The importance of assessing the fidelity of electrocardiographs by using a simple calibration signal.

ECG distortion, mimicking changes seen in acute myocardial infarction, occurred in traces transmitted by the South East Coast NHS Ambulance Trust. This was due to low frequency phase nonlinearity produced by baseline filtering. The very narrow calibration pulses made the detection of this distortion difficult. A 1 mV square wave signal revealed the cause. Adequate calibration pulses 0.3 s wide should be recorded with all ECGs, to show that the signal is being reproduced reliably.

Ultrasound enhances reporter gene expression after transfection of vascular cells in vitro.

BACKGROUND: Restenosis after percutaneous coronary intervention remains a serious clinical problem. Progress in local gene therapy to prevent restenosis has been hindered by concerns over the safety and efficacy of viral vectors and the limited efficiency of nonviral techniques. This study investigates the use of adjunctive ultrasound to enhance nonviral gene delivery. METHODS AND RESULTS: Cultured porcine vascular smooth muscle cells (VSMCs) and endothelial cells (ECs) were transfected with naked or liposome-complexed luciferase reporter plasmid for 3 hours. Ultrasound exposure (USE) for 60 seconds at 1 MHz, 0.4 W/cm2, 30 minutes into this transfection period enhanced luciferase activity 48 hours later by 7.5-fold and 2. 4-fold, respectively. Luciferase activity after lipofection of ECs was similarly enhanced 3.3-fold by adjunctive USE. USE had no effect on cell viability, although it inhibited VSMC but not EC proliferation. CONCLUSIONS: Adjunctive USE was associated with enhanced transgene expression in VSMCs and ECs and reduced VSMC but not EC proliferation in vitro, which suggests that ultrasound-assisted local gene therapy has potential as an antirestenotic therapy.

A prospective audit of pacemaker function, implant lifetime, and cause of death in the patient.

AIM: To audit prospectively the reasons for pacemaker implantation, the duration of the pacemaker use, the cause of death, and pacemaker function after removal from the patient. METHODS: Pacemakers were removed at necropsy, or from the bodies of patients awaiting cremation, in three hospitals over a three year period. The cause of death was taken from the results of the necropsy or from the certified cause of death. Demographic data, including the time of implant and reasons for implantation, were checked. The pacemakers were analysed in terms of battery status, program, and output under a standard 470 ohm load. RESULTS: 69 patients were studied. Average age at death was 78 and 80 years for men and women, respectively. The average duration since pacemaker implantation was 46 months. Eleven patients had necropsies, showing that three died from ischaemic heart disease, six from cardiomyopathy, one from an aortic aneurysm, and one from disseminated neoplasia. From the necropsy results and death certificates, the distribution of causes of death in the group as a whole were ischaemic heart disease (21), cardiomyopathy (8), cerebrovascular disease (11), neoplasia (11), chest infection/chronic obstructive airways disease (8), and other causes (10). In all cases the pacemaker box function was within normal limits. CONCLUSIONS: Neither primary nor secondary pacemaker dysfunction was found. The study highlights the impact of arrhythmias in cardiomyopathy, and raises questions about the true role of ischaemic heart disease in these pacemaker requiring patients. The relatively short gap between pacemaker implantation and death requires further study.

Screening for atrial fibrillation in primary care.

OBJECTIVE: To investigate a population of elderly people for atrial fibrillation and to determine how many of the cases identified might benefit from treatment with anticoagulants. METHODS: From a practice of four primary care physicians, 1422 patients aged 65 years and over were identified, of whom 1207 (85% of the total population) underwent electrocardiographic screening to detect the presence of atrial fibrillation. Patients with the arrhythmia were further evaluated by echocardiography and interview, to stratify their risk of stroke based on echocardiographic and clinical risk factors, their perceived risk from anticoagulation, and their attitude towards this treatment. Their primary care physician was also interviewed to determine the factors influencing the prescription of anticoagulants. RESULTS: The arrhythmia occurred in 65 patients (5.4% overall), its prevalence increasing markedly with age (2.3% in 65 to 69 years age group; 8.1% in those over 85). Warfarin was being prescribed to 21.4% of these patients, although the findings of the study indicate that a further 20% were eligible for this treatment. Symptoms suggestive of cardiac failure were common (32.1%) and coexisting pathology was often identified by cardiac ultrasound in these patients (left ventricular hypertrophy, 32.1%; impaired left ventricular contractility, 21.4%; left atrial dilation, 80.4%; mitral annular calcification, 42.9%; mitral stenosis, 7.1%; mitral regurgitation, 48.2%; aortic stenosis, 8.9%). In all but one case, the decision to anticoagulate was based on the clinical rather than the echocardiographic findings. CONCLUSIONS: Individual risk-benefit assessment in elderly patients with atrial fibrillation suggests that almost half (41.4%) are eligible for full anticoagulation with warfarin, whereas presently only one fifth are receiving this treatment. The decision to anticoagulate can be made on clinical grounds in most cases. If these results are confirmed, a doubling of the current number of patients taking anticoagulants can be anticipated.

Laser-assisted percutaneous angioplasty: initial clinical experience in peripheral arteries.

Experimental and animal studies have shown that laser energy can vaporize intra-vascular thrombus and atheroma, suggesting that it may have a role in percutaneous angioplasty. Argon laser energy transmitted via a flexible fibre introduced through a percutaneous catheter was used in 15 patients undergoing balloon angioplasty of femoral or popliteal arteries. Of four stenoses, laser alone produced improvement of the lumen in two. Of 11 occlusions some degree of clearance of the lumen was achieved by laser in eight prior to balloon dilatation. Extravasation of contrast medium indicating wall perforation occurred in two patients, without clinical sequelae. No other complications, such as embolism, arterial spasm or toxic effects were observed. There was one acute re-occlusion, almost certainly not related to the use of laser. There have been no late complications. The ability of laser to influence favourably vascular occlusion is confirmed, but technical advances are necessary to avoid vessel wall perforation consistently and to improve the production of an adequate lumen before its potential can be fully realized.

Percutaneous laser thermal angioplasty: initial clinical results with a laser probe in total peripheral artery occlusions.

A metal-tipped laser fibre was used during percutaneous angioplasty of femoral/popliteal or iliac artery occlusions in 56 patients. Primary success was achieved in 50 (89%) of these total occlusions, providing a channel for subsequent balloon dilatation. Before the procedure, 18 lesions had been judged untreatable by conventional angioplasty and four of the six failures were in these. Complications directly attributable to the laser probe were one case of vessel perforation and two cases of entry into vessel walls; these had no sequelae. Other acute complications were a distal thrombosis in a non-heparinised patient, requiring local streptokinase treatment, and two reocclusions and one transient peripheral embolic episode in the first 24 hours. The laser probe technique has potential for increasing the proportion of patients suitable for angioplasty.

Artefactual ST segment abnormalities due to electrocardiograph design.

Specifications recommended for electrocardiographs omit any reference to phase characteristics and place undue emphasis on an extended amplitude response. This does not, however, ensure faithful reproduction of the electrocardiogram and may result in less effective attenuation of unwanted noise than can be achieved with modern filters. The separate effects of phase and amplitude response on electrocardiographic signals were compared, and it was shown that distortion of the electrocardiogram by equipment with an inadequate phase response may cause changes resembling those seen in ischaemic heart disease. Case reports are presented in which distortion produced by commercial equipment impeded diagnosis. Specifications recommended as standard for electrocardiographs should be modified to include phase response and allow greater attenuation of frequencies below 0.5 Hz.

Single lead atrial synchronised pacing in patients with cardiogenic shock after acute myocardial infarction.

A pacing system requiring only a single lead was used to establish atrial synchronised pacing in eight patients with complete atrioventricular block and cardiogenic shock following acute myocardial infarction. Spontaneous atrial activity was sensed through electrodes positioned on the pacing lead and used to trigger ventricular demand pacing. A normal atrioventricular relation could be established in each of these critically ill patients without the complexity of inserting and finding a stable position for an additional atrial sensing lead. Atrial synchronised pacing at the spontaneous sinus rate had distinct haemodynamic advantages compared with conventional ventricular pacing at 100 beats/min. Mean cardiac output for the group was 3.3 1/min with atrial synchronised pacing compared with 2.6 1/min with conventional pacing, a significant difference of 27%. Peak systolic pressure averaged respectively 91 and 73 mm Hg in the two pacing modes. With conventional ventricular pacing a pronounced phasic alteration in blood pressure was observed, dependent on the altering relation of the paced beats to spontaneous atrial activity. Atrial synchronised pacing abolished this effect and resulted in a stable blood pressure at or above the peak pressure achieved with conventional pacing. Atrial synchronised pacing with a single lead system can be established rapidly. This mode of pacing has appreciable and significant haemodynamic superiority over conventional ventricular pacing in patients with cardiogenic shock and atrioventricular block following acute myocardial infarction.

A simple pacemaker inhibitor.

A design for a simple easy to use pacemaker inhibitor is described. The unit enables a pacemaker patient's native rhythm to be displayed even if the rate is less than the pacemaker's demand setting.

Five hundred patients with myocardial infarction monitored within one hour of symptoms.

Of 2886 patients monitored during acute myocardial infarction, 500 were observed within one hour of the onset of symptoms. Half of the early admission group were admitted in response to emergency 999 calls and 435 of them travelled in resuscitation ambulances, where surveillance for arrhythmias was instituted. Pulmonary oedema occurred in 130 patients (26%), cardiogenic shock supervened in 60 (12%), and 115 (23%) died in hospital. Ventricular fibrillation was observed in 98 patients (20%). Forty two of them survived to be discharged, including 20 of the 24 with primary fibrillation which had occurred first in hospital. In only one case did primary ventricular fibrillation occur after the first 10 hours of onset of illness. Sinus bradycardia, atrial fibrillation, ventricular tachycardia, and ventricular fibrillation were all observed more frequently in patients admitted within one hour after the onset of symptoms than in those admitted later. An element of selection is inevitable when early admission is encouraged by the existence of a resuscitation ambulance system; this will depend in part on the early recognition of risk and the geographical location of the attack. These factors may bias the group towards relatively high risk. Nevertheless, prompt admission after myocardial infarction should improve survival by permitting successful management both of ventricular fibrillation and of other arrhythmias which may influence short term and long term prognosis.