British Heart Journal, I97I, 33, 742-749. Br Heart J: first published as 10.1136/hrt.33.5.742 on 1 September 1971. Downloaded from Sinus bradycardia Dennis Eraut and David B. Shaw From the Cardiac Department, Royal Devon and Exeter Hospital, Exeter, Devon This paper presents thefeatures of 46 patients with unexplained bradycardia. Patients were ad- mitted to the study if their resting atrial rate was below 56 a minute on two consecutive occasions. Previous electrocardiograms and the response to exercise, atropine, and isoprenaline were studied. The ages of thepatients variedfrom I3 to 88years. Only 8 had a past history ofcardiovascular disease other than bradycardia, but 36 hJd syncopal or dizzy attacks. Of the 46 patients, 35 had another arrhythmia in addition to bradycardia; at some stage, i6 had sinus arrest, i.5 hadjunc- tional rhythm, 12 had fast atrial arrhythmia, I6 had frequent extrasystoles, and 6 had atrio- ventricular block. None had the classical features of sinoatrial block. Arrhythmias were often produced by exercise, atropine, or isoprenaline. Drug treatment was rarely satisfactory, but only i patient needed a permanent pacemaker. It is suggested that the majority of the patients were suffering from a pathological form of sinus bradycardia. The aetiology remains unproven, but the most likely explanation is a loss of the inherent rhythmicity of the sinoatrial node due to a primary degenerative disease. The descriptive title of 'the lazy sinus syndrome' is suggested. copyright. Bradycardia with a slow atrial rate is usually attempt to define the clinical syndrome of regarded as an innocent condition common in bradycardia with a pathologically slow atrial certain types of well-trained athlete, but occa- rate and to clarify the nature of the arrhyth- sionally it may occur in patients with symp- mia. toms of heart disease. Laslett in I909 de- http://heart.bmj.com/ scribed a 40-year-old woman who had a slow Plan of study pulse and complained of fainting attacks. Patients were admitted to the study if their resting Using a MacKenzie Polygraph, he showed atrial rate was below 56 a minute on two consecu- that the attacks were associated with arrest tive visits, providing they were not taking drugs of the whole heart. Subsequently, there have of the digitalis group, or propranolol, quinidine, been a number of reports of patients who procainamide, methyldopa, or bethanidine. tended to have a slow atrial rate and were Patients with untreated myxoedema, jaundice, or subject to other disorders of cardiac rhythm. known raised intracranial tension were excluded as were those with temporary slowing of the heart on September 30, 2021 by guest. Protected In some instances the bradycardia was con- in association with recent myocardial infarction sidered to be sinus (Campbell, I943; Pearson, (within 28 days), or acute carditis. 1945; Short, I954; Birchfield, Menefee, and Forty-six patients fulfilled the criteria of the Bryant, I957), while in others sinoatrial block study. Most of these were found after a direct was suggested as the mechanism (Levine, approach was made to the family doctors in the I9I6; Cowan, I939; Stock, I969; Rokseth et clinical area. Two hundred and ninety doctors al., 1970). The clinical details have varied were asked to give details of patients with heart from case to case, but commonly reported block or pulse rates below 56 a minute, and replies features both in those described as having were obtained from all but 8. A full report of this survey has been given by Shaw and Eraut (1970). sinus bradycardia and those with sinoatrial Nineteen patients were seen in routine hospital block are syncope and episodes of tachycardia. practice over a period of 6 years and 2 were re- The cardiograms have on occasions shown ported to us by colleagues who knew of our sinus arrhythmia, wandering pacemaker, sinus interest in the condition. The patients have been arrest, with and without junctional (nodal) followed up at intervals for periods up to 6 years. escape, paroxysmal atrial tachycardia, atrial Previous electrocardiograms were obtained in 23 flutter, and atrial fibrillation. The study pre- of the 46 patients, the average time between the sented in this paper was undertaken in an first and last cardiogram being approximately 5 years. Received 7 October 1970. Most of the patients were seen in the Cardiac Sinus bradycardia 743 Br Heart J: first published as 10.1136/hrt.33.5.742 on 1 September 1971. Downloaded from Department at the Royal Devon and Exeter the PP interval following the dropped sinoatrial Hospital. Six were unable to attend and were impulse is longer than the PP interval preceding visited at their homes only. One patient (Case 20) it. In cases of doubt the duration of the sinus was not seen by us; Dr. Cosh of Bath has kindly cycle can be calculated and the presence or absence , sent serial reports. The patients were asked if they of sinoatrial block tested by formulae suggested suffered from syncopal attacks, dizziness, dys- by Schamroth and Dove (I966). pnoea, or chest pain on effort, and inquiry was made for a past history of diphtheria, rheumatic Results fever, or myocardial infarction. After a general physical examination, a standard 12-lead cardio- Basic clinical data are given in Table i. The gram was recorded and the resting heart rate was age range of the patients with bradycardia was taken from a 3-foot strip of lead II. In 32 patients wide (I3 to 88), but over half were elderly, a continuous recording was made for 3 minutes being within the range 55 to 75. Only 8 pa- at a slow speed with a 3-channel mingograph tients had a history of heart disease other than recorder. Records were repeated after exercise in the bradycardia. Four patients had had a 42 patients, and in 27 patients records were taken myocardial infarction. Two patients had con- throughout the standard exercise test used in the disease: one of these had an department. This consists ofwalking up and down genital heart steps at a fixed rate for 3 minutes, followed by a atrial septal defect, and one had dextrocardia 3-minute rest with continuous cardiogram record- and situs inversus. One patient was considered ing. The effect of o06-i mg atropine was studied to have an idiopathic cardiomyopathy. One by serial cardiograms in 22 patients, the drug patient had rheumatic heart disease and a being given by intravenous injection in 3 and further 4 gave a history of childhood rheu- orally in the others. All experienced dryness of matic fever, but had no clinical history of the mouth. Isoprenaline was given by intravenous heart disease. Neurological disease was also injection in 3 patients and sublingual tablets (20 rare. Three had had cerebrovascular acci- mg) in 24 patients. and 3 had been considered to have The cardiogram was examined to check the dents, rhythm and atrial rate at rest and during exercise. epilepsy, though on review this diagnosis was A search was made for junctional (nodal) rhythm, subsequently abandoned in one who had mild copyright. periods of sinus arrest with or without escape presenile cerebral degeneration, and was un- beats, fast atrial arrhythmia, atrial tachycardia, substantiated in another. Two patients had flutter or fibrillation, coupled and frequent extra- suffered from myxoedema and were on systoles (more than i for io sinus beats), and for thyroxine, and one had had a partial thyroid- any evidence of abnormal atrioventricular con- ectomy but was euthyroid at the time of the duction. The PR interval and the duration and study. height of the P waves were measured in lead II. Thirty-six of the 46 patients had symptoms http://heart.bmj.com/ Where atrial arrest occurred, the duration of the arrest and the preceding and following PP inter- of circulatory impairment. Twenty-three ex- vals were measured to assess the presence or ab- perienced disturbance of consciousness, in I4 sence of single blocked complexes of sinoatrial there were episodes of complete loss of con- block or of Wenckebach conduction in sinoatrial sciousness, and iS had attacks of dizziness; 6 block. First and third degree sinoatrial block can- patients had both. Central chest pain on exer- not be recognized from the cardiogram (McGarry, tion was complained of by 17 patients; only I966). The criteria for the diagnosis of second 3 of these had a past history or cardiographic degree sinoatrial block used in this study are evidence of myocardial infarction. Twenty- on September 30, 2021 by guest. Protected -based on the work of Winton (1948), McGarry nine patients complained of breathlessness '(i966), and Stock (I969), and are as follows. on exercise, and I0 patients complained of swollen ankles. i Isolated single dropped beats with a prolonged PP cycle, length twice the length ofthe predomin- The mean blood pressure for the group was ant PP interval. I50/77 mmHg, the range being Ioo/6o to 2 Several consecutive dropped beats with a pro- 240/I00 mmHg. Only i had a diastolic blood longed PP length 3, 4, or 5 times the predominant pressure above ioo mmHg. PP interval. The resting atrial rate at the time of the last 3 Sudden doubling or trebling of the atrial rate, assessment when sinus rhythm was dominant often in response to exercise or atropine and im- ranged from 28 to 54 a minute, the mean for plying a relatively fixed 2: 1 or 3: I sinoatrial the group being 44 (see Table i). The rate block. increased with exercise but not to the same 4 Wenckebach conduction in sinoatrial block with beats dropped more or less regularly. In this extent as observed in normal subjects. The instance there should be progressive shortening mean maximal exercise atrial rate in the pa- ,of the PP interval up to the pause, the PP interval tients fully studied was some 20 a minute including a blocked sinoatrial impulse is shorter below the mean normal value for this depart- than twice the length of the PP interval preceding ment.