Hemodynamic responses to noninvasive external cardiac pacing.

Although improvements in noninvasive external cardiac pacing have led to a technique with reliable electrical capture and reduced patient discomfort, hemodynamic responses to this pacing mode have not been described previously. Accordingly, this technique was applied to 16 patients with a clinical diagnosis of angina pectoris undergoing cardiac catheterization. Three patients had normal coronary arteries, whereas the remaining 13 had significant coronary artery disease. All patients had noninvasive pacing at increasing heart rates to 85 percent of age-predicted maximal heart rate. At maximal pacing, all patients demonstrated a rise in atrial, pulmonary artery, and mean aortic pressures. Cardiac index remained unchanged, reflecting parallel increases in arteriovenous oxygen difference and oxygen consumption. One minute after cessation of pacing, pulmonary artery pressure and oxygen consumption remained elevated, whereas arteriovenous oxygen difference returned to baseline with a subsequent rise in cardiac index. Angina occurred in eight patients with coronary artery disease at peak pacing and was accompanied by a rise in left ventricular end-diastolic pressure after pacing. In eight patients without pacing-induced angina, including the three patients with normal coronary arteries, there was no significant change in left ventricular end-diastolic pressure after pacing. It is concluded that noninvasive external cardiac pacing produces a rise in both right and left heart filling pressures and in oxygen consumption that persist after pacing, and may provoke angina and hemodynamic abnormalities consistent with myocardial ischemia. This mode of pacing appears hemodynamically safe with maintenance of cardiac index and aortic pressure at 85 percent of maximal age-predicted heart rate.

External cardiac programmed stimulation for noninvasive termination of sustained supraventricular and ventricular tachycardia.

To examine the feasibility of using a noninvasive temporary pacemaker for termination of well-tolerated supraventricular (SVT) and ventricular tachycardia (VT), a standard external demand pacemaker was modified to allow stimulation with single or multiple extrastimuli and overdrive pacing. To evaluate the efficacy, safety and tolerance of external cardiac programmed stimulation, a standard arrhythmia termination protocol was used in 223 tachycardias in 22 patients. The technique of external cardiac programmed stimulation was used in 209 episodes of SVT in 13 patients. It terminated 95% of the episodes with success in 19 of 20 episodes of atrioventricular nodal reentrant tachycardia and 179 of 189 episodes of atrioventricular reciprocating tachycardia. Of 198 episodes of SVT terminated by the technique 168 (85%) were terminated by a single extrastimulus and 28 (14%) by double extrastimuli. Only 2 episodes of SVT required overdrive pacing for termination. External cardiac programmed stimulation did not result in atrial fibrillation or arrhythmia acceleration. Of 14 episodes of sustained monomorphic VT 5 were terminated by external cardiac programmed stimulation. One tachycardia was terminated by a single extrastimulus, 1 by double extrastimuli and 3 by overdrive pacing. Arrhythmia acceleration occurred once and was terminated by endocardial pacing. On 27 separate occasions patient evaluation of maximal discomfort included 4 ratings of mild, 10 of moderate, 11 of severe and 2 of intolerable discomfort. External cardiac programmed stimulation is effective and safe in patients with well-tolerated sustained supraventricular or ventricular arrhythmias.

Value of a noninvasively induced ventricular extrasystole during echocardiographic and phonocardiographic assessment of patients with idiopathic hypertrophic subaortic stenosis.

Fifteen patients with idiopathic hypertrophic subaortic stenosis had a ventricular extrasystole induced with a new external mechanical cardiac stimulator during noninvasive evaluation of left ventricular outflow tract obstruction. Ten patients were monitored with simultaneous echocardiogram, phonocardiogram and indirect carotid pulse tracing; five were monitored with the phonocardiogram and indirect carotid pulse tracing alone. Nine of the 15 patients showed obstruction in the beat after the ventricular extrasystole, as defined by appearance of the characteristic bifid carotid pulse contour and, where recorded, an increase in systolic anterior motion of the mitral valve on echocardiography. Six patients did not show obstruction. All nine patients with obstruction had greater than 20 msec prolongation of uncorrected systolic ejection time in the post-extrasystolic beat of the carotid pulse tracing. Change in the uncorrected ejection time was + 0.038 +/- 0.15 second (mean +/- standard deviation) in these nine patients compared with -0.003 +/- 0.005 second in the six not showing obstruction (P less than 0.01). Six patients underwent cardiac catheterization: Three patients without obstruction after a noninvasively induced ventricular extrasystole had no obstruction at catheterization and three patients with obstruction after noninvasively induced ventricular premature beats demonstrated obstruction at rest or after provocative maneuvers during catheterization. These results indicate that the noninvasive induction of a ventricular extrasystole is a useful and easily performed procedure for both diagnosing and evaluating the dynamic left ventricular outflow tract obstruction of idiopathic hypertrophic subaortic stenosis.

Emergency noninvasive external cardiac pacing.

Thirty-seven critical emergency department patients underwent attempts at external cardiac pacing over an 11-month period. Indications for pacing were asystole in 16, complete heart block (CHB) in 4, sinus bradycardia in 2, nodal bradycardia in 1, atrial fibrillation with bradycardia in 2, electromechanical dissociation in 1, idioventricular rhythm (IVR) in 10, and torsades de pointes in 1. Eight patients were successfully paced with improvement in their condition. Two were in asystole, two in CHB, three in sinus rhythm or atrial fibrillation with bradycardia, and one in idioventricular rhythm. Mean systolic blood pressure rise with pacing was 95 +/- 50 mm Hg. Six of these patients were ultimately discharged from the hospital. One asystolic patient survived to discharge. Other survivors presented with either CHB or bradycardia. Of the 29 patients who did not respond to pacing, 5 survived to hospital discharge. Surviving nonresponder presenting rhythms were CHB in one patient, sinus or nodal bradycardia in two, IVR in one, and torsades de pointes in one. External cardiac pacemaking appears to be effective in hemodynamically significant bradycardia. It does not appear to be effective in most instances of asystole or IVR resulting from prolonged cardiac arrest. When applied to patients with a responsive myocardium, it may result in significant hemodynamic improvement and may be lifesaving.

Noninvasive temporary cardiac stimulation.

A new noninvasive temporary cardiac pacemaker-monitor has been developed to stimulate effective ventricular contraction in ventricular asystole or symptomatic bradycardia. It is quickly and easily applied, safe, and well tolerated even in conscious patients. It produced electrical cardiac responses in 105 of 134 patients; almost all of the remaining 29 patients were severely hypoxic. Stimulation was clinically useful in 82 patients: 20 of 43 were resuscitated from emergency arrest and 23 of 26 from expected arrest; 38 of 40 were successfully treated in readiness for an expected arrest that did not materialize; and one of nine patients with tachycardia was tested noninvasively for likelihood of recurrent ventricular tachycardia.

External noninvasive temporary cardiac pacing: clinical trials.

An external cardiac pacemaker-monitor has been developed that provides safe, effective noninvasive ventricular stimulation that is well tolerated in conscious patients and allows clear recognition of electrocardiographic response. The noninvasive temporary pacemaker (NTP) has now been applied in 134 patients in five hospitals. Stimulation was tolerated well in 73 of 82 conscious patients, and nine found it intolerable. The NTP was effective in evoking electrocardiographic responses in 105 patients; the 29 failures were in the presence of prolonged hypoxia or severe discomfort. The NTP was clinically useful in 82 patients: 43 of 86 were resuscitated from emergency or expected arrest, 38 of 40 were maintained in standby readiness for up to 1 month but did not require stimulation, and one of eight patients with tachycardia obtained some clinical benefit. The NTP was especially useful in 25 patients with complications or contraindications to endocardial pacing and in 57 patients in whom insertion of an endocardial electrode was avoided.

A new, noninvasive technique for inducing post-extrasystolic potentiation during echocardiography.

Left ventricular function was evaluated in 34 patients with the echocardiogram, and an external mechanical cardiac stimulator was used to induce a ventricular premature contraction (VPC) noninvasively. Extent of post-extrasystolic potentiation (PESP) was determined by comparing systolic dimensional shortening and ejection fraction of the sinus beat preceding the VPC to that of the potentiated beat which followed it. Using this technique, a VPC could be introduced into the cardiac cycle of 30 of the 34 patients, six of whom were free of obvious cardiac disease and 24 of whom had valvular, coronary or myopathic heart disease. The only complication observed was mild breast ecchymosis in a female patient. Systolic dimensional shortening and ejection fraction increased from control values by an average of 21% and 17% respectively, with a range of 0-100%. The degree of PESP was very reproducible in repeat studies and when the same patients were subsequently evaluated during a spontaneously occurring or catheter-induced VPC. The technique can safely and reliably induce post-extrasystolic potentiation during echocardiography and is a potentially important adjunct to the noninvasive evaluation of left ventricular function.

Noninvasive external cardiac pacing for thallium-201 scintigraphy.

Improvements in noninvasive external cardiac pacing have led to a technique with reliable electrical capture and tolerable patient discomfort. To assess the use of this modality of pacing in combination with thallium scintigraphy as a noninvasive pacing stress test, we applied simultaneous noninvasive cardiac pacing, hemodynamic monitoring, and thallium-201 scintigraphy in 14 patients undergoing cardiac catheterization for chest pain syndromes. Two patients had normal coronary arteries, while the remaining 12 had significant coronary artery disease. Thallium scintigraphic responses to pacing were compared to routine exercise thallium stress testing in nine of these 14 patients. All patients were noninvasively paced to more than 85% of the age-predicted maximum heart rate. Twelve patients demonstrated reversible thallium defects, which corresponded in 11 cases to significant lesions seen on coronary angiography. Of nine patients who underwent both pacing and exercise thallium stress tests, comparable maximal rate-pressure products were achieved. Moreover, thallium imaging at peak pacing and during delayed views did not differ significantly from exercise thallium scintigraphy. A limiting factor associated with the technique was local patient discomfort, which occurred to some degree in all patients. We conclude that noninvasive external cardiac pacing together with thallium scintigraphy is capable of detecting significant coronary artery disease and may be comparable to routine exercise thallium stress testing. This new modality of stress testing could be useful in patients unable to undergo the exercise required for standard exercise tolerance testing, particularly if improvements in the technology can be found to reduce further the local discomfort.