Reduced human ventricular fibrillation threshold associated with contrast-induced Q-T prolongation

Transient loss of sensing and capture during coronary angiography in two patients with permanent pacemakers

Two cases of transient pacemaker failure to sense and capture during angiography are reported. This phenomenon is due to a transient increase in sensing and pacing thresholds beyond the pacemakers programmed settings. The underlying mechanism may be related to blood displacement, the electrochemical properties of the injectate, the high concentration of the contrast media, or a combination of these properties. Even though the chambers in which sensing and pacing loss occurred differed (ventricle in the first and atria in the second), the episode occurred repeatedly after injection of contrast media into the artery supplying the respective electrode-tissue interface. In pacemaker dependent patients, provisions for external pacing should be implemented prior to injection of contrast into the coronary arteries.

Significance of ventricular tachyarrhythmias complicating cardiac catheterization: a CASS Registry Study

Ventricular tachycardia and ventricular fibrillation are recognized complications of cardiac catheterization. Despite numerous reports documenting the frequency of these occurrences, their significance has not been systematically examined. Accordingly, the outcome of 108 patients who experienced either ventricular tachycardia or ventricular fibrillation during coronary angiography between 1975 and 1979 in the Coronary Artery Surgery Study (CASS) Registry were examined. There were 20,142 patients analyzed. Patients with ventricular tachyarrhythmias had more objective evidence of left ventricular impairment, clinical heart failure, and ventricular arrhythmia recorded as a clinical symptom. The overall 5-year survival rates were 83% and 88% for patients with and without ventricular tachyarrhythmias, respectively (p = 0.07). When ventricular function, age, gender, angina, and previous myocardial infarction were added in a stepwise Cox survival analysis, the presence of arrhythmias was not significant (p = 0.66). At 5 years, 80% of the medically treated patients and 82% of the surgically treated patients remained alive (p = 0.95). The only statistically significant differences in the patients with ventricular arrhythmias who were treated medically or surgically were age (medically treated patients 52 +/- 10 years, surgical patients 57 +/- 9 years, p = 0.01) and number of diseased vessels (p less than 0.001). In a stepwise Cox survival analysis, functional impairment secondary to congestive heart failure was the only significant covariate to affect survival in the medical and surgical groups (p = 0.0001). Surgical therapy itself was not significant (p = 1.00). The incidence of sudden death during 5 years for patients with and without ventricular tachyarrhythmias during catheterization was 5% and 4%, respectively (p = 0.28).(ABSTRACT TRUNCATED AT 250 WORDS)

Use of temporary pacemakers during coronary angioplasty: an evolving experience with ventricular fibrillation in 400 cases

Because of a perceived high frequency of ventricular fibrillation when a pacemaker catheter was placed in the right ventricular apex during PTCA, we reviewed our first 400 cases for this complication. The incidence of ventricular fibrillation in the entire group was 10 of 400 cases (2.5%) compared with 17 of 3,806 (0.4%) diagnostic coronary arteriograms performed in our laboratory during the same time period (P less than .001). Ventricular fibrillation occurred more frequently during PTCA when the pacemaker catheter tip was placed in the right ventricular apex (8 of 63 cases, 12.6%) than when it was positioned in either the pulmonary artery, vena cava, or when a pacemaker catheter was not used (2 of 337 cases, 0.6%, P less than .001). Based on these data we have developed a policy of inserting temporary pacemakers prophylactically during PTCA only for patients undergoing dilation of dominant right or dominant left circumflex coronary arteries and in patients with acute myocardial infarction.

Ventricular fibrillation during coronary angiography: the precatheterization QT interval

Ventricular fibrillation during coronary angiography is associated with contrast-induced changes in repolarization and thus pre-catheterization abnormalities could predispose to this event. We retrospectively examined angiograms, pre-catheterization electrocardiograms and records of 26 consecutive patients who had ventricular fibrillation during coronary angiography, and compared these patients to controls matched for age, sex, and left ventricular function. Diatrizoate meglumine was used as the angiographic contrast agent in all instances. Catheterization findings and the prevalence of prior myocardial infarction were similar in both groups. However, pre-catheterization QT intervals in the ventricular fibrillation group (0.43 +/- 0.05 sec) were significantly longer than in control patients (0.39 +/- 0.04 sec, P less than 0.005) as were their QT intervals corrected for heart rate (QTc) (0.47 +/- 0.04 vs 0.42 +/- 0.03 sec; P less than 0.001). Only seven of the 16 patients (44%) with ventricular fibrillation who had a precatheterization QTc greater than 0.44 sec had the arrhythmia during angiography of a critically stenosed (greater than 75%) coronary artery, whereas VF followed injection of critically stenosed vessels in eight of 10 (80%) of those with a normal QTc (p NS). After a follow-up period of 24 to 54 months (mean 39), two ventricular fibrillation patients have died (one suddenly), as compared to five in the control group (two suddenly) (p NS). Therefore, pre-catheterization QT prolongation was associated with ventricular fibrillation during coronary angiography, but ventricular fibrillation did not necessarily portend a worse long-term prognosis.

Cardiac arrhythmias associated with prophylactic pacing during coronary angiography

Data from 518 consecutive cardiac catheterizations were analyzed to test the value of prophylactic pacemaker insertion during coronary angiography and to compare the incidence of arrhythmic complications in patients with and without pacemakers. In patients without pacing (n = 273), 1 episode of ventricular fibrillation occurred, which responded promptly to defibrillation. Sinus bradycardia (fewer than 30 beats/min for 10 seconds) was recorded in 74 patients (27%) and required treatment in 30 (11%). No patient required or would have benefited from pacemaker placement. Of the 245 patients with prophylactic pacemakers, there was an increased incidence of all ventricular (9 vs 1; p less than 0.013) and supraventricular (5 vs 0; p less than 0.046) arrhythmias. Pacemaker-associated induction of ventricular fibrillation occurred in 2 patients and was clearly related to electrical stimulation during a normally non-vulnerable period of the cardiac cycle. In conclusion, routine prophylactic pacemaker insertion during coronary angiography is not warranted in patients with normal sinus rhythm and normal atrioventricular conduction. More information is needed to determine if pacing is needed in patients with conduction system disease.

The QT-sensitive cybernetic pacemaker: a new role for an old parameter?

A critical review of the available data on QT interval is presented to delineate techniques useful to the development of a QT-sensitive cybernetic pacemaker. The reason for the development of this unit stems from the ability of QT prolongation to predict the onset of life-threatening ventricular arrhythmias in some clinical situations; the QT interval is physiologically related to the cardiac cycle length, therefore providing adequate information to drive both ventricular and atrioventricular sequential rate-responsive pacemakers. This unit might also monitor cardiac rhythm and detect the pathophysiologic precursors of advanced grades of ventricular arrhythmias. A therapeutic role, both pharmacologic and electrical, may also be possible in the future. Integration of these concepts and cooperation between interested physicians, technicians and manufactors will be necessary to produce such a unit at a low cost-benefit ratio. The potential clinical application of this pacemaker deserves attention for the prophylaxis and treatment of sudden arrhythmic death.

Arrhythmias in patients with drug toxicity, electrolyte, and endocrine disturbances

The common rhythm disturbances related to electrolyte imbalance are due predominantly to abnormalities of potassium. An understanding of the mechanism underlying these abnormalities is facilitated by a brief review of normal electrical activity during impulse propagation in cardiac tissue. Also discussed are the actions of all cardioactive and antiarrhythmic drugs on membrane permeability to ions. Lastly, the nonspecific arrhythmias associated with endocrine disturbances are outlined.

Long QT: good, bad or indifferent?

A survey of current literature suggests an increasing interest in both the desirable and undesirable implications of a prolonged QT interval, the former perceived to be the beneficial effect of antiarrhythmic drugs that prolong the duration of ventricular action potential, and the latter considered to be a potential marker for sudden cardiac death in patients with ischemic heart disease. In addition, there has been an increasing interest in the congenital long QT syndrome associated with an apparent dysfunction of the autonomic nervous system and serious, potentially lethal ventricular arrhythmias. Circumstantial evidence suggests that these arrhythmias are due to increased dispersion of repolarization which may be aggravated by psychologic and emotional perturbations. In this review, the associations between the long QT interval, autonomic nervous system, dispersion of repolarization, antiarrhythmic drugs and ventricular arrhythmias are examined. Attention is directed to the difficulties of accurate QT measurement, problems related to the correction of the QT interval for heart rate and sex (QTc), the wide range of normal values and the modest QT alterations after various manipulations of the autonomic nervous system. Clinical conditions associated with marked, moderate and occasional QT lengthening are listed and discussed briefly in relation to the disturbances of nervous system, dispersion of ventricular repolarization and ventricular arrhythmias. It is proposed that the absence of relevant animal models of neurogenic or psychogenic QT prolongation hinders the investigation of the neurogenic factors associated with QT lengthening. QT prolongation is most often induced by antiarrhythmic drugs and ischemic heart disease. However, it is not known whether the occurrence of torsade de pointes type of ventricular tachycardia in patients treated with antiarrhythmic drugs is related to a critical drug dose or a critical degree of QTc prolongation. There is no conclusive evidence that QT lengthening has any predictive value either during the acute phase or during convalescence after myocardial infarction. Also, a serious deficiency in current knowledge is the lack of an established relation between the prolonged QT interval and the dispersion of ventricular repolarization. It is concluded that the number of unanswered questions discussed in this review still makes it difficult to judge when a prolonged QT interval is good, bad or indifferent.

Postextrasystolic alterations in refractoriness of the His-Purkinje system and ventricular myocardium in man

The changes in refractoriness of the His-Purkinje system (HPS) and ventricular myocardium (VM) that are associated with the occurrence of postextrasystolic beats in man are unknown. Accordingly, using a pacing model of the cycle length changes created by a ventricular extrasystole-postextrasystole sequence, we measured retrograde HPS and VM relative and effective refractory periods (RRP and ERP) in 15 patients with the use of ventricular test extrastimuli during preextrasystolic basic control drive (method I) and after programmed extrasystolic (method II) and postextrasystolic (method III) beats. The basic cycle length (same for all three methods) ranged from 500 to 700 msec (mean 613 +/- 74 msec) and the extrasystolic coupling interval (identical for methods II and III) comprised 68 +/- 4% of the basic cycle length. In method III the postextrasystolic pause was programmed to equal the basic cycle length (i.e., noncompensatory) so that method I could serve as control for method III. RRP-HPS decreased from 331 +/- 37 msec in method I to 245 +/- 37 msec or less during the extrasystolic beat (p less than .001). A less dramatic corresponding shortening of ERP-VM and RRP-VM was observed, i.e., from 245 +/- 21 and 264 +/- 23 msec (method I) to 233 +/- 23 and 251 +/- 22 msec (method II), respectively (p less than .001). With the postextrasystolic beat, however, RRP-HPS increased to exceed the control value of method I by 23 +/- 11 msec (p less than .001). This greater-than-expected RP prolongation was also associated with significantly increased retrograde HPS conduction times (in method III vs method I) at both long and short test stimulus coupling intervals.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased risk of ventricular fibrillation associated with temporary pacemaker use during coronary arteriography

Each injection of angiographic contrast dye during coronary arteriography represents a "natural experiment" in which the human ventricular fibrillation threshold is transiently reduced. Few factors, however, have been identified which favor the actual occurrence of ventricular fibrillation in this setting. Of 3906 consecutive patients undergoing selective coronary arteriography with sodium meglumine diatrizoate, 66 (1.7 percent) experienced dye-induced ventricular fibrillation, from which all were successfully defibrillated. Analysis of these cases revealed, unexpectedly, that patients in whom temporary right ventricular pacemakers were employed had an incidence of ventricular fibrillation nearly six times that found in the entire group undergoing arteriography (10 percent vs. 1.7 percent, respectively; P less than .001). Those individuals receiving pacemakers were distinguished from other studied patients only by a higher prevalence of conduction abnormalities. Although there is normally a low probability that mechanical stimulation by a pacing catheter can induce ventricular fibrillation, it is postulated that such an occurrence may be more likely after ventricular vulnerability has been increased by contrast dye.