Atrioventricular nodal reentry in the Wolff-Parkinson-White syndrome

Although supraventricular tachycardia in the Wolff-Parkinson-White (WPW) syndrome is generally due to atrioventricular reentry, the presence of the accessory pathway does not preclude other mechanisms of tachycardia. We observed AV nodal reentry in three of 95 consecutive patients (3.1%) referred for assessment of arrhythmias associated with WPW syndrome. The unique observation of spontaneous transition from atrioventricular reentry to AV nodal reentry at a similar cycle length was observed in one patient and is the subject of this report.     

Progression to left ventricular dilatation in patients with hypertrophic obstructive cardiomyopathy

Congestive heart failure with dilated left ventricle developed in two patients with symptomatic hypertrophic obstructive cardiomyopathy. Both patients previously underwent cardiac surgery for relief of their outflow obstruction. Alterations in structure and function of the left ventricle during their episode of cardiac failure and thereafter were documented by echocardiography. The findings suggest that progression to left ventricular dilatation is a potential complication in patients with hypertrophic obstructive cardiomyopathy.     

Atrial fibrillation: minimal sampling interval to estimate average rate

The average heart rate and maximal heart rate (average R-R and shortest R-R intervals) in atrial fibrillation are frequently calculated to assess drug effect. The minimum recording sample to obtain accurate estimates of "instantaneous" average and maximum heart rate has not been established. We analyzed the R-R intervals after a 4 minute ECG recording in 40 supine patients with chronic atrial fibrillation. A "life table" analysis revealed that the average heart rate derived from a 20 second sample of atrial fibrillation approximates (+/- 5%) the true value in an estimated 92.5% of patients. On the other hand, a two minute sample is required to approximate the shortest R-R interval within 5% of the true value in 90% of patients. Studies utilizing average R-R interval and shortest R-R interval as an index of drug response should use electrocardiographic sampling intervals of at least 30 seconds and two minutes respectively.     

Stress myocardial imaging in mitral leaflet prolapse syndrome

Mitral leaflet prolapse syndrome has been associated with anginal chest pain, atypical chest pain, electrocardiographic abnormalities and positive stress electrocardiograms. These features overlap those of ischemic heart disease. Furthermore, coronary artery disease is frequently associated with mitral leaflet prolapse. This study evaluated the usefulness of stress myocardial scintigraphy in distinguishing these two disorders. Thirty-two patients with an angiographic diagnosis of mitral leaflet prolapse were studied. Of the 22 patients (8 men and 14 women, mean age 48 years) with a normal coronary arteriogram, 5 had “typical” angina pectoris, 6 had resting electrocardiographic abnormalities and 6 had a positive stress electrocardiogram; all 22 patients had a normal stress myocardial scintigram. Of the 10 patients (7 men and 3 women, mean age 55 years) with at least 70 percent stenosis of one coronary artery, 6 had “typical” angina pectoris, 1 had resting electrocardiographic abnormalities and 7 had a positive stress electrocardiogram. Nine of these 10 patients had one or more demonstrable perfusion defects on stress myocardial scintigrams. It is concluded that mitral leaflet prolapse syndrome is not associated with regional myocardial ischemia as demonstrated with stress scintigraphy, and that stress scintigraphy, a noninvasive technique, is useful in distinguishing the mitral prolapse syndrome from mitral prolapse associated with coronary artery disease.     

Comparison of the electrophysiologic effects of intravenous and oral verapamil in patients with paroxysmal supraventricular tachycardia

The electrophysiologic effects of intravenous verapamil (a bolus dose of 0.15 mg/kg body weight followed by infusion of 0.005 mg/kg per min) were compared with those of oral verapamil (80 mg every 6 hours for 48 hours) in eight patients who had paroxysmal Supraventricular tachycardia. The mechanism of tachycardia was atrioventricular (A-V) nodal reentry in four patients and A-V reentry utilizing an accessory pathway for retrograde conduction in the remaining four. The electrophysiologic effects of oral and intravenous verapamil were similar. Both preparations significantly prolonged anterograde effective and functional refractory periods of the A-V node (p < 0.001). Both significantly increased the shortest pacing cycle length maintaining 1:1 anterograde conduction over the A-V node (p < 0.001). Retrograde conduction over the A-V node was greatly prolonged with verapamil in one patient but was unaffected in the others. There was no significant effect on sinoatrial conduction time, sinus nodal recovery time or atrial or ventricular refractoriness. Both preparations prevented induction of tachycardia in six patients none of whom had recurrence of sustained tachycardia while receiving long-term oral therapy (5 to 10 months). Neither preparation had a significant effect in two patients and this predicted failure of long-term oral therapy in one of these patients.The results of acute drug testing with intravenous verapamil can be extrapolated to predict the electrophysiologic results and response to long-term therapy with oral verapamil.     

Low energy counterchock using an intravascular catheter in an acute cardiac care setting

We examined the feasibility, effectiveness, and safety of using an intravascular catheter positioned in the right ventricular apex for countershock in a coronary care unit setting in 8 patients who had recurrent ventricular tachyarrhythmia. Countershock using 2.5 to 40 J stored energy (damped sinusoidal wave form) was attempted 115 times to terminate 100 episodes of ventricular tachyarrhythmia (ventricular tachycardia, 91; ventricular flutter, 3; ventricular fibrillation, 6). Eighty-six (87%) of 99 countershock attempts for ventricular tachycardia, 3 (60%) of 5 for ventricular flutter, and 4 (36%) of 11 for ventricular fibrillation were successful using this technique. The catheters remained in stable position for 1 to 16 days without dislodgment. A majority of the countershocks were delivered by the regular nursing staff in the coronary unit.We conclude that low energy countershock through an intravascular catheter system is feasible, safe, and effective in a coronary care unit setting. Such a system should be beneficial in the acute management of patients who have recurrent ventricular tachycardia or fibrillation. The catheter lead may also prove useful in managing ventricular tachyarrhythmias that occur during electrophysiologic studies.     

Value and limitations of clinical electrophysiologic study in assessment of patients with unexplained syncope

We assessed the value of clinical electrophysiologic study using intracardiac recording and programed electrical stimulation in 34 patients who had unexplained syncope and/or presyncope. All patients had normal electrocardiograms, and no abnormality was detected by clinical examination, ambulatory electrocardiographic recording, or treadmill testing. The electrophysiologic results were diagnostic in four patients (11.8 percent) and led to appropriate therapy that totally relieved symptoms. The results were abnormal but not diagnostic in two patients (5.8 percent) and normal in the remaining 28 patients (82.4 percent). The patients were followed for a mean period of 15 months (range two to 44) after electrophysiologic testing. Sixteen patients (47 percent) had no further episodes in the absence of any intervention. In four patients (11.8 percent), a definitive diagnosis was made during follow-up. In seven patients, permanent pacing was instituted empirically with relief of syncope. Two patients continued to have syncopal spells. We conclude that the diagnostic yield of electrophysiologic testing is low in a patient population that has no electrocardiographic abnormality or clinical evidence of cardiac disease. Empirical permanent pacing in patients with symptoms continuing after our study appeared to be beneficial, but this result is difficult to evaluate because of the high incidence of spontaneous remission in this group. Persistent attempts to document electrocardiographic abnormalities during a typical episode of symptoms appears to be the only definitive way to confirm or exclude an arrhythmic cause of the symptoms.     

Relative insesitivity of isovolumic phase indices in the assessment of left ventricular function.

1. The authors compared the sensitivity of the isovolumic phase indices (contractility indices) against LV function curves ("pump-function" indices) in assessing ventricular performance. 2. Certain modifications of the usual isovolumic phase indices, especially those introducing the concept of comparison of exercise with rest, seemed to us to be slightly more helpful in separating normal subjects from the patient with coronary artery disease or cardiomyopathies, but these differences were not striking when statistically evaluated, and could not be utilized in assessment of left ventricular function in individual patients. 3. The construction of left ventricular function curves, in our hands, yielded equally as satisfactory information and, in addition, was much simpler to perform. 4. It is concluded that contractility indices are relatively insensitive in the assessment of left ventricular function, and that they offer little advantage over "pump-function" indices for this purpose.     

Intracardiac phonocardiography in experimental left ventricular cavity obliteration: potential clinical applicability for the distinction of obliterating left ventricle from hypertrophic obstructive cardiomyopathy

Intracardiac sound was measured in six dogs, four with left ventricular cavity obliteration induced by isoproterenol, and two with catheter entrapment. In left ventricular cavity obliteration, no murmur occurred within the left ventricle. Whenever a systolic murmur occurred, it was distal to the aortic valve. In entrapment, no murmur occurred within the left ventricle or distal to the aortic valve. Previous studies in patients with hypertrophic obstructive cardiomyopathy showed that the systolic murmur was of greatest intensity within the left ventricular outflow tract. Therefore, intracardiac phonocardiography may assist in differentiating these conditions which produce an intraventricular pressure gradient.     

Pacing threshold changes after transvenous catheter countershock

The serial changes in pacing threshold and R-wave amplitude were examined after insertion of a countershock catheter in 12 patients referred for management of recurrent ventricular tachyarrhythmias. In 6 patients, values before and immediately after catheter countershock were monitored. Pacing threshold increased (from 1.4 ± 0.2 to 2.4 ± 0.5 V, mean ± standard error of the mean, p < 0.05) while the R-wave amplitude decreased (bipolar R wave from 5.9 ± 1.1 to 3.4 ± 0.7 mV, p < 0.01; unipolar R wave recorded from the distal ventricular electrode from 8.9 ± 1.8 to 4.6 ± 1.2 mV, p < 0.01; and proximal ventricular electrode from 7.7 ± 1.5 to 5.0 ± 1.0 mV, p < 0.01). A return to control values occurred within 10 minutes. In all patients, pacing threshold increased by 154 ± 30% (p < 0.001) during the first 7 days that the catheter was in place. It is concluded that catheter countershock causes an acute increase in pacing threshold and decrease in R-wave amplitude. A catheter used for countershock may not be acceptable as a backup pacing catheter.     

Intermittent preexcitation in the wolff-parkinson-white syndrome

Intermittent loss of the delta wave in the Wolff-Parkinson-White (WPW) syndrome may result from precarious conduction over the accessory pathway and, as such, would predict a benign prognosis in the event of the occurrence of atrial fibrillation (AF). We evaluated 52 consecutive patients referred for the assessment of the WPW syndrome and determined the prevalence of intermittent preexcitation using review of serial electrocardiograms, ambulatory monitoring, and treadmill testing. All patients subsequently had electrophysiologic testing using standard techniques to determine the properties of the accessory pathway. Of the 52 patients, 26 (50%) were found to have Intermittent preexcitation as defined by loss of the delta wave with concomitant prolongation of the P-R interval on at least 1 occasion. These patients had longer effective refractory periods of the accessory pathway (356 ± 114 versus 295 ± 29 ms, mean ± standard deviation, p < 0.05) and longer shortest cycle lengths maintaining 1:1 anterograde conduction (426 ± 171 versus 291 ±63 ms, p < 0.02) than their counterparts with constant preexcitation. During AF, 15% of patients with intermittent preexcitation had shortest R-R intervals between preexcited beats < 250 ms, versus 50% of patients with constant preexcitation (p < 0.01). These data support the hypothesis that intermittent preexcitation suggests a benign prognosis in the event of AF. A careful search for intermittent preexcitation may yield important prognostic information in asymptomatic subjects and obviate further investigation.     

Regional and global left ventricular function during intra-aortic balloon counterpulsation in patients with acute myocardial infarction shock

We evaluated the improvement in hemodynamic and left ventricular (LV) function in 15 patients with acute myocardial infarction and cardiogenic shock, who were treated with intraaortic balloon counterpulsation (IABP). They were studied by flow-directed right heart catheterization and nuclear angiography. IABP decreased LV end-diastolic volume from 134 to 114 ml and LV end-systolic volume from 100 to 72 ml. LV stroke volume increased from 34 to 42 ml and cardiac output from 3.0 to 3.6 L/min. Global LV ejection fraction increased from 27.6% to 36.1%, and this was due to improvement in regional ejection fraction in ischemic areas. Pulmonary capillary wedge pressure and pulmonary blood volume decreased. Right ventricular ejection fraction also increased significantly. IABP improved LV function in acute myocardial infarction.     

Radionuclide analysis of right and left ventricular response to exercise in patients with atrial and ventricular septal defects

In patients with ventricular or atrial septal defect, the ventricle which is chronically volume overloaded might not appropriately respond to increased demand for an augmentation in output and thereby might limit total cardiac function. In this study we simultaneously measured right and left ventricular response to exercise in 10 normal individuals, 10 patients with ventricular septal defect (VSD), and 10 patients with atrial septal defect (ASD). The normal subjects increased both right and left ventricular ejection fraction, end-diastolic volume, and stroke volume to achieve a higher cardiac output during exercise. Patients with VSD failed to increase right ventricular ejection fraction, but increased right ventricular end-diastolic volume and stroke volume. Left ventricular end-diastolic volume did not increase in these patients but ejection fraction, stroke volume, and forward left ventricular output achieved during exercise were comparable to the response observed in healthy subjects. In the patients with ASD, no rest-to-exercise change occurred in either right ventricular ejection fraction, end-diastolic volume, or stroke volume. In addition, left ventricular end-diastolic volume failed to increase, and despite an increase in ejection fraction, left ventricular stroke volume remained unchanged from rest to exercise. Therefore, cardiac output was augmented only by the heart rate increase in these patients. Right ventricular function appeared to be the major determinant of total cardiac output during exercise in patients with cardiac septal defects and left-to-right shunt.     

Combined verapamil and propranolol for supraventricular tachycardia

The electrophysiologic effects of intravenous verapamil and propranolol were compared alone and in combination in 14 patients (aged 21 to 69 years) with paroxysmal Supraventricular tachycardia (SVT). Ten patients had atrioventricular (AV) reentry utilizing a manifest (7 patients) or concealed (3 patients) accessory pathway. Four patients had AV nodal reentry. Electrophysiology studies were performed using standard techniques in the control state and after verapamil (0.15 mg/kg intravenous bolus and 0.005 mg/kg/min). The next day, studies were repeated after propranolol (0.1 mg/kg) and a combination of verapamil and propranolol. No adverse effects occurred with the drug combination. Each drug intervention prolonged anterograde functional refractory period of the AV node (control, 370 ± 50 ms; verapamil, 446 ± 90 ms; propranolol, 436 ± 92, p < 0.05), with the greatest increase occurring after the drug combination (502 ± 103 ms, p < 0.001). In 2 patients prolonged sinus node recovery time developed after the drug combination. Verapamil or propranolol prevented SVT induction in 7 patients (50%). However, only the drug combination prevented reinduction of sustained SVT in 6 patients. These 6 patients were treated chronically with verapamil and propranolol, with no recurrence of SVT in any patient after 2 to 26 months.     

The localization of coronary artery stenoses by 12 lead ECG response to graded exercise test: support for intercoronary steal.

In 39 consecutive patients with unequivocally positive postexercise ECG we have correlated the location and severity of the coronary artery stenoses with the ECG leads in which ischemic ST changes occured. Patients with major stenoses of the right coronary artery, with or without disease of the left coronary system, showed ischemic ST changes in Leads II, III, and aVF. Patients with major stenoses of the left coronary system, many of whom had suffered old inferior wall infarction, showed ST changes in Leads I, aVL, and the chest leads. A group of 11 patients showed ischemic ST changes in leads other than those expected on the basis of the location and severity of coronary artery stenoses. In each of these 11 patients large collateral channels were donated by the vessel in whose territory the ischemic changes occurred. This finding lends support to the concept of intercoronary "steal" during exercise in coronary artery disease, at the same time reducing the value of the postexercise 12 lead ECG in predicting the location and severity of coronary artery stenoses.     

Initial splanchnic extraction of ingested glucose in normal man

Estimates of initial splanchnic uptake of ingested glucose and the concomitant suppression of endogenous glucose production were obtained in man by validated tracer techniques for non-steady-state turnover measurement. Nine normal volunteers (18–44 yr old) fasted overnight received intravenous infusions of tracer (3-³H-glucose or 1-¹⁴C-glucose) and a low (45 ± 1 g) or high (96 ± 5 g) oral load of glucose labeled with an alternative tracer (1-¹⁴C-glucose or 2-³H-glucose). A two-compartment model was used to derive rates of peripheral appearance (Ra) of glucose from all sources (total) and the Ra of ingested glucose. Ra (total glucose) and Ra (ingested glucose) were integrated from the first appearance of ingested glucose until the basal Ra (total glucose) of 116 ± 6 (SEM) mg/min was reattained. The total amount of glucose reaching the systemic pool in this time was 95 ± 4 g and 46 ± 3 g with high and low doses, respectively. Of these quantities 86 ± 4 g and 40 ± 3 g originated in the oral glucose, representing 90% ± 4% of the administered glucose. The remainder (11% ± 2% of the total) represented endogenous production, suppressed by 66% ± 6% relative to basal. Sequestration of ingested glucose and subsequent release did not take place during the study since identical results were obtained with ingested 1-¹⁴C-glucose or 2-³H-glucose. The latter label would have been lost if the glucose had entered the hexose-phosphate pool. Thus, in normal man approximately 90% of an ingested glucose load is absorbed and passes through the liver to appear in the systemic pool.