapy that may decrease mortality and preserve myocardial function in certain circumstances. Its efficacy in a setting closer to the mainstream of cardiologic practice extends the favorable experience issuing from earlier clinical investigations.

Amount of Exercise Necessary for the Patient with Coronary Artery Disease

xercise training can both protect against and proE voke sudden coronary death.1 Accordingly, we are obliged to provide “safe” exercise recommendations, reducing the risk of cardiovascular complications to a minimum, while prescribing sufficient exercise to promote desired training effects. The intensity of exercise needed to attain health-related benefits may differ from what is generally prescribed for cardiorespiratory conditioning. Lower levels of physical activity than previously recommended have been shown to reduce the risk of certain chronic degenerative diseases and yet be insufficient to improve the aerobic capacity or maximal oxygen uptake (V02max),2 Low to moderate intensity exercise training (160% VOzmax) can elicit beneficial physiologic and psychosocial changes and possibly reduce cardiovascular-related mortality. Moreover, it appears that lowand high-intensity exercise training regimens produce comparable improvements in functional capacity and high-density lipoprotein (HDL) cholesterol, at least over the initial 3 months of conditioning.3 This review clarifies the amount of exercise required to promote favorable adaptation and improvement in functional capacity, cardiac function, coronary risk factors, psychosocial well-being and morbidity/mortality (Figure 1) in patients with coronary artery disease (CAD). Fmdional eapaeityr Recent studies suggest that low to moderate intensity exercise training will maintain or improve, or both, functional capacity after an acute coronary event. Simple exposure to orthostatic or gravitational stress during the bed rest stage of hospital convalescence may obviate much of the deterioration in exercise performance that follows myocardial infarction.4 Moreover, a “spontaneous” increase in VOzmax occurs in many deconditioned patients with CAD soon after hospital discharge,5 presumably because the aerobic requirements of many daily activities exceed the “threshold” intensity for training.6

Prevalence and Significance of Ventriculoatrial Conduction

Because retrograde atrioventricular conduction may predispose to pacemaker‐induced tachycardia when DDD pacing is employed, we assessed ventriculo‐atrial conduction in 117 patients undergoing electrophysiologic studies. Ventriculo‐atrial conduction was present in 40% with a mean (±sem) conduction time of 205 ± 12 ms. The maximum VA conduction time following minimum extrastimulus intervals averaged 258 ± 14 ms. Antegrade AV nodal properties predicted VA conduction in only 67% by using stepwise discriminant analysis. Only the PR interval, AH interval, and AV nodal effective refractory periods were helpful in predicting ventriculo‐atrial conduction. Although ventriculo‐atrial conduction time increased on most antiarrhythmic drugs, it was infrequently eliminated.

The effect of electrode position on atrial sensing for physiologically responsive cardiac pacemakers.

Fully automatic pacing systems rely on accurate identification of spontaneous atrial signals for physiologically responsive pacing. These signals must be discriminated from far-field ventricular activity, which might otherwise be sensed in the atrium. To amplify on the previously reported superiority of bipolar signals and high-impedance circuitry for atrial sensing, we studied the effects of various intraatrial electrode positions on the atrial and ventricular contribution to electrograms recorded in this chamber. Compared with other intraatrial endocardial sites, right atrial signals were greatest in amplitude and slew rate in the appendage (RAA), averaging 3.3 +/- 0.41 mV and 1.15 +/- 0.16 V/sec (mean +/- SEM), respectively. These values were substantially higher than in the low atrium (p less than 0.001 and 0.0005 for amplitude and slew rate, respectively) and the high lateral atrium (p less than 0.05 for slew rate). Appendage atrial electrograms also had significantly higher amplitude and slew rate than far-field R waves recorded here (p less than 0.0001 for both). Additionally, the greatest difference in spectral content between atrial and far-field ventricular signals was also observed in the RAA. Thus, parameters in the domain of both time and frequency identified the RAA as the superior location for atrial sensing. Except for phrenic nerve problems with pacing, the HRA also appears to be a suitable electrode location for sensing. These considerations are germane in light of a growing number of atrial active and passive fixation leads now being employed for physiologic pacing.

The Significance of Surface Changes on Explanted Polyurethane Pacemaker Leads

Although over 140,000 polyurethane leads have been implanted in humans, a controversy has recently arisen dealing with the significance of frequently detected irregularities on explanled insulator surfaces by scanning electron microscopy (SEM), and their relationship with lead failure. We therefore implanted ten, 6 Fratrial polyurethane leads and an equal number of 4 Fr ventricular leads in dogs for a mean 26 ± 2 and 29 ± 2 weeks, respectively. Fourteen leads were removed utilizing metered force. The remaining leads were removed surgically without force at the termination of the study. Specimens were stored in saline prior to physical testing (tensile strength and elongation) of intravascular and extravascular lead segments. Similarly stored samples were prepared for SEM analysis. The polyurethane insulator disconnected from the electrode on forcible removal in three atrial and two ventricular leads (concordant connected from the electrode on forcible removal in three atrial and two ventricular leads (concordant for two pairs). There was no significant relationship between the results of physical testing and extraction force, lead size, integrity on removal, sample location or SEM scores. Chemical analysis of surface changes employing both x‐ray and electron emission spectroscopy failed to reveal evidence of protein adsorption or liquid impregnation. Samples soaked in sodium hydroxide displayed the same SEM irregularities. The combined effects of fissuring and fluid absorption by polyurethane did not affect chronic anodal or cathodal thresholds, in conclusion, a clear relationship between chronic surface irregularities and the insulator function of polyurethane, its integrity in situ, or its strength atexplanthas not been established by this relatively short‐term study. On the other hand, a potential time‐dependent impact of these changes on lead performance has not been excluded. Moreover, only a single species of medical grade polyurethane has been clinically evaluated. Thus, the ultimate place of polyurethane leads in pacing systems hasyet to be determined.

Ethanol-Induced Changes of Myocardial Performance in Healthy Adults

The acute cardiac effects of ethanol (ETOH) have been studied in 32 normal volunteers. 40–60 min after completion of the consumption of an average 6 oz of 100 proof (50 %) vodka, mean serum ETOH level

The relative resistance of normal young women to ethanol-induced myocardial depression.

In contrast to previous reports from our own laboratory utilizing systolic time intervals (STI) and by others using ultrasound, no evidence of acute myocardial depression was observed in response to an ethanol (ETOH) dose of 1.25 ml/lb consumed over a period of 60 minutes by 6 young women (22.7 ± 7 years; 133 ± 6 lbs) who were monitored for 3 hours thereafter. Specifically, there was no significant change in fractional shortening (%ΔD), ejection frac tion, or mean circumferential fiber shortening velocity. Cardiac index and stroke index also remained stable, although heart rate increased (P < 0.005) and systolic and diastolic blood pressure fell (P < 0.01 and 0.25 respectively). To examine further this unanticipated cardiac resistance to ETOH, we re- examined the sex-specific difference of STI response to acute ETOH exposure in a previously reported group of 32 normal subjects (20 men and 12 women). Significant increases in PEP, PEPI, ICT, and PEP/LVET (P < 0.005, 0.005, 0.005, and 0.001 respectively) were observed in men only. Because we have previously observed that chronic ETOH consumption blunts acute myocardial depression, and because only 1 of 7 STI subjects historically consuming the least ETOH (< 1 oz/day) was a woman, STIs, were reassessed only in those subjects with a chronic consumption of 1 or more oz/day (14 men and 11 women). Myocardial depression as estimated by an increased ICT (P < 0.05) and PEP/ LVET (P < 0.02) was again observed in men only. We concluded that women are less susceptible than men to acute ETOH induced myocardial depression, as has recently been suggested for chronic ETOH consumption as well.

Exercise Prescription for Hypertensive Patients

Physical conditioning has been suggested as a useful adjunct or alternative to pharmacologic therapy in the treatment of borderline or mild hypertension. This recommendation stems from numerous studies that have demonstrated modest decreases in blood pressure in hypertensive individuals. Exercise guidelines should be based on preliminary exercise testing and modified to accommodate those patients who are taking a variety of antihypertensive medications. Although pure isometric exercise is generally contraindicated in hypertensive patients, potentially valuable training activities that involve a substantial static component, including arm crank ergometry and mild-to-moderate load weight training, probably requires individual assessment.