Precision Electrocardiology: A Rational Approach for Simple and Complex Arrhythmias

Electrocardiography (ECG) in all its forms, from 12-lead ECG to long-term monitoring, is considered, an old and increasingly irrelevant test in this high technology era. This article reviews the clinical utility of this tool and argues that the obsolescence is due to an increasing inability to read electrocardiographic tracings. The usual interpretative pitfalls are discussed and a logical approach is proposed with illustrative examples. Finally, the concept of precision ECG is presented and its meaning reviewed.

Arrhythmias in Patients with Implantable Devices

Pacemakers, cardioverter/defibrillators, and implantable loop recorders with their continuously improved diagnostic capabilities offer detailed information that can help interpreting a cardiac arrhythmia in implanted patients. Nevertheless, in some cases, analysis of the electrical signals stored in the device memory may not be easy. An accurate knowledge of the company-specific software and the meaning of the different markers used are necessary to correctly interpret the arrhythmia or diagnose an inappropriate device intervention due to under- or oversensing. This new technology does not replace the "old" surface electrocardiogram but supplements it to improve arrhythmia diagnosis.

Sick Sinus Syndrome

The sick sinus syndrome includes symptoms and signs related to sinus node dysfunction. This can be caused by intrinsic abnormal impulse formation and/or propagation from the sinus node or, in some cases, by extrinsic reversible causes. Careful evaluation of symptoms and of the electrocardiogram is of crucial importance, because diagnosis is mainly based on these 2 elements. In some cases, the pathophysiologic mechanism that induces sinus node dysfunction also favors the onset of atrial arrhythmias, which results in a more complex clinical condition, known as "bradycardia-tachycardia syndrome."

Advanced Concepts of Atrioventricular Nodal Electrophysiology: Observations on the Mechanisms of Atrioventricular Nodal Reciprocating Tachycardias

Atrioventricular node reentrant tachycardia (AVNRT) is a supraventricular arrhythmia easily diagnosed by 12-lead electrocardiogram. What is far more challenging, is the understanding of the reentrant circuit in its typical and atypical presentations. The function of the atrioventricular node is still incomplete and this knowledge gap is reflected in the reconstruction of the pathways used by AVNRT in its multiform presentations. This article illustrates the heterogeneous electrocardiographic manifestations of AVNRT. We reconstruct the reentrant circuits involved using more recent understanding of the anatomic and electrophysiologic characteristics of the atrioventricular node.

Atrioventricular Nodal Conduction Disease

This article describes the different anatomic structures involved in normal atrioventricular conduction and their pathologic states. It defines their effects on the electrocardiogram, and describes how to localize the level and evaluate the severity of conduction disease by electrocardiographic analysis. It illustrates the relevance of intracavitary recordings in the diagnosis of level of block.

Intraventricular Delay and Blocks

From the atrioventricular node, electrical activation is propagated to both ventricles by a system of specialized conducting fibers, His Purkinje System (HPS), guaranteeing a fast, synchronous depolarization of both ventricles. From the predivisional common stem, a right and left branch separate, subdividing further in a fairly predictable fashion. Synchronous ventricular activation results in a QRS with specific characteristics and duration of less than 110 milliseconds. Block or delay in any part of the HPS changes the electrocardiographic (ECG) morphology. This article discusses the use and limitations of standard ECG in detecting abnormal ventricular propagation in specific areas of the HPS.

Map reduce for optimizing a large-scale dynamic network - the Internet of hearts

Rapid advancements of sensing and mobile technology provide an unprecedented opportunity to empower smart and connected healthcare. Realizing the full potential of connected care depends, however, to a great extent on the capability of data analytics. Our previous study proposed a next-generation mobile health system, namely, the Internet of Heart (IoH). The IoH embeds patients into a dynamic network, where the distance between network nodes is determined by the dissimilarity of patients' conditions. Dynamics of the network reveal the change of clinical status of patients. However, it poses a great challenge for real-time recognition of disease patterns when a considerably large number of patients are involved in the IoH. In this present investigation, we develop a novel scheme to optimize the network in a parallel, distributed manner, thereby improving the efficiency of computation. First, a stochastic gradient descent approach is designed to embed patients with similar conditions into a local network. Second, local networks are optimally pieced together to obtain a global network. As opposed to directly embed all patients into one network, the proposed scheme distributes the network optimization into multiple processors for parallel computing. This, in turn, enables the IoH to handle large amount of patients and timely recognize disease patterns in the early stage. Experimental results demonstrated the effectiveness of the proposed scheme, e.g., it achieves 80-fold faster than conventional algorithms for optimizing a network with 20000 patients. The developed scheme is effective and efficient for realizing smart connected healthcare in large-scale IoH contexts.

Whole heart modeling - Spatiotemporal dynamics of electrical wave conduction and propagation

Cardiac electrical activities are varying in both space and time. Human heart consists of a fractal network of muscle cells, Purkinje fibers, arteries and veins. Whole-heart modeling of electrical wave conduction and propagation involves a greater level of complexity. Our previous work developed a computer model of the anatomically realistic heart and simulated the electrical conduction with the use of cellular automata. However, simplistic assumptions and rules limit its ability to provide an accurate approximation of real-world dynamics on the complex heart surface, due to sensitive dependence of nonlinear dynamical systems on initial conditions. In this paper, we propose new reaction-diffusion methods and pattern recognition tools to simulate and model spatiotemporal dynamics of electrical wave conduction and propagation on the complex heart surface, which include (i) whole heart model; (ii) 2D isometric graphing of 3D heart geometry; (iii) reaction-diffusion modeling of electrical waves in 2D graph, and (iv) spatiotemporal pattern recognition. Experimental results show that the proposed numerical solution has strong potentials to model the space-time dynamics of electrical wave conduction in the whole heart, thereby achieving a better understanding of disease-altered cardiac mechanisms.

Signal processing techniques for atrial fibrillation source detection

In clinical practice, Atrial Fibrillation (AF) is the most common and critical cardiac arrhythmia encountered. The treatment that can ensure permanent AF removal is catheter ablation, where cardiologists destroy the affected cardiac muscle cells with RF or Laser. In this procedure it is necessary to know exactly from which part of the heart AF triggers are originated. Various signal processing algorithms provide a strong tool to track AF sources. This study proposes, signal processing techniques that can be exploited for characterization, analysis and source detection of AF signals. These algorithms are implemented on Electrocardiogram (ECG) and intracardiac signals which contain important information that allows the analysis of anatomic and physiologic aspects of the whole cardiac muscle.

Usefulness of three-dimensional non-fluoroscopic mapping in the ablation of typical atrial flutter

BACKGROUND

Catheter ablation of the cavo-tricuspid isthmus is rapidly becoming the first line of treatment in the management of atrial flutter. The standard procedure is usually performed under fluoroscopy guidance and relays on multisite endocardial recordings to assess the completeness of the isthmus conduction block. Despite the high rate of success there is, at follow-up, a considerable number of recurrences which could reflect the limitations of conventional assessment of conduction block across the isthmus. This new non-fluoroscopic mapping system allowing high density mapping along the entire length of the ablation line, could provide a more accurate way of verifying complete conduction block. The aim of the present study was to describe our overall results and long-term follow-up using a three-dimensional mapping system to guide radiofrequency ablation of typical atrial flutter.

METHODS

A multipoint three-dimensional map of the cavo-tricuspid isthmus, septal and lateral atrial wall was performed in 87 patients prior to and following ablation for typical atrial flutter. Evidence of persisting gaps in the line of block was identified by visual inspection of the color-coded activation maps and these sites were re-ablated. The conduction sequence was also assessed with conventional bidirectional pacing and recording. The assess the reduction in fluoroscopy time, two groups of patients were compared: group A (14 patients) in whom the entire mapping-ablation procedure was guided by the three-dimensional system (Carto, Biosense-Webster, Diamond Bar, CA, USA) and group B (32 patients) in whom the same protocol was used but the procedure was guided by standard fluoroscopic imaging.

RESULTS

Acute success was achieved in every patient. During bilateral isthmus pacing, the mean local activation time increased from 20.3 +/- 13.3 ms pre-ablation to 148.3 +/- 53.2 ms (p < 0.01) post-ablation with a mean difference of 120 +/- 31 ms. In 11 patients (9.2%) there was evidence of persisting conduction across the line of block despite evidence of reverse activation of the cavo-tricuspid isthmus by conventional pacing. A gap in the ablation line was identified and re-ablated. At a mean follow-up of 16.3 +/- 2.2 months, there were 5 (4.2%) recurrences of atrial flutter and 12 (10%) recurrences of isolated atrial fibrillation. Four of the 5 recurrences occurred in patients in whom ablation was guided by conventional fluoroscopy (group B). The fluoroscopy time was 4.2 +/- 1.5 min in group A and 27.2 +/- 8.2 min in group B (p < 0.001).

CONCLUSIONS

Multipoint mapping of the ablation line following radiofrequency ablation of typical atrial flutter performed using the Carto system allows a more accurate assessment of the isthmus conduction block. This has the potential to reduce the recurrence rate to the level observed for other supraventricular tachycardias.

Gender differences in autonomic cardiovascular regulation: spectral, hormonal, and hemodynamic indexes

The autonomic nervous system drives variability in heart rate, vascular tone, cardiac ejection, and arterial pressure, but gender differences in autonomic regulation of the latter three parameters are not well documented. In addition to mean values, we used spectral analysis to calculate variability in arterial pressure, heart rate (R-R interval, RRI), stroke volume, and total peripheral resistance (TPR) and measured circulating levels of catecholamines and pancreatic polypeptide in two groups of 25 +/- 1.2-yr-old, healthy men and healthy follicular-phase women (40 total subjects, 10 men and 10 women per group). Group 1 subjects were studied supine, before and after beta- and muscarinic autonomic blockades, administered singly and together on separate days of study. Group 2 subjects were studied supine and drug free with the additional measurement of skin perfusion. In the unblocked state, we found that circulating levels of epinephrine and total spectral power of stroke volume, TPR, and skin perfusion ranged from two to six times greater in men than in women. The difference (men > women) in spectral power of TPR was maintained after beta- and muscarinic blockades, suggesting that the greater oscillations of vascular resistance in men may be alpha-adrenergically mediated. Men exhibited muscarinic buffering of mean TPR whereas women exhibited beta-adrenergic buffering of mean TPR as well as TPR and heart rate oscillations. Women had a greater distribution of RRI power in the breathing frequency range and a less negative slope of ln RRI power vs. ln frequency, both indicators that parasympathetic stimuli were the dominant influence on women's heart rate variability. The results of our study suggest a predominance of sympathetic vascular regulation in men compared with a dominant parasympathetic influence on heart rate regulation in women.

Ablation of incisional atrial tachycardias using a three-dimensional nonfluoroscopic mapping system

Incisional atrial reentrant tachycardias are macroreentrant arrhythmias in which surgical scars or prosthetic material constitute one of the constraining barriers of the circuit. Accurate reconstruction based on fluoroscopy-guided endocardial mapping of the reentrant circuit is often incomplete and time consuming explaining, at least in part, the modest long-term results of this technique. Mapping and ablation of these arrhythmias using a three-dimensional nonfluoroscopic mapping system that allows electroanatomic reconstruction of the reentrant circuit could help in identifying the ablation targets and improve long-term outcome. The study included 20 patients (12 men, mean age 45+/-18 years) with corrected congenital heart disease (4 patients), coronary artery bypass surgery (7 patients), mitral or aortic valve replacement or reconstruction (6 patients), valve replacement and coronary revascularization (2 patients), and mitral valve replacement with maze procedure for atrial fibrillation (1 patient). Endocardial mapping with this novel system was complemented by standard electrophysiological techniques used to identify a critical isthmus of conduction. Two or more nonconductive areas of atrial tissue or surgical prosthetic material delimiting a critical isthmus of conduction were identified in every patient. Radiofrequency linear applications spanning two to more boundaries successfully eliminated the tachycardia in every patient. At a follow-up of 11.5+/-5.1 months (range 17-5 months), two (10%) patients developed a new clinical arrhythmia. The remaining 18 had no recurrences off medical therapy. Mean fluoroscopy time was 45.7+/-15.2 minutes for patients with a single scar and 89+/-41.2 minutes in patients with two or more scars. In conclusions, this new nonfluoroscopic mapping system offers the opportunity to achieve a high rate of cure of complex macroreentrant atrial tachycardias by facilitating reconstruction of the macroreentrant circuit and its boundaries.

Epinephrine, vasodilation and hemoconcentration in syncopal, healthy men and women

Healthy young people may become syncopal during standing, head up tilt (HUT) or lower body negative pressure (LBNP). To evaluate why this happens we measured hormonal indices of autonomic activity along with arterial pressure (AP), heart rate (HR), stroke volume (SV), cardiac output (CO), total peripheral resistance (TPR) and measures of plasma volume. Three groups of normal volunteers (n = 56) were studied supine, before and during increasing levels of orthostatic stress: slow onset, low level, lower body negative pressure (LBNP) (Group 1), 70 degrees head up tilt (HUT) (Group 2) or rapid onset, high level, LBNP (Group 3). In all groups, syncopal subjects demonstrated a decline in TPR that paralleled the decline in AP over the last 40 s of orthostatic stress. Ten to twenty seconds after the decline in TPR. HR also started to decline but SV increased, resulting in a net increase of CO during the same period. Plasma volume (PV, calculated from change in hematocrit) declined in both syncopal and nonsyncopal subjects to a level commensurate with the stress, i.e. Group 3 > Group 2 > Group 1. The rate of decline of PV, calculated from the change in PV divided by the time of stress, was greater (p < 0.01) in syncopal than in nonsyncopal subjects. When changes in vasoactive hormones were normalized by time of stress, increases in norepinephrine (p < 0.012, Groups 2 and 3) and epinephrine (p < 0.025, Group 2) were greater and increases in plasma renin activity were smaller (p < 0.05, Group 2) in syncopal than in nonsyncopal subjects. We conclude that the presyncopal decline in blood pressure in otherwise healthy young people resulted from declining peripheral resistance associated with plateauing norepinephrine and plasma renin activity, rising epinephrine and rising blood viscosity. The increased hemoconcentration probably reflects increased rate of venous pooling rather than rate of plasma filtration and, together with cardiovascular effects of imbalances in norepinephrine, epinephrine and plasma renin activity may provide afferent information leading to syncope.

Usefulness of midodrine in patients with severely symptomatic neurocardiogenic syncope: a randomized control study

INTRODUCTION

The efficacy of midodrine for the management of patients with neurocardiogenic syncope was assessed prospectively in a randomized control study.

METHODS AND RESULTS

Patients who had at least monthly occurrences of syncope and a positive tilt-table test were included in the study. A total of 61 patients were randomly allocated to treatment either with midodrine or with fluid, salt tablets, and counseling. Midodrine was given at a starting dose of 5 mg three times a day and increased up to a dose of 15 mg three times a day when required. Midodrine was given during the daytime every 6 hours. Thirty-one patients were assigned to treatment with midodrine; the other 30 patients were advised to increase their fluid intake and were instructed to recognize their prodromes and abort the progression to syncope. Patients were followed-up for at least 6 months. A quality-of-life questionnaire was administered at the time of randomization and 6 months after. At the 6-month follow-up, 25 (81%) of 31 midodrine-treated patients and 4 (13%) of the 30 fluid-therapy patients had remained asymptomatic (P < 0.001). One patient had to discontinue taking midodrine due to severe side effects and another six patients experienced minor side effects that did not require drug discontinuation.

CONCLUSION

Midodrine appeared to provide a significant benefit in patients with neurocardiogenic syncope. To prevent recurrence of symptoms, dose adjustments were required in about one third of patients.

Time averaged spatial distribution of epicardial dominant frequencies during ventricular fibrillation

Recent evidence suggests that the dominant frequencies during ventricular fibrillation (VF) may be used as indicators of dispersion in repolarization and in activation patterns. In the present study, we quantified dominant frequencies from multiple epicardial electrodes to investigate if there are differences in the averaged frequencies within the electrograms recorded from the left and the right ventricles. Further, we quantified whether the difference in average frequency between the two ventricles changed during 30 seconds of VF. Results from eighteen trials in two pigs showed that during the entire duration of VF the average dominant frequencies of all electrodes over the left ventricle were higher than those over the right ventricle (p < 0.005). The dominant frequencies are reciprocal of cycle periods or activation intervals during VF. Our results show that on average, activations in the left ventricle occurred at a faster rate than those in the right ventricle. Activation intervals at any site are determined by the refractory period at that site and the arrival time of next activation. Although differences in cellular properties may have contributed to the observed differences in activation intervals between the ventricles, it is possible that activation arrival times may be different as well. It is possible that the increased tissue mass of the left ventricle may increase the probability that any site will get excited at a faster rate after it is recovered from previous activation.

Time-frequency representation of epicardial electrograms during ventricular fibrillation

In the present study we quantified changes in dominant frequency, which is reciprocal of activation interval or cycle period, during ventricular fibrillation (VF). We used a Smoothed Pseudo Wigner Distribution (SPWD) to estimate time-frequency representations of epicardial electrograms recorded in swines. We used a sock with 64 electrodes spaced equally to record electrograms during 30 seconds of electrically induced VF. Results from 29 trials in three animals showed a mean dominant frequency of 6.64 Hz. We observed considerable variation in dominant frequencies during VF. Temporally, the frequencies varied by as much as +/- 1.24 Hz (2 standard deviations). Spatial variation in frequencies was +/- 1.20 Hz. Cycle periods were computed as the reciprocal of dominant frequencies obtained from the SPWD. These cycle periods were verified to be numerically similar to the cycle periods estimated using activation times detected from differentiated electrograms. Results of recent studies by others have shown that cycle periods during VF are correlated with refractory periods. Our results show that a non-stationary analysis technique such as the SPWD can be used to track spatio-temporal variation in cycle periods. These changes can be used to investigate spatio-temporal variation in cellular properties such as the effective refractory periods during VF. The substantial temporal variation in dominant frequencies that we observed suggest the possibility that the excitable gap at any epicardial location also varies considerably from one instance to another during a VF episode.

Frequency of superior vena cava syndrome following radiofrequency modification of the sinus node and its management

In a series of 35 consecutive patients, the presence of a permanent pacemaker appears to be a strong risk factor for developing superior vena cava syndrome after radiofrequency modification of the sinus node. Treatment of this complication with balloon venoplasty is as effective as surgical repair.

False positive head-up tilt: hemodynamic and neurohumoral profile

OBJECTIVES

This study examined differences in mechanisms of head-up tilt (HUT)-induced syncope between normal controls and patients with neurocardiogenic syncope.

BACKGROUND

A variable proportion of normal individuals experience syncope during HUT. Differences in the mechanisms of HUT-mediated syncope between this group and patients with neurocardiogenic syncope have not been elucidated.

METHODS

A 30-min 80 degrees HUT was performed in eight HUT-negative volunteers (Group I), eight HUT-positive volunteers (Group II) and 15 patients with neurocardiogenic syncope. Heart rate and blood pressure (BP) were monitored continuously. Epinephrine and norepinephrine plasma levels, as well as left ventricular dimensions and contractility determined by echocardiography, were measured at baseline and at regular intervals during the test.

RESULTS

The main findings of this study were the following: 1) All parameters were similar at baseline in the three groups; and 2) During tilt: a) the time to syncope was shorter in Group III than in group II (9.5 +/- 3 vs. 17 +/- 3 min p < 0.05); b) there was an immediate, persisting drop in mean BP in Group III; c) the decrease rate of left ventricular end-diastolic dimensions was greater in Group III than in Group II or Group I (-1.76 +/- 0.42 vs. -0.87 +/- 0.35 and -0.67 +/- 0.29 mm/min, respectively, p < 0.05); d) the leftventricular shortening fraction was greater in Group III than in the other two groups (39 +/- 1 vs. 34 +/- 1 and 32 +/- 1%, respectively, p < 0.05); and e) although the norepinephrine level remained comparable among the groups, there was a significantly higher peak epinephrine level in Group III than in Group II and Group I (112.3 +/- 34 vs. 77.6 +/- 10 and 65 +/- 12 pg/ml, p < 0.05).

CONCLUSIONS

Mechanisms of syncope during HUT appeared to be different in normal volunteers and patients with neurocardiogenic syncope. In the latter, there was evidence of an impaired vascular resistance response from the beginning of the orthostatic challenge. Furthermore, in the patients there was more rapid peripheral blood pooling, as indicated by the echocardiographic measurements of left ventricular end-diastolic changes, leading to more precocious symptoms. In syncopal patients, the higher level of plasma epinephrine probably mediated the increased cardiac contractility and possibly contributed to the impaired vasoconstrictive response.

Epicardial mapping and radiofrequency catheter ablation of ischemic ventricular tachycardia using a three-dimensional nonfluoroscopic mapping system

Endocardial radiofrequency catheter ablation of ischemic left ventricular tachycardia has been of variable success due to multiple factors. Two such factors include the location of the reentrant circuit in the deep myocardium or on the epicardial surface and the inherent limitations of fluoroscopy as a guide for target localization. We report a patient in whom successful epicardial mapping and radiofrequency catheter ablation of an ischemic left ventricular tachycardia was performed using pericardial access and the CARTO electroanatomic mapping system.

Energy steering of biphasic waveforms using a transvenous three electrode system

The optimal electrode configuration for endocardial defibrillation is still a matter of debate. Current data suggests that a two pathway configuration using the right ventricle (RV) as cathode and a common anode constituted by a superior vena cava (SVC) and a pectoral can (C) is the most effective combination. This may be related to the more uniform voltage gradient created by shocks delivered using this configuration. We hypothesized that more effective waveforms could be obtained by varying the distribution of the shock current between the two pathways of a three electrode endocardial defibrillation system. In 12 pigs, we compared the characteristics and the defibrillation efficacy of six biphasic waveforms discharged using either a two (RV-->C) or a three (RV-->SVC + C) electrode combination with the following configurations: Configuration 1 (W1): the RV apical coil was used as a cathode and the subcutaneous C as anode (RV-->C). Configuration 2 (W2): The RV was used as cathode and the combination of the atriocaval coil (SVC) and the subcutaneous C as anode (RV-->SVC + C). Configuration 3 (W3): The RV-->C was used for the first 25% of f+ and RV-->SVC + C for the remainder of the discharge including f 2 Configuration 4 (W4): The RV-->C was used for the first 50% of f+ and RV-->SVC + C for the remainder of the discharge including f 2 Configuration 5 (W5): The RV-->C was used for the first 75% of f+ and RV-->SVC + C for the remainder of the discharge including f 2. Configuration 6 (W6): The RV-->C was used for f+ and RV-->SVC + C for f 2. As an increasing fraction of the waveform was discharged using the RV-->SVC + C pathways, the impedance and the pulse width decreased while the tilt, the peak, and the average current significantly increased. The waveforms delivered using the RV-->SVC + C configuration for 100% or 75% of their duration had significantly lower stored energy DFT than the other waveform. Current distribution between three endocardial electrodes can be altered during the shock and generates waveforms with different characteristics. Shocks with 75% or more of the current flowing to the RV-->SVC + C required the lowest stored energy to defibrillate. This method of energy steering could be used to optimize current delivery in a three electrodes system.

Human histopathologic findings following radiofrequency ablation of the tricuspid-inferior vena cava isthmus

Radiofrequency (RF) ablation of the tricuspid valve-inferior vena cava isthmus is now the first line of treatment in the management of typical atrial flutter. Successful ablation is associated with conduction block in this region, although the histopathologic changes following this procedure have never been reported. We describe the pathologic changes following RF ablation of this region in an explanted heart of a patient undergoing heart transplantation 4 months after successful atrial flutter ablation. The findings confirm the ability of RF ablation to create in the isthmus a chronic full thickness fibrosis, which represents the histopathologic counterpart of the conduction block demonstrated at the end of procedure.

The effects of endocardial defibrillation on left ventricular function: a transoesophageal echocardiographic study

This study evaluates the immediate effects of the endocardial electrical shocks delivered by a transvenous defibrillation system on left ventricular (LV) function in a pig model. A triple-lead system consisting of two endocardial electrodes, in the right ventricular apex and the junction of superior cava-right atrium, and a custom-made defibrillation can implanted subcutaneously in the thorax was set up in 10 close-chest pigs. Transesophageal echocardiography with two dimensional image, m-Mode, and pulse Doppler was performed at baseline and after several episodes of fibrillation/defibrillation (F/DF). Each animal underwent an average of 8 (range 6 to 11) episodes of ventricle F/DF for a total of 210 (range 165 to 290) joules of biphasic-waveform defibrillation shocks. Heart rate, blood pressure, LV end-systolic area, end-diastolic area and fractional area contraction, isovolumic relaxation time, and both ratios of velocities and time-velocity integrals in transmitral Doppler flow E and A waves were unchanged after the shocks. This animal study suggests that multiple countershocks up to 210 joules delivered by a transvenous defibrillation system do not cause LV global systolic and/or diastolic dysfunction.

Selective interference with pacemaker activity by electrical dental devices

OBJECTIVE

We sought to determine whether electromagnetic interference with cardiac pacemakers occurs during the operation of contemporary electrical dental equipment.

STUDY DESIGN

Fourteen electrical dental devices were tested in vitro for their ability to interfere with the function of two Medtronics cardiac pacemakers (one a dual-chamber, bipolar Thera 7942 pacemaker, the other a single-chamber, unipolar Minix 8340 pacemaker). Atrial and ventricular pacemaker output and electrocardiographic activity were monitored by means of telemetry with the use of a Medtronics 9760/90 programmer.

RESULTS

Atrial and ventricular pacing were inhibited by electromagnetic interference produced by the electrosurgical unit up to a distance of 10 cm, by the ultrasonic bath cleaner up to 30 cm, and by the magnetorestrictive ultrasonic scalers up to 37.5 cm. In contrast, operation of the amalgamator, electric pulp tester, composite curing light, dental handpieces, electric toothbrush, microwave oven, dental chair and light, ENAC ultrasonic instrument, radiography unit, and sonic scaler did not alter pacing rate or rhythm.

CONCLUSIONS

These results suggest that certain electrosurgical and ultrasonic instruments may produce deleterious effects in medically fragile patients with cardiac pacemakers.

Systolic and diastolic effects of variable atrioventricular delay in patients with complete heart block and normal ventricular function

This study was designed to demonstrate the effects of varying the atrioventricular delay (AVD) on ventricular diastolic filling dynamics and the resultant stroke volume in patients with complete heart block and normal cardiac function. We studied 7 patients with normal cardiac function in whom a dual chamber pacemaker had been implanted because of complete heart block. Doppler and M-mode echocardiography was performed at 70, 100, 140, 180, and 220 ms, AVD with the device in DDD mode at a rate of 80 beats/min. The effects of these variable intervals on the contribution of the E and A waveform to the diastolic filling, on the stroke volume, and on the systolic intervals were evaluated. Optimization of this interval, with a 19% increase in stroke volume was achieved in the group of patients at an AVD of 140 ms. When considered individually, the AVD associated with the largest stroke volume, was 100 ms in 2 patients and 140 ms in the remaining 5. At this individual optimal AVD the ventricular septal contraction occurred 31 +/- 14 ms, before the end of the transmitral flow. The optimal AVD is, therefore, the one which synchronizes the ventricular and atrial systole so that the first ventricular septal contraction occurs after the peak of the A wave, just before the end of the transmitral flow. Because of the different functional cardiovascular status of the single patient, this parameter should be individualized; this can be clinically important as it may lead, in this patient population, to an improvement of the stroke volume up to 42%.

The vanishing defibrillator syndrome: incidence, mechanism, and clinical relevance

Intraperitoneal migration of an abdominally implanted cardioverter defibrillator is a complication not yet fully described. In a consecutive series of 195 patients, migration occurred between 1 and 20 months in 5 (8%) of the 63 patients in whom a subrectus abdomini placement of the generator was chosen. It was unrelated to the patients' clinical characteristics or the defibrillator model. Dysuria and inability to interrogate the device were present in every subject, and the diagnosis was confirmed by the characteristic abdominal x-ray appearance and the findings at the time of surgery. Adhesions involving the omentum, and in one case, the small bowels, were present in three patients and seem to be related to the length of intraabdominal permanence of the generator. Because this complication may be due to specific anatomical characteristics of the aponeurosis of the abdominal muscles, it is likely that its incidence will be unchanged by the use of smaller devices. A close follow-up of the generators implanted deep to the rectus fascia is therefore advisable.