Electrophysiologic effects of intravenous dipyridamole

Changes of electrocardiogram and hemodynamics in response to dipyridamole: In vivo comparative analyses using anesthetized beagle dogs and microminipigs

Microminipigs are expected as a novel animal model for cardiovascular pharmacological experiments. Since inherent vulnerability of coronary circulation of microminipigs has not been characterized, we performed dipyridamole-stress test to both microminipigs and beagle dogs, and compared the results. Dipyridamole in doses of 0.056 and 0.56 mg/kg were intravenously infused over 10 min (n = 4 for each animal). Dipyridamole decreased the systolic/diastolic blood pressures and double product in dogs as well as in microminipigs; but it did not significantly alter the heart rate or the global balance between the myocardial oxygen demand and supply in either animal. While organic coronary arterial stenosis was not detected in either animal, dogs have well-developed epicardial intracoronary networks unlike microminipigs. Like in humans, dipyridamole did not affect the ST segment of microminipigs, whereas it substantially depressed that in dogs. The results indicate the onset of subendocardial ischemia by dipyridamole in dogs may be partly associated with their well-developed native coronary collateral channels. Microminipigs would be more useful to evaluate the drugs which may affect the coronary circulation in the pre-clinical study than dogs.

Conduction abnormalities during dipyridamole stress testing

Pharmacological stress tests using dipyridamole are considered to be safe. However, cases of atrioventricular (AV) block have been reported. We retrospectively analyzed ECG at baseline and during dipyridamole stress tests of 2010 consecutive patients (patients with second or third degree AV block were excluded). At baseline, 350 (17.4%) patients had conduction abnormalities. Following dipyridamole infusion 16 patients (0.8%) developed a transient change in AV conduction (15 patients) and or sinus arrest (1 patient). Compared to patients without baseline conduction abnormalities, patients with any conduction abnormalities at baseline were at a higher risk for the development of AV block after dipyridamole infusion [0.3% vs 3.14%, respectively; P < .0001].

Effect of dipyridamole on QT dispersion in vasospastic angina pectoris

Life-threatening ventricular arrhythmias have frequently been documented in patients with vasospastic angina. Moreover, the incidence of ventricular arrhythmias has been closely associated with increased QT dispersion. However, the underlying mechanism responsible for this arrhythmogenesis has not been clarified. The effects of dipyridamole and subsequent aminophylline administration on QT dispersion were examined in 35 patients with vasospastic angina and 30 patients with atypical chest pain. None of the patients enrolled in this study revealed any significant stenosis in coronary angiography. QT dispersion during dipyridamole followed by aminophylline administration was compared between the 2 groups. The baseline QT dispersion was similar in both groups (vasospastic angina: 27 +/- 8 ms; atypical chest pain: 28 +/- 7 ms). No significant changes in QT dispersion were observed in patients with atypical chest pain by dipyridamole (23 +/- 9 ms) and subsequent aminophylline administration (23 +/- 5 ms). However, the QT dispersion in patients with vasospastic angina increased significantly by dipyridamole administration (53 +/- 14 ms, p <0.0001) and returned to baseline by subsequent aminophylline administration (26 +/- 10 ms). Our data suggest that the disparity of ventricular repolarization in vasospastic angina may be mediated by increased endogenous adenosine.

Asystole during dipyridamole infusion in patients without coronary artery disease or beta-blocker therapy

The authors report two patients without coronary artery disease who experienced asystole during the IV infusion of dipyridamole on routine TI-201 myocardial perfusion imaging and review the literature for possible explanations of this rare side effect. Until now, this side effect was only reported in patients with coronary artery disease or beta-blocker therapy. Yet, the cases lacked both concomitant factors and autonomic dysregulation is suggested as a cause for asystole.

High-grade atrioventricular block during dipyridamole stress testing

Dipyridamole stress testing may be used in the diagnosis of coronary artery disease and risk assessment of patients who are unable to exercise. Although dipyridamole perfusion imaging has a good safety record, serious side-effects may rarely occur. We present a case in which dipyridamole induced high-grade atrioventricular (AV) block that responded promptly to intravenous aminophylline but not to atropine.

Sinus arrest associated with dipyridamole infusion

We describe a case of prolonged sinus arrest resolved by external cardiac massage following intravenous infusion of dipyridamole, during a thallium myocardial perfusion test. The arrhythmia, presumably due to an acute drug adverse effect, had not been previously described (to our knowledge) as a complication of dipyridamole stress testing.

Bradycardia progressing to cardiac arrest during adenosine thallium myocardial perfusion imaging in occult sino-atrial disease

Adenosine is used increasingly as an alternative to dynamic exercise during myocardial perfusion imaging because it is a powerful coronary vasodilator with a short half-life. Minor side-effects are common but life-threatening events are rare. We report two cases of provocation by adenosine infusion of profound sinus bradycardia progressing to atrial and ventricular asystole. Despite discontinuation of the infusion, asystole persisted for up to 1 min in one case and was accompanied by a grand mal seizure. Normal sinus rhythm returned spontaneously in both cases without long-term sequelae. Sino-atrial disease was later suggested in both cases by 24-h electrocardiographic monitoring. We conclude that patients to whom adenosine is given may have occult sino-atrial disease and may be susceptible to life-threatening arrhythmias. Significant sinus bradycardia during the infusion may provide a warning of its presence.

Arrhythmias during dipyridamole test. Report of 3 cases

The authors report three cases in which the dipyridamole test provoked: (1) junctional rhythm with AV dissociation; (2) sinus arrest; (3) 2:1 AV block. The three cases described above draw attention to the possible effect of dipyridamole on the AV conduction, which is not yet completely known. This unwanted effect suggests that careful ECG monitoring should be performed during the dipyridamole test.

Safety of intravenous high-dose dipyridamole echocardiography. The Echo-Persantine International Cooperative Study Group

Clinical data on 10,451 high-dose (up to 0.84 mg/kg over 10 minutes) dipyridamole-echocardiography tests (DET) performed in 9,122 patients were prospectively collected from 33 echocardiographic laboratories, each contributing greater than 100 tests. All patients were studied for documented or suspected coronary artery disease (1,117 early [less than 18 days] after acute myocardial infarction and 293 had unstable angina). Significant side effects including major adverse reactions and minor but limiting side effects occurred in 113 patients (1.2%). Major adverse reactions occurred in 7 cases (0.07%). In 6 of these cases, adverse reactions were associated with echocardiographically assessed ischemia and included 1 prolonged cardiac asystole (complicated by acute myocardial infarction and coma, with death after 23 days), 1 short-lasting cardiac asystole, 2 myocardial infarctions, 1 pulmonary edema and 1 sustained ventricular tachycardia. In all 6 cases, the cardiologist-echocardiographer performing the study had a limited experience (less than 100 tests) with DET, and at off-line reading in 5 cases, the obvious echo-positivity preceded the onset of complications by 1 to 5 minutes. The only ischemia-independent major side effect was a short-lasting cardiac asystole that was reversed by aminophylline and atropine. Significant side effects associated with echocardiographically assessed ischemia occurred in 89 additional cases (21 with and 68 without concomitant echocardiographically assessed myocardial ischemia). The most frequent of these side effects was hypotension or bradycardia, or both, which occurred in 40 patients with negative and 6 with positive DET. In all cases, side effects promptly subsided after aminophylline. In 1,857 cases, the high dose was not given for echo-positivity before the eighth minute.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrophysiologic effects of blocking and stimulating the opioid system in patients with unexplained heart palpitations

The opioid system plays a role in the regulation of the cardiovascular system. Endogenic as well as egzogenic administration of opioids influences the heart rhythm. This work was undertaken in order to assess the influence of crossover activity of the heart opioid system on the heart conduction system in patients with various disturbances of rhythm having an efficient circulatory system and a normal 12-lead stationary ECG. Subjects were 20 patients (9 men and 11 women of mean age of 38.7 years) reporting sudden heart palpitations. They were subjected to invasive programmable electrophysiological studies (PES). Naloxone was administered intravenously to 10 patients. Pentazocine was administered in the same way. In the remaining 10 patients the order of drug administration was reversed. PES was done in the basic state and after the administration of each drug. Study results were subjected to statistical analysis with no-parameter Wilcoxon test assuming differences to be significant at p less than 0.05. Blocking of the opioid system resulted in significant lengthening of the sinoatrial (SACT), intra-atrial (PA), and atrioventricular node (AH) conduction times, while no changes were induced in conduction in the His-Purkinje system (HV) and automation of the sinus node. Naloxone lengthened the atrial (ERPA) and atrioventricular node (ERPA AVN) effective refractory periods. Stimulation of the opioid system resulted in decreases of the following values: SACT, PA, AH, ERPA, ERPA AVN, while no effect was exerted on the SNRT, HV, ERPV. Neither drug influenced the QRS time, although naloxone lengthened QTc period significantly. Opioids did not influence the time of conduction in concealed extranodal atrioventricular pathways.(ABSTRACT TRUNCATED AT 250 WORDS)

Symptomatic bradycardia complicating the use of intravenous dipyridamole for thallium-201 myocardial perfusion imaging

Intravenous dipyridamole was given for routine thallium-201 myocardial perfusion imaging. The patient developed chest discomfort followed by cardiovascular collapse with sinus arrest and a nodal escape rhythm at 28 beats per minute. He was rapidly resuscitated without adverse sequelae. A reversible posteroinferior perfusion defect and proximal right coronary artery occlusion were found. Symptomatic bradycardia after dipyridamole may be mediated by ischaemia.