Electrophysiologic effects of adenosine-5'-triphosphate on atrioventricular reentrant tachycardia

Adenosine-A drug with myriad utility in the diagnosis and treatment of arrhythmias

Adenosine has been used in the emergency treatment of arrhythmia for more than nine decades. However, cardiologists are often unfamiliar about its basic mechanism and various diagnostic and therapeutic uses, considering it mainly as a therapeutic drug for supraventricular tachycardia. This article discusses the role of adenosine relevant to emergency physicians, cardiologists, and electrophysiologists. Understanding of the mechanisms of adenosine and its electrophysiological effects is discussed first, followed by dosing, side effects, diagnostic, and therapeutic uses. Finally, the role of adenosine in the electrophysiology laboratory is discussed.

Cardiac purinergic signalling in health and disease

This review is a historical account about purinergic signalling in the heart, for readers to see how ideas and understanding have changed as new experimental results were published. Initially, the focus is on the nervous control of the heart by ATP as a cotransmitter in sympathetic, parasympathetic, and sensory nerves, as well as in intracardiac neurons. Control of the heart by centers in the brain and vagal cardiovascular reflexes involving purines are also discussed. The actions of adenine nucleotides and nucleosides on cardiomyocytes, atrioventricular and sinoatrial nodes, cardiac fibroblasts, and coronary blood vessels are described. Cardiac release and degradation of ATP are also described. Finally, the involvement of purinergic signalling and its therapeutic potential in cardiac pathophysiology is reviewed, including acute and chronic heart failure, ischemia, infarction, arrhythmias, cardiomyopathy, syncope, hypertrophy, coronary artery disease, angina, diabetic cardiomyopathy, as well as heart transplantation and coronary bypass grafts.

The mechanism of the negative chronotropic and dromotropic actions of adenosine 5'-triphosphate in the heart: an update

Adenosine 5'-triphosphate (ATP) plays a critical role in intracellular metabolism and energetics. Extracellular ATP is rapidly degraded to adenosine by ectoenzymes. Both ATP and adenosine suppress cardiac pacemakers' automaticity and atrioventricular nodal conduction, albeit via the different mechanism of actions. This historical update summarizes the current knowledge regarding the negative chronotropic and dromotropic actions of ATP and discusses the clinical implications regarding the utility of ATP as a diagnostic and therapeutic agent in the management of neutrally mediated syncope and paroxysmal supra ventricular tachycardia.

Genesis and regulation of the heart automaticity

The heart automaticity is a fundamental physiological function in higher organisms. The spontaneous activity is initiated by specialized populations of cardiac cells generating periodical electrical oscillations. The exact cascade of steps initiating the pacemaker cycle in automatic cells has not yet been entirely elucidated. Nevertheless, ion channels and intracellular Ca(2+) signaling are necessary for the proper setting of the pacemaker mechanism. Here, we review the current knowledge on the cellular mechanisms underlying the generation and regulation of cardiac automaticity. We discuss evidence on the functional role of different families of ion channels in cardiac pacemaking and review recent results obtained on genetically engineered mouse strains displaying dysfunction in heart automaticity. Beside ion channels, intracellular Ca(2+) release has been indicated as an important mechanism for promoting automaticity at rest as well as for acceleration of the heart rate under sympathetic nerve input. The potential links between the activity of ion channels and Ca(2+) release will be discussed with the aim to propose an integrated framework of the mechanism of automaticity.

Reproducible induction of atrioventricular nodal reentrant tachycardia with adenosine triphosphate

A 29-year-old woman was referred for electrophysiological testing and radiofrequency ablation because of repeated episodes of palpitation of a 8-year duration. The 12-lead ECG during palpitations showed narrow QRS tachycardia at a rate of 160 beats/min. Dual AVN physiology according to electrophysiological criteria was not shown by single atrial extrastimulation and the tachycardia could not be induced. Slow/fast atrioventricular nodal reentrant tachycardia (AVNRT) was induced once by double atrial extrastimuli, but it was not reproducible. However, intravenous bolus injection of adenosine triphosphate (12.5 mg) during sinus rhythm led to reproducible initiation of slow/fast AVNRT.

Clinical significance of wide QRS complexes at the termination of paroxysmal supraventricular tachycardias

BACKGROUND

A wide QRS complex is not a rare electrocardiographic phenomenon at the termination of paroxysmal supraventricular tachycardia (PSVT), but no plausible underlying mechanism has yet been proposed. The purpose of the present study was to elucidate the frequency and the underlying mechanism of the wide QRS complexes at the termination of PSVT.

METHODS

We retrospectively reviewed 305 electrocardiograms (ECGs) from 100 patients, on which PSVT termination was recorded. The frequency of the wide QRS complexes was analyzed in 181 ECGs to avoid duplication, because there were 124 ECGs obtained from the same patients with same methods. The 181 ECGs were divided by morphology into three groups: Type A, termination with wide QRS complex without pause; Type B, wide QRS complex following initial pause after termination; Type C, wide QRS complex following the first narrow QRS after termination.

RESULTS

The wide QRS complex was recorded in 81/181 (44.8%) ECGs (Type A; 3/81 (3.7%), Type B; 44/81 (54.3%), Type C; 62/81 (55.6%) ) and its frequency was not dependent on the mechanism of PSVT. It was more frequently observed after a long pause, and was frequently induced by procedures that increase vagal tone, such as intravenous adenosine 5'-triphosphate administration (16/22: 72.7%) and vagal stimulation maneuvers (16/32: 50%). There were a total of 41 wide QRS complexes (44.6%) which had a preceding sinus P wave, out of a total of 92 wide QRS complexes in all three types. These 41 wide QRS complexes included 30/44 (68.2%) Type B wide QRS, and 11 (24.4%) Type C wide QRS complexes.

CONCLUSION

The aberrant conduction or escaped ventricular contraction was suggested to be the underlying mechanism of the majority of wide QRS complexes and ventricular premature contraction is less frequent.

Determination of coronary zero flow pressure by analysis of the baseline pressure-flow relationship in humans

The present study seeks to estimate the difference between coronary zero flow pressure (Pzf) by analysis of the baseline pressure-flow relationship and the Pzf calculated during a long diastole in humans. Although Pzf is likely to provide meaningful information about the characteristics of coronary circulation, there are no available data on Pzf in humans because Pzf is overestimated when it is calculated during normal cardiac cycles. Actual Pzf was determined in 15 subjects by analyzing the coronary pressure-flow relationship during a long cardiac cycle induced by an intracoronary adenosine triphosphate (ATP) infusion, and it was compared with the Pzf calculated during a normal cardiac cycle in order to estimate the difference. Pzf calculated during a normal cardiac cycle was 47 +/- 15 mmHg, which decreased to 36 +/- 9mmHg after intracoronary administration of ATP (0.05 mg) whereas actual Pzf was 21 +/- 7 mmHg. Pzf calculated in a pressure-flow relationship during a normal cardiac cycle under vasodilation correlated well with that during a long diastole (r = 0.75, p < 0.01), although it was 15 +/- 6 mmHg greater than the actual Pzf. It was concluded that Pzf during a normal cardiac cycle could be used to anticipate Pzf.

Supraventricular tachycardia

Supraventricular tachycardias (SVT) comprise those tachycardias that originate above the bifurcation of the bundle of His. They can be classified broadly as AV node dependent and AV node independent. The mechanism and clinical manifestation of SVTs, which is essential to their correct diagnosis, is reviewed. The therapeutic management of SVTs, including acute and chronic drug therapy and catheter ablation, is discussed also.

Differential effect of adenosine on anterograde and retrograde fast pathway conduction in patients with atrioventricular nodal reentrant tachycardia

INTRODUCTION

Several studies have shown that the fast pathway is more responsive to adenosine than the slow pathway in patients with AV nodal reentrant tachycardia. Little information is available regarding the effect of adenosine on anterograde and retrograde fast pathway conduction.

METHODS AND RESULTS

The effects of adenosine on anterograde and retrograde fast pathway conduction were evaluated in 116 patients (mean age 47 +/- 16 years) with typical AV nodal reentrant tachycardia. Each patient received 12 mg of adenosine during ventricular pacing at a cycle length 20 msec longer than the fast pathway VA block cycle length and during sinus rhythm or atrial pacing at 20 msec longer than the fast pathway AV block cycle length. Anterograde block occurred in 98% of patients compared with retrograde fast pathway block in 62% of patients (P < 0.001). Unresponsiveness of the retrograde fast pathway to adenosine was associated with a shorter AV block cycle length (374 +/- 78 vs 333 +/- 74 msec, P < 0.01), a shorter VA block cycle length (383 +/- 121 vs 307 +/- 49 msec, P < 0.001), and a shorter VA interval during tachycardia (53 +/- 23 vs 41 +/- 17 msec, P < 0.01).

CONCLUSION

Although anterograde fast pathway conduction is almost always blocked by 12 mg of adenosine, retrograde fast pathway conduction is not blocked by adenosine in 38% of patients with typical AV nodal reentrant tachycardia. This indicates that the anterograde and retrograde fast pathways may be anatomically and/or functionally distinct. Unresponsiveness of VA conduction to adenosine is not a reliable indicator of an accessory pathway.

Differential effects of adenosine on antegrade and retrograde fast pathway conduction in atrioventricular nodal reentry

Although adenosine depresses antegrade atrioventricular (AV) nodal conduction, the effects of adenosine on antegrade and retrograde fast pathway conduction in AV nodal reentry have not been determined. In 17 patients (five men, 12 women, mean age 49 +/- 12 years) with common slow-fast AV nodal reentrant tachycardia, the antegrade slow pathway conduction was selectively and completely ablated by radiofrequency catheter ablation while the antegrade and retrograde fast pathway conduction remained intact. During high right atrial pacing at a mean pacing cycle length of 474 +/- 36 msec, adenosine was rapidly injected intravenously at an initial dose of 0.5 mg followed by stepwise increases of 0.5 mg or 1.0 mg given at 5-minute intervals until second-degree AV block developed. During right ventricular apical pacing at the same pacing cycle lengths (mean 474 +/- 36 msec) as those in the study of antegrade conduction, intravenous injection of incremental doses of adenosine was repeated until ventriculoatrial (VA) block occurred. The adenosine-induced prolongation of VA conduction was also determined in the presence of verapamil (loading dose 0.15 mg/kg, maintenance dose 0.005 mg/kg/min) in seven of 17 patients. The dose of adenosine required to produce AV block, the increase in the atrio-His interval by 50% and the maximal response were 3.4 +/- 1.4 mg, 1.8 +/- 0.6 mg, and 58% +/- 5%, respectively. On the other hand, the dose of adenosine required to produce VA block, the increase in the VA interval by 50%, and the maximal response were 8.2 +/- 2.9 mg, 3.4 +/- 0.6 mg, and 20% +/- 5%, respectively, in the control and 3.7 +/- 0.5 mg, 3.5 +/- 0.7 mg, and 23% +/- 5%, respectively, in the presence of verapamil. In conclusion, adenosine has a differential potency to depress AV and VA conduction in patients with AV nodal reentry, with greater potency for slowing antegrade fast than retrograde fast pathway conduction. Verapamil had an additive effect to adenosine on slowing retrograde VA conduction, which further supports the evidence that the retrograde fast pathway in part involves an AV nodal-like structure.

Intracoronary administration of adenosine triphosphate increases myocardial adenosine levels and coronary blood flow in man

Adenosine triphosphate (ATP) is reported to be released mainly from presynaptic vesicles and cardiomyocytes. The released ATP, which can be degraded to adenosine, may cause coronary vasodilation. However, there is no clear evidence that ATP is degraded to adenosine and causes coronary vasodilation in humans. The present study was undertaken to test whether intracoronary administration of ATP increases myocardial adenosine levels and coronary blood flow. In 11 patients, 3 doses of ATP (0.1, 0.2, and 0.4 mg) were injected into the left anterior descending coronary artery. The velocity of coronary blood flow was measured by Doppler flow probe, and the adenosine concentration in the coronary sinus blood was measured. We also continuously infused ATP (0.2 mg/min) for 1 min in another 10 patients. Coronary blood flow increased dose dependently soon after injection of ATP. Coronary arteriovenous differences in adenosine concentration increased [from 21 +/- 15 to 178 +/- 15 pmol/ml (p < 0.05) 10 sec after the injection of ATP (0.4 mg)] and there were marked reductions in both aortic blood pressure and heart rate. The adenosine levels returned to baseline 20 sec after the injection of ATP, and aortic blood pressure and heart rate also recovered, although coronary blood flow remained increased. Furthermore, continuous infusion of ATP for 1 min increased coronary blood flow velocity and coronary arteriovenous differences in adenosine concentration from 25 +/- 14 to 71 +/- 13 pmol/ml (p < 0.05) in 10 patients. These results indicate that intracoronary administration of ATP immediately increases coronary blood flow and the adenosine concentration of coronary venous blood, which returns to the baseline level thereafter. The differences in the time courses of increases in coronary venous adenosine levels and coronary blood flow after ATP injections suggest that vasodilatory mechanisms other than adenosine, eg, nitric oxide and prostaglandins, may also be involved in the ATP-induced coronary vasodilation. ATP may be used as a cardioprotective agent as well as adenosine.

Treatment of out-of-hospital supraventricular tachycardia: adenosine vs verapamil

OBJECTIVE

To compare the use of adenosine and the use of verapamil as out-of-hospital therapy for supraventricular tachycardia (SVT).

METHODS

A period of prospective adenosine use (March 1993 to February 1994) was compared with a historical control period of verapamil use (March 1990 to February 1991) for SVT. Data were obtained for SVT patients treated in a metropolitan, fire-department-based paramedic system serving a population of approximately 1 million persons. Standard drug protocols were used and patient outcomes (i.e., conversion rates, complications, and recurrences) were monitored.

RESULTS

During the adenosine treatment period, 105 patients had SVT; 87 (83%) received adenosine, of whom 60 (69%) converted to a sinus rhythm (SR). Vagal maneuvers (VM) resulted in restoration of SR in 8 patients (7.6%). Some patients received adenosine for non-SVT rhythms: 7 sinus tachycardia, 18 atrial fibrilation, 7 wide-complex tachycardia (WCT), and 2 ventricular tachycardia; no non-SVT rhythm converted to SR and none of these patients experienced an adverse effect. Twenty-five patients were hemodynamically unstable (systolic blood pressure < 90 mm Hg), with 20 receiving drug and 13 converting to SR; 8 patients required electrical cardioversion. Four patients experienced adverse effects related to adenosine (chest pain dyspnea, prolonged bradycardia, and ventricular tachycardia). In the verapamil period, 106 patients had SVT: 52 (49%) received verapamil (p < 0.001, compared with the adenosine period), of whom 43 (88%) converted to SR (p = 0.11). Two patients received verapamil for WCT; neither converted to SR and both experienced cardiovascular collapse. VM resulted in restoration of SR in 12 patients (11.0%) (p = 0.52). Sixteen patients were hemodynamically unstable, with 5 receiving drug (p = 0.005) and 5 converting to SR; 9 patients required electrical cardioversion (p = 0.48). Four patients experienced adverse effects related to verapamil (hypotension ventricular tachycardia, ventricular fibrillation). Recurrence of SVT was noted in 2 adenosine patients and 2 verapamil patients in the out-of-hospital setting and in 23 adenosine patients and 15 verapamil patients after ED arrival, necessitating additional therapy (p = 0.48 and 0.88, for recurrence rates and types of additional therapies, respectively). Hospital diagnoses, outcomes, and ED dispositions were similar for the 2 groups.

CONCLUSION

Adenosine and verapamil were equally successful in converting out-of-hospital SVT in patients with similar etiologies responsible for the SVT. Recurrence of SVT occurred at similar rates for the 2 medications. Rhythm misidentification remains a common issue in out-of-hospital cardiac care in this emergency medical services system.

Zero flow pressure in human coronary circulation

Coronary pressure flow (P/F) relationship has been investigated mainly from the viewpoint of coronary resistance. However, recent experimental evidence suggests that the zero flow pressure intercept (Pzf) provides important characteristics of coronary circulation. Although Pzf is likely to provide meaningful information about characteristics of coronary circulation, no data are available about Pzf in humans. The authors attempted to determine Pzf in humans by analyzing P/F relationship during long cardiac pause. This relationship, provoked by intracoronary adenosine triphosphate (ATP) infusion, was analyzed in 9 patients (8 men, 1 woman) with coronary heart disease (ages: fifty-six +/- six years). After the diagnostic cardiac catheterization, ATP, 0.6 mg/3 mL, was administrated by bolus intracoronary injection during measurements of coronary blood flow velocity. Coronary blood flow velocity in the left anterior descending artery was measured with a 0.018-inch Doppler angioplasty guide wire (FloWire, Cariometrics, Inc., Mountain View, Calif.). The dynamic P/F relationship was obtained by correlation of the instantaneous aortic pressure and flow velocity with each other at constant intervals. The least square linear regression analysis was applied to the P/F data to yield the extrapolated Pzf axis. Immediately after intracoronary injection of ATP, long pause (5320 +/- 1498 msec) appeared and coronary blood flow velocity decreased to 11 +/- 8 cm/sec. Pzf calculated with P/F relationship was 14 +/- 7 mmHg.

CONCLUSIONS

Thus, the results clearly demonstrate that Pzf is higher than right atrial and left ventricular end-diastolic pressure in humans, indicating the complexity of the determinants of the Pzf.

Transesophageal echo phase imaging for localizing accessory pathways during adenosine-induced preexcitation in patients with the Wolff-Parkinson-White syndrome

Transesophageal phase images and precordial electrocardiography (ECG) were used to localize accessory pathways during adenosine-induced preexcitation in 30 patients (18 men, mean age +/- SD 33 +/- 14 years) undergoing endocardial mapping for suspected Wolff-Parkinson-White syndrome. Digitized 2-dimensional echocardiographic cine loops were mathematically transformed using a first harmonic Fourier algorithm before and after catheter ablation. Endocardial mapping found single accessory pathways with anterograde conduction in 20 patients, concealed pathways in 7, and atrioventricular reentry circuits in 3 patients. At baseline, precordial ECG correctly localized 8 pathways (40%) with anterograde conduction and predicted 5 adjacent locations (25%), but findings were normal in 7 patients (35%). Phase imaging correctly identified only 3 pathway locations (15%), findings were normal in 15 (75%), and could not be obtained in 2 patients (10%). Adenosine augmented manifest but minimal preexcitation in 9 patients and unmasked latent preexcitation in 7. In 4 patients, preexcitation was already maximal at baseline. During adenosine-augmented preexcitation, ECG correctly identified 13 locations (65%), but still predicted 7 adjacent locations (35%). However, phase imaging correctly identified 15 locations (75%) and predicted only 3 adjacent locations (15%). All midseptal (n = 2) and anteroseptal (n = 2) locations were correctly identified by phase imaging, but none by ECG. On follow-up studies in 16 patients, successful catheter ablation (n = 13) was equally well confirmed by ECG and phase imaging. Therefore, transesophageal echocardiographic phase imaging during adenosine-induced preexcitation is a readily available and safe procedure that appears clinically most useful for identifying septal pathways.

Thallium-201 myocardial tomography with intravenous infusion of adenosine triphosphate in diagnosis of coronary artery disease

OBJECTIVES

The purpose of this study was to evaluate the feasibility, safety and diagnostic accuracy of thallium-201 myocardial tomography with intravenous adenosine triphosphate (ATP) infusion in patients with suspected coronary artery disease.

BACKGROUND

Both ATP and adenosine are potent coronary vasodilators with a very short half-life. Several studies have confirmed that the diagnostic accuracy of adenosine thallium-201 scintigraphy is comparable to that with exercise. However, a high incidence of side effects, including atrioventricular (AV) block, has also been reported. Because the appropriate infusion rate for ATP has not yet been determined, this agent has not been tested in combination with myocardial scintigraphy.

METHODS

The study group included 253 consecutive patients who underwent thallium-201 myocardial tomography with ATP infusion (0.16 mg/kg body weight per min for 5 min). The occurrence of adverse effects was carefully monitored. Of the 120 patients with coronary angiography, 76 had significant coronary artery disease. Tomographic images were assessed visually and by computer-quantified polar maps, and they were compared with the results of coronary angiography.

RESULTS

Although 56% of the patients had some adverse effects, they were transient and mild. In all patients, the ATP infusion protocol could be completed, and no patient required aminophylline; AV block occurred in only 2% of the patients. The sensitivity and specificity were 88% and 80%, respectively, by visual analysis and 91% and 86%, respectively, by computer quantification.

CONCLUSIONS

Thallium tomography with ATP is feasible and has a diagnostic value similar to that with adenosine for detecting coronary artery disease. In addition, it may have fewer side effects than adenosine myocardial tomography.

Malignant wide complex tachycardia after adenosine administration to a postoperative pediatric patient with congenital heart disease

Adenosine has become the treatment of choice for paroxysmal supraventricular tachycardia because of its safety and efficacy. There have been no reports of malignant arrhythmias occurring after adenosine administration. This case report presents the occurrence of a malignant wide complex tachycardia after intravenous adenosine administration in a 10-year-old boy 2 days after a Fontan procedure. Thus the administration of adenosine in a critically ill postoperative patient can have morbidity or potential mortality and must be monitored closely.

Influence of tumor size on anesthetic management for pheochromocytoma resection

The relationship between tumor size and the complexity of anesthetic management was studied using several values: plasma catecholamine concentrations, requirement of vasoactive agents, surgical time, blood loss, plasma glucose concentrations, and hemodynamic variables. Ten patients with clinical and laboratory diagnosis of pheochromocytoma were prospectively studied. Each anesthesia was maintained using inhalational anesthetic agents. Control of arterial blood pressure (ABP), heart rate (HR), and pulmonary artery blood pressure (PABP) was attempted with only titrating the inhalational anesthetics and adenosine triphosphate (ATP). If the titration of both the inhalational anesthetic and ATP failed to control ABP, HR, or PABP, then phentolamine, propranolol, trinitroglycerine, or norepinephrine was additionally used. Tumor weight was significantly correlated with amount of blood loss, surgical time, duration of ATP requirement, maximal dose of ATP infusion used, maximal plasma glucose concentration, and plasma total catecholamine concentration. However, the tumor weight was not correlated with hemodynamic variables. Patients who required propranolol generally had a significantly larger tumor than those who did not. In conclusion, surgical removal of large pheochromocytoma required more complicated anesthetic management than that of small pheochromocytoma.

Effect of adenosine or adenosine triphosphate on antidromic tachycardia

OBJECTIVES

This study was designed to determine the effect of adenosine or adenosine triphosphate (ATP) on antidromic tachycardia.

BACKGROUND

Adenosine and adenosine triphosphate are useful for differential diagnosis of wide QRS tachycardia. It has been believed that tachycardia termination caused by these agents is due to the preferential depressive effect on the atrioventricular (AV) node, whereas their effect on accessory pathways is minimal.

METHODS

We studied the effect of adenosine or ATP on the termination pattern of antidromic tachycardia in 17 patients (10 men, 7 women; mean age [+/- SD] 32 +/- 11 years) with one or more accessory pathways. Adenosine (6 to 12 mg [n = 10]) or ATP (8 to 20 mg [n = 7]) was injected rapidly through a central venous line and followed by 10 ml of saline flush after induction of sustained antidromic tachycardia.

RESULTS

Tachycardia was terminated in < 2 min in 14 patients (82%) after the injection and remained unchanged in 3 (18%). Tachycardia termination was due to conduction block in the accessory pathway (anterograde limb) in seven patients (50%) and in the AV node (retrograde limb) in another seven. Adenosine or ATP caused accessory pathway block in seven (88%) of the eight patients lacking retrograde accessory pathway conduction and in none of the nine patients having retrograde accessory pathway conduction (p < 0.01). All five patients with an atriofascicular accessory pathway and unidirectional anterograde conduction had tachycardia termination due to anterograde accessory pathway block after injection of adenosine or ATP.

CONCLUSIONS

1) Adenosine or ATP effectively terminates antidromic tachycardia; 2) the termination is related to block in either the accessory pathway or the AV node; 3) accessory pathway block occurs in patients with a unidirectional, anterogradely conducting accessory pathway, especially an atriofascicular accessory pathway.

Therapeutic and diagnostic utility of adenosine during tachycardia evaluation in children

Adenosine has become the drug of choice for termination of regular, normal QRS tachycardia. Initial studies in adult and pediatric patients have shown that the drug is effective for tachycardias using the atrioventricular (AV) node as an integral part of the tachycardia circuit and has few serious side effects. Experience with adenosine administration in children was reviewed to examine the diagnostic and therapeutic usefulness, effective dose, and adverse effects of adenosine. Adenosine was administered to 38 children during 50 separate electrophysiologic evaluations. Eleven patients had structural or acquired heart disease. Tachycardia mechanisms included orthodromic-reciprocating tachycardia using an accessory AV connection (23 patients), primary atrial tachycardia (6 patients), AV node reentrant tachycardia (3 patients), ventricular tachycardia (2 patients), postoperative junctional tachycardia (1 patient), and antidromic-reciprocating tachycardia (1 patient). Adenosine successfully terminated 51 of 53 episodes (96%) of tachycardia using the AV node, 5 of 10 primary atrial tachycardias, 1 of 1 junctional tachycardia, and 1 of 3 ventricular tachycardias. Reinitiation of tachycardia was seen after 16 of 58 successful terminations (28%), reducing the effectiveness to 39 of 53 (74%) for tachycardia requiring the AV node. Average effective dose was 132 micrograms/kg, range 50 to 250 micrograms/kg, and was slightly higher for peripheral (147 micrograms/kg) than for central (120 micrograms/kg) administration. Significant complications occurred in 4 of 38 patients, including atrial fibrillation, accelerated ventricular tachycardia, apnea, and 1 minute of asystole. Although adenosine is useful therapeutically and diagnostically in children with tachycardia, its effectiveness is limited by tachycardia reinitiation and adverse effects. Higher doses may be required for peripheral intravenous administration.

Perfusion pressure control by adenosine triphosphate given during cardiopulmonary bypass

Administration of exogenous adenosine triphosphate (ATP) as a vasodilator during cardiopulmonary bypass was assessed in consecutive adult patients (n = 24) who demonstrated a high arterial perfusion pressure (mean, > 90 mm Hg). The action of ATP was characterized by rapid induction and stabilization of the blood pressure level. The dose of ATP ranged from 0.68 to 2.68 mg/min. Within 1 minute after the administration, there was a significant reduction in the perfusion pressure from 102 +/- 18 mm Hg (mean +/- standard deviation) to 72 +/- 19 mm Hg. The ATP was then able to maintain the desired pressure of 69 +/- 12 mm Hg at 5 minutes, 67 +/- 12 mm Hg at 10 minutes, and consistent values thereafter. After the ATP administration was discontinued, there was a prompt recovery of pressure without bradyarrhythmia. The frequency and amount of inotropes used were consistent with the control group (n = 26). Although the administration of ATP reduced the increase in serum catecholamine concentration, there were no significant changes in other vasoactive mediators (eicosanoid, angiotensin II, endothelin) between the two groups during cardiopulmonary bypass. There was neither an accumulation of metabolic products (uric acid, phosphate) nor a decrease in the level of divalent cation (Ca2+), which is observed when the cations combine with phosphates or adenosine nucleotides. This study confirmed the efficacy and safety of ATP infusion during cardiopulmonary bypass.

Clinical and electrophysiologic effects of magnesium sulfate on paroxysmal supraventricular tachycardia and comparison with adenosine triphosphate

Electrophysiologic studies have shown that intravenous magnesium sulfate prolongs atrioventricular (AV) nodal conduction and refractoriness and thus could play a role in the management of patients with paroxysmal AV reentrant supraventricular tachycardia (SVT). The present study evaluates the clinical and electrophysiologic effects of intravenous magnesium sulfate in patients with SVT and compares them with those of adenosine triphosphate (ATP), one of the most potent drugs in the treatment of this arrhythmia. Patients with inducible sustained SVT were treated with ATP (10 or 20 mg) and magnesium sulfate (2 g over 15 seconds) during electrophysiologic study. If the tachycardia failed to terminate by the sixth minute, an additional 2 g dose of magnesium was given. ATP (10 or 20 mg) was significantly better than magnesium for terminating induced tachycardias (14 of 14 vs 6 of 14, p less than 0.0001). Arrhythmia termination with ATP was due to anterograde AV nodal blockade in all but 1 patient who developed retrograde block over an accessory pathway with decremental conduction. Arrhythmia termination by magnesium was due to retrograde block over an accessory pathway in 3 patients (including the patient with accessory pathway exhibiting decremental conduction), anterograde AV nodal conduction block in 2 patients and premature ventricular complexes in 1 patient. During induced tachycardias, only AH intervals were prolonged by ATP, whereas magnesium significantly prolonged AH and QRS intervals. Short-lasting side effects (chest pain, flushing, nausea) occurred after both drugs were administered but were more severe after magnesium.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine and the treatment of supraventricular tachycardia

Adenosine has recently become widely available for the treatment of paroxysmal supraventricular tachycardia. In order to evaluate its role in the management of arrhythmias, we have reviewed the literature on the cellular mechanisms, metabolism, potential for adverse effects, and clinical experience of the efficacy and safety of intravenous adenosine. Adenosine produces transient atrioventricular nodal block when injected as an intravenous bolus. This is of therapeutic value in the conversion to sinus rhythm of the majority of paroxysmal supraventricular tachycardias, which involve the atrioventricular node in a re-entrant circuit. The mean success rate was 93% from over 600 reported episodes. Compared with other antiarrhythmic agents, adenosine is remarkable for its rapid metabolism and brevity of action, with a half-life of a few seconds. It commonly produces subjective symptoms, particularly chest discomfort, dyspnea, and flushing, which are of short duration only. No serious adverse effect has been reported. Arrhythmias may recur within minutes in a minority of patients. Comparative studies have shown that adenosine is as effective as verapamil in the treatment of supraventricular tachycardia, and has less potential for adverse effects. Patients with supraventricular tachycardia should initially be treated using vagotonic physical maneuvers. Immediate electrical cardioversion is indicated if the arrhythmia is associated with hemodynamic collapse. Adenosine is the preferred drug in those patients in whom verapamil has failed or may cause adverse effects, such as those with heart failure or wide-complex tachycardia. The safety profile of adenosine suggests that it should be the drug of first choice for the treatment of supraventricular tachycardia, but only limited comparative data to support this view are available at present.

Adenosine-induced atrioventricular block: a rapid and reliable method to assess surgical and radiofrequency catheter ablation of accessory atrioventricular pathways

Adenosine has been shown to inhibit anterograde and retrograde conduction through the atrioventricular (AV) node while having little or no effect on accessory pathway conduction. Its rapid onset of action and short half-life make it particularly suitable for repetitive measurements. In this study, the utility of adenosine was tested in assessing completeness of accessory pathway ablation. Sixteen patients with an accessory pathway were studied (eight surgical ablations, eight catheter ablations with radiofrequency energy). Before ablation, no accessory pathway was sensitive to adenosine. Twelve patients with pre-excitation showed high grade AV node block with maximal pre-excitation on the administration of adenosine during atrial pacing. Four patients with a concealed accessory pathway demonstrated high grade AV block without evidence of latent anterograde accessory pathway conduction. Preablation ventriculoatrial (VA) block was not observed in any of the 16 patients in response to adenosine during ventricular pacing. Immediately after accessory pathway ablation, all patients developed AV and VA block with the administration of adenosine during atrial and ventricular pacing, respectively. These findings were confirmed during follow-up study 1 week later. Atrioventricular block during atrial and ventricular pacing with adenosine affords a reliable and immediate assessment of successful pathway ablation.

Repetitive sinoatrial exit block as the major mechanism of drug-provoked long sinus or atrial pause

Prolonged sinus or atrial pause occurred in six patients with paroxysmal supraventricular tachycardia after drug administration. All six patients had normal sinus node function during control electrophysiologic study; the sinus cycle length ranged from 510 to 900 ms (mean 743 +/- 141) and the longest sinus node recovery time ranged from 800 to 1,230 ms (mean 1,018 +/- 168). A long sinus or atrial pause occurring at the termination of tachycardia or cessation of atrial pacing, ranging from 3,100 to 8,200 ms (mean 6,270 +/- 1,674), was provoked by the administration of various drugs. These included an intravenous bolus injection of adenosine triphosphate (5 mg; one patient), intravenous bolus injection of verapamil (5 mg; one patient), a combination of a single oral dose of diltiazem (120 mg) and propranolol (20 to 40 mg; three patients), oral diltiazem (240 mg/day; one patient) and a combination of oral diltiazem (240 mg/day) and propranolol (160 mg/day; one patient). In five patients, low frequency deflections suggestive of sinus node activity with a cycle length between 620 and 3,500 ms were recorded during pauses. These findings suggest that repetitive sinoatrial exit block was responsible for the pause. Sinus slowing with a long arrest suggesting suppression of sinus automaticity was also noted in three of these five patients; the longest sinus arrest in these three patients was 4,160, 4,800 and greater than 4,910 ms, respectively. The remaining patient with a pause of 6,840 ms had no recordable sinus activity, either reflecting suppression of sinus automaticity or technical failure.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine-5'-triphosphate-induced sinus tachycardia mediated by prostaglandin synthesis via phospholipase C in the rabbit heart

Effects of adenosine 5'-triphosphate (ATP) and adenosine on cardiac sinus pacemaker activity were examined in the rabbit heart. Electrocardiograms of hearts were recorded while using the Langendorff perfusion method. Both adenosine and ATP, added to the perfusate, slowed the sinus pacemaker activity in a concentration-dependent manner. But in about 40% of the cases. ATP higher than 300 microM initially accelerated and then slowed the heart. The sinus slowing caused by adenosine and ATP was blocked by theophylline (a P1 receptor antagonist) and disappeared in the hearts pre-treated with islet-activating protein (1AP). In contrast, the ATP-induced sinus acceleration was not affected by either theophylline or IAP. In about 75% of the IAP-treated hearts. ATP persistently accelerated the sinus pacemaker. In the remaining 25% of the hearts, ATP caused junctional tachycardia, which may have masked the ATP-induced sinus acceleration. Apamin specifically blocked the ATP-induced sinus acceleration, suggesting that P2 receptors are involved. Among various adenine nucleotide analogues, the order of potency in inducing tachycardia in IAP-treated hearts is adenosine-5'-[gamma-thio]triphosphate greater than adenylyl imidodiphosphate greater than adenosine 5'-[alpha, beta-methylene]triphosphate = ATP greater than adenosine diphosphate = adenosine 5'-[beta, gamma-methylene]triphosphate. ATP-induced acceleration was partially blocked by indomethacin and aspirin (cyclooxygenase inhibitors), but not by nordihydroguaiaretic acid (a lipoxygenase inhibitor). These results suggest that cyclooxygenase and not lipoxygenase metabolites of arachidonic acid, e.g. prostaglandins, may be involved in the generation of tachycardia.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute management of paroxysmal atrioventricular junctional reentrant supraventricular tachycardia: pharmacologic strategies

A vast array of effective antiarrhythmic agents offers the attending physician attractive options for termination of PJRT. Calcium channel blockers, adenosine compounds, amjaline, and the newer drugs flecainide and propafenone offer an efficacy rate of more than 80% for acute termination of PJRT. Choice should be based on the patient's clinical characteristics including any underlying cardiac or noncardiac pathologic conditions, hemodynamic status, and current medications. Drugs with a very short half-life (adenosine compounds) offer the possibility of repeated administration at increasing dosages or of subsequent administration of a second antiarrhythmic drug without fear of increased adverse effects or drug interactions. Drugs with a long half-life, such as calcium channel blockers, flecainide, and propafenone, have the potential advantage of preventing an immediate recurrence of the arrhythmia. Adenosine compounds are the fastest acting drugs, resulting in termination of PJRT in less than 30 seconds. The cardiac side effects of all antiarrhythmic drugs represent an exaggeration of their intrinsic electrophysiologic and hemodynamic effects. Thus hemodynamic decompensation and bradyarrhythmias resulting from sinus nodal, AV nodal, or infranodal dysfunction are of major concern. Side effects of adenosine compounds are extremely common but very short lasting. Verapamil is both highly effective and safe except in very special circumstances. Guidelines for therapy of PJRT in specific groups of patients are provided.

Intravenous adenosine triphosphate during wide QRS complex tachycardia: safety, therapeutic efficacy, and diagnostic utility

PURPOSE

Inappropriate administration of intravenous verapamil to patients with wide QRS complex tachycardia due to ventricular tachycardia or atrial fibrillation with Wolff-Parkinson-White syndrome occurs frequently because of misdiagnosis, and may precipitate a cardiac arrest. We evaluated the safety and the diagnostic and therapeutic utility of adenosine triphosphate administered to a consecutive series of 34 patients during wide QRS complex tachycardia due to a variety of mechanisms.

PATIENTS AND METHODS

Patients who had a hemodynamically and electrically stable, monomorphic, wide (greater than 120 msec) QRS complex tachycardia induced during an invasive cardiac electrophysiologic test were studied. Hemodynamic stability was defined by a systolic blood pressure greater than 80 mm Hg and no clinical evidence of cerebral or myocardial ischemia. Adenosine triphosphate, 20 mg, was administered as a rapid intravenous bolus via a peripheral vein during wide QRS complex tachycardia. Five surface electrocardiogram leads, at least three intracardiac electrograms, and blood pressure were monitored.

RESULTS

Ventricular tachycardia was present in 14 patients (mean age 50.6 +/- 19 years, cycle length 326 +/- 67 msec) and adenosine triphosphate terminated the arrhythmia in one case. Ventricular tachycardia cycle length did not change. Among 10 patients with supraventricular tachycardia with mechanisms not involving the AV node (average ventricular cycle length 346 +/- 82 msec), one case of ectopic atrial tachycardia was terminated. The ventricular rate was transiently increased in patients with Wolff-Parkinson-White syndrome and atrial fibrillation (average R-R interval 351 +/- 84 msec in control and 317 +/- 82 msec after adenosine triphosphate, p less than 0.001). Reentrant tachycardias involving the AV node (cycle length 302 +/- 52 msec) terminated in seven of 10 patients. The drug was well tolerated, and no patient developed hemodynamic compromise necessitating cardioversion as a result of adenosine triphosphate.

CONCLUSION

In the setting of electrophysiology testing, adenosine triphosphate is a safe agent, even when administered inappropriately during arrhythmias for which it is relatively ineffective, such as ventricular tachycardia, and Wolff-Parkinson-White syndrome with atrial fibrillation. It is an effective agent in terminating supraventricular tachycardia involving the AV node. Tachycardia termination following adenosine triphosphate, when used as a diagnostic test to indicate obligatory participation of the AV node, had a sensitivity of 70%, specificity of 92%, and a positive predictive accuracy of 85%. Thus, adenosine triphosphate also has diagnostic utility, but should be used after the appropriate arrhythmia diagnosis has been made based on the clinical history and analysis of the 12-lead electrocardiogram.

Adenosine or adenosine triphosphate for supraventricular tachycardias? Comparative double-blind randomized study in patients with spontaneous or inducible arrhythmias

The effects of intravenous adenosine and adenosine triphosphate (ATP) were studied in a double-blind randomized study during 68 episodes of supraventricular tachycardia in 39 patients. Adenosine restored sinus rhythm in 20 patients (25 of 27 episodes) and produced atrioventricular block to reveal atrial arrhythmias in nine. ATP restored sinus rhythm in 17 patients (22 of 25 episodes) and revealed atrial tachyarrhythmias in six. In patients receiving both compounds, the effective dosage of adenosine was 3.8 mg and of ATP it was 6.6 mg (p less than 0.05), suggesting molar equipotency. Transient side effects were common, occurring in 81% of episodes with adenosine and in 94% with ATP. Symptom scores (0 to 10) were not significantly different (median score for adenosine was 5, for ATP it was 6). Adenosine and ATP were equally effective for the diagnosis and treatment of supraventricular tachycardias and the incidence and severity of side effects were similar. Adenosine has the advantage of being more stable.

Dose related efficacy of adenosine triphosphate in spontaneous supraventricular tachyarrhythmias

Intravenous adenosine triphosphate has been proved to be useful for the treatment of supraventricular tachyarrhythmias. The optimal dose to be employed, however, has yet to be stated. Forty-two episodes of spontaneous paroxysmal supraventricular tachycardia, observed in 33 patients (16 men and 17 women, mean age 51 years) were treated with intravenous boluses. These were given in 10 mg increments at increasing doses from 10 to 50 mg at intervals of three minutes if the arrhythmia persisted despite the previous dose. When using a dose less than or equal to 40 mg, tachycardia was terminated in 37 of 42 episodes in less than 50 seconds. In four of the remaining five, atrial flutter and ectopic atrial tachycardia were diagnosed after administration of adenosine triphosphate. The other patient was subsequently found to have an atrioventricular reentrant tachycardia incorporating two accessory pathways. More than half of the treated episodes of supraventricular tachycardia terminated with the minimal dose of 10 mg and 7.1% required 40 mg. In five patients, arrhythmia ceased and reappeared despite the use of adenosine triphosphate. All the patients experienced an unpleasant feeling of dyspnoea or suffocation after injection of the drug. Sinus pauses and bradycardia following termination of the arrhythmia were directly correlated with the dose employed (P less than 0.05). We conclude that adenosine triphosphate is a useful, safe and effective drug at low dose in correctly diagnosed reentrant tachycardias involving the atrioventricular node. It is also useful as a diagnostic tool in patients with supraventricular tachyarrhythmias.

Adenosine triphosphate: a potential therapy for hypoxic pulmonary hypertension

In this study we investigated whether a low-dose infusion of ATP-MgCl2 could ameliorate the pulmonary hypertension resulting from hypoxic pulmonary vasoconstriction. Three-week-old piglets were anesthetized, intubated, ventilated with room air, and cannulated for the measurement of pulmonary and systemic arterial pressure and pulmonary artery flow (cardiac output). The ventilator inflow was then changed to a mixture containing 10% oxygen, 4% CO2, and balance nitrogen. Serial infusions of ATP-MgCl2 at 0.1, 0.5 and 1.0 mg/kg/min were compared to preinfusion hypoxia baselines. Hypoxia alone produced a significant elevation in pulmonary artery pressure. Although all dose rates of ATP-MgCl2 produced a significant decrease (30%) in mean pulmonary artery pressure, we observed a maximum decrease in MPAP at the lowest rate of ATP infusion. Pulmonary artery flow rose slightly during ATP infusion; therefore, it was the change in pulmonary vascular resistance that accounted for the decrease in pulmonary artery pressure. In contrast, the systemic pressure was significantly decreased only during the 1.0 mg/kg/min infusion. The predominant pulmonary effects are a result of the virtual clearance of ATP-MgCl2 in a single pass through the circulation. Adenosine in the presence or absence of MgCl2 produced only a 10% reduction in mean pulmonary artery pressure, and MgCl2 had no effect when infused alone. From these results, we conclude that a low-dose infusion of ATP-MgCl2 could ameliorate the vasoconstriction associated with hypoxic pulmonary hypertension without significant deleterious systemic side effects.

Comparative effects of adenosine triphosphate on accessory pathway and atrioventricular nodal conduction

Adenosine triphosphate (ATP) has potent negative dromotropic effects on the atrioventricular (AV) node, but variable effects on accessory pathway conduction have been described. The effects of an intravenous bolus injection of 8 mg ATP on accessory pathway and AV nodal conduction were determined during electrophysiologic testing with controlled atrial and ventricular rates. AV conduction was monitored during atrial or ventricular pacing at a constant cycle length, 30 msec longer than the cycle length at which block occurred. During atrial pacing antegrade block after administration of ATP occurred in 1 of 30 (3.2%) patients with accessory pathway conduction and 12 of 13 (92%) patients with AV nodal conduction (p less than 0.001). During ventricular pacing only 5 of 26 (16%) patients had accessory pathways blocked, whereas 25 of 35 (71%) patients with AV nodal conduction had block (p less than 0.001). Thus, failure of ATP to produce ventriculoatrial block identified the presence of an accessory pathway with a sensitivity of 84%, specificity of 71%, and predictive value of 72%. There was no correlation between accessory pathway properties and the effects of ATP. The effects of ATP on the AV node were concordant with the effects of a combination of verapamil and propranolol in 21 of 23 patients, suggesting that this dose ATP is an equipotent AV nodal blocker with a short duration of action. Thus, although the effects of ATP on accessory pathways and the AV node differ, block in ventriculoatrial conduction after administration of ATP cannot be used as the sole criterion to distinguish the mechanism of conduction.

Comparative quantitative electrophysiologic effects of adenosine triphosphate on the sinus node and atrioventricular node

A pharmacologic approach was used to characterize the sinus node (SN) and atrioventricular (AV) node responses to intravenous adenosine triphosphate (ATP) in 21 patients during electrophysiologic testing. ATP produced dose-dependent prolongation of spontaneous sinus cycle length. The mean maximal increase in sinus cycle length was 294 +/- 60 ms (n = 10). The mean dose of ATP required to produce this maximal sinus cycle length prolongation was 3.5 +/- 1.0 mg. The dose-response curve for sinus cycle length prolongation was sigmoid in shape with an EC50 of 0.39 mg derived from a median effect plot. There was a negative correlation between the control sinus cycle length and the dose of ATP required to produce the maximal prolongation of cycle length (p less than 0.05). In contrast, the mean dose of ATP producing AV block was 4.4 +/- 0.97 mg and the EC50 was 2.98 mg. There was a positive correlation between the AV nodal functional refractory period and the prolongation of the AH interval with a 2 mg dose (p less than 0.05). Consistent with the AV nodal dose-response curves, 8 mg ATP terminated paroxysmal reentrant supraventricular tachycardia at the AV node in 8 of 9 patients. Thus, SN and AV node responses to ATP have differences in their electrophysiologic correlates and EC50. These findings suggest that ATP has potentially different mechanisms of action on SN automaticity and AV nodal conduction that requires further investigation.

Termination of focal atrial tachycardia by adenosine triphosphate

An atrial aneurysm gave rise to incessant atrial tachycardia in a 21 year old Seychellian soldier. This arrhythmia was suppressed by intravenous adenosine triphosphate and ajmaline. Resection of the aneurysm abolished the arrhythmia and re-established sinus rhythm.

[Cardiac effects of adenosine. Mechanism of action, pathophysiologic and clinical significance]

Adenosine has a negative inotropic effect in cardiac atrial preparations ("direct" negative inotropic effect). This effect is probably due to an activation of a potassium outward current which shortens the action potential duration and hence reduces the force of contraction. A pertussis toxin-sensitive N-protein is involved in the signal transduction from the adenosine receptor to atrial potassium channels. In ventricular cardiac preparations adenosine has no negative or even a weak positive inotropic effect, but it reduces the force of contraction in the presence of cAMP-increasing agents such as isoprenaline ("indirect" negative intropic effect). This effect is due to an inhibition of the slow Ca2+ inward current which has previously been enhanced by an increase in the cellular cAMP content. This "indirect" negative inotropic effect of adenosine is also present in the human heart. Since increased amounts of adenosine are released during cardiac stimulation via beta-adrenoceptors, the "indirect" effect might protect the heart against excessive stimulation by catecholamines. In addition, adenosine has negative chronotropic actions and prolongs AV conduction by an activation of potassium channels or an inhibition of the slow Ca2+ inward current (AV node). Cardiac bradyarrhythmias in hypoxia have been attributed to an increased formation and release of adenosine. Furthermore, adenosine has been shown to terminate supraventricular tachycardias involving the AV node. Since it has a very short duration of action it might prove safe and hence advantageous to conventional therapy in the treatment of supraventricular tachycardias.

Rapid and safe termination of supraventricular tachycardia in children by adenosine

Adenosine (0.05-0.25 mg/kg intravenously) successfully terminated resistant supraventricular tachycardia (SVT) in three seriously ill newborn infants and one older child. Termination of tachycardia was achieved in each case within 20 s. Adenosine, unlike many other anti-arrhythmic agents, has no substantial negative inotropic effect under these circumstances and may become the drug of choice in haemodynamically compromised children with SVT. However, it has no value in prophylaxis against recurrent SVT.

Intravenous adenosine triphosphate disodium: its efficacy and electrophysiologic effects on patients with paroxysmal supraventricular tachycardias

We studied the electrophysiologic effects of intravenous adenosine triphosphate disodium (ATP-2Na) on 17 patients with paroxysmal supraventricular tachycardias (PSVTs). One patient had sinus node (SN) reentry, two had intraatrial (IA) reentry, 7 patients had AV nodal reentry and seven had atrioventricular reentrant tachycardias (AVRTs) with accessory pathways (APs). ATP-2Na was injected during ventricular pacing in patients with AV nodal reentry and AVRTs with APs. A bolus injection of ATP-2Na terminated all the PSVTs within 50 s except for one case of IA reentry (case 2). The sites of block at termination were the atrium in SN reentry and IA reentry, between A and H (AH) or between H and A (HA) in AV nodal reentry, and AH block in all the PSVTs with APs. The sites of action on the patients with AV nodal reentry were both the antegrade and retrograde pathways, while the modes of block were Mobitz type I and type II, respectively. ATP-2Na during ventricular pacing in patients with AV nodal reentry produced Mobitz type II ventriculoatrial block (VAB) in four of seven cases. ATP-2Na during ventricular pacing in patients with AVRTs with APs produced changes of atrial activation sequences in two patients, induction of PSVT in two patients, and Mobitz type II VA block in three patients. The former two phenomena suggested a retrograde AV nodal block and raised the possibility of a simple test for retrograde atrial fusion during ventricular pacing in patients with WPW syndrome. Chest discomfort of short duration was most commonly noted after ATP-2Na administration.

Adenosine triphosphate and adenosine: perspectives in the acute management of paroxysmal supraventricular tachycardia

Adenosine triphosphate (ATP) and adenosine exert strong and transient depressant effects on the sinoatrial and atrioventricular (AV) nodes of the human heart. The AV nodal effects of these drugs explain their high efficacy in either terminating AV re-entrant supraventricular tachycardia or in slowing ventricular rate during atrial tachyarrhythmias. Their very short half-life enables repeated administration of increased doses without reaching toxic effects and explains the transient character of their frequent but benign side effects. These agents represent a good alternative to verapamil in the acute management of paroxysmal supraventricular tachycardia both in infants and adults.