Richard Vincent

Signal Distortion in the Electrocardiogram Due to Inadequate Phase Response

Electrocardiographic monitoring is used for arrhythmia analysis and for the detection of myocardial pathology, especially ischaemia and infarction, when waveform distortion must be minimized if reliable results are to be obtained. ST segment distortion has been noted to occur with ambulatory recorders and some electrocardiographs.

Multiple Neuropsychological Deficits Due to Anoxic Encephalopathy: A Case Study

In this article we report the case of a woman who survived an out-of-hospital cardiac arrest but was left with severe neuropsychological impairments due to anoxia. The deficits included anterograde and retrograde amnesia, dysphasia, disorientation, intellectual deterioration, visual impairments, ataxia, and myoclonus. Despite this degree of impairment the patient retained some insight into her condition which, in turn, created additional emotional problems. Rehabilitation and the problems of long-term care are considered.

Frequency Analysis of the P Wave: Comparative Techniques

Frequency domain analysis of the signal‐averaged P wave (SAPW) may provide additional information over time domain analysis in patients with paroxysmal atrial fibrillation (PAF), but an optimum method has not yet been defined. We compared two different approaches using SAPW and test signals. We analyzed the frequency spectrum of the entire P wave (method A) or of only its terminal 100 msec (method B) using SAPW from 24 patients with idiopathic PAF and 34 normal controls. Absolute powers in frequency bands above 20, 30, 40, 60, and 80Hz (P20, P30, P40, P60, and P80) and power ratios about these frequencies (PR20, PR30, PR40, PR60, and PR80) were calculated. Patients had greater P30, P60, and P80 using method A (P30: 28.6 [± 2.2] vs 22.8 [± 1.6] μV2.s; P = 0.04; P60: 4.7 [± 0.5] vs 3.4 [± 0.3] μV2.s; P = 0.03; P80:1.9 [± 0.2] vs 1.3 [± 0.09] μV2.s; P = 0.01) but differences were smaller with method B. Moving the P wave endpoint 10 msec into the P wave had no effect on frequency domain parameters using method A but produced important changes using method B. Both methods were also applied to test signals of different durations but equal powers and power ratios. Method A gave predicted values for power and PR40 at all signal durations, but method B produced variable results. Frequency domain analysis of the SAPW shows significant increases in P wave energy in patients with PAF compared to controls. Analysis of the entire P wave is influenced less by signal duration and variations of the P wave endpoint than analysis of the terminal P wave alone and may define patient and control populations more precisely.

Signal-Averaged Electrocardiography of the Sinus and Paced P Wave in Sinus Node Disease

The detection of paroxysmal atrial fibrillation (AF) in patients requiring a permanent pacemaker for sinus node disease may influence the choice of both pacemaker and programmed mode. While signal‐averaged ECG of the P wave (SAEP) during sinus rhythm may detect patients with paroxysmal AF, the value of SAEP in the presence of sinus node disease is unknown. We therefore evaluated SAEP in patients with sinus node disease during sinus rhythm and atrial pacing. We investigated 10 patients with sinus node disease alone (SND), 10 with sinus node disease and paroxysmal AF (SND‐PAF), and 20 normal controls (NC) using a P wave specific, signal‐averaging system. In sinus rhythm, duration and energy were greater in SND‐PAF than in SND and NC (mean [SEM] duration: 153 [4] msec, 140 [4] msec, and 134 [2] msec, P < 0.001; energy from 20–150 Hz: 76 [18] μV2‐sec, 48 [7] μV2‐sec, and 36 [3] μV2‐sec, P = 0.006). Atrial pacing in SND‐PAF produced an 11% prolongation of atrial activation but little further abnormality in P wave characteristics. In SND, atrial pacing caused a 20% prolongation of the P wave and increased P wave energy to a greater extent than in SND‐PAF. We conclude that in patients with SND, atrial activation appears similar to normal controls during sinus rhythm but changes significantly on pacing. In patients with SND‐PAF, atrial activation is abnormal during sinus rhythm with little further change when the atrium is paced. SAEP may be useful in detecting a predisposition to paroxysmal AF in the presence of sinus node disease and might help optimize pacemaker prescription.

Editorial note Coronary thrombolysis — the route for success?

Thrombolytic therapy using streptokinase in the management of acute myocardial infarction was reported first in 1959 [l] although it is only in the present decade that the full potential of such treatment is being realised. The logic for using streptokinase or an alternative thrombolytic agent in acute myocardial infarction is straightforward. Coronary atheroma ruptures or dissects triggering a complex sequence of events that contribute to the dynamic process of intraluminal thrombosis. The resulting coronary occlusion leads to progressive ischaemic necrosis of the distal myocardium [2]. Early restoration of coronary flow by thrombolysis should therefore lead to a reduction in infarct size with consequent preservation of left ventricular function and an improvement in clinical outcome [3]. Intracoronary streptokinase is undoubtedly effective in restoring the patency of thrombosed coronary vessels. Most investigators report an angiographically proven recanalisation rate of 70-858. In a comparative study of intracoronary versus intravenous streptokinase published in this issue of the Jowmaf Natarajan et al. [4] confirm this finding in a group of 17 patients treated within 4 hours of the onset of the infarction: The intracoronary route for thrombolysis has several clear benefits. The infarctrelated artery can be delineated prior to therapy allowing accurate delivery of a high concentration of drug to the region of advancing thrombosis. The effect of the thrombolytic agent can be readily assessed by comparing baseline angiographic appearances with sequential views taken during and after the infusion of streptokinase. The acute effect of thrombolytic therapy on wall motion can be studied by preand post-dose left ventricular angiography. Finally, streptokinase by the intracoronary route should minimise the likelihood of unwanted systemic effects.

The signal averaged P wave in atrioventricular block—evidence for abnormal atrial conduction?

The incidence of atrial fibrillation in patients with atrioventricular block (AVB) appears increased over that for the unpaced population even if atrioventricular synchrony is maintained by dual chamber pacing. To assess whether atrial fibrillation in these patients might be due to concurrent abnormality in atrial activation we performed signal averaged P wave (SAPW) recordings in 15 patients with dual chamber pacemakers implanted for AVB and compared the results to those from 21 unpaced controls. The median (range) age was 69 (53-89) years for patients and 60 (51-78) years for controls. Eleven patients and 12 controls were male. All patients were pacing in VDD mode at the time of study. SAPW recordings were obtained using our previously reported selective P wave averaging system. We measured P wave duration after high pass filtering at 40 Hz, the rate of change of P wave voltage over time (spatial velocity) and low and high frequency spectral energy after Fourier transformation of the P wave signal. We found increased P wave duration, mean spatial velocity and lower frequency energy in patients with AVB compared to controls [duration, 144 (5) vs. 134 (2) ms, p<0.05; mean spatial velocity, 5.6 (0.4) vs. 4.6 (0.1) mV/s, p<0.05; energy 20-150 Hz, 57.4 (8.2) vs. 36.3 (2.8) muV2.s, p<0.01. All values mean (SEM)]. These results suggest that the increased incidence of atrial fibrillation in patients paced for AVB may be related to intrinsic abnormalities of atrial activation and not solely to the pacing mode. Ensuring sequential atrioventricular pacing in these patients may not completely abolish the increased incidence of atrial fibrillation.

Detection of his bundle potentials

Conducting system potentials were first recovered from the body surface in dogs in 1973 using a sequence of high-gain amplification and filtering followed by digital signal averaging. Subsequent application of similar methods to man by more than 18 research groups world-wide have shown it feasible to record His Purkinje signals non-invasively in about 75% of subjects studied. Surface signals are of the order of 0.5-2.0 µV in amplitude. In 70-100% of cases they correlate well in time with the simultaneous internal His bundle electrogram but the pattern of surface signals varies from patient to patient. Their appearance fails to correlate with any specific underlying pathological change in AV conduction and is affected both by lead position and as a result of filtering. “High resolution” recordings made without signal averaging have been achieved in a few centres but with greater technical difficulty and a lower rate of signal recovery.