Magnitude of ST segment depression during paroxysmal supraventricular tachycardia.
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Adult↗
Biomedical subjects
H Calkins
Publications and source records attributed to H Calkins.
Current treatment for Wolff-Parkinson-White syndrome: results and surgical implications.
From July 1986 to January 1991, 123 patients with Wolff-Parkinson-White syndrome underwent operation for ablation of aberrant conduction pathways. There were 85 male and 38 female patients ranging in age from 11 months to 68 years. Associated anomalies included Ebstein's anomaly, sudden death syndrome, coronary artery disease, cardiomyopathy, abdominal aortic aneurysm, neurofibromatosis, other arrhythmias, or other complex congenital heart disease. Forty-one patients had multiple accessory pathways. Operative results showed a 7% initial failure rate, which dropped to 3% after reoperation. One patient had undergone previous operation for Wolff-Parkinson-White syndrome at another institution. Procedures performed concomitantly included mitral or tricuspid valve repair or replacement (6), right ventricular conduit replacement, subaortic resection, Fontan repair, corrected transposition repair, coronary artery bypass, and placement of an automatic internal cardioverter defibrillator. There was no operative mortality. Late follow-up is 27 +/- 16 months, and complications included mitral regurgitation and myocardial infarction. By comparison, in the last 12 months 124 patients with the Wolff-Parkinson-White syndrome underwent catheter ablation using radiofrequency current. There were 9 patients with multiple pathways. One hundred twelve patients (90%) had all accessory atrioventricular connections ablated and have remained free of symptomatic tachycardia. There have been 12 failures (10%), of which 5 have had operation and 7 are being treated medically. Mean follow-up is 7 +/- 5 months, and complications included circumflex coronary artery occlusion, excessive bleeding, valve perforation, and cerebral vascular accident.(ABSTRACT TRUNCATED AT 250 WORDS)
Adolescent↗
Repolarization abnormalities after catheter ablation of accessory atrioventricular connections with radiofrequency current.
The purpose of this study was to evaluate the serial changes in T wave configuration in patients undergoing successful radiofrequency catheter ablation of accessory atrioventricular (AV) connections. Twenty-nine consecutive patients with overt preexcitation and 16 patients with a concealed accessory atrioventricular (AV) connection were included. An electrocardiogram (ECG) was recorded before ablation and 15 min, 1 or 2 days and 1 and 3 months after ablation. Postablation T wave abnormalities occurred in 22 (76%) of the 29 patients who had overt pre-excitation but in none of the 16 patients with a concealed accessory AV connection. The T wave abnormalities were not related to myocardial necrosis or echocardiographic abnormalities. The ECG location and severity of T wave changes were dependent on the accessory AV connection location and degree of baseline pre-excitation, respectively. Fourteen of 19 patients with a posteriorly located AV connection (left, right or septal) had T wave inversion or flattening in the inferior leads and 3 patients had precordial T wave peaking. Two patients with an anteroseptal AV accessory connection had both inferior T wave inversion or flattening and precordial T wave peaking. Among seven patients with a manifest left lateral accessory AV connection, two had lateral T wave inversion or flattening and two had precordial T wave peaking. There was 95% concordance between the directional change of the T wave after ablation and the direction of the delta wave on the baseline ECG.(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
Electrophysiological effect of varied rate and extent of acute in vivo left ventricular load increase.
STUDY OBJECTIVE: The aim was to determine whether the rate, the magnitude, or both, of increased left ventricular wall stress in vivo has consistent and prominent effects on repolarisation, afterdepolarisations, or arrhythmogenicity. DESIGN: Ten anaesthetised dogs underwent transient proximal aortic occlusion. Wall stress was estimated from pressure-volume data obtained by volume catheter, normalised to preocclusion values, and correlated with simultaneously determined changes in monophasic action potential duration (MAPd). Data were obtained during both fast (greater than 50% rise in wall stress within two beats) and slow occlusions, as well as during innervated and denervated conditions. EXPERIMENTAL MATERIAL: Adult mongrel dogs (20-25 kg) were used. MEASUREMENTS AND MAIN RESULTS: Two- to threefold increases in wall stress resulted in less than 5 ms shortening in MAPd and there was little correlation between wall stress and MAPd shortening. The strongest relation between normalised wall stress (EWSnorm) and MAPd was observed under denervated conditions during rapid aortic occlusion (delta MAPd = -2.5 x EWSnorm +2.1, r2 = 0.44, p less than 0.001). Afterdepolarisations were observed in fewer than 10% of occlusions and were not related to the magnitude or rate of loading change. Ventricular ectopy occurred more frequently during rapid than slow occlusions (87% v 56%, p = 0.01), but was unrelated to the level of wall stress increase or the presence of afterdepolarisations. CONCLUSIONS: Marked acute increases in left ventricular loading in vivo minimally alter repolarisation, and rarely lead to afterdepolarisations. The speed rather than magnitude of load change appears more important in the development of ventricular ectopy. These findings suggest that load induced ventricular ectopy is due to stretch induced automaticity rather than triggered activity or re-entry.
Action Potentials↗
Diagnostic evaluation and management of syncope.
Syncope is a common and important clinical problem that occurs in up to 30% of adults and accounts for up to 6% of general hospital admissions. Syncope of cardiovascular origin is particularly important to identify as it is associated with a high risk of sudden cardiac death. A complete history and physical examination may suggest a diagnosis in the majority of patients, but additional evaluation is often required. Electrophysiologic testing is of highest diagnostic yield in patients with structural heart disease. Negative electrophysiology test results are also of importance as they predict a very low incidence of sudden cardiac death during follow-up. Tilt-table testing is a recently developed tool that allows a diagnosis of vasopressor syncope to be established despite an atypical clinical history. Tilt-table testing can also be used to guide therapy.
Adult↗
Effect of antiarrhythmic drug therapy on the incidence of shocks in patients who receive an implantable cardioverter defibrillator after a single episode of sustained ventricular tachycardia/fibrillation.
Seventy-four patients (16 women, 58 men, age 58 +/- 11 years, mean +/- standard deviation) who received an implantable cardioverter defibrillator (ICD) after experiencing a single episode of ventricular tachycardia or ventricular fibrillation were followed to determine if antiarrhythmic drug therapy affects the incidence of ICD discharges. Thirty-three patients (group A) were treated with an antiarrhythmic drug that was either untested or previously demonstrated during electropharmacological testing to be ineffective in suppressing the induction of ventricular tachycardia. Forty-one patients (group B) were not treated with an antiarrhythmic drug. There were no significant differences between the two groups in regards to age, sex, incidence of coronary artery disease, left ventricular function or the type of ICD pulse generator used. During a mean follow-up of 14 months for the entire cohort, 15 patients (46%) in group A and 18 patients (44%) in group B experienced at least one ICD shock. The time to the first appropriate shock (5 +/- 5 months in both groups) and the frequency of ICD shocks (0.3 +/- 0.2/month in group A vs 0.4 +/- 0.5/month in group B) were similar in both groups. The incidence of syncope at the time of ICD discharge was higher in group A than group B patients (31% vs 5%, P less than 0.05). In conclusion, antiarrhythmic drugs that are untested or have failed electropharmacological testing do not appear to reduce the probability of ICD discharge over a short-term (mean 14 months) follow-up in patients who have had only one clinical episode of VT/VF and may increase the risk of syncope during ICD discharge.(ABSTRACT TRUNCATED AT 250 WORDS)
Anti-Arrhythmia Agents↗
Prospective comparison of a conventional and an accelerated protocol for programmed ventricular stimulation in patients with coronary artery disease.
BACKGROUND: This study compared the sensitivity, specificity, and efficiency of a "conventional" and "accelerated" programmed stimulation protocol in 293 patients with coronary artery disease who had a history of sustained or nonsustained monomorphic ventricular tachycardia (VT). METHODS AND RESULTS: In the conventional protocol, one and two extrastimuli were introduced during sinus rhythm and during basic drive trains at cycle lengths of 600 and 400 msec at the right ventricular apex and then at the outflow tract or septum. In the accelerated protocol, one, two, and then three extrastimuli were introduced at each of three basic drive train cycle lengths (350, 400, and 600 msec) at the right ventricular apex; the procedure was repeated at a second right ventricular site. Six hundred thirty-four electrophysiological tests were performed using one of these two protocols either in the baseline state (293 tests) or during drug testing (341 tests). The yield of sustained, monomorphic VT was 89% with the conventional protocol and 92% with the accelerated protocol during baseline tests in patients who had a history of sustained VT (p = 0.05); 20% and 34%, respectively, during baseline tests in patients with a history of nonsustained VT (p = 0.06); and 70% and 77%, respectively, during drug testing (p = 0.2). To induce sustained, monomorphic VT, 10.1 +/- 5.0 (mean +/- SD) protocol steps and 14.4 +/- 8.7 minutes were required with the conventional protocol, compared with 4.0 +/- 3.7 steps and 5.6 +/- 6.1 minutes with the accelerated protocol (p less than 0.001 for each comparison). Among the tests in which sustained, monomorphic VT was induced, sustained polymorphic VT or ventricular fibrillation was induced more often with the conventional protocol (3.6%) than with the accelerated protocol (0.9%, p = 0.05). CONCLUSIONS: The efficiency of programmed stimulation can be improved by the early use of a basic drive train cycle length of 350 msec and three extrastimuli. Compared with a conventional stimulation protocol, the accelerated protocol used in this study reduces the number of protocol steps and duration of time required to induce monomorphic VT by an average of more than 50% and improves the specificity of programmed stimulation without impairing the yield of monomorphic VT.
Cardiac Pacing, Artificial↗
Effects of drive train stimulus intensity on ventricular refractoriness in humans.
BACKGROUND: The strength-interval relation between the intensity of premature stimulus and the ventricular effective refractory period (VERP) has been well characterized. The effects of variation in the intensity of the basic drive train stimuli (S1) on VERP are not as well defined. This relation was studied in 44 patients undergoing clinically indicated electrophysiological study. METHODS AND RESULTS: The outputs of two stimulus isolation units were connected in parallel, allowing the intensity of S1 to be varied independently of intensity of the extrastimulus (S2). To prevent confounding effects from cycle length change, continuous overdrive pacing was performed for 3 minutes before each measurement of VERP. The effect of S1 intensity on VERP was assessed in 24 patients with S2 intensity kept constant at twice threshold. VERP shortened from 232 +/- 19 msec at an S1 intensity of 1.5 times threshold to 219 +/- 20 msec at 5 mA and 211 +/- 19 msec at 10 mA (p less than 0.0001 for baseline versus 5 mA and for 5 mA versus 10 mA). Autonomic blockade with atropine and propranolol blunted but did not completely eliminate this effect. To assess whether the effect of S1 intensity on VERP was independent of S2 intensity, S2 strength-interval curves were generated in 10 patients at low (1.5 times threshold) and high (10 mA) S1 intensities. All portions of the strength-interval curve were shifted to the left by an increase in S1 intensity. The time course of change in VERP after an abrupt increase in S1 intensity was assessed in an additional 10 patients. VERP changed slowly, requiring 18 +/- 28 seconds to shorten by 2 msec and 64 +/- 46 seconds to decrease by 10 msec after a change in S1 intensity from 1.5 times threshold to 10 mA. In a final group of 10 patients, VERP was measured using an eight-beat drive train and a 4-second intertrain interval. With this more conventional protocol, VERP shortened by 14 +/- 8 msec with an increase in S1 intensity from 1.5 times threshold to 10 mA. CONCLUSIONS: Increasing S1 intensity results in clinically significant, progressive shortening of VERP in man. This effect is independent of S2 intensity. The prolonged time course of the change in VERP after an increase in S1 intensity and the attenuation of this effect by autonomic blockade are consistent with stimulation of sympathetic nerve terminals and catecholamine release as a result of intense stimulation.
Adolescent↗
Radiofrequency catheter ablation of the atrioventricular junction from the left ventricle.
BACKGROUND: The purpose of this study was to describe a new technique for catheter ablation of the atrioventricular junction using radiofrequency energy delivered in the left ventricle. METHODS AND RESULTS: Catheter ablation of the atrioventricular (AV) junction using a catheter positioned across the tricuspid annulus was unsuccessful in eight patients with a mean +/- SD age of 51 +/- 19 years who had AV nodal reentry tachycardia (three patients), orthodromic tachycardia using a concealed midseptal accessory pathway, atrial tachycardia, atrial flutter (two patients), or atrial fibrillation. Before attempts at catheter ablation of the AV junction, each patient had been refractory to pharmacological therapy, and four had failed attempts at either catheter modification of the AV node using radiofrequency energy or surgical and catheter ablation of the accessory pathway. Conventional right-sided catheter ablation of the AV junction using radiofrequency energy in six patients and both radiofrequency energy and direct current shocks in two patients was ineffective. The mean amplitude of the His bundle potential recorded at the tricuspid annulus at the sites of unsuccessful AV junction ablation was 0.1 +/- 0.08 mV, with a maximum His amplitude of 0.03-0.28 mV. A 7F deflectable-tip quadripolar electrode catheter with a 4-mm distal electrode was positioned against the upper left ventricular septum using a retrograde aortic approach from the femoral artery. Third-degree AV block was induced in each of the eight patients with 20-36 W applied for 15-30 seconds. The His bundle potential at the sites of successful AV junction ablation ranged from 0.06 to 0.99 mV, with a mean of 0.27 +/- 0.32 mV. There was no rise in the creatine kinase-MB fraction and no complications occurred. An intrinsic escape rhythm of 30-60 beats/min was present in seven of the eight patients. Each patient received a permanent pacemaker and has been asymptomatic during 3-13 months of follow-up. CONCLUSIONS: Catheter ablation of the AV junction can be achieved effectively and safely using radiofrequency energy delivered in the left ventricle when the conventional right-sided approach is unsuccessful.
Adult↗
Radiation exposure during radiofrequency catheter ablation of accessory atrioventricular connections.
BACKGROUND: Catheter ablation of accessory atrioventricular (AV) connections has been demonstrated to be effective in more than 85% of patients. One of the risks of this procedure is radiation exposure during the fluoroscopic imaging necessary to guide catheter manipulation. The objective of the present study was to measure the radiation received by patients and physicians during radiofrequency catheter ablation and to estimate the resultant somatic and genetic risks. METHODS AND RESULTS: Radiation exposure to patients and physicians was measured during attempts at radiofrequency catheter ablation of accessory AV connections in 31 consecutive patients. Radiation exposure was measured using thermoluminescent sensors placed on the patient and on the physician. Somatic and genetic risks were estimated based on the radiation levels recorded using these sensors. The durations of fluoroscopy and of the catheter ablation procedure were recorded for each patient. Catheter ablation was successful in 28 of 31 patients (90%). Mean +/- SD duration of fluoroscopy was 44 +/- 40 minutes. The largest patient radiation dose was measured over the ninth vertebral body posteriorly (median, 7.26 rem [roentgen equivalents man]; range, 0.31-135.7 rem). Median radiation dose to the thyroid was 0.46 rem (range, 0.06-7.26 rem), and median radiation dose to the posterior iliac crest was 2.43 rem (range, 0.01-8.3 rem). The greatest radiation dose to the operator was recorded at the left hand (99 mrem). Mean radiation dose to the operator's eyes was 28 mrem. CONCLUSIONS: Radiofrequency catheter ablation of accessory AV connections may result in significant radiation exposure to the patient and to the physician. Each hour of fluoroscopic imaging is associated with a lifetime risk of developing a fatal malignancy of 0.1% and a risk of a genetic defect of 20 per 1 million births. Although these risks must be recognized, they are relatively small compared with the risks associated with alternate approaches to management, including no therapy, antiarrhythmic drug therapy, and surgery.
Adolescent↗
Clinical interactions between pacemakers and automatic implantable cardioverter-defibrillators.
Concomitant use of a pacemaker and an automatic implantable cardioverter-defibrillator (AICD) is common. Seventeen percent of patients receiving an AICD at The Johns Hopkins Hospital also had a permanent pacemaker implanted before (16 patients), at the same time as (2 patients) or after (12 patients) AICD implantation. Four types of interactions were noted: 1) transient failure to sense or capture immediately after AICD discharge (seven patients); 2) oversensing of the pacemaker stimulus by the AICD, leading to double counting (one patient); 3) AICD failure to sense ventricular fibrillation resulting from pacemaker stimulus oversensing (three patients, one only at high asynchronous output); and 4) pacemaker reprogramming caused by AICD discharge (three patients). No clinical sequelae of these interactions were noted during follow-up study. Thus, potentially adverse clinical interactions are common and routine screening is recommended. With proper attention to lead placements and programming of the devices, clinical consequences of these interactions can be avoided.
Anti-Arrhythmia Agents↗
Feasibility and cost savings of outpatient electrophysiologic testing.
The feasibility of outpatient electrophysiologic testing was examined by reviewing 100 consecutive outpatient tests performed in 95 patients. Seventy-one of the patients (75%) had no underlying heart disease. The electrophysiologic tests were performed to evaluate supraventricular tachycardias (n = 47), nonsustained ventricular tachycardia (n = 20), unexplained syncope (n = 21), palpitation (n = 9) or intermittent heart block (n = 2). A mean of 2.8 +/- 0.5 6F electrode catheters were inserted through a femoral vein. An electrode catheter was inserted into a subclavian or internal jugular vein in 28 tests and a 5F cannula was inserted into a femoral artery to monitor the blood pressure in 20 tests. The results of 61 tests (61%) were abnormal. Patients were monitored for a mean of 3.8 +/- 1.2 h after the procedure and then discharged. No complications occurred. For cost analysis a subgroup of 60 of these patients was matched for age, gender, heart disease and indication for electrophysiologic testing with a group of 60 patients who underwent electrophysiologic testing as inpatients. Physicians' fees for the two groups were similar; however, the mean hospital charge was $5,845 +/- 3,763 for the inpatient group compared with only $2,120 +/- 1,244 for the outpatient group (p less than 0.001). Thus, outpatient electrophysiologic testing is feasible and safe and results in substantial cost savings in patients without life-threatening arrhythmias.
Adult↗
The effect of rate on prolongation of ventricular refractoriness by quinidine in humans.
In this study, the rate dependent effect of quinidine on the ventricular effective refractory period (VERP) was evaluated in 30 patients undergoing electropharmacological testing with quinidine. The VERPs were measured in the baseline state and after at least 2 days of treatment with 1,458-2,044 mg/day of quinidine gluconate (mean plasma quinidine concentration 2.2 +/- 0.7 mcg/mL). In 20 patients, the VERP was measured using conventional basic drive trains of 8 beats and basic drive cycle lengths of 600, 500, 400, and 350 msec. In another 10 patients, the VERP was measured after 3 minutes of continuous ventricular pacing at cycle lengths of 600 and 400 msec, and compared to the VERPs measured at the same basic drive cycle lengths using basic drive train durations of 2 and 8 beats. In the baseline state and after treatment with quinidine, the VERP shortened progressively as the basic drive train cycle length decreased and as the drive train duration increased to 3 minutes (P less than 0.001). Quinidine consistently prolonged the VERP by 9%-11% (P less than 0.001), regardless of the basic drive train cycle length. Quinidine's effect was also not affected by the basic drive train duration. In conclusion, the effect of quinidine on VERP in humans is independent of the rate of the basic drive train, both when measured using conventional 8-beat basic drive trains and when a three minute drive train duration is used in order to attain the maximum effect of the basic drive train cycle length on the VERP.(ABSTRACT TRUNCATED AT 250 WORDS)
Cardiac Pacing, Artificial↗
Long-term results of catheter ablation of idiopathic right ventricular tachycardia.
Ten consecutive patients with recurrent episodes of symptomatic, idiopathic, sustained monomorphic ventricular tachycardia (VT) originating in the right ventricle underwent an attempt at catheter ablation of the ventricular tachycardia. There were seven women and three men, with a mean age of 39 +/- 14 years (+/- SD). None of the patients had any evidence of structural heart disease. The VT had a left bundle branch block configuration and an inferior axis in each patient, and the mean cycle length was 313 +/- 75 msec. Based on the methods of induction of the VT and the response of the VT to verapamil, the VT mechanism was presumed to be reentry in six patients, triggered activity in three patients, and catecholamine-sensitive automaticity in one patient. Sites for ablation were guided by pace mapping, and an appropriate target site was identified in the right ventricular outflow tract in each patient. From one to three shocks of 100-360 J (mean total, 336 +/- 195 J) were delivered from a defibrillator between the tip of the ablation catheter (cathode) and a patch electrode on the anterior chest (anode). An electrophysiology test 7-9 days after ablation demonstrated that VT was still inducible in only one patient, who was treated with amiodarone. One other patient had a recurrence of VT 3 weeks after ablation and was treated with verapamil. Eight of 10 patients were not treated with antiarrhythmic medications and have had no episodes of symptomatic VT during 15-68 months of follow-up (mean follow-up, 33 +/- 18 months). There were no acute or long-term complications.(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
Electrophysiological effect of volume load in isolated canine hearts.
In isolated isovolumic ventricles and in in situ ventricles under nonsteady-state conditions, alterations in load have been shown to affect electrophysiological properties via contraction-excitation feedback. However, the effect of alterations in loading conditions on electrophysiological properties in normal ventricles under physiological loading conditions remains unknown. Furthermore, the arrhythmogenic significance of these load-induced electrophysiological changes is uncertain. We increased end-diastolic volume (27 +/- 4 ml vs. 51 +/- 6 ml) and assessed conduction, refractoriness, ventricular fibrillation thresholds (VFTs), and inducibility of ventricular arrhythmias in 14 isolated blood-perfused ejecting canine ventricles under steady-state conditions. We also examined the effect of increased end-diastolic volume on refractoriness and monophasic action potential (MAP) duration and contour under isovolumic versus ejecting conditions. Under ejecting conditions, increased end-diastolic volume resulted in very small (less than 1.5%) changes in the absolute refractory period (10 mA) and in local activation time but no change in local electrogram duration, overall dispersion of refractoriness, MAP duration or contour, VFT, or inducibility of ventricular arrhythmias. Increased volume loading under isovolumic conditions resulted in a very slight (less than 1%) shortening of MAP duration and refractoriness but had no effect on the MAP contour. These findings provide strong evidence that alterations in volume load are of little electrophysiological or arrhythmogenic importance in normal canine ventricles under physiologically loaded conditions (contraction-excitation feedback, load and arrhythmias, volume load).
Action Potentials↗
Effect of acute volume load on refractoriness and arrhythmia development in isolated, chronically infarcted canine hearts.
In normal isolated, perfused canine ventricles, increased ventricular volume leads to shortening of refractoriness. To test the hypothesis that myocardium within an infarction zone is more susceptible to volume-induced changes in refractoriness than is normal myocardium, we measured strength-interval curves at low and high end-diastolic volumes at control and infarcted sites in 14 isolated, blood perfused, canine hearts with chronic (greater than 25 days) infarctions. In addition, the effect of volume load on inducing ventricular arrhythmias was studied at one to six sites in 11 hearts. Differences in refractoriness and inducibility at low (22 +/- 5 ml) and high (48 +/- 6 ml) end-diastolic volumes were compared. At control sites, volume load reduced the absolute refractory period from 178 +/- 16.5 to 175 +/- 16.7 msec (p less than 0.05), but no significant change in the relative refractory period occurred. At infarcted sites, the change in refractoriness with volume load was greater, and the absolute refractory period decreased from 171.5 +/- 21 to 160.6 +/- 26.3 msec (p less than 0.01), and the relative refractory period decreased from 180.1 +/- 22.1 to 169.9 +/- 26 msec (p = 0.05). This differential effect of volume load on refractoriness led to an increased dispersion of overall refractoriness at high volume. Infarcted sites showing the largest changes in refractoriness were characterized by patchy scars extending at least to the midmyocardium, whereas sites located within areas of transmural scar, endocardial scar, or rare microfoci of fibrosis showed no increased sensitivity to volume load. Of eight hearts in which no tachyarrhythmias were inducible during programmed electrical stimulation at low volume, four had tachyarrhythmias induced at high volume. Sites of stimulation associated with a conversion from noninducible to inducible tachyarrhythmias showed a larger degree of shortening of refractoriness (change in absolute refractory period: 24.7 +/- 16.5 vs. 3.9 +/- 6.5 msec, p less than 0.05). These data indicate that volume loading may have electrophysiologic significance and that it may be of greater functional importance under pathologic conditions.
Animals↗
Changes in myocardial repolarization in patients undergoing balloon valvuloplasty for congenital pulmonary stenosis: evidence for contraction-excitation feedback in humans.
Alterations in ventricular loading conditions lead to changes in action potential duration and arrhythmias via contraction-excitation feedback; a decrease in load leads to prolongation of repolarization. To determine whether changes in right ventricular load alter ventricular repolarization in man, the corrected QT interval, a measure of overall ventricular repolarization, was measured in 32 patients before and after valvuloplasty for pulmonary stenosis. Right ventricular systolic pressure decreased (82.5 +/- 30.7 to 40.5 +/- 9.5 mm Hg, p less than .001) and the QTc increased concurrently (409.1 +/- 24.3 to 440.7 +/- 28.0 msec, p less than .001) after successful valvuloplasty. The increase in QTc was most marked for those patients with a greater than 30 mm Hg decrease in right ventricular pressure (40.0 +/- 23.3 vs 16.3 +/- 21.3 msec, p = .006). In a subset of seven patients in whom monophasic action potentials were recorded, monophasic action potential duration, a measure of local repolarization, was prolonged (230.0 +/- 24.3 vs 216.9 +/- 21.9, p less than .001) after successful valvuloplasty, confirming that the QTc prolongation reflected changes in local ventricular repolarization. In addition, during nine acute right ventricular outflow tract occlusions in a subset of six patients, monophasic action potential duration shortened (206.6 +/- 17.6 vs 221.7 +/- 20.9 msec, p less than .01) and early afterdepolarizations developed consistent with contraction-excitation feedback. These data suggest that, in humans, changes in mechanical load are associated with changes in ventricular repolarization consistent with contraction-excitation feedback.
Action Potentials↗
Studies on osteoporosis III. Effect of estrogens and fluoride.
Total skeletal calcium levels were determined in female mice with the aid of whole body neutron activation analysis. Three months treatment with heparin produced significant osteoporosis in C3-H/St(Ha) mice but not in C57/BL6 (J) mice. Treatment with a conjugated natural estrogen preparation (Premarin) prevented heparin accelerated osteoporosis, but high level fluoride in the drinking water had no preventive effect. In some experiments there was a suggestion of a deleterious effect of fluoride.
Animals↗