Low-level ionizing radiation from noninvasive cardiac imaging: can we extrapolate estimated risks from epidemiologic data to the clinical setting?

Clinical decision-making regarding the use of low-level ionizing radiation for diagnostic and/or therapeutic purposes in patients with cardiovascular disease must, as in all other clinical scenarios, encompass the broad range of the risk-benefit ratio. Concerns regarding the late carcinogenic effects of exposure to low levels, i.e., <100 mSv, of ionizing radiation stem from extrapolation of exposure-outcome data in survivors of World War II atomic bomb explosions. However, ongoing debate regarding the true incremental risk to subjects exposed to doses currently administered in cardiovascular procedures fails to take into account the uncertainty of the dose-response relationship in this lower range, as well as tissue-specific reparative responses, also manifest at lower levels of exposure. The present discussion draws attention to both of these aspects as they relate to clinical decision-making.

Epinephrine-induced QT interval prolongation: a gene-specific paradoxical response in congenital long QT syndrome

OBJECTIVE

To determine the effect of epinephrine on the QT interval in patients with genotyped long QT syndrome (LQTS).

PATIENTS AND METHODS

Between May 1999 and April 2001, 37 patients (24 females) with genotyped LQTS (19 LQT1, 15 LQT2, 3 LQT3, mean age, 27 years; range, 10-53 years) from 21 different kindreds and 27 (16 females) controls (mean age, 31 years; range, 13-45 years) were studied at baseline and during gradually increasing doses of intravenous epinephrine infusion (0.05, 0.1, 0.2, and 0.3 microg x k(-1) x min(-1)). The 12-lead electrocardiogram was monitored continuously, and heart rate, QT, and corrected QT interval (QTc) were measured during each study stage.

RESULTS

There was no significant difference in resting heart rate or chronotropic response to epinephrine between LQTS patients and controls. The mean +/- SD baseline QTc was greater in LQTS patients (500+/-68 ms) than in controls (436+/-19 ms, P<.001). However, 9 (47%) of 19 KVLQT1-genotyped LQT1 patients had a nondiagnostic resting QTc (<460 milliseconds), whereas 11 (41%) of 27 controls had a resting QTc higher than 440 milliseconds. During epinephrine infusion, every LQT1 patient manifested prolongation of the QT interval (paradoxical response), whereas healthy controls and patients with either LQT2 or LQT3 tended to have shortened QT intervals (P<.001). The maximum mean +/- SD change in QT (AQT [epinephrine QT minus baseline QT]) was -5+/-47 ms (controls), +94+/-31 ms (LQT1), and -87+/-67 ms (LQT2 and LQT3 patients). Of 27 controls, 6 had lengthening of their QT intervals (AQT >30 milliseconds) during high-dose epinephrine. Low-dose epinephrine (0.05 microg x kg(-1) x min(-1)) completely discriminated LQT1 patients (AQT, +82+/-34 ms) from controls (AQT, -7+/-13 ms; P<.001). Epinephrine-triggered nonsustained ventricular tachycardia occurred in 2 patients with LQTS and in 1 control.

CONCLUSIONS

Epinephrine-induced prolongation of the QT interval appears pathognomonic for LQT1. Low-dose epinephrine infusion distinguishes controls from patients with concealed LQT1 manifesting an equivocal QTc at rest. Thus, epinephrine provocation may help unmask some patients with concealed LQTS and strategically direct molecular genetic testing.

Negative impact of cardiac evaluation before vascular surgery

The optimal preoperative evaluation of cardiac risk in patients with peripheral vascular disease is controversial. In developing a paradigm for preoperative cardiac workup, potential adverse effects of evaluation and cardiac intervention must be considered. This study analyzed the deleterious outcomes of extensive, comprehensive cardiac evaluation and intervention before planned vascular surgery in patients treated at the Denver Department of Veterans Affairs Medical Center. Over a 12-month period between 1994 and 1995, 161 patients were scheduled to undergo major vascular operations; 153 patients came to operation. The decision to pursue a cardiac evaluation was variously made by a combination of surgeons, cardiologists, and anesthesiologists. No defined protocol was followed. Cardiac history, chest X-rays and ECGs were obtained for all patients. Extended cardiac evaluation included these studies plus special tests, including echocardiography (echo), radionuclide ventriculography (RNVG), dipyridamole thallium scintigraphy (DTS), and cardiac catheterization (CC). Extended cardiac evaluations were undertaken in 42 patients. Complications related to percutaneous transluminal coronary angioplasty (PTCA) and coronary artery bypass grafting (CABG) were also recorded. Cardiac mortality and morbidity after vascular interventions were itemized in all 153 patients. Forty-two male patients, aged 68 +/- 9 years, underwent extended cardiac evaluations before planned vascular operations. The median elapsed time for cardiac workup was 14 days (mean 30 +/- 59 days). The median and mean times from cardiac workup to vascular surgery were 25 days and 76 +/- 142 days, respectively. Eighteen (43%) patients had echo or RNVG; 22 (52%) patients had DTS; 27 (64%) had CC; 9 (21%) had PTCA; 7 (17%) had CABG. Sixteen (38%) patients had untoward events related to cardiac evaluation. Eight patients (19%: one with cerebrovascular disease, and seven with aortic aneurysms) refused vascular surgery after extended cardiac workup. Complications attributable to CC, PTCA, and CABG included prosthetic graft infection, pseudoaneurysms (two), sternal wound infections (two), renal failure and brain anoxia. Two patients with severe limb ischemia who were candidates for revascularization ultimately required amputations because of delay due to cardiac evaluations. Extensive cardiac evaluation prior to vascular operations can result in morbidity, delays, and refusal to undergo vascular surgery. The underlying indication for vascular operations and the local iatrogenic cardiac complication rates must be considered before ordering special studies.

[Malignant vasovagal syncope: a case of prolonged asystole induced by the "tilt" test and aggravated by therapy with a beta blocker (a clinical case and diagnostic, physiopathologic and therapeutic review)]

The authors describe a case of a middle-age male with recurrent syncope, in whom the tilt test was useful in the diagnosis and therapeutic evaluation. Malignant criteria of vasovagal syncope were established and the beta blocking worsening effect was documented, in spite of the general agreement of the first choice drug.

[Risk of cardiological interventions]

The risk of cardiac interventions has to be assessed in relation to the possible benefit and in comparison to the natural history and to alternative interventions. The relationship between complications (mortality, morbidity) and age, severity of the disease, gender and technique on one hand, and between risk of the intervention versus risk of uninfluenced natural history on the other, are discussed. Diagnostic, therapeutic and prophylactic interventions are presented separately; the benefit needs to be defined differently for each: diagnostic accuracy or symptom relief, improved quality of life and survival, and prolonged life respectively. Finally, it is stressed that the choice of an intervention is not only dependent on the determinants of risk, but also on the availability of a certain method, operator experience, cost and, last but not least, patient preference.

Non Q-wave myocardial infarction following hyperventilation test

We report a case of acute myocardial infarction following a hyperventilation test performed at coronary angiography. The potential pathophysiological mechanisms and clinical implications are discussed.

[Prinzmetal's syncopal angina during an electroencephalogram. Triggering role of the hyperpnea test]

We are reporting a cardiac arrest occurring during an electroencephalogram with hyperventilation. The diagnosis is made on the Holter recording which shows a Prinzmetal's angor tracing followed with ventricular arrhythmias, leading to asystoly. The physiopathology of the spasm is not clear and we are discussing the possible mechanisms. We stress again the harmful role of beta-blockers in this pathology. In addition, we insist on electrocardiographic manifestations surrounding sudden death. As for the hyperventilation test, its potential risks call for caution during its performance.

[Myocardial ischemia induced by the cold pressor test in patients with exertion angina. Case contribution]

The aim of the present study was to assess the incidence of myocardial ischemia during cold pressor test in patients with stable exertional angina pectoris. Thirty-seven patients with proven coronary artery disease were submitted to cold pressor and exercise stress testing; computer assisted electrocardiographic recordings were obtained throughout the examinations. Cold stimulation provoked electrocardiographic signs of subendocardial ischemia only in 3 patients. They had suffered of a previous myocardial infarction and showed low exercise tolerance and severe coronary lesions (one with triple vessel and 2 with left main disease). Interestingly, only one of these patients gave an history of angina during cold exposure. Thus these data indicate that chest pain and electrocardiographic signs of ischemia are an uncommon event during cold pressor stimulation which occurs more likely in patients with fairly severe coronary narrowings. More sensitive markers of ischemia and/or different modalities of cold application are required for studies concerning the relationship between cold exposure and angina pectoris.

[Rare cases of severe heart rhythm disturbances during the hypoxic function test]

Cases of severe rhythm disorders of cardiac activity--the syncope developing lasting up to 34 seconds, are described in practically healthy individuals undergoing the hypoxic functional test. It is concluded that the hypoxic functional tests require a specially trained physician who must not only stop the test, but also give the patient immediate aid.

[Frequency of life-threatening complications associated with exercise testing (author's transl)]

Most of the statistics on complications of ergometric exercise tests come from the United States and are largely related to treadmill ergometry. A questionnaire was sent in the summer of 1978 to 198 investigative units in the German-speaking regions. The results of 1065 923 person-tests were made available. Exercise testing of 353 638 sports-persons revealed no serious complications. On the other hand, testing of 712 285 patients, predominantly with coronary heart disease, lead to 17 deaths and a total of 96 life-threatening complications. The result of this survey indicates that one must expect one such complication for every 7500 ergometry tests. The danger of pulmonary oedema on exercise in recumbency is about five times higher than that on sitting or standing. The most frequent complication was ventricular fibrillation. A defibrillator should therefore always be immediately available during exercise tests.

[Complication during the dipyridamole-test (author's transl)]

Performing the dipyridamole-test for evaluating coronary artery disease a man at the age of 57 years developed after application of 15 mg dipyridamole intravenously angina pectoris. For removal of angina pectoris 240 mg aminophylline were injected, after what bradycardia and finally cardiac arrest occurred. Resuscitation was successful. Possible reasons and some precautions were discussed.

Sequential atrioventricular pacing as a stress test. Evaluation of left ventricular function in second-degree AV heart block developing during atrial pacing

Advanced or second-degree atrioventricular (AV) heart block pre-existing or developing during atrial pacing (AP) at low heart rates of smaller than 130 per minute, limits the value of AP to stress the left ventricle. When Wenkebach type AV block is present, the heart rate can be increased by administration of atropine before atrial pacing or by right ventricular pacing. Atropine, however, occasionally may cause serious supraventricular or ventricular arrhythmias, and high rate right ventricular pacing is not tolerated by many patients with left ventricular dysfunction because of the absence of the atrial contribution. Twenty-eight out of 101 patients with angina pectoris (27.7 percent) developed second degree AV heart block during atrial pacing studies performed for evaluation of left ventricular function. In 8 of the 28 patients, sequential AV pacing (SP) was performed successfully, with the heart rate being increased to 150-167 per minute. In 4 of the 8 patients, left ventricular dysnfunction was demonstrated during and immediately after SP. Typical angina pectoris developed in two of the four patients during SP, one of whom proved to have normal coronary arteriogram. Sequential AV pacing is an alternative method to increase the heart rate for the purpose of stressing the left ventricle when advanced degree or second-degree AV heart block pre-exists or develops during right atrial pacing. In some patients the method of SP might be preferable to administration of atropine or to ventricular pacing.