The autonomic pathways mediating the bradycardia response to facial immersion (FI) have not been fully elaborated in man. By means of parasympathetic and sympathetic blockade we studied the heart rate response to FI in nine highly trained young swimmers, at rest and during dynamic cycle exercise. With no blockade, heart rate at rest declined with FI 36 +/- 18%. Under beta-blockade with propranolol or alpha-blockade with phentolamine FI produced a similar decrement. Atropine reduced the response. During exercise FI produced 48 +/- 9% decline without blockade. The response was similar with beta-blockade, but was completely abolished with atropine. Systolic blood pressure responses to FI measured by cuff in three subjects were small and bore no relation to the heart rate response. The results are compatible with parasympathetic efferent mediation of the heart rate response to FI. They are incompatible with a role for sympathetic mediation except as a complex interaction between parasympathetic and sympathetic influences. Hypertension and other sympathetic responses to FI do not play a role in production of bradycardia, but are apparently incidental effects. The heart rate decrement produced by FI increases with greater steady-state heart rate.

Nine patients with recurrent ventricular tachycardia (VT) that could be repeatedly terminated by a Valsalva maneuver are described. In two, the tachycardia would cease for only a few seconds and then resume, whereas in seven, the tachycardia could be permanently and reproducibly terminated with a Valsalva maneuver. In all patients the tachycardia ended during the strain phase of the Valsalva maneuver, when blood pressure and radiographic measurement indicated that cardiac dimensions had been reduced dramatically. The speed with which the Valsalva maneuver terminated VT incresed in direct proportion to the strain pressure. Maneuvers such as standing or nitroglycerin, which independently reduce cardiac dimensions, enhanced the potency of the Valsalva maneuvers. Pretreatment with atropine or propranolol in four patients did not alter the response of VT to the Valsalva maneuver. Thus, it appears that a strong Valsalva maneuver can terminate some forms of VT, most likely related to an abrupt reduction in cardiac dimensions.

SUMMARY The capacity of deep inspiration and the dependent body position to terminate episodes of tachycardia was studied in 11 patients with recurrent paroxysmal supraventricular tachycardia (PSVT). In eight patients, a deep inspiration and a dependent position repeatedly terminated episodes of PSVT. Reasons for failure were found in the other three patients. A deep inspiration or assumption of a dependent position dramatically raised arterial blood pressure and terminated episodes of PSVT by reflexly increasing vagal drive. The magnitude of the rise in blood pressure was directly proportional to the depth of the inspired volume and to the extent of body dependency. The upright position attenuated the respiratory-induced increase in blood pressure and blocked PSVT termination. Likewise, vagal blockade with atropine did not affect the effects of respiration or dependent position on blood pressure but prevented termination of PSVT.PATIENTS with paroxysmal supraventricular tachycardia (PSVT) are encouraged to explore techniques to effect self-termination of the tachycardia." 2 Among the most common maneuvers are carotid sinus massage and the Valsalva maneuver.'-4 These methods are not always successful or especially easy to perform properly. Because some patients who suffer from PSVT report tachycardia termination from simpler maneuvers such as deep inspiration or a dependent body position we decided to investigate how these maneuvers might terminate PSVT. Our purpose was to define the mechanisms of action of these maneuvers and to delineate conditions in which they would be successful and those in which they might fail. Materials and MethodsEleven consecutive patients who suffered from PSVT for many years were selected for tlhis study (table 1). All had undergone extensive unsuccessful drug trials over a period of years. Characteristically, these patients had episodes of tachycardia that lasted for many hours without spontaneous termination and required multiple hospital visits for electroversion or treatment with potent vagal maneuvers. Although PSVT in all cases could be terminated by vagal techniques, none of these patients had ever tried to terminate PSVT by deep inspiration or by assuming a dependent body position. All patients were referred because they had requested a permanent atrial radio frequency pacemaker for self-termination of the arrhythmias.5' 6 In this context, we extensively explored the actions of respiration and body position on the tachycardia process.From the Department of Medicine, University of Toronto, and the Cardiovascular Unit, Toronto General Hospital, Toronto, Ontario, Canada. Supported in part by grants from the Ontario Heart Foundation and the Canadian Heart Foundation. The techniques used to explore the electrophysiologic character of PSVT and the suitability of a permanent radio frequency pacemaker to effect selfconversion have been extensively described."' 6Stimulating electrodes were placed in the right atrium and/or the right ventricle to initiate tachycardia. Aortic blood p...

The use of pacemakers in the treatment of tachycardias is one of the most exciting and rapidly expanding applications of cardiac pacing. One of the more recent developments in this field has been the use of patient-activated radio frequency transmitted rapid atrial stimulation (RAS) in the treatment of paroxysmal supraventricular tachycardia (PSVT). Based on the previously established ability of asynchronous atrial pacing to interrupt a variety of re-entrant supraventricular rhythm disturbances, this modality of treatment is gaining increasing applicability in patients with PSVT associated with debilitating symptoms or other severe cardiovascular consequences in whom standard pharmacological regimens have either failed or are impossible to maintain for indefinite periods. This report describes our experience with five patients who underwent implantation of RAS units. The detailed electrophysiological studies required to ensure success and avoid any possible future complications are described. Over a follow-up period of four months to four years (mean 16 months) very few problems arose in the use of these units which have immeasurably improved the quality of life of the recipients. Our experience with RAS units has led to a few suggestions for future improvement and these are outlined in this report. The excellent patient acceptance and the reliability of this technique in terminating episodes of PSVT should, in the future, render RAS the treatment of choice in certain selected patients suffering from this common disorder.