Analysis of PR subintervals in normal subjects and early studies in patients with abnormalities of the conduction system using surface His bundle recordings.

Utilizing several different approaches to noise reduction, satisfactory beat by beat His bundle activity was recorded from the chest surface in 41 (80%) of 52 normal subjects. Surface atrial to His intervals (PAH) and His to ventricular intervals (HV) were measured in this group and compared with subintervals of the PR segment recorded endocardially from 47 persons with normal electrophysiologic findings. A recent modification in the selection algorithm allows on-line identification of the four of five possible recording sites for utilization in a spatial summation. The ability to record in less favorable circumstances has been improved to the extent that records of suitable clarity for measurement were also obtained in 17 (77%) of 22 individuals with conduction system abnormalities. Comparison of the surface and endocardially acquired data in the normal group reveals no statistically significant difference in the surface acquired PAH and endocardially acquired high right atrial to His (HRAH) intervals, nor in the HV intervals. In a small subset of patients data were acquired by both techniques and no significant differences were found. Thus, when programmed stimulation or endocardial mapping is not required to answer specific clinical questions, in the majority of persons it is possible to record meaningful subintervals from the body surface from each cardiac cycle. Additionally, in instances in which surface P wave activity is obscure in the routine electrocardiogram, this technique enhances atrial electrical activity.

Unusual neurotoxicity associated with amiodarone therapy.

One hundred two patients with recurrent, drug-refractory tachyarrhythmias were treated with amiodarone for nine +/- eight months (mean +/- SD) (range, one to 50 months). Forty-five patients exhibited some form of neurotoxic reaction that was severe enough in nine patients to require discontinuation of treatment or reduction in dosage of the drug. The most frequent neurotoxic findings were tremor (44 patients), peripheral neuropathy (ten patients), and ataxia (seven patients). Five patients developed unusual neurotoxic manifestations: brainstem dysfunction characterized by downbeat nystagmus, hemisensory loss and ataxia, severe dyskinesia, jaw tremor, and proximal myopathy. Neurophysiologic studies revealed varying degrees of predominantly demyelinating peripheral neuropathy. Neurotoxic symptoms improved after discontinuing treatment or decreasing the dosage of the drug. Age of the patient and total cumulative dose did not seem to be risk factors for development of neurotoxicity. These neurotoxic findings suggest that amiodarone-induced neurotoxic reactions are not only confined to the peripheral nervous system, but also that parts of the central nervous system (eg, basal ganglia, brain stem, or their connections) may also be involved.

Late potentials in normal subjects and in patients with ventricular tachycardia unrelated to myocardial infarction.

Fifty normal male and female athletes, or athletically active subjects, were evaluated, and a search for low-amplitude late potentials in the terminal part of ventricular activation was performed. Recordings from 3 normal men met the definition of abnormal late potentials, and were indistinguishable by present analytic techniques from those encountered in patients who have ventricular tachycardia (VT) after myocardial infarction (MI). Of 24 patients studied, 11 had VT, but only 2 had had an MI, which occurred in the remote past. Another patient had 1 narrowed coronary artery on arteriography. Group differences could be demonstrated using amplitudes and durations of late potentials, but late potentials generally did not prove the impressive marker of the patient with VT, which other workers, as well as ourselves, have encountered in patients after MI. Late potentials were an impressive marker in a subset of the VT group in whom cardiomegaly developed. Thus, the absence of late potentials is an effective marker in the normal subject, but the presence of late potentials is not an effective marker in identifying the patient with non-MI-related, nonsustained VT before development of cardiomegaly.

Cibenzoline for high-frequency ventricular arrhythmias: a short-term comparison with quinidine and a long-term follow-up.

Cibenzoline, a new class I antiarrhythmic drug, was compared with quinidine in an open crossover study of 20 patients with frequent (greater than 30/hr) premature ventricular depolarizations (PVDs). Eight patients treated with cibenzoline experienced more than 75% reduction in PVD frequency. Cibenzoline completely suppressed ventricular couplets in eight of 17 patients and inhibited ventricular tachycardia (VT) in four of 13 patients. Only four patients (20%) responded to quinidine with a similar reduction in PVDs. Quinidine completely suppressed ventricular couplets in eight of 17 patients and episodes of VT in six of 13 patients. Cibenzoline prolonged PR, QRS, and QTc intervals. Eight patients who had shown more than a 75% reduction of PVDs were treated with cibenzoline for an extended period. At the end of three months, only five of eight patients continued to have 75% or greater reduction of PVDs. At the end of six and 12 months, four of five patients continued to have 75% or greater reduction of PVDs. Cibenzoline was similarly effective in suppressing complex arrhythmias. Thus, cibenzoline was only slightly superior to quinidine in suppressing ventricular arrhythmias. With long-term use of cibenzoline, significant PVD suppression was noted at the end of three months but not afterward.

Blepharospasm accompanying hypoxic encephalopathy.

Severe bilateral blepharospasm with left hemiplegia occurred in a 50-year-old woman, who developed cardiac arrest following ventricular aneurysmectomy. The blepharospasm was present constantly, even during sleep, and increased during attempts at voluntary eye opening. CT scan revealed multiple hypodense areas involving basal ganglia bilaterally and the right perisylvian area. The blepharospasm improved gradually over a 6-month period, although the left hemiplegia remained unchanged.

Automatic implantable scanning burst pacemakers for recurrent tachyarrhythmias.

Ninety patients (13 patients with supraventricular tachycardia and 72 patients with ventricular tachycardia) underwent electrophysiological study. Six out of 18 patients with supraventricular tachycardia (33%) and one out of 72 patients with ventricular tachycardia (1.4%) were considered suitable candidates for the scanning pacemaker. However, only six of the seven patients underwent implantation. The seventh patient decided not to undergo implantation and continued to have recurrent episodes of supraventricular tachycardia. The scanning pacemaker delivers extrastimuli at preset initial and coupled delay after four cycles of tachycardia. If tachycardia is not terminated, another set of extrastimuli are delivered with a decrement in the coupling cycle. During the follow-up period of 7-25 months (mean, 14.3 months), tachycardia cycle lengths and termination windows changed in four patients. The pacemakers in these patients were reprogrammed multiple times (2 to 6 times with a mean of 3.5) as the previous number of extrastimuli and intervals were ineffective in the termination of tachycardias. The major limitations of the extrastimulus pacemaker were: 1) only a small percentage of patients were suitable candidates for its use; (2) the initially selected termination window in the majority of patients was ineffective during the follow-up period due mainly to the changes in tachycardia cycle length and subsequent termination windows; and (3) the majority (five out of six patients in this series) of patients needed additional pharmacologic therapy to modify their tachycardia rates. However, despite these limitations, the scanning pacemaker may be an additional tool in the management of recurrent tachyarrhythmias in selected patients.

Neonatal refractory supraventricular tachycardia: successful treatment with amiodarone.

A 3-week-old neonate with supraventricular tachycardia unresponsive to traditional therapy was treated successfully with amiodarone. An electrophysiologic study suggested the presence of a concealed left-sided accessory atrioventricular pathway. Because of its significant side effects, amiodarone should be used only as a last resort in the treatment of neonatal supraventricular tachycardia.

Myotonic dystrophy: ambulatory electrocardiogram, electrophysiologic study, and echocardiographic evaluation.

Myotonic dystrophy is frequently associated with functional and anatomic derangements in the myocardium. Ten myotonic dystrophy patients (seven men and three women, ages ranging from 35 to 58 years) were evaluated with a 12-lead ECG, 24-hour Holter monitor recording, invasive electrophysiologic studies, and echocardiographic examination. Nine patients displayed abnormalities in the conduction system. ECG and Holter monitor abnormalities were first-degree atrioventricular block (n = 8), second-degree atrioventricular block (n = 1) (Wenckebach type), complete left bundle branch block (n = 2), left anterior fascicular block (n = 5), left posterior fascicular block (n = 1), sinus bradycardia (n = 6), sick sinus syndrome (n = 2), frequent premature ventricular complexes (n = 4), and ventricular tachycardia (n = 2). Electrophysiologic study abnormalities included AH interval less than or equal to 140 msec (n = 7), AH interval greater than 140 msec (n = 3), HV interval greater than 60 msec (n = 9), and ventricular tachycardia induction (n = 1). Echocardiographic examination revealed mitral valve prolapse (n = 6). We conclude that diffuse conduction abnormalities were seen in a majority of our patients with myotonic dystrophy. Ventricular arrhythmias, including ventricular tachycardia, were seen in some of these patients, and mitral valve prolapse was a frequent finding.