Stepwise Evaluation of Unexplained Syncope in a Large Ambulatory Population

Background: Up to 60% of syncopal episodes remain unexplained. We report the results of a standardized, stepwise evaluation of patients referred to an ambulatory clinic for unexplained syncope.
Methods and Results: We studied 939 consecutive patients referred for unexplained syncope, who underwent a standardized evaluation, including history, physical examination, electrocardiogram, head-up tilt testing (HUTT), carotid sinus massage (CSM) and hyperventilation testing (HYV). Echocardiogram and stress test were performed when underlying heart disease was initially suspected. Electrophysiological study (EPS) and implantable loop recorder (ILR) were used only in patients with underlying structural heart disease or major unexplained syncope. We identified a cause of syncope in 66% of patients, including 27% vasovagal, 14% psychogenic, 6% arrhythmias, and 6% hypotension. Noninvasive testing identified 92% and invasive testing an additional 8% of the causes. HUTT yielded 38%, CSM 28%, HYV 49%, EPS 22%, and ILR 56% of diagnoses. On average, patients with arrhythmic causes were older, had a lower functional capacity, longer P-wave duration, and presented with fewer prodromes than patients with vasovagal or psychogenic syncope.
Conclusions: A standardized stepwise evaluation emphasizing noninvasive tests yielded 2/3 of causes in patients referred to an ambulatory clinic for unexplained syncope. Neurally mediated and psychogenic mechanisms were behind >50% of episodes, while cardiac arrhythmias were uncommon. Sudden syncope, particularly in older patients with functional limitations or a prolonged P-wave, suggests an arrhythmic cause.     

Heart Rate Variability in Myocardial Infarction With and Without Malignant Arrhythmias: Comparison with Heart Transplant Recipients and Normal Subjects

Myocardial autonomic denervation occurs after acute MI. This process is followed by a reduction of heart rate variability (HRV) and an increase of malignant ventricular arrhythmias and sudden death. This study investigated whether there are any significant differences in HRV among the population of MI who did and did not have malignant ventricular arrhythmias (MVAs), normal subjects and heart transplant recipients, the paradigm of the denervated heart. We studied 25 subjects aged 42 ± 17 years, with normal clinical and cardiac noninvasive evaluation (group A); 70 patients aged 57 ± 14 years, who had MI hut no arrhythmic event in 36 months of follow-up (group B); 13 patients with MI aged 65 ± 9 years, who had had sustained VT, VF, or sudden death (group C); and 16 cardiac transplant recipients aged 35 ± 14 years (group D). The ECG was sampled for 256 seconds. We calculated, in time and frequency domain, the standard deviation of the RR cycle length and the spectral component's very low frequency (< 0.05 Hz), low frequency (0.05–0.15 Hz), and high frequency (0.15–0.35 Hz). The values of HRV in group A were significantly greater than in groups B, C, and D (P < 0.001) and greater in group B than in groups C and D (P < 0.001). Groups C and D did not differ (P = 0.610). These data indicate that HRV of patients who have had an MI and MVAs is very similar to that of heart transplant recipients. This is an indirect evidence that myocardial autonomic denervation may play an important role in the genesis of malignant arrhythmic events.     

Vasovagal Syncope: Diagnostic Role of Head-Up Tilt Test in Patients with Positive Ocular Compression Test

We investigated the relative merits of the ocular compression test and the head-up tilt test to aid differentiation of syncope and seizures in young patients. Sixteen patients (10 males and 6 females) with a mean age of 14 ± 4.7 (SD) years (range 7–22 years) underwent graded head-up till (15°, 30°, and 45° for 2 minutes each, then 60° for 20 minutes) following positive ocular compression testing defined as precipitation of asystole for at least 3 seconds (mean 5 seconds ± 2 seconds, range 3–12 seconds). Each patient presented with recurrent unexplained loss of consciousness (mean number of episodes 30 ± 45, mean duration of illness 52 ± 40 months), and seven patients were receiving anticonvulsant medications, three of these had normal EEGs. Eleven patients (69%) developed vasovagal syncope during head-up tilt, reproducing their clinical episodes (systolic blood pressure decreased from 105 ± 10 mmHg to 84 ± 13 mmHg, diastolic blood pressure from 75 ± 9 to 22 ± 25 mmHg, and heart rate from 89 ± 13 beats/mm to 37 ± 20 beats/min). Asystole occurred in two patients during vasovagal syncope lasting 11 seconds in one and 16 seconds in the other, and, it was associated with myoclonic movements in both (convulsive syncope). Based on these findings, and given the perceived potential hazards of the ocular compression test, the head-up tilt test may be a safer procedure that adds useful information to the diagnostic evaluation of these patients.     

Maturation of the Sensed Electrogram Amplitude Over Time in a New Subcutaneous Implantable Loop Recorder

The cause of recurrent syncope may be difficult to determine if the diagnosis is not establisbed from initial noninvasive and invasive testing. Eighteen patients with recurrent syncope and negative tilt table and electrophysiological testing underwent implantation of a left pectoral subcutaneous loop recorder. This device "freezes" the preceding 7.5 or 15 minate rhythm strip after magnet application after spontaneous syncope. Baseline and follow-up electrograms were routinely recorded, and patients were followed until syncope recurred. Three patients bad syncope within 1 month of implantation and were excluded from this report. Implantation electrogram amplitude was 250 ±124 /μV and increased to 291 ±114 μV at 2–3 months, and increased further to 353 ± 167 μV at 4–6 months (P < 0.001, ANOVA). Syncope recurred in 14 of the 15 patients. An arrhythmic basis for syncope was established (n = 7) or excluded (n = 7) in every patient who had recurrent syncope. All syncopal episodes were associated with diagnostic sensed electrograms. The increase in sensed electrogram amplitude over time suggests a maturation of the device-tissue interface. These results support the long-term viability of this implantable monitoring technique.     

Early Benefit of Implantable Cardioverter Defibrillator Therapy in Patients Waiting for Cardiac Transplantation

The ICD can effectively recognize and treat ventricular arrhythmias that can lead to sudden death. Sudden death is a major problem in patients awaiting heart transplantation. We reviewed our experience with the ICD in patients with malignant ventricular arrhythmias waiting for cardiac transplantation. Nineteen patients were included. Seventeen were men, mean age was 54 ±11 years (range 17–66) and the left ventricular ejection fraction was 22%± 10% (range 9%–46%). After a mean follow–up of 6 ± 5 months (range 1–20 months), 17 patients reached heart transplantation. One patient died and the other is waiting for a transplant. Before transplantation 71 % of patients received an appropriate discharge. The mean time to the first appropriate discharge was 2 ± 2 months (range < 1–6 months), which was significantly shorter than the mean time to first discharge in the other patients (n = 182) receiving a defibrillator in our center (11 ±10 months; range 1–58 months) (P < 0.0004). In conclusion, cardiac transplantation candidates with life–threatening ventricular arrhythmias can effectively be protected against sudden arrhythmic death by ICD. These patients have a high incidence of appropriate shocks occurring very early after implantation.     

Natural and Unnatural History of Patients with Severe Carotid Sinus Hypersensitivity: A Preliminary Study

Natural history of patients with symptomatic severe carotid sinus hypersensitivity is not clearly known. In order to evaluate the effectiveness of pacing therapy in these patients we performed a randomized treatment/no-treatment prospective study in 35 patients. They were randomly assigned to two groups: 19 patients received no therapy, 16 patients received a VVI (# 11) or DDD (#) pacemaker implant. During the 8.4 ± 4.3 month follow-up period patients receiving no therapy had recurrence of syncope in 9 cases (47%) and minor symptoms in 13 (68%); at the 16th month, actuarial curve showed absence of syncope in 36% of patients and of any symptoms in 30%. During the 7.2 ±4.1 month follow-up period, the patients receiving the pacemaker implant had no recurence of syncope, minor symptoms in three (19%); at the 16th month, actuarial curve showed absence of syncope in 100% of patients and of any symptoms in 78%. During follow-up, 12 patients in no-treatment group received a pacemaker implant because of the recurrence of severe symptoms; successively they had a strong reduction of symptoms. In conclusion, this study definitively demonstrates that patients with severe symptomatic carotid sinus hypersensitivity had a high rate of recurrence of spontaneous symptoms and that in these patients cardiac pacing is a useful therapy.     

Dual Chamber Pacing for Neurally Mediated Syncope with a Prominent Cardioinhibitory Component

The role of cardiac pacing for treatment of recurrent neurally mediated syncope (NMS) remains controversial. We hypothesized that dual chamber pacing in NMS patients with a prominent cardioinhibitory component may be beneficial. Twelve patients (mean age = 37.8 ± 17 years, range 15–78 years, 7 men and 5 women) with a mean of 4 ± 2.2 episodes of syncope underwent tilt table evaluation. Patients were passively tilted to 70° head-up position for 20 minutes and then returned to the supine position. Isoproterenol was then infused at 1–2 μg/min to increase heart rate by ≥ 25% and tilt was repeated. Patients lost consciousness after 16 ± 6 minutes of tilt; nine patients had syncope in the baseline state and three during isoproterenol infusion. All patients had at least 5 seconds of asystole with a mean of 9.5 ± 4 seconds (range 5–20 s). A dual chamber permanent pacemaker with a special feature allowing heart rate acceleration in response to bradycardia was implanted in all patients. During a mean follow-up of 18.6 ± 4.2 months, 11 (92%) of these patients were free of syncope and had negative tilt table test. One (8%) patient had two episodes of syncope. We conclude that dual chamber pacing may be beneficial in patients with NMS with a prominent cardioinhibitory component.     

Holter Monitoring vs Tilt Testing in the Investigation of Suspected Vasovagal Syncope

The aim of this study was to compare the diagnostic yield of 48-hour Holter monitoring with head-up tilt (HUT) test in patients presenting with blackouts suggestive of vasovagal syncope. One hundred and eighteen consecutive patients, 68 women, aged (mean [SD])   50 ± 20  years   (range 16–88 years), underwent 48-hour Holter monitoring and 60° HUT test within 3 months. Endpoints were symptom-ECG correlation during Holter monitoring and positive HUT test. Syncope occurred in 3 (3%) patients during Holter monitoring, the rhythm being sinus tachycardia in all. Presyncope was reported in 22 (19%), the rhythm being sinus tachycardia in 6, persistent atrial fibrillation in 2, and normal sinus rhythm in the remainder. Asymptomatic arrhythmias were recorded in 103 (87%) patients. Positive HUT tests occurred in 39 (33%), the pattern being mixed (VASIS type 1) in 14 (36%), cardioinhibitory (VASIS type 2) in 3 (8%), and vasodepressor (VASIS type 3) in 22 (56%). Change in patient management occurred in 3 (3%) patients following Holter monitoring and 39 (33%) patients following HUT test. Holter monitoring produces a low yield of clinically useful information in the investigation of suspected vasovagal syncope. An HUT test should be considered the primary investigation of choice in such patients. (PACE 2003; 26[Pt. I]:1523–1527)     

Results of Delivered Therapy for VT or VF in Patients with Third-Generation Implantable Cardioverter Defibrillators

Third-generation implantable cardioverter defibrillators (ICDs) offer tiered therapy and can provide significant advantage in the management of patients with life-threatening arrhythmias. Three different types of ICDs were implanted in 21 patients with ventricular tachycardia (VT) or ventricular fibrillation (VF). Arrhythmia presentation was VT(76%), VF(10%), or both (14%). The mean left ventricular ejection fraction for the group was 32.4 ± 7%. No surgical mortality occurred. Prior to discharge individual EPS determined the final programmed settings of the ICDs. During a mean follow-up of 13 ± 1.4 months (range 2–20) the overall patient survival was 85.7%. No sudden arrhythmic or cardiac death occurred. Twenty of 21 patients (95%) received therapy by their device. In 14 patients (67%) antitachycardia pacing (A TP) was programmed "on," 13 of which was self-adaptative autodecremental mode. There were 247 VT episodes, 231 of which were subjected to ATP with 97% success and 3% acceleration or failure. Low energy shocks reverted all other VT episodes. VF episodes were successfully reverted by a single shock (93%), two shocks (6%), or three shocks (1 %). We conclude that ATP therapy of VT is successful in the large majority of episodes with rare failures, and that VF episodes are generally terminated by a single ICD shock.     

Heart Rhythm During Syncope and Presyncope: Results of Implantable Loop Recorders

NIEROP, P.R., et al. : Heart Rhythm During Syncope and Presyncope: Results of Implantable Loop Recorders. Ambulatory ECG monitoring in patients with recurrent syncope is nondiagnostic in the majority of cases. Recently, an ECG implantable loop recorder (ILR) has been introduced. The ILR performs continuous ECG monitoring over a period of at least 14 months. From February 1997 to September 1999, 35 patients underwent implantation of an ILR. During a mean follow-up of  11 ± 8 months  , 24 (69%) patients had recurrent syncope or presyncope events. Four (11%) patients were not capable of activating the ILR to save the event. A symptom-rhythm correlation could be studied in 20 (83%) of 24 patients. Forty of 44 recurrences were captured by the ILR. There were 14 (40%) patients with at least one syncopal episode. An arrhythmic cause for syncope was found in eight of them (bradycardia in four and tachycardia in four). In the other six patients the heart rhythm was normal. In 17 (49%) patients with 1-year follow-up, the mean syncope event rate 12 months before ILR implantation was  4.7 ± 2.4  , whereas the mean syncope event rate 12 months after ILR implantation was  1.3 ± 0.7  (  P < 0.01  ). Resolution of symptoms was observed in 6 (17%) patients. These patients were significantly younger than patients without resolution (  50 ± 18 vs 69 ± 14 years, p < 0.01  ) and five were women. Three (9%) patients died during follow-up, all of them were noncompliant during their follow-up. In conclusion, the ILR made symptom—rhythm correlation possible in 83% of patients with recurrent syncope. Syncope recurrences decreased significantly after implantation of the device, especially in the younger patients. Noncompliant patients had a high mortality rate.     

Current and emerging indications for implantable cardiac monitors

Implantable cardiac monitors (ICMs) continuously monitor the patient's electrocardiogram and perform real-time analysis of the heart rhythm, for up to 36 months. The current clinical use of ICMs involves the evaluation of transitory symptoms of possible arrhythmic origin, such as unexplained syncope and palpitations. Moreover, ICMs can also be used for the evaluation of difficult cases of epilepsy and unexplained falls, though current indications for their application in these sectors are less clearly defined. Finally, the ability of new-generation ICMs to automatically record arrhythmic episodes suggests that these devices could also be used to study asymptomatic arrhythmias, and thus could be proposed for the long-term evaluation of the total (symptomatic and asymptomatic) arrhythmic burden in patients at risk of arrhythmic events. In particular, ICMs may have an emerging role in the management of patients with atrial fibrillation and in those at risk of ventricular arrhythmias. (PACE 2012; 35:1169-1178).     

Results of Holter ECG Guided Therapy for Ventricular Arrhythmias: The ESVEM Trial

The Electrophysiological Study Versus Electrocardiographic Monitoring (ESVEM) trial randomized 486 patients with spontaneous sustained ventricular tachycardia (VT), ventricular fibrillation (VF) or unmonitored syncope, who manifested reproducibly inducible sustained ventricular arrhythmias by provocative stimulation and 10 or more premature ventricular contractions per hour on Holter monitoring, to two groups treated with pharmacotherapy guided by suppression of stimulation-inducible VT/VF or suppression of spontaneous or exercise induced ventricular arrhythmias. There was no difference over four years of follow-up in the rates of recurrence of arrhythmias, arrhythmic mortality, cardiac mortality, or mortality from any cause between the two groups of patients but more patients [77%) received pharmacotherapy in ihe group treated on the basis of suppression of spontaneous arrhythmias than the group treated on the basis of electrophysiological study. In this trial, rates of recurrence of arrhythmias were higher (37% at one year and 66% at four years) than generally reported, but cardiac and arrhythmia mortality were comparable or lower than generally reported. Of the seven agents tested, six were sodium channel blockers (imipramine, mexiletine, procainamide, propafenone, pirmenol, and quinidine) and the other was sotalol. Sotalol had a significantly higher rate of efficacy predictions by EPS (35%) than the others (15%) and a comparable rate by Holter monitor. Sotalol was significantly more efficacious in preventing recurrences, arrhythmic mortality, cardiac mortality, and total mortality than the other agents and it was better tolerated. Probability of successful long term therapy with a sodium channel blocker tested by electro-physiological study was low (5% at one year). These results indicate sotalol is a reasonable first option for pharmacotherapy io prevent recurrent VT/VF in patients comparable to the patients included in ESVEM and that Holter monitoring is an acceptable mode of guiding therapy.     

Dual Chamber Rate Responsive Pacing to Allow Sotalol Therapy for Ventricular Tachycardia

In order to allow the use of sotalol to control ventricular tachycardia (VT), dual chambe rate responsive (DDDR) pacemakers were implanted in ten patients aged 6 to 73 years (mean 50 years) Nine presented with monomorphic VT (seven inducible at baseline electrophysiological study (EPS)) ant one with syncope (monomorphic VT at EPS). On sotalol, VT was initiated in only one. This patien received sotalol in the absence of an effective alternative agent. The mean dose was 468 ± 269 mg/day Indications for pacing were symptomatic sotalol induced bradycardia (7), sinus node dysfunction (1) postoperative complete heart block (1), and infra-His block at baseline EPS (1). At least five of these patients would have been candidates for an implantable cardioverter defibrillator had sotalol required discontinuation. Initially, nine patients were paced in DDDR mode and one, with normal AV conduciioi on sotalol, in AAIR. One patient was unable to tolerate sotalol despite pacing. One patient died suddenly after 35 months of symptom-free follow-up. There was a significant improvement in symptomatic statu, (P = 0.03) after pacing among the other eight patients with no recurrence of VT. The implantation of DDDR pacemaker may be indicated in selected patients with serious cardiac arrhythmias. With such < device programmed to an appropriate mode, sotalol can be used successfully where otherwise contraindi cated by bradycardia or preexisting conduction disease. For some patients this may obviate the expense inconvenience, and attendant risks of implantable cardioverter defibrillator implantation.     

Noninvasive Arrhythmia Risk Stratification in Idiopathic Dilated Cardiomyopathy: Design and First Results of the Marburg Cardiomyopathy Study

The Marburg Cardiomyopathy Study (MACAS) is a prospective, observational study designed to determine the value of the following potential noninvasive arrhythmia risk predictors in at least 200 patients with idiopathic dilated Cardiomyopathy (IDC) over a 5-year follow-up period: NYHA-class, left ventricular ejection fraction (LVEF), left ventricular end-diastolic diameter, left bundle branch block and atrial fibrillation on ECG, QT/JT dispersion on 12-lead ECG, signal-averaged ECG, ventricular arrhythmias and heart rate variability (HRV) on 24-hour Hotter ECG, baroreflex sensitivity, and microvolt T wave alternans during exercise. This article describes the findings among the first 159 patients with IDCs enrolled in MACAS until May 1998 (40 women, 119 men;age:49 ± 12 years; LVEF: 32 ± 10%). Twenty-nine patients (18%) had atrial fibrillation and 130 patients (82%) were in sinus rhythm. Patients with sinus rhythm were further stratified according to LVEF < 30% (n = 54) versus LVEF ≥ 50% (n = 76). Compared to patients with LVEF ≥ 30%, patients with LVEF < 30% more often had left bundle branch block (43% vs 25%, P < 0.05), nonsustained VT (44% vs 22%, P < 0.05), decreased HRV (SDNN: 95 ± 39 vs 128 ± 42 ms, P < 0.01), decreased baroreflex sensitivity (5.6 ± 4 vs 8.3 ± 6 ms/mmHg, P < 0.01), and T wave alternans (59% vs 37%, P < 0.05). The prognostic significance of these findings will be determined by multivariate Cox analysis at the end of a 5-year follow-up. Primary endpoints in MACAS are overall mortality and arrhythmic events (i.e., sustained VT or VF, or sudden cardiac death).     

Electrophysiologic studies of patients with hypertrophic cardiomyopathy presenting with syncope of undetermined etiology

Patients with hypertrophic cardiomyopathy (HC) have a high risk of sudden death. The best clinical predictors of sudden death from HC are young age, strong family history of sudden death, ventricular tachycardia (VT), and progression of symptoms such as syncope. We performed 24-hour Holter monitoring and electrophysiologic studies (EPS) on 26 patients with HC, some with the obstructive form of the disease and some with syncope, in order to predict their vulnerability to syncope and to potentially malignant arrhythmias. Holter monitoring demonstrated supraventricular tachycardia (SVT) in 9/26 patients whereas atrial programmed electrical stimulation induced SVT in 17/26 patients. Of the 17 patients, nine had symptomatic hypotension with SVT while lying supine. Holter monitoring demonstrated nonsustained VT in 7/26 patients whereas ventricular programmed electrical stimulation induced VT or ventricular fibrillation (VF) in 6/26 patients. The patient who had the longest run of nonsustained VT on Holter had VF induced by ventricular programmed electrical stimulation. He was cardioverted to normal sinus rhythm with no untoward effects. We found that atrial programmed electrical stimulation induced SVT with hypotension best predicted a history of syncope in these patients. Although one patient required direct current cardioversion, EPS was conducted safely in all patients. Further long-term studies are needed to demonstrate the value of clinical decisions based upon EPS in patients with HC.     

Cardiac Pacemakers in Pediatric Heart Transplant Recipients: Incidence, Indications, and Associated Factors

This study was undertaken to assess the incidence, indications, and predisposing factors for pacemaker placement in a pediatric heart transplant population. From November 1985 to May 1994, 246 pediatric patients have undergone cardiac transplantation at Loma Linda University Medical Center. Seven (2.8%) have received pacemaker placement with an 8–50 month follow-up period. Median age at transplant was 462 days (0 days to 2.5 years). The median time to pacemaker placement was 190 days (18–1,672 days) after transplantation. Indications were sick sinus syndrome (SSS) in 5 and heart block in 2 patients (1 during acute rejection). Three patients with SSS underwent electrophysiology studies (EPS); 1 was normal and 2 showed sinus node dysfunction. The mode of pacing was WIR in 6 patients and WI in 1 patient. All 6 survivors are doing well and 5 patients' pacemakers still provide support. These 7 patients were compared with 185 pediatric patients (0 days to 12-years-old) transplanted during 1985 through 1993 who survived at least 6 months after transplantation. There was no correlation between the receipt of a pacemaker and graft cold ischemic time, rejection history, donor age, or recipient age at transplantation. The 5 patients with SSS had significantly lower average heart rates in the first month after transplantation (108 ± 16 vs 130 ± 12; P = 0.0002). The need for permanent pacemakers in this population is uncommon. Pacemakers, however, can be safely performed when necessary with excellent clinical results.     

Broad Applicability of Ultrarapid Train Stimulation as an Efficient Alternative to Conventional Programmed Electrical Stimulation

FISHER, J.D., et al.: Broad Applicability of Ultrarapid Train Stimulation as an Efficient Alternative to Conventional Programmed Electrical Stimulation. Background and study objective:Conventional programmed electrical stimulation (PES) is useful for establishing inducibility or noninducibility of clinical ventricular arrhythmias (VA), but is complex and time-consuming. This study compared a standard PES protocol with ultrarapid train stimulation (UTS) in a broad range of patients with and without a history of ventricular arrhythmias or structural heart disease. Methods: Patients prospectively underwent electrophysiologic testing with both UTS and conventional PES protocols in a randomized, crossover design. Results: The results were concordant in 79% of 150 matched pairs of comparisons in 104 patients (NS). There were no differences related to underlying heart disease or arrhythmia, or antiarrhythmic treatment. Induction of nonclinical arrhythmias with the two methods was similar   (P = 0.524)   . Inhibition phenomena were minor except in some patients receiving amiodarone. Fewer drive-extrastimuli sequences and less time were needed to complete the trains protocol   (P < 0.0001)   . Conclusions: In cases where the main intent is to induce ventricular arrhythmias, UTS yields results that are similar to those of conventional PES protocols in a shorter length of time. (PACE 2003; 26[Pt. II]:518–523)     

Heart Rate Variability and Major Arrhythmic Events in Patients with Idiopathic Dilated Cardiomyopathy

This prospective study of 71 patients with idiopathic dilated cardiomyopathy (IDC) and preserved sinus rhythm was designed to evaluate the relation between heart rate variability (HRV) and subsequent major arrhythmic events. Standard time- and frequency-domain HRV parameters were obtained from analysis of 24-hour Holter ECG recordings. During a mean follow-up of 15 ± 5 months, major arrhythmic events including sustained ventricular tachycardia, ventricular fibrillation, and sudden cardiac death occurred in 10 of the 71 study patients (14%). Neither time- nor frequency-domain indices of HRV differed significantly between patients with and patients without subsequent major arrhythmic events. However, there was a trend toward a lower standard deviation of the average normal RR interval for all 5-minute segments of the 24-hour recording (68 ± 17 ms vs 80 ± 31 ms; P = 0.06) in patients with major arrhythmic events. In addition, the percentage of adjacent normal RR intervals differing > 50 ms over the recording period tended to be lower in patients with major arrhythmic events (6%± 3% vs 9%± 6%; P = 0.08). Our results indicate a tendency toward attenuated parasympathetic activity in IDC patients with subsequent major arrhythmic events compared to arrhythmia-free patients. Larger studies with longer follow-up periods are necessary to clarify the role of HRV measurements for arrhythmia risk prediction in patients with IDC.     

Life-threatening tachyarrhythmias in athletes.

The arrhythmias in competitive athletes may be classified as "benign," "paraphysiological" due to prolonged athletic training, or "pathological" due to hemodynamic effects on the athletic performance-risk-arrhythmogenic substratum. Pathological arrhythmias include life-threatening forms that are severe enough to produce symptoms (presyncope, syncope, cardiac arrest) during athletic activity. These forms are in particular rapid VT, VF, torsades de pointes, preexcited atrial fibrillation, sinus atrial and AV block. Our study population includes 766 competitive athletes, mean age 21.1 years (74 top international level), investigated with a cardioarrhythmological work-up for symptoms and for arrhythmias from 1974 to June 30, 1991. Three leading categories, represented by 16 aborted sudden death, 8 sudden death, and 7 induced VF (by EES or TAP) athletes, are described. All athletes with life-threatening arrhythmias, previously as asymptomatic or with minor symptoms had an arrhythmogenic substratum due to underlying silent cardiopathy or primary arrhythmic disorders. Athletic activity can be regarded as a trigger of electrical destabilization.     

A Comparison of Ventricular Arrhythmias Induced with Programmed Stimulation Versus Alternating Current

In patients undergoing implantation and testing of the implantable cardio-verter defibrillator (ICD), alternating current (AC) may be used to induce ventricular tachyarrhythmias in a prompt, safe, and efficient manner. These arrhythmias have been previously reported to be similar to those induced during programmed electrical stimulation (PES). We compared the ventricular tachyarrhythmias induced by both methods in 14 patients: 8 male, 6 female; mean age 61 years; coronary disease in 10, cardiomyopathy in 4; mean ejection fraction 31%. The presenting arrhythmia was nonsustained ventricuiar tachycardia (VT) in four, sustained monomorphic ventricular tachycardia (SMVT) in five, ventricular fibrillation (VF) in four, and unknown in one patient with syncope. PES (single, double, triple extrastimuli; burst pacing) and AC (1–2 sec application) stimulation via right ventricular endocardial electrode catheter was performed off antiarrhythmic drugs in the nonsedated state. PES induced SMVT in nine, polymorphic VT in two, and VF in three. AC induced VF in all patients. Although AC can reliably induce ventricular tachyarrhythmias during de/ibrillation threshold and ICD testing, there is poor correlation to PES induced tachyarrhythmias.