David B. Shaw

Unexplained Syncope—A Diagnostic Pacemaker?

We describe our initial experience with a pacemaker which performs the dual function of registering episodes of cardiac arrest and pacing the heart when necessary. The appartus has a prolonged escape interval (2.30–2.65 seconds) and is capable of counting up to 128 “events.” Twenty‐five patients complaining of infrequent episodes of loss of consciousness have been studied. Blackouts ceased and episodes of ventricular standstill were recorded in 14 cases; the unit helped to establish a non‐cardiac etiology for the attacks in two cases. It is suggested that a bradycardia‐recording facility incorporated into a programmable pacemaker would provide a much needed tool in the diagnosis and management of patients with infrequent episodes of loss of consciousness in whom a cardiac mechanism is suspected but unproven.

Xamoterol in sinus node disease

A pharmacological alternative to pace-maker implantation would be useful in some patients with sinoatrial disorder particularly since the single lead ventricular system usually fitted has disadvantages. Xamoterol, a cardioselective beta-receptor partial agonist, has been shown to increase heart rate both in animals and in man. We, therefore, studied the effects of Xamoterol in patients with sinoatrial disease in a double blind, cross-over trial in 10 patients. Mean heart rates and number and duration of pauses were compared during the treatment phases of the trial with Holter monitoring. Mean heart rates were significantly increased between 01:00 h and 05:00 h (P < or = 0.02) and between 05:00 h and 09:00 h (P < or = 0.01) on Xamoterol. The number of sinus pauses were eliminated or reduced on Xamoterol in six patients, but there was an increased frequency in three patients. Xamoterol, therefore, does increase the heart rate and reduce the number of pauses in sinoatrial disorder, but only in some patients.

A dual-sensor diagnostic pacemaker for ambulatory cardiac monitoring

Unexplained blackouts are a very common medical problem. Some patients presenting themselves at hospital with such symptoms have underlying bradycardia or extreme tachycardia with a profound decrease in cardiac output. Modern treatment of these patients may be highly effective but accurate diagnosis of their exact condition may be needed. A novel ambulatory dual-sensor diagnostic pacemaker has been developed to meet this requirement. The device monitors intracardiac ECG and intraventricular pressure through a special lead introduced perveneously into the right ventricle and detects and counts events such as bradycardia, tachycardia, pauses in the electrical or pressure signals and electrical interference. Analogue recordings of the electrical and pressure waveforms of 16 of these events can be made during the operating period of 3 weeks and pacing is incorporated via a specially-adapted commercial pacemaker if a prolonged episode of bradycardia or a pause is sensed. The device forms part of a complete diagnostic system also incorporating a computer which is used to set up the parameters of the diagnostic pacemaker and to display and analyse the recorded data.

Clinical trials of a dual-sensor diagnostic pacemaker

The results of clinical trials of a dual-sensor diagnostic pacemaker are described. The system monitors and records intraventricular electrical and pressure waveforms using a special lead incorporating bipolar electrodes together with a piezoelectric pressure transducer. The recorded waveforms, which are shown in conjunction with Holter recordings made simultaneously, demonstrate the value of pressure measurements and illustrate several cardiac events, including an ECG pause, bradycardia, a pressure pause, ectopic beats and tachycardia. The pacing function of the device is shown and capture is demonstrated.

Development and preliminary clinical tests of an impedance sensing VDD recording pacemaker for diagnosis and research

Episodes of serious but infrequently occurring cardiac arrhythmias can be difficult to detect and analyse, even with modern Holter monitoring. A previous diagnostic pacemaker developed by this group provided VVI pacing therapy and recorded intracardiac ECG signals but had no atrial sensing or impedance measuring capability. A new external diagnostic pacemaker system is described that has been developed to assist in diagnosing intermittent arrhythmias by selectively recording intracardiac signals. Unlike other ambulatory monitors, in addition to recording ECG, the device combines VDD pacing therapy with the capability of monitoring and recording intracardiac impedance and pressure waveforms through a temporary intracardiac lead. A PCMCIA memory card allows storage of 48 arrhythmic events of 21 seconds each. Twelve seconds of waveform are retained before the event occurs and nine seconds after. Data retrieval and processing is performed with a PC which reconstructs each waveform for display. The ECG provides data on cardiac rhythm while cardiac function is inferred from the haemodynamic signals. During simulated trials, 14 event types were presented to the system. All events were successfully detected and recorded. During in vivo clinical tests 83 waveform recordings were made. Impedance fluctuations with typical peak-to-peak values of 64 ohms were successfully recorded.