Cardiac death and stored electrograms in patients with third-generation implantable cardioverter-defibrillators

OBJECTIVE: The study's aim was to analyze the type of cardiac involvement in fetuses or infants with twin-twin transfusion syndrome. STUDY DESIGN: Seventeen pairs of monochorionic diamniotic twin fetuses with twin-twin transfusion syndrome underwent serial Doppler echocardiographic studies. Repeated decompressive amniocenteses were performed in all pregnancies. RESULTS: No specific cardiac involvement was seen in donor twins in utero or after birth. All recipient twin fetuses showed variable degrees of biventricular hypertrophy and dilation with tricuspid regurgitation. These features were also evident in 45% of the recipient twin neonates. The fluid unbalance resolved with serial amniocenteses in 9 cases and in a further 2 after the death of the donor twin; in all 11 of these recipient twin fetuses there was some degree of improvement of the cardiac involvement, which became normal in all surviving recipient twin infants within 40 days to 6 months after birth. CONCLUSION: Features of cardiac hypertrophy with signs of a prehydropic or hydropic state develop during fetal life in recipient twins in twin-twin transfusion syndrome; this impairment is reversible with the resolution of the fluid imbalance or after delivery.     

Spectral analysis of electrograms during ventricular tachycardia in a canine model: relation with epicardial isochronal maps

The purpose of this study was to assess the capability of magnitude-squared coherence and bicoherence to differentiate monomorphic ventricular tachycardia (MVT) and polymorphic ventricular tachycardia (PVT) in a canine model and to relate these results to the epicardial isochronal maps on a beat-to-beat basis. Unipolar electrograms were simultaneously recorded from the surface of both ventricles with a 127-lead sock electrode array in 12 open-chest anesthetized dogs. The sampling frequency was 500 Hz. Atrioventricular block was induced by formaldehyde injection into the atrioventricular node. The left anterior descending coronary artery was occluded for 60 minutes under ventricular pacing (140 beats/min). During reperfusion, 12 MVT episodes lasting more than 42 seconds were recorded. Left stellate ganglion stimulation induced five PVT episodes lasting more than 42 seconds. Each of these recordings was divided into seven segments of 3,072 points (6.144 seconds). After visual selection, 104 segments were extracted and classified as 73 MVT and 31 PVT segments. Magnitude-squared coherence was estimated as the cross-spectrum from two epicardial signals (on the right and left ventricles, respectively), normalized with the respective autopower spectrum. Bicoherence was estimated as the bispectrum normalized with the autopower spectrum. Magnitude-squared coherence correctly identified 96% of MVT and 81% of PVT segments for a total accuracy of 91%. Bicoherence estimated with the left ventricular lead correctly identified 100% of MVT and 77% of PVT segments with an accuracy of 93%. Beat-to-beat epicardial maps of MVT displayed a cluster of sites of origin close to the reperfusion area, while the sites of origin from beats during PVT were much more dispersed over both ventricles. A strong and significant correlation was found between the number of electrodes with the earliest epicardial activation and coherence (r = .76, P < .0001) and bicoherence (r = .68, P < .0001), respectively. A high and significant correlation was also found between both spectral estimators (r = .74, P < .0001). Coherence and bicoherence discriminated accurately between MVT and PVT. Coherence achieved better results compared with bicoherence. Coherence and bicoherence measurements showed a quantitative relation with the spatial dispersion of the sites of origin. Both spectral techniques seemed powerful enough to be used in the development of implantable devices.     

Prediction of outcome of patients with life-threatening ventricular arrhythmias treated with automatic implantable cardioverter-defibrillators using SPECT perfusion imaging

BACKGROUND: In the present study, we examined the predictors of outcome of 103 patients with coronary artery disease and left ventricular dysfunction who had life-threatening ventricular arrhythmias and were treated with implantable cardioverter-defibrillators with the use of single-photon emission computed tomography (SPECT). METHODS AND RESULTS: During a mean follow-up of 29 months, there were 29 cardiac deaths. In comparison with patients who died, survivors had less diabetes mellitus (45% versus 19%, P < .007), higher left ventricular ejection fraction (23 +/- 9% versus 27 +/- 11%, P = .04), and fewer perfusion defects as determined with stress SPECT (15 +/- 5 versus 12 +/- 5, P < .004). Most of the perfusion defects were fixed, indicative of scarring; the extent of reversible defects did not differ (2 +/- 3 in survivors and 3 +/- 4 in nonsurvivors). Multivariate Cox survival analysis identified the number of fixed defects as the only independent predictor of death (chi 2 = 10, P = .002). There were six deaths among 42 patients (14%) with < 8 fixed defects compared with 23 deaths among 61 patients (38%) with > or = 8 defects (P = .005). The 4-year survival was better in patients with < 8 segmental fixed defects than in those with > or = 8 fixed defects (80% versus 36%) (chi 2 = 8, P = .005). CONCLUSIONS: The myocardial perfusion pattern is an important determinant of outcome in patients with life-threatening ventricular arrhythmias who are treated with a implantable cardioverter-defibrillator. The extent of scarring separates patients into high- and low-risk groups with a 2.7-fold difference in death rate.     

Idiopathic verapamil-responsive left ventricular tachycardia: clinical characteristics and long-term follow-up of 33 patients

Long-term prognosis, pharmacological prophylaxis and transcatheter ablation in a large group of patients with idiopathic verapamil-responsive left ventricular tachycardia (IVRLVT) are reported in this study. Thirty-three patients with a mean age of 27 +/- 16 years at their first IVRLVT episode, were studied retrospectively. Ventricular tachycardia was of the right bundle branch block morphology in all cases, with left axis deviation in 29 and right axis deviation in five (one patient had the two morphologies). Mitral valve prolapse was present in four patients; no heart disease was found in the remaining 29. Ventricular tachycardia could be electrophysiologically induced in 90% of the patients; Holter monitoring showed only sporadic ventricular extrasystoles in 76%; late potentials were found in 33% of the cases. At the end of a follow-up of 5.7 +/- 4.7 years, no patient had died. Thirty-one patients (94%) received a mean of 2.5 +/- 1.2 drugs; beta-blockers were effective in 71% of the cases, verapamil in 25%, class 1 drugs in 22%, class 3 drugs in 18%. Two patients who never received prophylaxis and four in whom it was stopped, were controlled with verapamil in case of recurrence. Six patients underwent catheter ablation; two with DC shock in whom it was successful in one, and four with radiofrequency energy, with a total success rate. The good prognosis of IVRLVT has been confirmed in a long-term follow-up; a new finding is the high efficacy of beta-blockers for prophylaxis. Radiofrequency transcatheter ablation is an effective and safe therapy for patients with symptoms not controlled by drug treatment.     

Use of atrial and ventricular electrograms from a dual chamber implantable cardioverter defibrillator to elucidate a complex dysrhythmia

Stored intracardiac electrograms provided by third-generation ICDs have proved their use in the analysis of the mechanism of tachydysrhythmic events. There are cases in which the analysis of ventricular electrograms is insufficient for the elucidation of certain dysrhythmias. The availability of atrial electrograms provided by dual chamber ICDs improves the diagnostic capability of electrogram analysis and could prove most useful especially in complex dysrhythmias.     

Circannual variation of malignant ventricular tachyarrhythmias in patients with implantable cardioverter-defibrillators and either coronary artery disease or idiopathic dilated cardiomyopathy

We studied the possible relation between the frequency of ventricular tachyarrhythmic events and thermal stress in patients with an implantable cardioverter-defibrillator (ICD) living in a locally limited area under homogeneous climatic conditions. The frequency of tachyarrhythmic events was correlated with the thermal stress level according to the "Klima Michel Model," a complete thermophysiologic model that calculates "felt-temperature" values on the basis of the outdoor temperature and further meteorologic data. During a mean follow-up time of 40 +/- 17 months (range 4 to 72), 761 ventricular tachyarrhythmic events occurred in 50 of 138 consecutive ICD recipients. Analysis of the monthly felt-temperature levels and the mean circannual variation of the registered ventricular arrhythmias suggested that very cold and very hot conditions may be associated with an increased frequency of ventricular tachyarrhythmias. This finding was confirmed by calculation of the sum of tachyarrhythmias on all 2,039 days of the follow-up period divided into 5-degree-step felt-temperature classes. Thus, thermal stress may be 1 factor triggering the occurrence of ventricular tachyarrhythmias in patients with cardiac disease and suppressed cardiac function. Part of the increase in cardiac mortality under above-average hot and cold atmospheric conditions may be attributed to ventricular arrhythmic events.     

Configuration of unipolar atrial electrograms during electrically induced atrial fibrillation in humans

BACKGROUND: During atrial fibrillation (AF), the atrium is activated by multiple wavelets that continuously change in size and direction. The aim of this study was to correlate the temporal variation in AF electrogram configuration with the varying spatial patterns of activation. METHODS AND RESULTS: In a group of 25 Wolff-Parkinson-White patients undergoing cardiac surgery, the free wall of the right atrium was mapped (244 points) during electrically induced AF. The unipolar electrograms recorded during 4 seconds of AF were classified into four categories: (1) single deflections, (2) short-double potentials, (3) long-double potentials, and (4) fragmented potentials. The proportion of these four types of electrograms during AF was as follows: singles, 77 +/- 12%; short-doubles, 7 +/- 3%; long-doubles, 10 +/- 7%; and fragmented, 6 +/- 4%. Electrogram morphology was an indicator for rapid uniform conduction (single potentials; positive predictive value [PPV] of 0.96), collision (short-double potentials; PPV of 0.33), conduction block (long-double potentials; PPV of 0.84), and pivoting points or slow conduction (fragmented potentials; PPV of 0.87). In type I, II, and III AF, the proportion of long-double potentials was 4 +/- 2%, 12 +/- 3%, and 18 +/- 7% (P < .05); the proportion of fragmented complexes was 2 +/- 2%, 6 +/- 3%, and 10 +/- 4% (P < .05), respectively. During electrically induced and self-terminating episodes of AF, no preferential anatomic sites for double or fragmented potentials were found in the right atrium. CONCLUSIONS: The morphology of single unipolar electrograms during AF reflects the occurrence of various specific patterns of conduction. This might be used to differentiate between different types of AF and to identify regions with structural conduction disturbances involved in perpetuation of chronic AF.     

Antitachycardia pacing in patients with implantable cardioverter-defibrillators: inverse circadian variation of therapy success and acceleration

We analyzed spontaneous ventricular tachycardias treated by antitachycardia pacing during long-term follow-up in 138 recipients of an implantable cardioverter-defibrillator. An inverse circadian variation of the antitachycardia pacing termination and acceleration rates with the worst antitachycardia pacing success during the time period with the highest episode frequency (morning hours) was demonstrated.     

Radiofrequency catheter ablation of ventricular tachycardia in 26 patients

Electrophysiology study and radiofrequency catheter ablation (RFCA) were performed in 26 patients with refractory sustained ventricular tachycardia (VT). After induction of VT, 12-lead electrocardiogram (ECG) was recorded and QRS morphology and axis of induced VT were studied to identify the origin of VT. The precise site of VT origin were localized by pace mapping and activation mapping carefully. RF energy was delivered through a big-tip deflectable electrode catheter when the earliest site of endocardial activation and a high-frequency and low-amplitude potential of Purkinje fiber, preceding surface QRS by more than 25 ms, were identified and/or a pace map was obtained showing identical QRS complexes in at least 11 of 12 ECG leads. VTs were ablated successfully in 24 of 26 patients (success rate was 92%). For successful ablation, it is essential that the pace map QRS morphology in 12 leads should be identical with that in spontaneous or induced VT as far as possible in performing pace mapping. Pace mapping is safe, simple and has no unfavourable effect hemodynamics although it takes longer time. Activation mapping takes shorter time and has a high success rate. QRS configuration in spontaneous VT can help to localize the site of VT origin. Deliberate mapping at the site suggested to bo the origin of VT by surface ECG can shorten the duration of mapping and increase the success rate of RFCA. RFCA of VT in patients without structural heart disease is effective, safe, and has a high success rate, so it may be considered as an early therapy for these patients.     

Sudden cardiac death and the use of implantable cardioverter-defibrillators in pediatric patients. The Pediatric Electrophysiology Society

BACKGROUND: During the past decade, the implantable cardioverter-defibrillator (ICD) has emerged as the primary therapeutic option for survivors of sudden cardiac death (SCD). Investigation of the clinical efficacy of these devices has primarily assessed outcome in adults with coronary artery disease. The purpose of this cooperative, international study was to evaluate the impact of ICDs on the pediatric population of SCD survivors, based on an analysis of the clinical characteristics and outcomes of young patients who underwent ICD implantation following an episode of life-threatening ventricular tachycardia or resuscitation from SCD. METHODS AND RESULTS: An initial data base, established by contacting the manufacturers of the various commercially and investigationally available devices, identified 177 patients who were less than 20 years of age at the time of initial implantation of an ICD. With this data base as a reference, detailed responses were subsequently obtained from physicians involved in the care of 125 (71%) of these patients. The patients ranged in age from 1.9 to 19.9 years (mean, 14.5 +/- 4 years) and weighted 9.7-117 kg (mean, 44.6 +/- 14 kg). Of the 125 patients, 76% were survivors of SCD, 10% had drug refractory ventricular tachycardia, and 10% had syncope with heart disease and inducible sustained ventricular tachyarrhythmias. The most common types of associated cardiovascular disease were hypertrophic and dilated cardiomyopathies (54%), primary electrical diseases (26%), and congenital heart defects (18%). Ventricular function was abnormal in 46% of the patients. During a mean follow-up of 31 +/- 23 months, at least one ICD discharge occurred in 85 of the 125 (68%) patients. Seventy-three patients (59%) received at least one appropriate ICD discharge, and 25 patients (20%) had one or more spurious or indeterminate discharges. Duration of follow-up > 24 months (p = 0.001) and inducibility of a sustained ventricular arrhythmia (p = 0.05) were correlated with appropriate ICD discharges. There were nine deaths during the study period: five sudden, two due to recurrent ventricular arrhythmias, and two related to congestive heart failure. Abnormal ventricular function (p = 0.002) and prior ICD discharge (p = 0.01) were univariate correlates of patient mortality; by multivariate logistic regression, abnormal ventricular function was the only significant correlate of death (p = 0.005). By actuarial analysis, the estimated overall post-ICD implant survival rates at 1, 2, and 5 years were 95%, 93%, and 85%, respectively. The corresponding sudden death-free survival rates were 97%, 95%, and 90%. CONCLUSIONS: Pediatric patients resuscitated from SCD appear to remain at risk for recurrence of life-threatening tachyarrhythmias. During a mean follow-up of 31 months, the ICD provided an effective therapy for such arrhythmias in the majority of patients in this study. Following ICD implant, impaired ventricular function was the primary factor correlated with mortality. The patterns of ICD discharge observed in young patients and, thus, inferred risk of recurrent life threatening arrhythmias are similar to those of adult survivors of SCD. Thus, the use of ICDs in pediatric patients, with implant selection criteria similar to adults, appears valid.     

Prospective evaluation of new and old criteria to discriminate between supraventricular and ventricular tachycardia in implantable defibrillators

This study was designed to evaluate the ability to distinguish between supraventricular tachycardias (SVTs) and ventricular tachycardias (VTs) based on onset, stability, and width criteria in an implantable defibrillator. Inappropriate detection of atrial fibrillation and sinus tachycardia is a common problem in patients with implantable defibrillators. The onset, stability, and width criteria were studied in 17 patients who underwent implantation of a Medtronic 7218C implantable defibrillator by inducing sinus tachycardia and atrial fibrillation. Additional data on the width criteria was obtained by pacing at separate sites in both the left and right ventricle. Patients were studied at different times for up to 6 months to determine any changes in the criteria. The onset and stability criteria caused inappropriate detections in 36% and 12% of the episodes, respectively. The addition of the width criteria decreased the inappropriate detection using the onset and stability criteria to 5% and 2%, respectively. Pacing from the RV apex, RV outflow tract, and LV apex was appropriately detected as wide in 76%, 41%, and 94%, respectively. The width criteria changed over time in individual patients, but was stable by 6 months in all but one patient. No single criterion is satisfactory for distinguishing between SVT and VT in this patient population, but the combination of criteria seems to provide better discrimination. The width criteria can change dramatically over time and needs to be monitored carefully. Newer algorithms will need to be developed to allow better detection of supraventricular tachycardias.     

Verapamil-sensitive left anterior fascicular ventricular tachycardia: results of radiofrequency ablation in six patients

INTRODUCTION: Verapamil-sensitive left ventricular tachycardia (VT) with a right bundle branch block (RBBB) configuration and left-axis deviation has been demonstrated to arise from the left posterior fascicle, and can be cured by catheter ablation guided by Purkinje potentials. Verapamil-sensitive VT with an RBBB configuration and right-axis deviation is rare, and may originate in the left anterior fascicle. METHODS AND RESULTS: Six patients (five men and one woman, mean age 54+/-15 years) with a history of sustained VT with an RBBB configuration and right-axis deviation underwent electrophysiologic study and radiofrequency (RF) ablation. VT was slowed and terminated by intravenous administration of verapamil in all six patients. Left ventricular endocardial mapping during VT identified the earliest ventricular activation in the anterolateral wall of the left ventricle in all patients. RF current delivered to this site suppressed the VT in three patients (ablation at the VT exit). The fused Purkinje potential was recorded at that site, and preceded the QRS complex by 35, 30, and 20 msec, with pace mapping showing an optimal match between the paced rhythm and the clinical VT. In the remaining three patients, RF catheter ablation at the site of the earliest ventricular activation was unsuccessful. In these three patients, Purkinje potential was recorded in the diastolic phase during VT at the mid-anterior left ventricular septum. The Purkinje potential preceded the QRS during VT by 66, 56, and 63 msec, and catheter ablation at these sites was successful (ablation at the zone of slow conduction). During 19 to 46 months of follow-up (mean 32+/-9 months), one patient in the group of ablation at the VT exit had sustained VT with a left bundle branch block configuration and an inferior axis, and one patient in the group of ablation at the zone of slow conduction experienced typical idiopathic VT with an RBBB configuration and left-axis deviation. CONCLUSION: Verapamil-sensitive VT with an RBBB configuration and right-axis deviation originates close to the anterior fascicle. RF catheter ablation can be performed successfully from the VT exit site or the zone of slow conduction where the Purkinje potential was recorded in the diastolic phase.     

Clinical spectrum, therapeutic management, and follow-up of ventricular tachycardia in infants and young children

Prostaglandins mediate many biological processes. Arachidonic acid, the common precursor for all prostaglandins, is released from membrane phospholipids by both secretory and cytoplasmic forms of phospholipase A2. Free arachidonate is converted to prostaglandin H2, the common precursor to all prostanoids, by prostaglandin synthase. Both mitogen-induced prostaglandin synthesis in fibroblasts and endotoxin-induced prostaglandin synthesis in macrophages require expression of the inducible prostaglandin synthase-2; arachidonate released in these contexts is unavailable to prostaglandin synthase-1 constitutively present in fibroblasts or macrophages. In contrast to the results for fibroblasts and macrophages, prostaglandin synthesis by activated mast cells is mediated by prostaglandin synthase-1. Mast cell activation also provokes release of secretory phospholipase A2 (sPLA2). We now demonstrate that sPLA2 released from activated mast cells can mobilize arachidonate from distal Swiss 3T3 cells. This arachidonate is then used by prostaglandin synthase-1 present in 3T3 cells for prostaglandin synthesis. We thus distinguish two pathways for prostaglandin synthesis: (i) an intracellular pathway by which arachidonate released following ligand stimulation is made available only to prostaglandin synthase-2, and (ii) a transcellular pathway by which sPLA2 of proximal cells mobilizes, in distal cells, arachidonate available to prostaglandin synthase-1. Molecular and pharmacologic approaches to modulating prostaglandin-mediated events will differ for these two pathways.     

Determinants of inducible ventricular tachycardia in patients with clinical ventricular tachyarrhythmia and no apparent structural heart disease

Thirty-seven patients with symptomatic ventricular tachyarrhythmia and no apparent structural heart disease were evaluated with multiple cardiovascular tests to establish the relationship between the results of programmed electric stimulation and other clinical and arrhythmia variables. Of 37 patients, 12 (32%) had inducible sustained ventricular tachycardia. Factors associated with the results of programmed electric stimulation included a history of ventricular tachycardia > or = 30 seconds requiring intervention for termination and global right heart abnormality documented by echocardiography. During treatment for a mean follow-up of 50 months, 29 patients did well, 6 patients had recurrences of major arrhythmia symptoms, 1 was lost to follow-up and 1 had a noncardiac death. Those patients with an adverse outcome were more likely to have inducible ventricular tachycardia. Thus certain clinical and echocardiographic data are associated with the results of programmed electric stimulation, which in turn have important prognostic value in this group of patients. Sustained ventricular tachycardia is unlikely to be induced in patients with no evidence of structural heart disease and clinical nonsustained ventricular tachycardia.     

Effects of incremental doses of procainamide in patients with sustained uniform ventricular tachycardia

INTRODUCTION: Although intravenously administered procainamide has been used extensively during electropharmacologic testing for more than 10 years, there is little information available on the effects of incremental dosing of procainamide in patients with inducible, monomorphic ventricular tachycardia (VT). METHODS AND RESULTS: Twenty-nine patients with coronary artery disease had sustained monomorphic VT reproducibly induced in the baseline, drug-free state. Programmed stimulation was repeated 5 minutes after loading infusion (50 mg/min) of 7.5 and 15 mg/kg (all patients) and 22.5 mg/kg of procainamide (15 patients), while maintaining continuous infusion of 0.055, 0.11, and 0.165 mg/kg per minute after each increment in dose, respectively. Corresponding procainamide plasma concentrations were 5.6 +/- 2, 10.5 +/- 3, and 14.5 +/- 3 mg/L before, and 4.7 +/- 2, 9.6 +/- 3, and 14.6 +/- 4 mg/L after electrophysiologic study at each increment in dose of procainamide, respectively. Each incremental dose of procainamide resulted in significant prolongation of tachycardia cycle length and QRS duration during sinus rhythm and right ventricular pacing. Five (17%), 7 (24%), and 1 (7%) patients, respectively, had no inducible sustained VT following the incremental dosing of procainamide. Three of five patients who had no inducible VT at 7.5 mg/kg had VT induced again at a higher dose of procainamide. Four of 24 patients whose VT remained inducible at 7.5 mg/kg of procainamide had no VT induced at 15 mg/kg of procainamide. Twelve (41%), 15 (52%), and 6 (40%) patients, respectively, no longer had VT with baseline morphology induced following the incremental dosing of procainamide. VT with new morphology compared to baseline was induced in more than 40% of patients at one or more of the three different procainamide dosing regimens. The mean cycle length of VTs with new morphology was significantly shorter than the cycle length of tachycardias with baseline morphology at each particular dose of procainamide. CONCLUSION: Similar serum procainamide concentrations before and after programmed stimulation can be achieved at the described dosing regimen. Although 7.5 and 15 mg/kg of procainamide are both effective in suppressing induction of all VT in 20% to 25% of patients, non-inducibility at a particular dose of procainamide does not predict noninducibility at a respectively higher or lower dose. New morphologies of VT that are frequently faster than VTs with baseline morphology at a particular dose of procainamide can be induced in approximately half of the patients, and the clinical significance of these arrhythmias remains to be determined.     

Analysis of vagal effects on ventricular rhythm in patients with atrial fibrillation

1. Animal studies suggest that the heart-rate-lowering effect of vagal stimulation during atrial fibrillation is due to: (1) a direct depressant effect on atrioventricular node conductivity, (2) enhancement of concealed atrioventricular nodal conduction of atrial impulses through augmenting fibrillatory activity, thereby indirectly prolonging atrioventricular nodal refractoriness. The purpose of the present study was to analyse these effects in man. 2. Sixteen patients with chronic atrial fibrillation were studied. After administration of propranolol (0.2 mg/kg intravenously) baseline ventricular rhythm was recorded (500 R-R intervals). Recordings were repeated after methylatropine (0.02 mg/kg intravenously). The shortest R-R interval was taken to represent atrioventricular nodal refractoriness. The ratio of the longest to the shortest R-R interval and the coefficient of variation of R-R intervals were used as parameters of concealed conduction. 3. Methylatropine foremost shortened long R-R intervals: values for the mean, shortest and longest R-R intervals decreased from 834 to 685 ms (-18%) (P < 0.001), 573 to 498 ms (-13%) (P < 0.001) and 1228 to 924 ms (-25%) (P < 0.001), respectively. Accordingly, the ratio of the longest to the shortest R-R interval decreased: 2.12 to 1.89 (-11%) (P < 0.05). Also, the coefficient of variation decreased: 0.24 to 0.20 (-17%) (P < 0.05). 4. This study supports the contention that vagal stimulation lowers ventricular rate during atrial fibrillation both by exerting a direct effect on the atrioventricular node and by augmenting concealed conduction.     

Magnesium reversal of digoxin-facilitated ventricular rate during atrial fibrillation in the Wolff-Parkinson-White syndrome

The purpose of this investigation was to determine whether pyrophosphate, the anticalculus component of tartar-control dentifrices, exerts antimicrobial activity against oral bacteria commonly found in supragingival plaque. Minimal inhibitory concentrations of pyrophosphate were determined for Streptococcus sanguis, Streptococcus mutans (serotype c), Actinomyces viscosus and Actinomyces naeslundii. All of the bacteria tested were susceptible to pyrophosphate with identical minimal inhibitory concentrations of 0.67% wt/vol (25 mM). Bactericidal kinetics assays revealed that both S. mutans and A. viscosus were killed by pyrophosphate, with the latter being considerably more susceptible. The mechanism of killing was not due to high ionic strength, as comparable controls showed no loss in numbers of viable cells. Brief exposure (two 5-min incubations) of S. mutans to pyrophosphate and sodium dodecyl sulfate caused pronounced inhibition of growth over the 24-h test period. Under the constraints of the conditions used, these studies indicate that pyrophosphate and sodium dodecyl sulfate can substantially inhibit the growth of oral bacteria. These compounds may affect the oral microflora of patients who routinely use tartar-control dentifrices and mouthrinses.